Reasonable price $82.95. 16" barrel is hard on brass even in 308win carbine length gas. 16" 6.5creed would undoubtably be worse at suppressed or not. Aero Precision list port size on their barrels under specs.
- Thread starter rockwind1
- Start date
If there's not enough weight and/or load pressure behind the bolt an agb can only do so much? If you're only dealing with ejection patters, then an agb can help.
so right now, my spring is the stiffest that jp makes. however i can increase the weight a little bit by adding another tungsten weight instead of steel.
i know, i started one thread when the federal ammo had pressure, i started this one to see if anyone had found lighter load factory ammo and in the meantime, i fixed the problem with the hornady varmint express 95 gr amax.
what is H3 or H4?
That will add ~.85ozs changing from steel to tungsten. Also did see you're using a scs, but is it standard or heavy scs? SCS needs to make contact with the bcg when closing the upper to a point of almost pushing the scs back with a thin blade screwdriver. If not, you need to add the C-clip that came with unit. That extra play between the scs and the bcg can be an/the issue!
Just heavier than the H2 in weight. Not sure how much difference as it changes between mfgrs by a few tenths or hundredths.
i don't even see the H3 or H4 on their website? i believe i have the heavy scs, because it is the ar10 version and i have the 110 red/yellow painted spring. it is the heaviest spring. thanks for tip on that washer, didn't know that was what it was for. but i checked and the scs and my bolt lightly touch as it goes together. sigh.. maybe i should add it anyway!
sent message.
i checked my spring,, it is already the heaviest one they have. at this point i can add about .85 oz to my weights and see what happens. i may add a bigger suppressor as well, perhaps that will help. i have a couple 338 cans not doing anything. they weight twice as much as the ultra 7 though
If you have the heaviest spring, you may want to drop the weight of that spring down by one, and add all the weight you have. That will be a good test.
For the first 5 shoot without the can. Then try 5 with. Save all that brass and take pics to post.
The 338 volume can may help the issue. I'm running a dominus myself and I am dealing with high back pressure as well but I think I have a good handle on it. I plan to swap to the magnus once it's freedom.
I would ditch the jp silent capture.
An AR10 shooting 260/6.5 CM or like work best with a very specific set up providing that gas is correct:
1. 7-5/8" internal length receiver extension
2. 308 standard weight rifle length spring
3. 3.250" Buffer weight between 5 and 8+ oz.
For the first 5 shoot without the can. Then try 5 with. Save all that brass and take pics to post.
The 338 volume can may help the issue. I'm running a dominus myself and I am dealing with high back pressure as well but I think I have a good handle on it. I plan to swap to the magnus once it's freedom.
I would ditch the jp silent capture.
An AR10 shooting 260/6.5 CM or like work best with a very specific set up providing that gas is correct:
1. 7-5/8" internal length receiver extension
2. 308 standard weight rifle length spring
3. 3.250" Buffer weight between 5 and 8+ oz.
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what would dropping down to a weaker spring do, if the goal is to keep bolt from moving back too soon? not arguing at all, just trying to understand the physics and diagnostic process for future
That will need to be an A5 tube for that to work with a 3.25" buffer.
On a SCS it wouldn't help suppressed. What is the gas system length?
Have you tried it unsuppressed?
I think the scs system is good, but not for overgassed guns, unless you want to add a heavy bcg especially suppressed. I'll check the gas port on the cbi I have (standard rifle length gas w/20" barrel).
with the federal fgmm 130 gr berger, i have had only 1 blown primer but definite pressure signs on rest,, i did try a few shots with the suppressor off and the pressure signs still appeared on head. hard to tell if the pressure was reduced in any small amount or not by just looking at the marks.
i did get the blown primer AFTER switching from 338 tbac suppressor to the ultra 7 30 cal.
I am resigned to the fact that maybe some ammo just won't work in it, like that federal. so i am now onto a different path with the new hornady 95gr and now my new goal is to lessen the amount of blowback if at all possible.
without going crazy, the 2 things i can easily and cheaply do is add the .8oz to my buffer and put the 338 can back on
I can't believe it! The cbi has the same port size as the AP barrel (.076"). With the same ammo the cbi pops primers and the ap doesn't.
Are you rolling your own or buying factory? A faster powder will give you less pressure down the line and possibly less gas volume.
i stopped reloading a few years ago,, huge time suck. the blown primer and pressure was with factory ammo,, federal gold medal match that came factory loaded with berger 130 gr hybrid OTM
which is why this pressure was a surprise to me in the ar10 platform, i figured it would handle sammi spec ammo.
Probably made for BA's from test guns. Here's my cbi setup.
Attachments
You aren’t having pressure issues most likely. Your bolt is unlocking and trying to extract too early which is mimicking overpressure. A 16” 6.5CM may require more buffer weight than you can get with that JP stuff you are using. You will need to weight up that buffer significantly.
Now is there a chance you have an out of spec chamber which is causing the false signs as well? Possibly but less likely.
I'm copying from a message that I wrote to the OP as reference:
"Standard AR-10 SCS are the equivalent of 3.8oz buffer, heavy is 4.6. Not sure you can replace the bottom weight, you used to not be able to. Ultra 9 is in the top zone for back pressure, the Ultra 7 is a bit better, but still high. Your 16" RLGS barrel is ideal, but with that can, the dwell is the equivalent of a 20"+ barrel. You're unlocking under excessive pressure. the only way to delay the bolt unlocking is to increase the buffer weight, like up to 8.5oz. Or a flow through can. Lots of details if you change your action/recoil sys."
