I took my 6.8mm SPC AR-15 SBR out to the range Sunday and had immediate failures to feed, meaning it started right away, not after a number of rounds had been fired.
Pertinent rifle specs are:
11.3" Wilson Combat barrel, carbine gas
Wilson Combat AR-15 BCG (not M-16)
H buffer
Standard carbine buffer spring
Ammunition was hand loads using Hornady brass, CCI #41 primers, 27.5 gr H322, Hornady 110 gr BTHP bullets, and a COAL of 2.240+/-.005". These are not max loads by any stretch, but I didn't want to increase the powder charge more due to the use of the CCI #41 primers. Magazines used were a AR Stoner 25-rd, and a PRI 15-rd. I had just used the PRI mag in my 18" AR with no issues.
The failures were about 50/50 with the empty case left in the chamber and a fresh round trying to jam in behind it, or an empty case fully out of the chamber with a fresh round jammed against it trying to get into the chamber. It happened nearly every round, but every now and then I could fire 2 rounds before it jammed. The bolt would lock back on an empty magazine, and when it did eject cases, they were landing 6-8 feet away at the 3:30-4:00 position.
My initial thought was that it is overgassed, with the bolt unlocking and moving rearward before the chamber pressure drops to the point of "releasing" the case, and the extractor stripping over the rim. However, the ejection pattern would suggest that it is not overgassed, and there is no unusual damage to the case rims from the extractor.
I have a few things that I am going to try right away, including swapping out the AR-15 BCG for a M-16 BCG, swapping out the H buffer for an H2 buffer, and trying a few other types of ammunition. If it is overgassed, the correct solution would be a new barrel, adjustable gas block, heavier buffer, and heavier BCG, in that order by my thinking. Hate the idea of a new barrel, and dislike the adjustable gas block idea because the one I have now is also a flip up front sight. I haven't been able to find adjustable gas blocks with flip up front sights, so that would drive me to an adjustable A2 sight/gas block, or a low profile adjustable gas block, new hand guard, and new front sight. A heavier buffer and/or BCG might compensate for the overgassing, but are really just masking the real issue.
Any other thoughts from the forum?
Pertinent rifle specs are:
11.3" Wilson Combat barrel, carbine gas
Wilson Combat AR-15 BCG (not M-16)
H buffer
Standard carbine buffer spring
Ammunition was hand loads using Hornady brass, CCI #41 primers, 27.5 gr H322, Hornady 110 gr BTHP bullets, and a COAL of 2.240+/-.005". These are not max loads by any stretch, but I didn't want to increase the powder charge more due to the use of the CCI #41 primers. Magazines used were a AR Stoner 25-rd, and a PRI 15-rd. I had just used the PRI mag in my 18" AR with no issues.
The failures were about 50/50 with the empty case left in the chamber and a fresh round trying to jam in behind it, or an empty case fully out of the chamber with a fresh round jammed against it trying to get into the chamber. It happened nearly every round, but every now and then I could fire 2 rounds before it jammed. The bolt would lock back on an empty magazine, and when it did eject cases, they were landing 6-8 feet away at the 3:30-4:00 position.
My initial thought was that it is overgassed, with the bolt unlocking and moving rearward before the chamber pressure drops to the point of "releasing" the case, and the extractor stripping over the rim. However, the ejection pattern would suggest that it is not overgassed, and there is no unusual damage to the case rims from the extractor.
I have a few things that I am going to try right away, including swapping out the AR-15 BCG for a M-16 BCG, swapping out the H buffer for an H2 buffer, and trying a few other types of ammunition. If it is overgassed, the correct solution would be a new barrel, adjustable gas block, heavier buffer, and heavier BCG, in that order by my thinking. Hate the idea of a new barrel, and dislike the adjustable gas block idea because the one I have now is also a flip up front sight. I haven't been able to find adjustable gas blocks with flip up front sights, so that would drive me to an adjustable A2 sight/gas block, or a low profile adjustable gas block, new hand guard, and new front sight. A heavier buffer and/or BCG might compensate for the overgassing, but are really just masking the real issue.
Any other thoughts from the forum?