AR Sponsor
Posted: 11/10/2008 4:23:52 AM EDT
|
I pulled a bonehead stunt, and shortened my 24" stainless barrel to 17", and now my Bushmaster upper on an AnvilArms lower won't pick up a new round. The gas port is about 3" from the end of the barrel. The port is .093", and the gas tube and key are properly aligned. It's only had a few hundred rounds through it, and everything is smooth and well-lubed. I suspect that the bullet is exiting the barrel too soon to force the carrier fully to the rear. Extraction is successful, with no obvious gouges in the extraction rim from excessive cartridge sticking in the chamber. It just seems as if there isn't enough pressure to get the carrier back far enough to pick up a new round. The bolt locks open sometimes, but not even half the time, on the last round in a mag. I'm using fairly hot factory ammo (PMC and UMC), and some fairly hot handloads, all with similar results.
Can this be fixed with a less-stiff action spring, or is there some other cure, short of a new barrel with a properly located gas port? Thanks, in advance. |
|
Going with a lighter recoils spring is just going to lead to dwell and cycle problems (like the B/C charging correctly from the hand charged position).
With the short distance from the gas port to muzzle, you in the 10.5" barrel range of finicky barrels, and will need to work with specific ammo types to increase the barrel gas port until you get reliably cycling for such ammos. Bottom line is you may luck out and find a gas port size that works with all you ammo's being used, but don't panic if the planets just don't align up for such; it's just the nature of the beast. |
|
I'm already resigned to the fact that I may have to replace the barrel, so is it worth monkeying with the gas port size to see if I can get it to work? Do I just drill it a little larger (by a few thou), and test it out, until I get it to work? What's the largest reasonable gas port size I should consider?
I suppose, worst case, I cut it off shorter, drill a new gas port, and build an AR pistol! Thanks for your response. |
|
Single size at a time, and work with one round in the mag until you get bolt lock back on the empty mag cleany with the ammo type that your going to be using.
Once you get the bolt to lock back, stop going larger since larger than that may put the rifle into over function mode. Your best bet is to work with Wolf and M-193 to see if you can find a setting between the two that will run in the rifle (read use the M-193 first, then limit your self to one size up to see if you can get the Wolf to run as well). |
|
Getting the gas port too large, hence the bolt trying to unlock too soon as the spent case is still too over pressured against the side walls of the chamber to be pulled cleanly, and will give you the same outcome as short stroking from being under gas'd. Here, too much of the B/C reward force is lost on trying to extract the over pressured spent case from the chamber, and give you the short stroke.
Take a look at the tacked thread "How it works" to get an idea of the barrel residual pressure at unlock (dwell) you are trying to achieve for a clean stroke. Also note that different types of powder will have different pressures at barrel port, depending on there burn rate and even the bullet grain being used. |
|
Thanks to Dano523, I was able to get it working, again. I took the rifle, drill index, and cordless drill to the range on Saturday, and worked around all the Fudds sighting in their 30-30s. I checked the port size using the drills, and increased in single size steps until the bolt would reliably lock open. Then, I went one step larger, and ran through a magazine with no failures. On my next trip, I'll try some lighter handloads, and see if they will work. If not, I'll go one size larger, but no more. If I have to take it any larger, I'll just replace the barrel. I don't want to introduce new problems.
So far, so good, though, and I may have saved a decent barrel. Thanks, again, for all the great info! |
AR Sponsor