Buffers and spring have to work together, but they have different characteristics during the BCG cycle.
In regards to delaying the bolt unlocking, the buffer operates under Newton's Laws of Motion. The buffer has its greatest force opposing BCG movement at the beginning of the cycle after firing. That opposing force decreases until the buffer bottoms out in the RE. The greater the buffer weight, the more it opposes BCG movement, thus delaying the bolt unlocking, hopefully enough that chamber and bore pressure drops to acceptable levels.
Springs have the least amount of force upon the BCG at the beginning of the cycle after firing. The springs opposing force on the BCG increases until the buffer bottoms out. This is true even with flatwire springs, but to a lesser range. Delaying the bolt unlocking solely by increasing spring strength is difficult without creating other issues.
Bottom line - increase the buffer weight to delay the bolt and increase the spring strength enough (if needed) to tame the buffer from slamming into the RE. Then you get to deal with the other half of the cycle - feeding.
ETA: I believe OP already has as AGB
"Standard AR-10 SCS are the equivalent of 3.8oz buffer, heavy is 4.6. Not sure you can replace the bottom weight, you used to not be able to. Ultra 9 is in the top zone for back pressure, the Ultra 7 is a bit better, but still high. Your 16" RLGS barrel is ideal, but with that can, the dwell is the equivalent of a 20"+ barrel. You're unlocking under excessive pressure. the only way to delay the bolt unlocking is to increase the buffer weight, like up to 8.5oz. Or a flow through can. Lots of details if you change your action/recoil sys."
Buffers and spring have to work together, but they have different characteristics during the BCG cycle.
In regards to delaying the bolt unlocking, the buffer operates under Newton's Laws of Motion. The buffer has its greatest force opposing BCG movement at the beginning of the cycle after firing. That opposing force decreases until the buffer bottoms out in the RE. The greater the buffer weight, the more it opposes BCG movement, thus delaying the bolt unlocking, hopefully enough that chamber and bore pressure drops to acceptable levels.
Springs have the least amount of force upon the BCG at the beginning of the cycle after firing. The springs opposing force on the BCG increases until the buffer bottoms out. This is true even with flatwire springs, but to a lesser range. Delaying the bolt unlocking solely by increasing spring strength is difficult without creating other issues.
Bottom line - increase the buffer weight to delay the bolt and increase the spring strength enough (if needed) to tame the buffer from slamming into the RE. Then you get to deal with the other half of the cycle - feeding.
ETA: I believe OP already has as AGB
I measured the fired brass, and it seems to have measurements consistent with a normal sized chamber
Have to be careful with that. Measuring spent brass is not the best indicator. The pressure impact, and force on the brass aren't always happening under full chamber support.
The only way to tell is to measure the chamber.
so, it is the same otherwise than the barrel, and it is acting completely different? that is crazy. what do you think it is?
I’ve been looking around for an8.5oz buffer weight. Searches have not found
what brand or shop would you recommend for an 8.5oz buffer. which spring have you used and prefer, lb wise?
With a pcc buffer (which can be longer than a AR15 carbine buffer) can get you close to that weight and not sure what type of setup will be needed? KAK has a 9.3oz rifle length buffer (I bought in case for 7saum and 6.5prc builds).
Nope that is rifle length. Your receiver extension screws directly into the back of the lower receiver with no castle nut to hold it in place. You must be using the JP buffer system with the spacer in place.
Good news is you can purchase AR10 rifle length spring and a AR10/LR308 rifle length buffer. I believe these come standard at 5.6 or 5.8 oz. Inside is 5 steel weights. These can be replaced with tungsten weights which gives you .8 oz more weight each weight you swap. In other words you can get to nearly 10oz if need be. You can purchase tungsten buffer weights separately and can experiment from there. Save that JP SCS for another more common tried and true build or sell it because most “my rifle don’t work right” threads all seem to have that part in common.
Tungsten Recoil Buffer Weights H3 AR-15 Accesories | Shop Pur Tungsten
Heavy Tungsten recoil buffer weights that serve as a direct replacement for the stock weights found in your AR15 carbine buffer tube. Get the H3 weight kit!
pur-tungsten.com Slash and the spring he sells
You have to either use a spacer(cheaper) or swap your rifle extension. I listed the parts out in a previous post. The spacer will allow you to retain your current stock set up on the rifle length extension.
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I wouldn’t purchase any of his rifle length stuff. He can buy a LR308 rifle length buffer and tungsten weights for less than half of the cost and is user adjustable. As far as how much weight he needs, I don’t know. I’ve never had a 16” 6.5CM.
I do know a 20” rifle gas 6.5cm will do the same exact thing the OP is having issues with with the light and short 2.5oz buffer in a carbine extension when suppressed and with an AGB. One of my buddies has had pierced primers and tortured brass. He needs to weight up as well. Rifle length gas port is definitely not for any 6.5cm barrel over 18”.
Best way to measure your buffer tube is from the inside from rear to the slot where the retainer catches. Outside dimensions are 8" on the A5 and 7.25" on standard carbine tubes. If it's rifle length tube it has a ring at the front behind the threads (undoubtedly no mistake on that). Between the A1 and A2 is only a spacer at the rear of the tube for the buttstock that requires a longer (about 3/8 or 5/8") screw.
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