ar-15 not cycling

davsco · Mar 20, 2019

help please! so i put together an upper. aero m4e1 enhanced upper. 14.5" ballistic advantage barrel. mid length gas. bolt and charging handle out of another upper that's been working fine (16" barrel), full lower (incl buffer & spring) from that same rifle that has been working fine. seekins adj gas block .750.

started with gas adj screw all the way in (closed/blocked). backed it out a full turn or so. no ejection of spent casing. did this a few more times in half turns, and case ejected but only flew a foot or two, new round wasn't chambered. with block all the way open, 4 complete turns out, it stopped ejecting.

i plugged the barrel with a foam earplug and held that in place. put a hex key in the gas tube. put 80psi air down the barrel and the hex key went flying, so seems the block is aligned and air is going thru the tube. i cannot see the gas tube seating into the gas key on the bcg, but in looking at the relation of the front of the bolt to the gas key, and how far the bcg sits, sure looks like the gas tube is going inside the key.

what am i missing?

danb · Mar 20, 2019

Reloads or factory?

Bcg- all tight there?

Also, not familiar with the seekins, but are you sure you are turning the adjustment screw and not the set screw? Some of these have the set screw on the adjustment screw, it's easy to think your turning the adj screw when in fact you are turning the set screw or both.

3paul10 · Mar 20, 2019

Maybe the gas block, I don't use adjustable gas blocks on carbines, only pistols.... are you sure the gas tube isn't upside down?

davsco · Mar 21, 2019

danb said:
Reloads or factory?

Bcg- all tight there?

Also, not familiar with the seekins, but are you sure you are turning the adjustment screw and not the set screw? Some of these have the set screw on the adjustment screw, it's easy to think your turning the adj screw when in fact you are turning the set screw or both.

factory pmc bronze 55g

yeah bolt seems tight, same bolt, CH and full lower that works in another rifle.

and yeah, funny about the seekins' screws because their website isn't very descriptive and it does seem they've changed them around. but on this one, the open/close screw is on the side (i looked in the block and could see it opening/closing, and the locking screw is at the muzzle end).

davsco · Mar 21, 2019

3paul10 said:
Maybe the gas block, I don't use adjustable gas blocks on carbines, only pistols.... are you sure the gas tube isn't upside down?

i have a fixed block on order, but did visually look at this block and see the port is all the way open. and yeah i double checked the orientation of the tube's port when it didn't work the first time i went thru this. i did shoot a hex key across the room when i blew the tube (that doesn't sound right...) though of course a hex key is way lighter than a bcg being held back by a buffer spring.

inkd · Mar 21, 2019

I had a similar problem and tried the air test as well. Air was flowing just fine. I sent the upper to Chad and when he borescoped it, the block was partially misaligned.

If you know anyone who has a borescope, I would borrow it before you do anything else.

Decoy · Mar 21, 2019

It could be an undersized gas port or a misaligned gas block.

Cornelius · Mar 21, 2019

Was the lower with buffer and spring also from a mid-length gas system? I did a switcheroo last year that had a similar cycling problem and I felt like a moron because my buffer/spring was too heavy for the shorter gas system. So it was having a tough time overcoming that resistance. I'm not a smart man.

eruby · Mar 21, 2019

Cornelius said:
Was the lower with buffer and spring also from a mid-length gas system? I did a switcheroo last year that had a similar cycling problem and I felt like a moron because my buffer/spring was too heavy for the shorter gas system. So it was having a tough time overcoming that resistance. I'm not a smart man.

Shineboxes being priced, bit not ordered.

Cornelius · Mar 21, 2019

eruby said:
Shineboxes being priced, bit not ordered.

You'll have to explain that for me. Again, not a smart man.

babalou · Mar 21, 2019

eRuby is the Dennis Miller of MDS. I have to reference lookup some of his stuff. Different level playing field with him. Hahahaha

Cornelius · Mar 21, 2019

babalou said:
eRuby is the Dennis Miller of MDS. I have to reference lookup some of his stuff. Different level playing field with him. Hahahaha

So, of course I get the Goodfellas reference, right, but forums tend to have their own inside jokes and references so I'm completely lost on this one. I'm too new to have a clue. :smack:

danb · Mar 21, 2019

I am voting for misaligned gas port. Set screws can come out, the gas block can move around. The part that keeps bugging me is "4 complete turns out, it stopped ejecting" which means maybe the gas was fine until it wasnt. I am doubtful about buffer or spring issues. Most ARs are way overgassed so there should some setting on the adjustable that makes it go.

Also, make sure you are lubed up!

davsco · Mar 21, 2019

to help/check gas block and port alignment, this morning i got a plastic paper clip about the same diameter as the barrel's gas port, cut it so it went all the way in flush with the outside, affixed the gas block, turned it over so that the pin slid into the gas block (and still in the barrel port) and the block was pretty much where i had it before. so pretty sure alignment isn't an issue.

i'm using the buffer, spring (and complete lower) and bolt off my 16" AR that has the same length gas system (and works no problem there).

davsco · Mar 21, 2019

danb said:
The part that keeps bugging me is "4 complete turns out, it stopped ejecting" which means maybe the gas was fine until it wasnt.
Also, make sure you are lubed up!

yeah it is WET.

i agree with the open/close screw. almost think gas is leaking thru that as it is opened more (if you keep turning it out, the screw will of course come out of the block at some point), but there is no carbon black there that would indicate leakage.

danb · Mar 21, 2019

MDS is having issues today.

"pretty much in the same place" - if your gas port was even small amount off not sure you would notice. It does not take much, its a small hole. If you have it apart, only thing left to do is put it back together and try again see if it cycles. At least you have ruled out gas port alignment.

other thing you might try is take the gas block/tube off the other rifle and put it on this barrel. it should cycle. If not, its either the barrel (gas port too small maybe, although I think its unlikely) or a defective gas block IMO.

erwos · Mar 21, 2019

I agree that this sounds a lot like you've got a misaligned gas port or a loose gas block.

DavidA · Mar 21, 2019

My guess is a defective gas block. There are a lot of different issues. Not sure how the seekins works. But the block distributes the gas and deductively I would come to believe it is the issue. Switch blocks of s working rifle and you will know.

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clandestine · Mar 21, 2019

Those gas blocks are terrible. If you want adjustable there is only one worth having, it's SLR.

All adjustable gas blocks leak so if the barrel is ported properly it may not cycle reliably with any adjustable. You often have to open up one # drill bit size when you install an adjustable gas block.

I would troubleshoot with a fixed gas block. If you need one for testing I can send you one.

It's still possible the gas block is slightly misaligned.

Short headspace, too much buffer/spring, excessive carrier travel, roll pin on the buffer protruding, buffer spring coil diameter too large, bad bolt catch spring, binding gas key, too small of a gas port, bad gas rings, barrel with the gas block shoulder in the wrong place (controls gas tube protrusion in the upper), and even the FCG can cause cycling issues.

inkd · Mar 21, 2019

clandestine said:
All adjustable gas blocks leak so if the barrel is ported properly it may not cycle reliably with any adjustable. You often have to open up one # drill bit size when you install an adjustable gas block.

I forgot about that. I had that problem on the two barrels that had correct sized ports and they didn't work with the SLR's. You had to open them up for me.

ar-15 not cycling

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