Hey guys,

So I am having a really hard time deciding between a complete BCM upper and just building my own. So here are my thoughts

Reasons I like BCM: less work good price

BCM cons: mk2 12.5 upper is and has been out of stock.  1:7 twist when I have quite the stockpile of m193 55gr


So for building my own I would do a criterion 12.5 1/8 twist 223wylde barrel. Criterion has the "hybrid" medium profile barrel in stock. How is the durability of that profile vs govt profile? The pictures make it look basically the same but I'm new to this so appreciate the advice.

Also if I do my own part of the benfit I'd think would be saving some money but I don't wanna cheap out on parts. What are some high quality stripped uppers. I was wanting a bcm mk2 stripped but those also seem to be out of stock to oblivion.

ADM has an upper and lower set for like $585 but my plan was to go with the cheaper AERO m4e1 lower and get a nicer upper but I can't seem to figure out which companies that would be beside like ADM or Radian. The Radians include the rail and seem priced a little high. This is another area I'd really appreciate advice on.

So tell me what you think guys. I'm gonna be buying parts over the next month and I'm hoping to have a complete build by the end of October.

Thanks in advance!

BCM is solid product, but I’d say roll your own. I own a 16” Mk2, and an 11.5 Mk2 complete. Might end up parting ways with the 16” as I wanted this rifle in an SPR type role, and accuracy seems less than desirable FOR that intended role. The 11.5 is great as-is and I will keep it around. Wish they’d re-stock the stripped Mk2 uppers soon, but that’s a pipe dream.

If BCM has a 1/8 twist for the 12.5 upper I'd be sold other then the fact that the mk2 is never instock.

I am having trouble finding a stripped upper that's higher then Aero quality but isn't the price of like a noveske gen 3 or adm upper.

There's nothing wrong with 1/7 for 55g and aero receivers are good quality. Either would work fine for you. Given BCM's lack of availability I'd pick up an aero receiver set and build your own.

Ended up doing a BCM 12.5 upper and BCM lower. It is really nice and I’m super happy with the finished product. Absolutely zero issues with accuracy, it’s more accurate then my 16in saint victor. I can’t help but wonder if all these BCM accuracy threads are a little overblown or maybe I just got lucky. The pistol feels solid as hell and shoots better then I could have hoped for using M193 55gr

So what?


55 Grain FMJ Ammunition Fired From AR-15s With 1:9” and 1:7” Twist Barrels


The Internet Command: "55 grain FMJ bullets are over-stabilized and inaccurate when fired from an AR-15 with a 1:7” twist barrel."


Statements such as the one above always seem to be proclaimed by the Internet Commando, without posting any valid, statistically significant data to support that these effects occur, or that if they do occur, that they do so to any degree that has any significant effect on the accuracy/precision spectrum involved with AR-15s firing M193-type ammunition out to distances of 100 yards.

By definition, an “unstable” bullet will have a gyroscopic stability factor of less than 1.0 at the muzzle.  A typical 55 grain FMJ bullet loaded in M193-type ammunition will have a gyroscopic stability factor of approximately 4.27 when fired from a 20” barrel with a 1:7” twist.

[CaptainObvious] 4.27 is not less than 1.0. [/CaptainObvious]


The following demonstration compares the results of firing four, 10-shot groups of the same lot of 55 grain Prvi Partizan M193 ammunition from two different AR-15 barrels; one barrel with a 1:9” twist, the other barrel with a 1:7” twist.  When chronographed from a 20” Colt M16A2 barrel, the muzzle velocity of this lot of PPU M193 was 3219 FPS with a standard deviation of 35 FPS.

The accuracy specification for M193 cited in MIL-C-9963F is as follows:
The average of the mean radii of all targets of the sample cartridges, fired at 200 yards, shall not exceed 2.0 inches.
These averages are from 10-shot groups fired from machine rested, bolt-actioned test barrels.  All things being equal (which of course they seldom are) this specification equates to a mean radius of 1 inch at 100 yards.








The first barrel used in testing was a 16” Colt HBAR with chrome-lining, a NATO chamber and a 1:9” twist.  This is the barrel found on the Colt 6721.  All of my free-floated Colt 6721 barrels have turned in sub-MOA 10-shot groups at 100 yards when using match-grade hand-loads.

The second barrel used in testing was a 20” Colt HBAR, also with chrome-lining, a NATO chamber and of course a 1:7” twist.  I've owned three of these barrels and they have all turned in 10-shot groups at 100 yards that hover just above one MOA when free-floated and shooting match grade handloads.  I purposely selected the shorter barrel with a 1:9" twist and the longer barrel with the 1:7" twist in order to exacerbate any possible statistically significant influence that the differing twist rates and intendent muzzle velocities might have on the precision of M193-type ammunition when fired at a distance of 100 yards.


