PROJECT: ACCURATE MODERN SPORTING RIFLE
13, 2019 – John Snell
I'm trying to discover the elements of building a sub-moa AR in 5.56 NATO - This exercise is to learn facts.
This story starts with a friend wanting to use an AR platform to shoot ground squirrels, and me trying to 'guild the Lilly' (what's new there?)
In the last few years we have been told that we can buy an accurate MSR (Modern Sporting Rifle) from several commercial builders, who will naturally charge for their experience, time and materials. In general, the pitch is that you can expect sub MOA (Minute of Angle) when using 'quality' or 'match' ammunition. Apparently these builders are satisfying their customers, as you never hear of any going out of business.
So my friend purchased a very nice Rock River rifle, and I purchased a STAG Varmint upper to use with either my DPMS or Ruger lowers. Since I had already put a better trigger in the Ruger, its been the host for the uppers I'll be telling you about in this story.
My friend's rifle shot about 1.5 MOA with several commercial and military surplus load. For him this was adequate because he says its more accurate than he can shoot. In my case, having been ground squirrel shooting for several years now, I know I will get the best experience from a rifle that can reliably hit the squirrels vital zone (1”x1-1/2”) at 500 yards or more. My Savage 12 FCP in 204 Ruger has been shooting 0.2 to 0.3 MOA groups ever since I finished load development, it takes an expensive and heavy for caliber 40 grain Berger bullet, turned case necks, neck sizing and loading with hand dies to consistently achieve that level of precision. I want at least 0.5 MOA from my MSR or it won't be much use on the tiny targets. In addition, I want to use the thousands of 5.56 NATO cases I have (mostly Lake City), and I want to load them on a progressive press. Nothing like a 'tall order' is there?
Back in the stone age (1980) I was doing a lot of competitive pistol shooting in the NRA Handgun Silhouette discipline. At that time Hornady's “Projector” progressive press was my choice, but I was paying attention to Dillon and using their powder measure. That Hornady press worked – right up until it crushed the primer delivery system. Attempts to fix the actuator and transport never were adequate, and at about the same time, I found myself 3,000 miles away and work/life didn't permit shooting or loading. A decade or two slipped by in the blink of an eye, and I finally had things organized so I could consider shooting again. I dug out the Hornady press, and sure enough, it still didn't work. I contacted Hornady, but by now they had no parts for the old press, and their new press didn't even accept any of the parts that might reasonably be expected to interchange. Bah-humbug! Again I looked at Dillon. They still had the exact same press(es) as a couple decades before, plus some new 'stuff'. Their customer service received consistenly top-notch reviews. But before I bought a new progressive press, I dug out my RCBS Rock Chucker that I had purchased in 1966. That press loaded all the rifle ammo I shot for several years, and between work and family, I turned to other pursuits. Fast forward to 2013, the year I retired. I was enthralled with shooting the abundant Piyute Ground Squirrles that inhabit Southwestern Idaho. The opportunity to shoot them played a large role in choosing this area to retire to. Once again the presses were resurrected from storage. And once again, the RCBS Rock Chucker was instantly ready to go to work. The Hornady remained out of service, and even eBay was no help!
A friend let me shoot his Savage 12 FCP in 204 Ruger. I watched squirrels vaporize at 100, 200, 300, and sucumb dramatically at 400 and 500 yards – I was smitten! I immediately purchased my own Savage 12 FCP and went to work on load development. Just before retiring I comissioned Russ Haydon to build a 308 varmint rifle using a new Remington 700 action. This was the last rifle Russ built before he retired, and it is a tribute to his years of bench rest competition. He blueprinted the action, chambered and installed a Shilen barrel, and bedded it in a thumbhole stock I provided. The rifle shot in the 0.3 MOA range from the very first shot. When Russ and I were wrapping up the 308, he introduced me to Wilson Hand Dies which use an arbor press (see the notebook). He also introduced me to neck turning, so I came away with a K&M lathe and all the bits and pieces necessary to turn necks accurately. As I was trying to get the 204 into the sub-half minute range, I purchased Wilson Hand Dies for it and added 204 components to the K&M lathe. Between the two I finally got the rifle consistently into the 0.25 MOA range. Using hand dies while satisfying and actually somewhat faster than conventional dies in the Rock Chucker, just wasn't going to keep up with the ammunition volume demanded by the squirrels. It was about this point where I realized I could use a 17HMR on short range squirrels and save what remained of the 204's barrel life on 300 yard plus shots. It was a year or two later, my friend (who has a 'prepper' approach to rifles) talked me into the AR platform for squirrels (it wasn't a hard sell).
