New pistol build and too many jams. help please – page 1 – ar15.com o gascon

View QuoteIf you have a gas block then checking that the hole in the barrel and gas block are lined up correctly would be the first thing to do. If the gas block is lined up correctly then also make sure the gas tube is connected to the block properly and air travels freely, you can blow on the muzzle while covering the chamber with a finger to test for leaks and air flow. If the gas block and gas tube are not the problem then the gas port may be to small or something is causing friction on the carrier or the gun is trying to extract to early or your buffer or spring tension is to high.

How tight are the gas rings? The gas rings should just hold up the carriers weight when the carrier group is rested on the bolt face. They should not be overly tight. You can squeeze the gas rings with pliers and reinstall to shrink them a little if they are overly tight. I like the carrier to slide into battery naturally and freely without the need to slam the carrier from the charging handle or using the forward assist. If the carrier does not go fully forward without momentum and from buffer spring tension alone I am not happy.

Does the bolt slide into the barrel extension without binding? Is the barrel extension and bolt lined up properly and not creating friction? You stated the bolt is tight. If the barrel extension is not timed to the bolt you can loosen the barrel nut and turn the barrel left or right to adjust it’s alignment with the bolt. You may need to shave the index pin of the barrel or the index pin cut of the receiver if there is no play to turn the barrel.

Do rounds slide into and out of the chamber easily by hand? If the chamber is to tight or contains an imperfection on the chamber walls then it will cause casings to stick and create drag on the carrier during extraction. Honing the chamber smoother will help a tight chamber.

What carrier are you using? Some carriers react differently to gas and will change how fast a casing is extracted and how much gas is put toward cycling. If you have the ability to try different carriers it could be as easy as swapping the carrier. I have 9 AR’s and they all work reliably but some only work reliably with certain carriers so I make sure to keep the correct carrier with the correct guns. I have one AR that works reliably with only one out of my 9 carriers but works perfectly every time with that particular carrier?

Another thing to consider is that the gun is trying to extract the case to early while it is still under pressure. If the extraction happens to early then the casing will still be stuck to the chamber under pressure and cause the carrier to use to much of it’s energy to pull the case and not have enough momentum to fully cycle. Again, a different carrier may react differently and fix it.

If everything else is working and the gun simply has to little gas to cycle then drilling the gas port larger to introduce more gas may be necessary. I would only do this if your sure nothing else is causing a problem. Upping the gas could create a whole new set of issues.

will need more info, but last time that happened to me it was over gassed.What might be happening is the bolt speed is too fast for the stack of rounds to get pushed up by the magazine spring. The bolt is overriding the cartridge and pushing it out of the mag digging into the side of the case.

Try a heavier buffer. Crane authorized the use of up to H4 for the SBR’s in service to control bolt speed for armorer’s at those unit levels. I’m no expert but I have yet to hear of a pistol which had too much buffer, but we have more than a few posts about AR’s with too light a buffer. Note the rifle with rifle gas uses the heaviest of all and nobody seems to have the issue with hot NATO rounds.

I picked up a spare rifle buffer at the flea market precisely to take it down for the weights. $10 was cheaper than trying to find them, and heavy buffers aren’t cheap.What you describe does sometimes happen and a heavier buffer would be a possible fix for that.

The OP’s gun is not locking back on empty mags and most likely the bolt is also not traveling far enough back to hit the rear of the casings in the mags. It would need to be crazy fast and extreme over gassed cycling to both not lock back and not feed rounds. Jumping the bolt catch is over gassed, outrunning the mag would be extremely over gassed. Since we know his gas port is undersized it’s not likely to be so extremely over gassed.

View Quote2 jams out of 200 is a big improvement. It was obviously under gassed and short stroking if upping the port size fixed it. You now know for sure that upping the gas was able to make the bolt travel rearward enough to pick up cases from the mag correctly. Since you are still borderline short stroking with some ammo you could cut a twist off the buffer spring to alleviate a bit more tension or try a different spring. Your spring may be a bit stiffer than usual. Cutting a half or full twist from the spring would likely make it run perfect with any ammo. Pulling a weight out of the buffer and replacing it with a rubber or PVC insert would drop the buffer weight and probably be another improvement for your gun.

Another thing to consider is AR’s will run weaker when the temperature gets down below freezing and especially in the teens. If your AR is running on the weak side with the temperature like it was today it may go back to short stroking in the winter. Getting a bit more cycle strength would still be a good idea.

2 jams out of 200 is a big improvement. It was obviously under gassed and short stroking if upping the port size fixed it. You now know for sure that upping the gas was able to make the bolt travel rearward enough to pick up cases from the mag correctly. Since you are still borderline short stroking with some ammo you could cut a twist off the buffer spring to alleviate a bit more tension or try a different spring. Your spring may be a bit stiffer than usual. Cutting a half or full twist from the spring would likely make it run perfect with any ammo. Pulling a weight out of the buffer and replacing it with a rubber or PVC insert would drop the buffer weight and probably be another improvement for your gun.

Another thing to consider is AR’s will run weaker when the temperature gets down below freezing and especially in the teens. If your AR is running on the weak side with the temperature like it was today it may go back to short stroking in the winter. Getting a bit more cycle strength would still be a good idea.