16" Midlength AR Problems

[rbernie]

You can't complain about reliability if you're shooting Tula or Wolf. Deal with it, or switch to quality ammo like Federal

Per the OP:

With the lower spec ammo (mostly American Eagle .223 and Independence 5.56), 75% of the time it will eject, and simply skip over the next round. The other 24% of the time it will jam with bolt halfway across the ejection port, with a round at a sharp angle caught between the opening of the chamber and the bottom of the bolt face, often with a nasty dent/gouge in the cartridge. I have had a few failure to extract/ejects with the American Eagle and Independence, and one stuck case with the Silver Bear.

American Eagle *is* Federal, and if it won't run on that then it needs attention.

 

[kwg020]

We have resolved the lube issue and if it is not shooting American Eagle without an issue, you have a problem. But it is hard to tell if it is extremely over gassed or under gassed. Put in an H1 or heavier buffer and if it gets worse it's an under gas issue. If the heavier buffer fixes it, it's over gassed. The only other issue is the magazines but I assume you have checked that already.
kwg

 

[Noah]

Yep, mags are fine. I tried a new block and am still getting occasional "skipping" over rounds with 5.56 and near about 50% skips and jams with .223 spec ammo. Which is weird because with the old block it would run hot 5.56 *almost* 100% (2 failures of about 150 rounds, frequent failures to lock on empty) but refused to run .223 (Incl. Federal) at all.

I really hadn't considered it being an overgassing issue. What are some things to look for with that? I appreciate the help.

 

[Mad Machinist]

Here is another simple thing to check that doesn't seem to have been mentioned.......strip the bolt out of the carrier and drop the carrier in the upper ....then turn the upper so the carrier can fall out....if it doesn't .....you have a gas tube dragging in the key and it can cause the problems you describe. Either the barrel nut is a little off....the gas block is a little off....or the gas tube is bent.

 

[MistWolf]

I disagree. A middy that is built right should run everything from Tula to hot handloads, just as all of mine do-including 40 gr. loads that clock 3,600 FPS from the 16" tubes. Of the four 16" guns in the other room, three have midlength gas, and are not the least bit ammo sensitive, nor do they exhibit excessive carrier speeds

Some do, some don't. It's a rule of thumb, not an absolute

I tried a new block and am still getting occasional "skipping" over rounds with 5.56 and near about 50% skips and jams with .223 spec ammo. Which is weird because with the old block it would run hot 5.56 *almost* 100% (2 failures of about 150 rounds, frequent failures to lock on empty) but refused to run .223 (Incl. Federal) at all

I think you've located your trouble spot. I recently swapped a gas block and the AR went from functioning fine to not cycling at all. After taking some measurements, it turns out the gas port in the barrel is .295" from the shoulder and the gas port in the gas block was .308 inches from the back of the block creating a misalignment of .013" before adding the handguard cap. Had to do a bit of sanding on the gas block to get the holes to line up

I really hadn't considered it being an overgassing issue. What are some things to look for with that? I appreciate the help.

If the rifle were over gassed to cause problems with functioning, the recoil would feel particularly sharp and there would be a stinging slap felt through the trigger bow

 

[carbine85]

Did you measure the gas port in the barrel when you removed the gas block? You need to know that and get that out of the way.

 

[kwg020]

Over gassed would be a bolt carrier moving so fast the magazine cannot push up the next round fast enough. The bolt carrier would go right over the top of the round in the magazine. Mistwolf described the over gassed well. I'm thinking there is a problem with the gas hole diameter or there is a misalignment of the gas hole and the gas block.

kwg

 

[Bartholomew Roberts]

What does the rim of extracted and ejected cases look like? Big bites or bent rims? In any case, it sounds more and more like your problem is either misaligned gas block or undersized gas port (or a combination of the two).

 

[Noah]

I have carefully inspected different ejected casings to look for clues. They look just fine.

 

[kwg020]

If your cases look fine I would say over gassed is not an issue. Over gassed can bend bases and rip a piece out of the case. I'd look at the gas hole in the barrel or see if you are misaligned. kwg

 

[Rudedog]

If a barrel is made by a reputable manufacturer and set up for mid-length or any other length gas tube then the gas port should be the correct size.
I would also look at the gas block to see if it fits the barrel tight enough to make a good seal, may be getting blow-by around the barrel where lower pressure ammo will not cycle.
I have seen gas blocks that simply slide on and off with no resistance.

 

[readyeddy]

I had the same short stroking problem when I went from a 16" upper to 20" upper with a carbine lower. I ordered a replacement carbine buffer spring, thinking I would cut off one of the coils to lower the spring power. Turned out the replacement spring was already shorter than my stock spring, so I installed the replacement spring, with no modification, and problem solved.

For some reason, the stock spring that came with my early 1990's XM15 was stout.