Ok, now I've got you caught up as to what and why I am interested in for the AR. Let me finish up about presses.
To satisfy the high demand I knew we would have for the AR's where squirrels were concerned, I suggested to my friend that we split the cost of a progressive press. This time I chose Dillon, as I should have back in 1980. The XL650 with automatic case feeder assembled quickly, and started producing good quality ammo immediately. In the course of searching for accuracy for the AR's I upgraded from Dillon Steel dies to Redding Type 'S' bushing full length sizer and Redding Competition seating die. Concentricity has improved significantly, and the previously fired Lake City loads I make on the XL650 now show less than 0.005” runout at the bullet tip.
My advise to any of you who are thinking about getting a progressive press, is to give Dillon a hard look. I'm very happy with mine, its easy to setup correctly, easy to use, and easy to convert between caliber be they rifle or pistol.
For the 'Accurate AR' project, I wanted to make use of the MSR platform's configurability. I chose to use my Ruger SR556 (piston) rifle's lower and upgrade as necessary or desirable. The lower already had an upgrade Ruger trigger, Magpul STR stock, Ruger enhanced grip, Magpul MOE trigger guard, and Magpul B.A.D lever. The B.A.D lever is possibly the best money spent on this lower. It allow you to release the bolt using the tip of your trigger finger. No breaking cheek weld! Initially my goal for upgrading this lower was to create the best SHTF combat lower for my personal use.
In order to re-purpose this lower to achieve best accuracy I plan to add two more accuracy enhancing options.
I will be replacing the Ruger Enhanced trigger with a Trigger Tech 'Adaptable AR Primary Trigger' https://triggertech.com
This trigger will be much lighter and far more crisp than the Ruger Enhanced, and it will cost more too. The real question to be answered by shooting it, is … was it worth it?
So here's what I'm thinking today, as I have yet to order the trigger.
I learned to shoot competitavely at the tender age of seven using a Mossberg target rifle. As I grew the next couple of years, I moved up to the Remington 40x rifles our US Army supported club owned. The Remington 40X has a legendary trigger. At the time, I thought it was the best there was, and I got really, really good at NRA Smallbore with that rifle. In fact I got so good, that I was winning state championships. The thinking went that I should have my own target rifle, and that since the Olympics were a goal, I should have the rifle most often used in the Olympics, which at the time was Anschutz's 1413 International. Don't get me wrong, I LOVED the Anschutz, but I always could shoot just a fraction better with the Remmington 40X, and I believe it was the trigger that made the difference.
In the years since, I've shot every crappy trigger I've been handed better than anyone else could. It sort of got to a point where it didn't seem to matter, I had an 'educated' trigger finger. Shooting big Smith and Wesson revolvers in double action (just because I could) at NRA Regional Matches and so on.
This business of wringing sub-moa out of an AR has turned my world upside down!
In analysing why it is that I continue to be stuck at 1-1/2 to 2 MOA I've come to the painful realization that after the trigger breaks, if there is trigger over-travel, if there is excessive lock time, and if there is an opportunity for the relationship between the lower and upper to change, that it may be possible for the mechanical systems of the rifle to be the cause of the large dispersion.
