Need help with AR-15

[tommeboy]

I went through a similar thing last year. It ended up being the lower was not milled deep enough for the bolt catch to fully extend to catch the bolt stop. I ended up shortening the pin that operates it a little on the lathe and perfect function.

It just shows that there can be other things that can cause it. I figured it out by every time I set the gun down it would release the bolt. You could hand cycle it and it would catch the latch but not when actually firing it.

 

[Chiquita]

What buffer weight are you currently running? M16 carrier? What exactly isn't the rifle doing? Failure to eject? Failure to lock back? Failure to feed? It's possible the bolt my be moving too fast for proper operation. The first step is to determine if it is indeed short stroking or if it is cycling too fast. Do White Oakes test.

If it is a failure to lock back, are you running a bad lever?

The rifle does eject but does not load the next round.

I have the following update.
Barrel 19.5" Krieger 7.7 twist
Gas block from the muzzle about 6.5"
JP bolt was purchased with the Krieger barrel as a a matching set
Spring is 11" long
Buffer is 3.0 oz
Carrier and the handle are my old one by Ground Zero Precision that was from my budget build.

I inserted my bore scope right by the gas port, squirted FreeAll in the gas tube from the receiver end, while videoing the gas port, I pressed air into the gas tube from the receiver end to see if FreeAll will come out. It did, so the gas port is lined up properly with the gas block.

I can remove a weight from the buffer to make it 2.3 oz and see if that makes a difference. I will do the white Oak test next time I am at the range.

Video and pictures of the gas port.

3 new items by Edward Gorginian

photos.app.goo.gl

 

[Chiquita]

Don't start chopping on springs until you get the rifle working. A little more info on the rifle would help - barrel length, gas port position.

I won't yet

What do you mean by the bolt does not cycle. You fire one round and then what happens.
Does it eject, does it not load the second round an go into battery or does it jam, malfunction.
more info needed.

It fires and ejects every time, It does not pickup the next round.

Try another known working bolt and carrier.
If tolerances in them isn’t right they leak excessively.

I don't have another carrier or changing handle.

 

[Walt Krafft]

It fires and ejects every time, It does not pickup the next round.

That could be caused by too much gas causing excessive bolt speed. Or, to little gas causing it to short stroke. Preform the previously mentioned White Oak test. Does the bolt lock open when fired with an empty magazine? Have you tried other magazines?

 

[DHD]

My last build was a SBR using an Aero M4E1 lower and 2 different caliber uppers (300BO and 223). I had a similar issue with the 223 upper not fully cycling. Both uppers were the same brand, used a set screw SA adjustable gas block, and both are run suppressed 100%. I check gas block alignment with a bore scope so I'm not guessing before dimpling for the second set screw so that was not a consideration. What ended up being my issue was the Armaspec SRS gen4 buffer/spring and the carriier used with the 223.

I had 2 different brands of BCG's involved here (300BO was a Young Manufacturing NM and the 223 was a Odin Works). As I have so many spare parts I swapped out the original Armaspec SRS to a spare Armaspec SRS and the 223 upper now cycled 100% (WTH?). I still was curious and decided to use the 300BO's YM NM carrier (carrier only) with the 223 upper and the original Armaspec SRS. The 223 worked 100% in this configuration too. Was it the Odin Works carrier or the original Armaspec SRS? After looking at what was happening again with everything back in the original configuration, my Odin Works carrier was not allowing the 223 bolt to go all the way into battery with the original Armaspec SRS. Since the Aero M4E1 lower was the SBR, it had to work with both uppers.

I did not have a gas issue, a buffer weight issue, or a spring strength issue but a tolerance stacking issue (for lack of a better description). In short, I swapped the Odin Works carrier to a JP FMOS carrier I was saving for something else and both uppers run without issue with the original Armaspec SRS. Why did the Odin Works carrier not work? I don't really know as it was within a couple thousandths length of the Young Manufacturing NM carrier and the JP FMOS carrier but there it is anyway.

My recommendation would be to try another carrier (carrier only as you already have the best bolt available though I am not a fan of the one piece gas ring) or another spring/buffer. Your description of what's happening to your rifle is similar to the issue I had I think. The bolt is not going all the way into battery.

For final clarification, does the bolt go far enough into battery that you are getting a "click" when you pull the trigger or just a "mush" when you pull the trigger? When the rifle cycles in the configuration it is in now, can you push the carrier forward using the forward assist (if your rifle has one) and the rifle fires?

