So I bought a DPMS 308 with the 18” mid heavy profile , 875 gas block on a high rail pattern, a fixed type old school A2 IIRC 10 or more years ago. I replaced that stock with a magpul prs. I shoot many uppers off that lower. 308, 260rem, 6.5 creed, 6mm creed, now I’ve ran into a problem with the 7mm 08 build. It’s accurate and ejects bout 12” at 3 o’clock but short strokes bout 3/4 way, with factory 139grn Hornady and published hand loads, all else is good gas block alignment- set screw, tube pined, bcg key tight, all unobstructed. I’m considering a reduced power spring as a hopeful fix. Any experience here with the AR 7-08, why it’s gonna act a butthole when at least 10 other uppers work 100% without a hitch. I will say I have a 243 yet to shoot it so I don’t know how it’ll act, there’s also the 6 mm Creedmoor, never short stroked but it’s soft shooting and doesn’t eject very far. What’s special bout this 7-08???
DPMS LR 308b
- Thread starter thehartofthings
- Start date
Do you have an adjustable gas block on your 7 08 barrel? If not, that should be the first thing to install and adjust.
I believe I’ve narrowed it down. So I used a Wilson Combat barrel, nothing wrong with the barrel as it is, it is very accurate. Wilson puts their own gas blocks on their barreled uppers and complete rifles. I used a strike force gas block, one that I’ve used on a couple of other builds. It is a set screw type , I usually go with a clamp type but have used the set screw type before if the barrel was dimpled. I don’t do dimpling. Big lesson learned , just because there is a set screw doesn’t mean the barrel gas port and underside gas block entrance port line up completely. Some measuring is showing it to be about 020 offset. My guess is it’s probably 25-30% closed off. I put the dremel to work. Gonna test tomorrow and hopefully put this build to rest. I was shooting some 162grn eld at 600 around 2250 with 43 grains of MR2000, it’s a hammer at 600 and bucks wind pretty good at that distance. I’ll report results tomorrow
Do you mean 2250 fps muzzle speed? My first guess was gas block, too, but that's a pretty light load. There might just not be enough oomph to cycle the action with 2250fps mv. Just for reference I'm getting about 2600fps from a 20" barrel with 162 amax in a bolt rifle. I used to get 2700fps and change, but I dropped back to a very gentle 2600fps.
Well the barrel is only 18”, quick load was about 20 FPS off. I know it would be considerably faster with a full 24” tho.
Mine is 41.9 grains of Varget, 162 amax, Winchester brass, Br2 primers, OAL of 2.90x" (where x is a little number between about 2 and 5---I call it a "tidge"). Note that I'm using a 20" barreled bolt rifle (suppressed) and that my oal is about .100" over SAAMI specs. You probably know this, but the longer oal gives me a little more wiggle room with pressure. Same with bolt vs ar some say. My point is be careful :^)
Disclaimers and etc.
Disclaimers aside, I would shoot for at least 2450fps out of your rig. Once you get there, and if it's cycling, then I'd look upward for the sweet spot.
Disclaimers and etc.
Disclaimers aside, I would shoot for at least 2450fps out of your rig. Once you get there, and if it's cycling, then I'd look upward for the sweet spot.
That sure would make an issue... please let us know how it works out.
And BTW, the SLR dimpling blocks, can be bought for pretty cheap when they run a sale.... super easy to use.
That solved the issue!!! It took about 4 or 5 rounds before it sealed itself off, after that it was cycling. Primers look good , I’m at 46 grns of mr2000 with a 139 btsp giving me 2680 out of the 18” Wilson, unsuppressed with a fairly aggressive brake. 1st issue of this kind for me. Strike force Industries block, Wilson Combat barrel. Glad it finally worked out.