Think about it this way; you hold the rifle in four places. The forend (resting on a bipod), the cheek weld, the pistol grip, and your shoulder. Of these, 3 out of 4 are on the lower receiver. You aim the rifle using sights attached to the upper. When the trigger releases the hammer it takes about 10 mS (1/1,000 Seconds) to travel from its cocked position to its fired position, hit the firing pin and detonate the primer. From that moment it takes about 750 uS (1/1,000,000 Seconds) for the bullet to exit the barrel.
To move the point of impact 1” at 100 yards (ok 1.04”) requires 1 MOA of change in the direction the barrel is pointed. If we use a 16.25” barrel and assume the chamber is the 'point of the triangle' then the muzzle would have to be displaced by 0.005”. To give this meaning, a sheet of printer paper is typically 0.004”
The hammer being released causes an equal and opposite reaction which may move the lower, or both the lower and upper. Then the impact of the hammer hitting the firing pin causes an opposite reaction again maybe moving the lower or bother lower and upper. The acceleration of the bullet then causes an equal and opposite reaction (recoil) which definitely moves the upper, and may move the lower. The motion begins the moment the bullet begins to accelerate, and continues until the bullet exits the barrel, then the gas jet pushes the upper some more, but at this point the bullet is no longer under our control.
Its all that motion that we attempt to control with our hold, our posture, etc.
Long range shooters will tell you that 'torque' on the trigger is definable in the groups shot at long range. They never mention how to make that torque uniform, instead they eliminate it by moving the thumb of their firing hand to the same side of the stock as their trigger finger. In other words, they don't grasp the stock with their thumb. Most also refrain from grasping with their fingers (for the same reason). If we follow this advise, we now only have contact/control of the rifle at three places (forend, cheek, and butt).
keep the relationship between the hammer and the firing pin
consistent, to keep the point of aim consistent, and to remove
all doubt … I'm going to install a 'National Match Shim' from
Wheel Diamond http://www.wheeldiamond.com/nationalmatchshim.htm
I am beginning to understand that there is a bit more to stabalizing upper to lower than asthetics. Consider the energy dissipation as the trigger is pulled, first with a sloppy then tight fitting upper. In the first case, the equal and opposite reaction to the trigger movement will start the lower moving backward, and then the impact on the firing pin reverses the direction of movement. If the upper to lower fit is sloppy, a cheek weld and/or grip will modulate that movement, and in a sloppy fitting upper by the time the primer explodes, it may no longer be pointed exactly where it was when the trigger broke. Somehere in this discussion I've calculated that on a 16 inch barrel it takes 0.005” change in muzzle position to cause a 1 MOA point of impact shift, where the chamber is stationary. Modifying that situation slightly to hold the muzzle in place and move the chamber the same amount is the same problem, with the same answer, 0.005” movement will offset the point of impact 1 MOA.
So eliminating the potential for 0.005” movement between the upper and lower is a very good idea when building a precision rifle.
The Wheel Diamond “National Match Wedge” takes a while to hand fit, but because it eliminates play in both top-bottom and left-right planes I believe it is superior to through grip screws that apply up-down pressure between the lower and upper, as these rely on the takedown pins being under lateral compression to stabalize in the left-right plane. If you already have either a tight fitting upper, or a grip screw, I would not spend the time/money to install the National Match Wedge. However if your upper/lower is sloppy, then I think the National Match Wedge is the best solution.
Up until July 2020 I was using the STAG upper and switching barrels in and out of it. At this point, I discovered an inexpensive stripped upper (AR Stoner by way of Midway USA) which comes without the possibility of installing a forward assist, and without the dust cover. A dust cover can be installed if desired.
I resurrected the STAG 24” Varmint barrel and installed it into the AR Stoner upper.
STAG upper simply was not shooting below 2 MOA reliably with
anything from MILSURP to Hornady and Black Hills MATCH ammo, nor
was I able to reduce group size by hand loading. Incidentally
muzzle velocity variation (ES) was typically 50-150 fps with
CFE223 and 55 grain bullets. CFE2223 with heavier bullets (up to
70 grains) typically had lower ES of about 30 fps. The few VARGET
loads I tested had Muzzle Velocity Extreme Spreads (ES) of
between 20-30 fps, and the same was true for BL-C2 loads with 55
and 69 grain bullets. Black Hills 77 OTM ES 29 for 5 shots, First
I scoured the PRS blog, and YouTube then poked around here and
there for nuggets of truth.