I'll leave my rambling above, but I re-read your description and it is not picking up the next round. Have you tried another magazine? Is the bolt catch actually locking or is the bolt hanging up? Is the bolt catch the standard one that came with the lower or one of the ambidextrous abortions?

 

[karrarararararar]

I think you actually need more buffer weight. Everything you've described tells me you need more weight. A 3oz buffer is "carbine" weight which is pretty much the lightest buffer you'll find. My guess is you'll need a h1 or h2. As mentioned, the Whiteoak test will help confirm. How's your ejection pattern?

Reference for buffer weights, from what you described, you have a rifle length gas system.

AR-15 Buffer Weights: Difference Is, and How to Choose

While AR-15 buffer weights are often overlooked in an 80% build, choosing the right one is important for your rifle's performance. Find out more at 80 Percent Arms!

www.80percentarms.com

 

[Chiquita]

The bolt is oiled and runs smooth, not to a point that has leaking or evidence of leaking oil.

@karrarararararar I will try the test next time I am at the range. I will order the buffers. Thanks.

@DHD it goes click but no fire. I have to pull the bolt back to pick up the next round. I don't think the bolt locks back on the last round. This issue with two magazines. I have another two that I will try.

 

[DHD]

The bolt is oiled and runs smooth, not to a point that has leaking or evidence of leaking oil.

@karrarararararar I will try the test next time I am at the range. I will order the buffers. Thanks.

@DHD it goes click but no fire. I have to pull the bolt back to pick up the next round. I don't think the bolt locks back on the last round. This issue with two magazines. I have another two that I will try.

So the rifle fires, the bolt cycles, but just does not go all the way into battery? If this is the case, can you push the carrier all the way forward with your finger? Try this or just swap out the buffer and spring.

Do you have another heavier buffer (H1 is a good catch all weight) and or another spring? If you don't, it is never a bad idea to have extras. Another back up carrier is never a bad idea either.

If your situation is what I was describing in my first sentence, try a heavier buffer at least. Another heavier buffer and spring together isn't a bad idea. If you have to buy these things, I'd try a stronger Springco (they are labeled by colors). It's easy to get lost in the weeds with all of the spring/buffer options available and the cost can be not too high to ridiculous.

 

[DocBII]

Chiquita,​

I ran into the same problem with an Aero style lower. Sent the lower back to the vendor, who said they "Realigned/reattched" the buffer tube to resolve the problem. Don't know if that's true or not, but the lower worked perfectly after they returned it to me.

HTH,
DocBII

 

[Chiquita]

Chiquita,​

I ran into the same problem with an Aero style lower. Sent the lower back to the vendor, who said they "Realigned/reattched" the buffer tube to resolve the problem. Don't know if that's true or not, but the lower worked perfectly after they returned it to me.

HTH,
DocBII

Great to know.
Thanks.

 

[Chiquita]

What buffer weight are you currently running? M16 carrier? What exactly isn't the rifle doing? Failure to eject? Failure to lock back? Failure to feed? It's possible the bolt my be moving too fast for proper operation. The first step is to determine if it is indeed short stroking or if it is cycling too fast. Do White Oakes test.

If it is a failure to lock back, are you running a bad lever?

So I did the mentioned test. The bolt does not lock back on either position.

I changed springs (original spring, David Tubb spring), buffer weights (3oz, then switched with two tungsten weights), adjusted the gas block, still nothing. It fires, ejects between 3-4 but does not load the next round.
I changed one item at a time.

FWIW, when I was trying different combinations, at one point it was rejecting and locking back at the last round just fine, but for some reason I it doesn't do it anymore.

I am going back to the range tomorrow and see if I can get it to work.

 

[jelenko]

If it fails the WOA test, it means there is an issue with the gas system; i.e.,

Leaky gas key; misaligned gas tube, worn gas rings, worn bolt tail, gas port too small, 'bulb' on end of gas tube worn.

 

[Chiquita]

So, I disassembled the gas system, the bolt and the buffer system. Cleaned everything, made sure there are no obstruction, the buffer has the three steel weights, original spring. Installed the gas block, opened the gas block all the way.

It shoots, ejects between 3 to 4. Still doesn't pick up the next round to chamber.

BTW, I tried the test mentioned in post 3, and it didn't pass..