6.5CM AR-10 Action Guidance

[thirstman]

I'm building my first AR-10 and I'm going to be using the following JP parts:
Supermatch barrel with high-pressure bolt
Either the low mass or variable mass(h2) bolt carrier
Silent capture spring(h2)

My areas of concern are:
Maintaining the integrity of the cases I'm reloading.
Reducing the violence inside the chamber to prolong service life.

I am going to use an adjustable gas block to allow additional tuning, but my question is this, do I use the low mass carrier or the heavy variable mass? And does that choice change if I put a can on? I'm not sure what the recommendation is for 6.5CM

I intend to acquire a can at some point, but I will also be shooting loud for quite some time until then.

Will it beat the crap out of my bolt, chamber, and barrel if I choose the wrong weight and how would that change with a can on?

I feel like a heavier carrier will move slower but have more energy when it impacts, as opposed to a light carrier moving faster but having less energy when it impacts, so which one is actually harder on the rifle? And how does one need to consider weight when increasing pressure by throwing a can on?

 

[GreenCanoe]

Not sure what you mean by "maintaining the integrity of the cases I'm reloading". Please elaborate.

Seems like the operative decision you've made is the adjustable gas block. With that you'll be able to tune your gun pretty well for with/without can and carrier weight. There's not a whole lot you can do to adjust the "impact" of the BCG with the gas block though, the DI system blows the carrier back, the buffer spring pushes it back forward, so it's a balancing act getting the right spring weight, BCG mass and gas setting. No matter what though you don't want it to shoot too "soft" otherwise it won't cycle reliably.

My recommendation, either carrier you get, adjust your gas system and your powder type/charge to make it cycle reliably before you play with carrier mass. Too many variables at the same time make for hellish troubleshooting.

 

[SD Carpenter]

I just built a seekins sp10 using your parts, JP low mass bcg, bolt, scs h2, and it cycles reliably. The brass does get banged up pretty good though, but it's a gas gun and that tends to happen.

 

[bfoosh006]

I'm building my first AR-10 and I'm going to be using the following JP parts:
Supermatch barrel with high-pressure bolt
Either the low mass or variable mass(h2) bolt carrier
Silent capture spring(h2)

My areas of concern are:
Maintaining the integrity of the cases I'm reloading.
Reducing the violence inside the chamber to prolong service life.

I am going to use an adjustable gas block to allow additional tuning, but my question is this, do I use the low mass carrier or the heavy variable mass? And does that choice change if I put a can on? I'm not sure what the recommendation is for 6.5CM

I intend to acquire a can at some point, but I will also be shooting loud for quite some time until then.

Will it beat the crap out of my bolt, chamber, and barrel if I choose the wrong weight and how would that change with a can on?

I feel like a heavier carrier will move slower but have more energy when it impacts, as opposed to a light carrier moving faster but having less energy when it impacts, so which one is actually harder on the rifle? And how does one need to consider weight when increasing pressure by throwing a can on?

From what I see... the JP Supermatch barrel has a +2 GLS, that alone helps quite a bit for a lower chamber pressure while extracting the fired case.

The HP bolt will have a smaller diameter firing pin and firing pin hole... also helpful.

Honestly... I would wait on the Adj. GB, as the +2" gas system helps mitigate chamber pressure extraction issues. You can always add it now or later for "fine" tuning if needed or desired.

A can will add backpressure but it shouldn't be beating the crap out of the +2 gas system.

In all honesty, I would suggest you e-mail JP as well... they will know gas port sizes on their barrels and have daily ( hourly ) experience with their products. Explain what you are trying to accomplish and your thoughts.

JP makes fine products, so I won't suggest any polishing tricks.

FWIW, and I don't use a can..but.... I run as heavy buffer weights as possible ( 5.3oz DPMS pattern, 5.4oz Armalite pattern, and 9.3oz rifle length ), Tubbs 308 Flatwire recoil springs in all the various buffer tube lengths, Adj. SLR gas blocks ( opened 6 of the available 15 clicks ) and MLGS and RLGS on all mine and I do polish various spots to aid smooth feeding.... they all are pussy cats at the bench.

I have never felt the BCG slamming hard into the barrels breech face. Frankly they run so "soft" during the recoil cycle, the ammo feeding slows it to a respectable cyclic speed.
The heavy weight setups have worked so well, I haven't bothered trying a Light weight setup... the OEM volume of cycling gas made me steer down the "heavier" path.