1. The BARREL is the most important item. It must be a high quality barrel. The chamber must be installed by indicating on center, then reaming with a piloted reamer. Experience counts. I purchased a discontinued Proof Research button rifled 16" barrel after calling Proof to confirm that they stand behind its accuracy.
1A. The barrel must be seated to the upper correctly. This requires most uppers to be squared using lapping compound and an inexpensive tool (if you own a lathe, make your own, if not look at Wheeler for a kit).
1B. The barrel must not move between shots. Restated, the barrel must 'point' to the EXACT same place every shot. The sights establish the aiming point, and translate that position to the barrel through the scope mechanism, scope mount, upper 1913 rail/barrel mortise, barrel nut, barrel flange/extension tennon.
1C. You can use Locktite 620 (green) to glue the barrel extension into the upper. If you do, you will have to use a torch to heat the upper to more than 500F to remove it, and you will probably have to burn the Locktite off the barrel extension to clean it up if you plan to reuse the barrel. I know this because my first barrel was a STAG 24" Varmint barrel that simply would not shoot under 1.5 MOA. If you Locktite the barrel it WILL NOT MOVE regardless the barrel nut torque applied.
1D. If you do not use a glue, then use a copper infused anti-seize (NAPA). On my second barrel (the Proof Research) I changed gas system and handguard, which changed the barrel nut to a hex nut (I LIKE the hex nut, I don't like the cost of a 1-1/16" crows foot to fit the torque wrench!). Using the SEEKINS barrel nut, I first tired 50 lb-ft torque. Got 1.5 MOA. Then 65 lb-ft the barrel nut moved about 3 degrees as I brought it up (always increased torque, never backed nut off), the nut moving did not affect the gas tube alighnment, but in a conventional barrel nut (with gas tube holes) it would have been a poblem. At 65 lb-ft 1.5 MOA continues. Eventually bumped it up to 75 lf-ft and expect to leave it there. It does not appear that torque changes (above 50 lb-ft) have any affect on accuracy with my barrels (I did something similar to the STAG 24" Varmint barrel, it turns out that barrel had it's chamber installed (wait for it … ) 1-2 MOA out of true. I know because I cast the chamber and measured.
2. The TRIGGER is the second most important piece of hardware. "Everyone" says so. I started shooting competitively at age 7 and was a contender for the US Olympic Team the year I won the Southeast Asia lottery. I've got an 'educated' trigger finger, and I can shoot any military trigger at expert level. I didn't want to believe a 'better' trigger would make $200 worth of difference. Recently I bought a TRIGGER TECH AR15 ADAPTABLE trigger. It's a two stage with the first stage takeup about the same as the center blade on a Savage AccuTrigger. I adjusted the trigger to nearly it's lowest weight (2.5 lbs). This trigger really does feel like a quality 1911 trigger when it breaks. I can't prove I shoot any better with it, but I think I have a slight improvement in eye-hand (trigger finger) coordination that may be worth 0.25MOA in 'pointing where I want it to go off'. The hammer is a bit faster so lock time is probably a bit quicker (always a good thing), and I believe that (faster lock time) is the big improvement for me. Anyway the trigger feels so good that I think its worth the cost, even if it doesn't show up as any better groups for me. For someone without the 'couple million' trigger pulls's I've done, this trigger may very well create a measurable improvement in accuracy.
