AR-15 gas hole size for 6.8SPC

dieselone · September 16, 2009, 03:03 AM

I just finished an AR-15 with a custom 16" 6.8 barrel that I made from a blank. I used the mid-length handguards and a flat-top gas block. I drilled the gas hole to .104 (forget what # drill size that is), same as a 5.56 barrel I have in the shop. After some initial bugs; I was able to fire 3 rounds from a magazine without any problems. Didn't want to shoot too much in the yard, so, a week later, I took it to the range and couldn't get it to shoot 2 in a row. Now it appears to be short stroking. The bolt is catching the next round in the middle of the case and jamming. It seems like I might need a bigger gas hole. Anybody have info on the optimum size?

10-96 · September 17, 2009, 02:06 PM

What ammo are you using? To get a bunch of Remington ammo shot up- I simply went with a lighter (carbine) buffer. As for hole size- sorry, can't help much there.

sadsack · September 18, 2009, 04:12 AM

Deiselone: Your gas port is really at the upper limit for a mid-lenth barrel. Your ammo (powder burning rate), as 10-96 suggested, may be the cause of your jams. You might check to see if your gas block is lined up with the port and sealing good (not leaking off gas pressure).

September 16, 2009, 03:03 AM	#1
dieselone Member Join Date: November 15, 2008 Posts: 40	AR-15 gas hole size for 6.8SPC I just finished an AR-15 with a custom 16" 6.8 barrel that I made from a blank. I used the mid-length handguards and a flat-top gas block. I drilled the gas hole to .104 (forget what # drill size that is), same as a 5.56 barrel I have in the shop. After some initial bugs; I was able to fire 3 rounds from a magazine without any problems. Didn't want to shoot too much in the yard, so, a week later, I took it to the range and couldn't get it to shoot 2 in a row. Now it appears to be short stroking. The bolt is catching the next round in the middle of the case and jamming. It seems like I might need a bigger gas hole. Anybody have info on the optimum size?

September 17, 2009, 02:06 PM	#2
10-96 Senior Member Join Date: October 19, 2005 Location: Tx Panhandle Territory Posts: 4,159	What ammo are you using? To get a bunch of Remington ammo shot up- I simply went with a lighter (carbine) buffer. As for hole size- sorry, can't help much there. __________________ Rednecks... Keeping the woods critter-free since March 2, 1836. (TX Independence Day) I suspect a thing or two... because I've seen a thing or two.

September 18, 2009, 04:12 AM	#3
sadsack Senior Member Join Date: February 4, 2006 Posts: 206	Deiselone: Your gas port is really at the upper limit for a mid-lenth barrel. Your ammo (powder burning rate), as 10-96 suggested, may be the cause of your jams. You might check to see if your gas block is lined up with the port and sealing good (not leaking off gas pressure).