SBR build questions...

[burnsome]

got out this AM to do some more testing after cleaning the barrel and putting a riser under the scope. Ordered an H2 buffer but in the meantime, tried an Endine hydraulic buffer in my carbine lower and it fed and extracted fine. all the brass landed at 3-oclock and no malfunctions noted. even worked fine on full auto (with the suppressor) and the bolt locked back on the last shot. anybody else run an Endine buffer in their 6.5's? mine seems to like it so far. the earlier jams i had i'm sure were due to using the lightweight (standard) CAR buffer as mentioned above.

[bwaites]

I run an Enidine, but the one designed for adjustable stock Grendels. There is a precaution to using any that aren't designed for the Grendel, because it was believed they could cause both cycling issues and contribute to increased risks of bolt damage/breakage.

[NordicG3K]

Finally got the chance to chrono some loads through both my 12.5" and 18" Grendels.

Hornady 123gn A-Max

18" barrel
2533fps average
35fps extreme spread
13fps standard deviation

12.5" barrel
2243fps average
26fps extreme spread
11fps standard deviation

Wolf 120gn MPT

18" barrel
2487fps average
20fps extreme spread
9fps standard deviation

12.5" barrel
2262fps average
43fps extreme spread
17fps standard deviation

Nosler 120gn BT (handload)
31.0gns of BLC2
CCI 200 primers
fireformed IMI 7.62x39mm brass
OAL 2.235"

18" barrel
2501fps average
15fps extreme spread
6fps standard deviation

12.5" barrel
2217fps average
3fps extreme spread
1fps standard deviation

6.5x39mm fireforming load (lite load, just enough for reliable function)
PRVI 139gn JSP
24.5gns W748
Remington 9-1/2 primers
IMI 7.62x39mm brass run through Redding sizer die
OAL 2.175"

18" barrel
1991fps average
29fps extreme spread
10fps standard deviation

12.5" barrel
1775fps average
10fps extreme spread
3fps standard deviation

All loads fed, fired, and ejected flawlessly. Curiously, the SBR kicked out all empties very consistently, at about 5:00 and 4 to 6 feet back. My 18" Grendel, however, threw them all over the place, mostly forward. Some dropped right on the table I was shooting from while others were thrown out to about 6 feet.

[burnsome]

There is a precaution to using any that aren't designed for the Grendel, because it was believed they could cause both cycling issues and contribute to increased risks of bolt damage/breakage

interesting....can you elaborate?

[LRRPF52]

The plunger on the Enidine system doesn't provide the same resting motion inertia resistance that a standard buffer does. This can lead to reduced or faster unlocking times, which is bad in a self-loader. The bolt and cartridge case take the brunt of the inopportune operating parameters, leading to possible failures of either. Once you start playing with what was a balanced design, and change the variables on one side of the equation, you need to equalize the other side as well.

In Bill's case, he reduced the buffer resistance on the recoil management and operating system cyclic rate side with the Enidine, AND then reduced the gas flow on the gas port with the adjustable as block( and consequently the gas tube flow, carrier key flow, and impingement chamber expansion rate formed by the bolt carrier and the rear of the bolt gas ring flange arrangement). When dealing with the AR's gas impingement system, I think it is helpful to approach it from this crucial center point, i.e.: the piston chamber formed by the hard-chromed bolt carrier, and the gas ring flange on the bolt itself. Whatever is done on one side of that, needs to be compensated for on the other.

The very first area of resistance is the carrier weight-to-gas volume thrust ratio, then the buffer body weight and projectile weight-to-rifling rate-of-twist, then the recoil spring strength and dwell time.

The genius of the direct impingement design keeps the reciprocating masses in-line with the bore-to-shoulder axis, as well as the expanding action of the gas within line of the bore-to-shoulder axis, making an extremely low-recoiling and minimally muzzle-rising system. I thought I fully understood it as a kid looking at cutaway diagrams of the process, but I am still learning more underlying benefits of the system decades later.

[burnsome]

well said sir-good logic there. thanks LRRPF52

[burnsome]

back out yesterday and put 100 rounds downrange using some different buffers. no problems encountered at all. used an H2, Endine, and Spikes T2 and the gun ran like a champ on semi and full auto. the more i shoot this gun the more i like it.

[LRRPF52]

What bullet weights are you shooting and how was controllability? I noticed that there was very little muzzle climb or recoil pushing the 100gr NBT's...I could spot my own impact with only maybe 1 Mil of jump to the right off a shooting bag, and that's with a very lightweight 16" Grendel and a small 1-4x Scope.

[burnsome]

for full auto use, have been using the 120 Wolf MPTs and controllability is not bad, especially with the endine buffer in the gun. i've fired a lot of machine guns, and its more controllable than a 7.62x39 AR or AK, definately less than a 308 auto. I think its more of a function of bullet weight in cases like this, as a 9mm full auto AR kicks more and rises more than a 223 due to pushing a much heavier bullet. Got a Smith Enterprises muzzle brake on the gun when not shooting suppressed. been using a 1-4x scope myself and on semi-auto, am able to see bullet impact on target at 150 yards with the scope set on 4 power. jumps more than you describe above though. I might have to get some reloading dies and try some 100gr bullets one of these days....

[LRRPF52]

Looks like you have a 5/8x24 TPI muzzle, correct? Yes, I think you'll fall in love with the 100gr pills in that rig.

9mm AR's kick lick a crazed horsy because there is no locking system in most of them, and they tend to be about a 5lb carbine with a direct blowback operating system.

[burnsome]

yes sir, 5/8x24. Smith Enterprises brake is made specifically for the 6.5 G as well.....