3. SIGHTS. In International Smallbore and Service Rifle competition we used iron sights to make 0.5 MOA corrections that were measurable and repeatable. The days when my eyes could do that are long gone. Now I use a scope exclusively. I used to have a lot of different and very expensive scopes on my rifles. Then Vortex came out with the DIAMONDBACK TACTICAL 5-25x50 FFP and priced it well below its performance point. I traded in all my NightForce, Burris, and other scopes to replace every one of my scopes with the same model. Now I only have to learn one reticle, one set of adjustments, one … well you get the idea. So when this rifle (wearing that scope) would not shoot well (back when it was the STAG barrel), I used my 308 and 204 to 'qualify' their Vortex Diamondback scopes with TALL TARGET and BOX tests so I knew the scopes were working correctly, predictably, and by how much to correct for 'click' error. Then I took the scope off my 204 (it's a consistent 0.3 MOA rifle) and swapped with the AR scope. No change, still getting 1.5 MOA on the AR. The AR's scope is now on the 204 and is consistently printing sub-half MOA. The mounts on the bolt guns are massive tactical style attachments, while the AR has a Vortex 'cantilever' scope mount. The jury is out about this mount, but I know I need to keep the scope forward and high and attached on the upper (never the forened) to ensure it doesn't move between shots. I had some 'issues' with the Vortex mount to start with that I solved by boring out the holes for the screws that apply gripping pressure to the PIC rail. I also used some of that Copper infused anti-seize grease to ensure the clamp would move into its tight position without restriction or excess friction, and of course I torqued it to spec. I'm 'pretty sure' this mount isn't the problem.
GAS SYSTEM. The gas tube must not be under any tension when the
bolt is closed. If it is, then when the bolt moves, the barrel
will move, and not in a uniform way. You can check this easily
when building by watching the gas tube while closing the bolt,
you can also smoke check the gas tube to gas-key fit to ensure
there is no lateral pressure. In my latest configuration I am
using an adjustable gas block that has set screw that coordinates
with a dimple in the barrel to set the gas block location
correctly. if you use a clamp style gas block, keep in mind that
the block should not touch any shoulder on the barrel. The
AR15-A1 hand guard had a 0.015" thick steel plate that was
captured between the gas block and that shoulder. Your gas block
should install with a 0.015" gap if there is a shoulder.
4B. An instructive test of your gas system works like this: (Be sure your rife is unloaded! Have a safe landing zone for your BCG!)
1. With the upper removed from the lower.
2. Remove the Charging Handle and the BCG.
3. Reinstall the BCG without the Charging Handle.
3 With the bolt carrier group fully forward, and the bolt in full lockup.
4. Apply compressed air to the barrel at the muzzle.
You will likely be very surprised at how little air pressure it takes to unlock the bolt, and toss it out the back of the upper. If you wanted to get the system wet, you probably could easily do this with your lungs!
Anyway, you can use the changes in the sound of the air as you manipulate the BCG to get some idea what the relationship of the gas tube to gas key is. Keep in mind that gas ports through the gas key to the right side of the BCG.
5. LOWER. There is very little other than the trigger about the lower that affects accuracy directly. As long as the lower fits well enough to fire the rifle it should be capable of good accuracy. That's what my brain says. When I hear the upper/lower rattle, when I feel the upper/lower move around, I just don't feel accurate. There is a very good and simple fix. WHEELDIAMOND (.com) produces a little horseshoe shaped piece of Aluminum that you can fit to your upper that will (if correctly installed) totally eliminate all movement between the upper and lower. I absolutely love mine. I guess things that make you feel better might make you shoot better, it's not going to make the rifle shoot any better though.