Colt 16” HBAR




Colt 20” HBAR






Accuracy (technically, precision) testing was conducted from a distance of 100 yards following my usual protocol. The barrels were free-floated during testing.  The fore-ends of the weapons rested in a Sinclair Windage Benchrest and the butt-stock rode in a Protektor rear-bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was used. The wind conditions on the range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.





The Wind Probe . . .




Four 10-shot groups of the PPU M193 were fired from the 1:9” twist barrel. Those groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius of that composite group was 1.08”.
As with the 1:9” twist, four 10-shot groups were fired from the 1:7” twist barrel.  Those groups were also over-layed on each other to form a 40-shot composite group; the results were nearly identical to those obtained from the 1:9” twist barrel.  The  composite group had a mean radius of 1.01”. The two composite groups are shown side by side for comparison.






The entire test as described above was also conducted using a second 16" chrome-lined, NATO chambered Colt HBAR with a 1:9" twist and a second 20" chrome-lined, NATO chambered Colt HBAR with a 1:7" twist.  The ammunition used in this test was all from the same lot of Wolf 55 grain FMJ "Performance Ammunition."  

As before, four 10-shot groups fired from each barrel at 100 yards were over-layed on each other using RSI Shooting Lab and just as before, the mean radii for these 40-shot composite groups showed no statistically significant difference.







Quality, modern lightweight bullets of copper-jacket/lead-core construction can shoot superbly from AR-15s with fast twist barrels. Typical 55 grain FMJ bullets found in M193-type ammunition do not fall into the quality category.

The 10-shot group pictured below was fired at a distance of 100 yards using 55 grain Sierra BlitzKings from one of my Krieger barreled AR-15s.  The barrel has a 1:7.7” twist.  The group has an extreme spread of 0.439 MOA.











……


An Accuracy Comparison of M855 When Fired From AR-15s With 1:9” Twist and 1:7” Twist Barrels.







This test will compare the accuracy (technically, precision) of IMI M855 at a distance of 100 yards, when fired from an AR-15 with a chrome-lined, NATO chambered barrel with a 1:9” twist and an AR-15 with a chrome-lined, NATO chambered barrel with a 1:7” twist.  The IMI M855 is one of the most accurate and consistent loadings of all the M855 clones that I have tested.

IMI M855 is loaded with a 62 grain FMJ bullet with a cannelure. It also has a steel penetrator seated in the ogive portion of the projectile. This makes the projectile unusually long for its weight, as well as giving it a lower specific gravity. The ammunition is charged with "ball powder". The primers are sealed and crimped in placed. The bullet is also crimped in place and the case mouth is sealed with an asphalt sealant.





Chronograph data for the IMI M855 was obtained using an Oehler 35P with "proof screen" technology. All velocities listed are muzzle velocities as calculated from instrumental velocities using Oehler's Ballistic Explorer software program. All strings of fire consisted of 10 shots each.





This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group reduction techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrels used in the evaluation were free-floated. The free-float handguard of the rifle rested in a Sinclair Windage Benchrest with the aid of a Sinclair fore-arm adaptor, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was used.  Wind conditions on the shooting range were continuously monitored using a Wind Probe. All rounds were fired from the magazine. Each upper was fired using the same lower.


The barrels used in this evaluation were both Colt HBARs with NATO chambers and chrome lining. The 1:7” twist barrel was 20” in length and the 1:9” twist barrel was 16” in length. I purposely selected the shorter barrel with a 1:9" twist and the longer barrel with the 1:7" twist in order to exacerbate any possible statistically significant influence that the differing twist rates and intendent muzzle velocities might have on the precision of the M855 ammunition.

The first barrel used in testing was 16” Colt HBAR with chrome-lining, a NATO chamber and a 1:9” twist. This is the barrel found on the Colt 6721. All of my free-floated Colt 6721 barrels have turned in sub-MOA 10-shot groups at 100 yards when using match-grade hand-loads.

The second barrel used in testing was a 20” Colt HBAR, also with chrome-lining, a NATO chamber and of course a 1:7” twist. I've owned three of these barrels and they have all turned in 10-shot groups at 100 yards that hover just above one MOA when free-floated and shooting match grade handloads.



Three 10-shot groups were fired from the upper with the 1:9” twist barrel in the manner described above. The extreme spreads for those groups measured:

2.72”
2.19”
2.24”

for a 10-shot group average of 2.38”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the composite group was 0.76”.



In the same manner as above, three 10-shot groups were fired from the upper with the 1:7” twist barrel. The extreme spreads of those groups measured:

2.14”
3.01”
1.71”

for a 10-shot group average of 2.29”. As before, the three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for this composite group was 0.68”.





....

Your absolutely right, I didn’t know any better before actually getting the BCM, i def fell prey to those internet commandos. I have taken it out twice now and it is more accurate then my 1:8 twist 16in saint victor. my results where great with Winchester M193 I was shooting 1 MOA at 50 yards and at 100 yards. I ended up going BCM upper and Lower and the fit and finish is amazing, I’m glad I did that instead of the aero lower because they fit together so perfectly and there are no extra screws to worry about.