Trying to decide on either + 2 or 3 on a short mag build. Does it make any difference or is barrel length more of a deciding factor? While I do have a 22" 6.5prc w/+2 gas giving it a 14.7" up to the front of the receiver would a 24-28" be served better with the extra inch? 1 problem is that the maker that offers the chamber doesn't offer the +3. Any other insights for this query?
+ length gas systems
- Thread starter ARlife4me
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lyle2231
Well-Known Member
Compass Lake Engineering in Florida might be able to help.
kfd518
Active Member
The +2 is going to give longer for gas's pressure in the barrel to drop closer to designed operating pressure and timing of the unlocking of the bolt.
IIrc most of the short mags have issues with breaking extractors. The biggest reason for this is too much pressure still holding the brass to the chamber at time of unlocking. Buffer weight and spring rate can help this but I don't know about them FIXING it. Depending on journal length you could have it drilled for a GB 1" further away and possibly get your +3"
IIrc most of the short mags have issues with breaking extractors. The biggest reason for this is too much pressure still holding the brass to the chamber at time of unlocking. Buffer weight and spring rate can help this but I don't know about them FIXING it. Depending on journal length you could have it drilled for a GB 1" further away and possibly get your +3"
With extended gas port lengths. Its really about the length between the gas port and end of barrel .
barrel lengths pass 24" i use +3 on 260 rem
i have a 27" 223 i run +2
i have no experience on large cals .
i use craddock precision on custom ar barrels
paul is knowledgeable and can offer insite
barrel lengths pass 24" i use +3 on 260 rem
i have a 27" 223 i run +2
i have no experience on large cals .
i use craddock precision on custom ar barrels
paul is knowledgeable and can offer insite
Munch
Well-Known Member
When it comes to direct impingement rifles (AR10/15) getting the dwell time correct is critical to reliable performance.
Dwell time is the variable based on the distance from the gas port to the muzzle end of the barrel, not including any vented muzzle brakes or flash hiders. Not a distance from the gas port aft to an indeterminate reference point.
Generally, a 7 - 9" dwell time is desirable in an AR10. Thus, the gas tube length will be determined by the distance from the gas port to the crowned muzzle.
Proof Research uses a Rfile length gas tube in their 308 20" AR barrels which achieves a 7" dwell time. PR uses a Rifle+2 in the 6.5CM 20" barrel for a 5" dwell time. While I have no doubt the PR engineers are confident with their decision regarding a 5" dwell time, I have read too many technical papers stating a 5" dwell time is on the short side. So I went with the PR 22" 6.5CM barrel with Rifle+2 to achieve a 7" dwell time. My rifle does not have any dwell time issues; or any other issues for that matter.
Too little or too much dwell times will adversely effect reliability causing feeding and extraction problems. And not the same feeding/extraction problems if over or under optimum dwell time.
Dwell time is the variable based on the distance from the gas port to the muzzle end of the barrel, not including any vented muzzle brakes or flash hiders. Not a distance from the gas port aft to an indeterminate reference point.
Generally, a 7 - 9" dwell time is desirable in an AR10. Thus, the gas tube length will be determined by the distance from the gas port to the crowned muzzle.
Proof Research uses a Rfile length gas tube in their 308 20" AR barrels which achieves a 7" dwell time. PR uses a Rifle+2 in the 6.5CM 20" barrel for a 5" dwell time. While I have no doubt the PR engineers are confident with their decision regarding a 5" dwell time, I have read too many technical papers stating a 5" dwell time is on the short side. So I went with the PR 22" 6.5CM barrel with Rifle+2 to achieve a 7" dwell time. My rifle does not have any dwell time issues; or any other issues for that matter.
Too little or too much dwell times will adversely effect reliability causing feeding and extraction problems. And not the same feeding/extraction problems if over or under optimum dwell time.
My 24" 284 is a plus 3, and it's way overgassed. For a 26" or 28" 6.5prc, I would be ordering a +4 or +5. I don't like uppers that require lowers that have non-standard buffers.
My 28" rifle +1 7.62x39 is slightly overgassed with a carbine buffer. ARs just don't need that much gas.
My 28" rifle +1 7.62x39 is slightly overgassed with a carbine buffer. ARs just don't need that much gas.
Having standard and +2 length in 6.5creed, the standard length from Aero Precision has been the BEST! CBI with standard length has had issues, but has best accuracy. PR with +2 has been just as bad as standard (AP excluded). All using standard weight springs and buffers. I've found port size perfection is more reliable than + lengths. I'll know more when I reload using different powders that produce different gas volumes and pressures at specific lengths. PR is more marketing backed. Not saying they don't have good products as they do offer good products. I've seen gas ports within the last 2" of the muzzle that work well. I can add sping weight and/or buffer weight, but not having more weight to cycle is my goal.
lyle2231
Well-Known Member
Could a adjustable gas block help solve a over gassed AR?
Munch
Well-Known Member
Maybe...depends WHY it is over-gassed.
Depends on a few things...........how much overgassed, gas system length and cartridge? Most AR15's don't have this issue, but AR10's have many. Having many different barrel manufacturers with different gas system lengths in 6.5creed I've found out gas port size solves the issue. Aero Precision barrels with rifle length gas system in 6.5creed has port size nailed down! I have 3 barrels with 3 different lengths and all have standard rifle gas length systems. None of them use an adjustable gas block and all use standard weight buffer springs and buffers (rifle and carbine). Criterion and Faxon use standard length and Proof Research use +2. All 3 of those brands are overgassed when using the same ammo shot in AP barrels (Hornady 123sst's). AP states gas port size on their site after selecting barrel.