6. AMMO. In order of importance this is probably really number one or two. Barrel manufacturers will guarantee accuracy only with match quality factory ammo, because if the ammo is inconsistent, the accuracy is inconsistent. However consistent ammo alone can not make a rifle accurate. My Proof Research barrel has a 1:8 twist. It should be good for 55-75 maybe 80 grain or heavier bullets. So far hand loads and factory match ammo from Black Hills and Hornady are still not consistently sub-MOA regardless the bullet weight. Some are atrocious! For example XM855 will not shoot consistently below 2 MOA (which used to be ok for National Match, but I'm looking to hit ground squirrels at 300+). Black Hills consistently shows ejector swipes on the case head (over pressure), and has not shot well in any of my barrels, HORNADY MATCH is not shooting sub-moa, and my handloads, mostly using CFE223 have not been impressive except for velocity. I use QuickLoad, a lot of loading manuals, and direct measurement to understand a load. I've found setting up QL for 5.56 NATO and using the actual case volume of water has allowed me to work in a much higher velocity range than most manuals recommend. My PRESSURE TRACE confirms the QL predictions for pressure, and my LAB RADAR is right in line with QL velocity predictions. Thing is, I am not having a good time getting ES (extreme velocity spread) down to below 50 fps. Typically in 10 shots of a given load the ES wiil be 100-200 fps. I've tried sorting for case volume, more powder, less powder, crimp, no-crimp and neck tension adjustments with nothing pointing to a 'better way'. I've loaded one-at-a-time in a single stage press, and 'production-mode' on my Dillon XL650. I seem to be able to get Dillon loads that work as well as any I can load single-stage. Neck turning didn't improve group size either, but it did improve concentricity. I've measured runout on loaded ammo, then cycled it through the rifle from the magazine by dropping the bolt from bolt-lock. My adjustable gas block is set to 'just work' plus 'a little' which shoots soft and reliably. One would think the difference between bolt-lock and shot-to-shot loading would be minimal. Anyway the runout of 'cycled' ammo is the same as it was before loading it into the rifle. I've marked up bullet noses to check for contact, and only see very light scratches, and left or right feed appear the same (but on opposite sides of the bullet). At present, I'm chasing a 5 shot 0.4MOA group that probably was a statistical anomaly. It was a Hornady 40g VMAX load. I think the 40g VMAX may shoot very well in this rifle, and the latest round of testing though mostly 1.0-1.5 MOA the groups were more round and group size vs charge was more consistent than previously. My memory is 'itching' telling me there is a chance that flyers are coming from the 3rd and 5th shots more often than not. Don't know what that means yet, if anything.
The sub-MOA AR15 may not be a 5.56 NATO (or Wylde) rifle. All of my very accurate guns have the ability to load the bullet to zero jump, and find their highest accuracy at a point less than 0.050" of jump. My AR15 barrel can not be magazine fed at a jump less than 0.080" although there are some (SPEER 80g) bullets that have an ojive very near the point that I have not explored enough to discount.
Shooting position and form are important, consistency is important. Trigger pull is important. So far, I have tried tight holds, loose holds, free-recoil (had a little better accuracy - sometimes), and what 'just feels right'. I'm using a high quality bipod and a sandbag under the butt. I've got pointing wobble down to <0.25 MOA, and recoil is only moving me about 2 MOA up-left (gotta time the muzzle brake I guess). The new trigger makes it easier to shoot better (feel better about each shot being fired correctly).
The barrel pointing toward the exact same place the scope reticle points shot to shot is a function of mechanical design and execution. I think I've accounted for and eliminated every source of shot-to-shot variation.
The bullet hitting where the barrel is pointing is a function of powder burn rate (gas conversion rate), barrel position at the moment the bullet exits the barrel, and external ballistics (wind mostly). I'm still having problems in this area because I can't get the consistency I see in my 308, 6.5 CM, or 204. (I have tried turning off the gas port to make the AR a single shot, although it was a while ago, I didn't see any better ES). I'm starting to think the problem is the cartridge and chamber design.
But! There are manufacturers (including Proof Research - who will get a chance to address this directly soon), who deliver sub-MOA accuracy as a function of build quality. They sometimes use the same parts my rifle is built with, so why isn't mine working?
I started out in the Spring of 2019 thinking that a Varmint grade Stag-15 would shoot sub minute of angle (less than 1” at 100 yards). The Stag-15 upper I purchased came with a 5.56 NATO chambered 24” heavy stainless1:8 twist barrel and a Hogue overmoulded handguard. I mounted the upper on my Ruger SR556 lower (at the time it included a Ruger 'enhanced' trigger). I tried many commercial loads, many handloads, and never got the rifle to shoot less than 1-1/2” at 100 yards.