I am glad I did... following online advise...my tuned, polished, snugged up PSA's have produced respectable groups.

Just remember, what worked for me might not work for the next rifle.... and when I built mine, ammo was cheap... and that allowed me to try a huge variety factory loads to see what every barrel prefers. So as always... YMMV.

 

[wade2big]

From what I see... the JP Supermatch barrel has a +2 GLS, that alone helps quite a bit for a lower chamber pressure while extracting the fired case.

The HP bolt will have a smaller diameter firing pin and firing pin hole... also helpful.

Honestly... I would wait on the Adj. GB, as the +2" gas system helps mitigate chamber pressure extraction issues. You can always add it now or later for "fine" tuning if needed or desired.

A can will add backpressure but it shouldn't be beating the crap out of the +2 gas system.

In all honesty, I would suggest you e-mail JP as well... they will know gas port sizes on their barrels and have daily ( hourly ) experience with their products. Explain what you are trying to accomplish and your thoughts.

JP makes fine products, so I won't suggest any polishing tricks.

FWIW, and I don't use a can..but.... I run as heavy buffer weights as possible ( 5.3oz DPMS pattern, 5.4oz Armalite pattern, and 9.3oz rifle length ), Tubbs 308 Flatwire recoil springs in all the various buffer tube lengths, Adj. SLR gas blocks ( opened 6 of the available 15 clicks ) and MLGS and RLGS on all mine and I do polish various spots to aid smooth feeding.... they all are pussy cats at the bench.

I have never felt the BCG slamming hard into the barrels breech face. Frankly they run so "soft" during the recoil cycle, the ammo feeding slows it to a respectable cyclic speed.
The heavy weight setups have worked so well, I haven't bothered trying a Light weight setup... the OEM volume of cycling gas made me steer down the "heavier" path.

I am glad I did... following online advise...my tuned, polished, snugged up PSA's have produced respectable groups.

Just remember, what worked for me might not work for the next rifle.... and when I built mine, ammo was cheap... and that allowed me to try a huge variety factory loads to see what every barrel prefers. So as always... YMMV.

Are your 9.3 oz rifle length rifles noticeably smoother than the lighter and shorter buffers and tubes? I’m not a fan of any stock that mounts on a rifle length receiver extension. I haven’t tried the plain jane magpul moe rifle stock. That one might be short enough. All the others are far longer than I like for semi autos.

 

[bfoosh006]

Are your 9.3 oz rifle length rifles noticeably smoother than the lighter and shorter buffers and tubes? I’m not a fan of any stock that mounts on a rifle length receiver extension. I haven’t tried the plain jane magpul moe rifle stock. That one might be short enough. All the others are far longer than I like for semi autos.

The Adj. GB's are tuned to each buffer weight, I can tell the slight difference while the tuning the adj. GB.

And since I use the Tubbs 308 Flatwire in all the buffer tube lengths, the added compression from the shorter buffer tube lengths seems to pre-load the recoil impulse.

Ultimately, I don't notice much recoil difference between the 9.3oz and the 5.4ish.
I use the rifle length stocks for bench / long range shooting because of comfort and control.

 

[r.tenorio671]

....since 2015 I have been running a 16" AR10 built on Aero receivers, BCG, carbine buffer/spring/tube, BA Hanson barrel and use a SLR AGB on it. Commercial CBC FMJ, Federal M80 and FGMM 168 all cycle with no issues. My handloads using W748, 8208XBR & AR-Comp w/HDY 155 BTHP, HDY 168 & HDY 175 all cycle reliably w/AGB setting of 5 and is very soft shooting. I feel I can improve on the timing of the bolt unlocking with a heavier buffer so I bought the KAK "LR-308 Carbine Heavy Buffer" which is 5.3oz -vs- the Aero 3.8oz. The KAK unit is all SS and matches the 2.5" of the Aero buffer and is more durable and should improve longevity as well. I also bought some of KAK's "AR-15 Configurable Buffer Kit's" for the weights (3x aluminum, steel & tungsten) so I can explore varying overall weights in the buffer (which KAK confirmed the weights will work in the AR10 & AR15 buffers they sell). The kit price is lower than just buying the tungsten weights alone. The current AGB configuration works and works well, but I think I can go higher on charge weight for higher FPS but will need finer tuning of the bolt unlocking, which I hope the weight modifications combined with the AGB's adjustability will achieve. The kits will also allow me to explore more refined tuning of my AR15 platforms in multiple calibers. YMMV