I have built a AR 10 in the 6.5 CM with a Shilen 24" barrel with a Rifle length gas system, I am having problems with it short stroking and double feeding. I had a JP SCS in it and thru it in the recycling bin and went to a full length buffer with a PRS stock, I am now able to fire about 5 rounds before it jams up again.... Any thoughts?
Problems with the AR 10 in 6.5 CM
- Thread starter Derrick Tanner
- Start date
Where is the gas port drilled? My .260 AR-10 has the port drilled 1.8" farther forward than standard rifle position. If yours is at standard position this would be the reason. Also what powder are you using? In my 15s H322 shoots really nice with 77s, but the cycling is just long enough to get a round from the magazine. Same can happen in the 10 if you are using a quick powder.
Another thing you may want to check are the shoulders, are you setting them back 0.003" which is a good rule of thumb for semis.
Another thing you may want to check are the shoulders, are you setting them back 0.003" which is a good rule of thumb for semis.
Standard rifle length position can be fine. Short stroking is due to not enough gas. Test with one shot in magazine, does it reliably lock back with bolt catch on bolt face (not bolt carrier)?
I would recommend you remove and clean gas tube, gas block and check alignment upon reassembly. While gas system is off, use back of drill bit as pin gauge to determine gas port size in barrel.
If that cleaning/aligning doesn't fix it, then and only then think about what parts to throw at it.
-Mac
I would recommend you remove and clean gas tube, gas block and check alignment upon reassembly. While gas system is off, use back of drill bit as pin gauge to determine gas port size in barrel.
If that cleaning/aligning doesn't fix it, then and only then think about what parts to throw at it.
-Mac
I am shooting the Hornady 120 gr A-MAX factory.. that is all I have right now..
Ok, yup that should cycle a rifle length fine. I'm running an A2 with standard 308 buffer and 308 sproing (oops I mean spring).
Check gas block alignment (look for carbon soot on barrel), check for tube to BCG alignment (carbon soot/shiny wear areas), and may have some buildup in gas tube/gas port. clean as required.
I just checked and had to move my gas block, I had to put a .070 shim between the block and shoulder, Why would they do that on rifle length systems? I am waiting on my shipment of ammo to come in today to try it and see if it works... Thank you I never would have thought of checking that distance....
My 260 was put together by Medesha and he puts it 1.8" farther forward, even my 308 upper that EGW made has the port I think 1.6" farther forward. The earlier post is correct that it is due to the amount of gas but this is related to the port position. Using my H322 loads with 77s as an example they function fine in the mid length upper but in the standard rifle length upper they just about short stroke, and in my brothers match upper with a farther port they do short stroke. The reason the ports are farther forward when built by people like Medesha or other people for match shooting is the powders used in the 6's and 6.5's are slower burning than that of a 308 and thus you need the port farther away to get the pressure so it operates correction. All of this was learned when Tubb was trying to get his SR-25 running in 6.5-08 for course shooting. This is the same reason why you can't use slow powders in an M1 or M14 because the slower powder increases the pressure farther down the barrel at the port.
I want to thank all of you for the help. it turned out to be the gas hole was drilled .070 to far forward. next time I am just going to turn my own block to fit when using Shilen barrels.....
The barrel shoulder is like that because they set it for a A2 hand guard assembly probubably so it can be used for long range high power if you like. Not the end of the world but it is annoying if your not expecting it. Glad to see you got it figured out
I really have to wonder sometimes at complex solutions to simple problems. Moving the location of the gas port barrel hole is OK but limiting in terms of workable loads. The simple solution is an adjustable gas block, which can be adjusted for pretty much any load. Put one round in the mag and adjust until it just locks back on the empty mag and just a touch more. Leaves the gas port hole in the barrel in the standard position doesn't beat your action to death and allows for a wide selection of loads.
This happens with SPRs all the time. They barrels are set up to pinch the front of the handguard keeper for non-free float handguards, creating the extra distance to the gas hole.
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