In an effort to improve performance, I used Locktite 620 to bed the barrel tennon to the receiver mortise. This did not make any difference to accuracy at all.
I called STAG Customer Servic eexplained the situation , and they suggested I send the upper to them for testing. Turns out all they did was shoot it (maybe) and decide I had voided the warranty.
When the barrel came home, I tried some additional load development using bullet weights from 55 to 75 grains with nothing turning in any sort of consistent accuracy. In frustration I decided to replace the barrel, and after canvasing every barrel maker I could find, Proof-Research was the only company to respond to my question “How do you install your chambers?” with anything reassuring. Their answer was “We indicate on center, and use piloted reamers.” which to me is the only correct answer for accuracy. Based on that conversation, I purchased a Proof Research Reece contour 16.25” stainless steel button rifled barrel in 223 Wylde.
I removed the STAG barrel from it's upper by heating the upper receiver to 500 ºF to release the Locktite 620. Apparently because I didn't apply the 620 directly to the barrel mortise, it came off the mortise with little effort, but the barrel tennon was another matter. To avoid reducing the barrel tennon diameter, I burned off the stubborn 620 with a torch, leaving the barrel tennon at a 'light straw' color. The barrel did not change color, nor did the barrel extension become loose. I put that barrel away, planning to never shoot it again.
Removing and installing the STAG barrel and the Hogue barrel nut/forend was the work of strap wrenches. To estimate torque I took a short 2-1/2” piece of galvanized pipe large enough to fit easily over the strap wrench handle and bored then filed a 1/2” square hole at it's mid-point to accept a torque wrench. The Hogue system isn't bad, but the one I have isn't happy with repeated installations, and to make matters worse I had removed the sling swivel stud and installed an Accu-Shot BT30 to accept my bipod. The repeated torquing and mucking about with the face of the reciever caused the handguard to eventually tighten up with the BT30 at about 5:30. This and the strap wrench game irritated me enough to buy a Seekins handguard for the new Proof Research barrel.
Having convinced myself during testing of the STAG barrel that torque over 30 ft-lb is alone sufficient to freeze the barrel to upper joint, I install the barrel using NAPA Copper Infused Ant-Seize Assembly Grease on the barrel extension, barrel flange, and all threads. I use 50 ft-lb torque. A Wilson jig that fits the upper's bolt raceway and has an oversize gas tube fixture is used to ensure the big barrel nut is aligned, and because there is assembly grease on all surfaces, a strap wrench easily holds the big barrel nut in alignment while the small nut is brought up to torque.
The Seekins MCSRv2 handguard features a large round barrel nut that engages the upper's threads, and provides a solid platform to attach the very lightweight handguard. The large nut has 4 gas tube holes, and is installed so that the handguard just fits the hole pattern (not touching the upper receiver directly at any point). The smaller barrel nut fits over the barrel flange and screw into the large nut. The small nut has 1-1/16” flats, so a crowfoot wrench of that size connects the torque wrench easily. Tightening the two nuts will force the barrel flange tight against the end of the upper's barrel mortise.
I then spent the Spring of 2020 trying to get the Proof Research barrel to consistently shoot sub MOA with little success. All the commercial and MILSPEC loads including match loads shot to about 1-1/2 MOA with this barrel as well.
At this point, I began wondering how much I was affecting the problem. During testing I often use my very accurate 308 (0.25 MOA) and 204 (0.35 MOA) to confirm my shooting ability or test scope performance, just to be sure, but doubts lingered. I decided to invest in a very expensive trigger, and purchased a Trigger Tech Adaptable AR Primary Trigger with a straight flat face. I adjusted the trigger to feel about like the very excellent Savage Accu-Trigger on my 204. I'm pretty sure it's just above 2.5 pounds. This trigger has zero takeup, zero creep, crisp break, and short overtravel and reset. It feels exactly like a fine single stage 1911 match trigger, and I absolutely love it! At first I wasn't sure it would help, but the longer I use it, the more I realize this trigger does improve my shooting accuracy.
While I was upgrading the trigger I decided to get rid of the upper/lower slop and installed a Wheel Diamond wedge. Took several hours to get it just right (a bit too tight on the takedown pin), but I wanted to 'shoot it in' in case there were any recoil induced changes. About 500 rounds later I'm ready to slowly ease it down to where I can press the takedown pin out by hand.
Still unhappy with the Proof Research barrel's paper accuracy I took it out after ground squirrels (it's original intended victims), and managed to land several 300+ yard shots on the tiny targets. The load used is one I will NOT recommend to anyone (you do this load at your own peril!). First you should understand I engineered this load to NATO Pmax, not 223 SAMMI Pmax. It consists of Lake City brass, CCI Small Rifle Primers, 40 grain Hornady Vmax bullets, and enough CFE223 to fill the case into the neck. It is a compressed load. In my rifles it does not generate as much pressure as a Black Hills 77 grain OTM Match load. It is the most accurate load I've found for the Proof Research barrel, and just in time for the 2020 Squirrel season.
Now that the 2020 squirrel season is over (little buggers went to bed a month and a half early this year!) I'm back to trying to improve accuracy. I've heard (and seen) that White Oak barrels can shoot sub-MOA, and they are not overly expensive. So I started putting together the parts to build a second test upper.
It was at this point, I thought 'I wonder how the STAG barrel would shoot this 40g Vmax load?' and 'I wonder if the new trigger will improve the STAG barrel's performance?'.
I dug out the STAG barrel, and decided to install it in the new Seekins handguard (this is going to be my standard handguard from now on). As I was assembling it, I discovered the STAG barrel is 1.050” diameter from the flange to the gas port shoulder, and the Seekins small barrel nut would not fit over the barrel. I called Seekings and they are sending (it arrived today) a 'spare' barrel nut. In the mean time I took a deep breath, and inside turned the small barrle nut so that it would just fit over the STAG barrel. There is very little material between the thread valley bottom and the inside of the nut, but it was able to withstand 50 ft-lb torque and as of today about 50 rounds of that very fast 40g Vmax load.
While I was buying parts, I got to thinking I didn't want to buy yet another scope, and I really didn't like the Vortex Cantilver mount I had been using, so I got a Warne QD XSKEL mount. One very cool feature of this mount is that the tension screws have a click detent built in. The instructions say to tighten the tension screws until the lever is able to go to lock 'easily'. Turns out there's a 3 click difference between the STAG-15 upper and the AR Stoner upper, with the Stoner being the wider 1913 rail (probably the FED coating). It turns out this mount will in actual proven fact ('cause I did it multiple times today), return to zero within 0.5 MOA on the same upper, and will (drum roll please!) move from rifle to rifle with repeatable POI adjustments yielding an undetectable shift from the last time it was on that particular upper! In this particular case the Stoner upper (STAG barrel) requires UP 8.25 MO, 4.5 MOA Left coming from 0,0 on the STAG-15 upper (Proof barrel)
While 5 shot groups are only precursor indicators, today I shot the tightest group I've ever shot with any of the AR platform configurations. It was a 0.560” 100 yard group from the STAG barrel. One possible explination may be that the ammo had spend an hour or more in 80F bright sun inside a clear plastic jug (it was sizzling!) before I shot it. V0(avg) 3544 fps, ES: 48 fps, SD 17.22 fps. Another possible explaination may be that I removed the monopod and replaced it with a PRS style squeeze bag at the rear, cutting down my sight wobble to about 0.5 MOA from about 0.75 MOA
Much more work to be done. The project is far from complete. If you want to build an accurte MSR the only thing I can tell you that isn't incorporated into this test is to buy and upper that has a flange to mount the hand guard rather than a barrel nut to mount the handguard. This seems to be one point of isolation shared by many of the factory sub-MOA guaranteed rifles.