2 AR15s won't cycle. Need Help please.

[Lead Heads]

I have two AR15 builds doing the same thing. They will not cycle and pick up the next round or lock the bolt back. Bolt will lock back manually. I pull the trigger and the rifle goes bang for the first round and ejects the case, shot two the rifle just goes click. One rifle was able to do two shots every now and then. I checked the gas blocks and gas tubes for obstructions and they are all clear. Triple checked the blocks for alignment, perfect. I switched out the lowers and bolts with ones that I know work, same problem. I am out of ideas. Please help. Any ideas would help greatly. Below is a main components build list for the rifles.
Rifle 1:
Seekins billet lower and IMR upper
Rock 18" rifle gas length barrel
Seekins .750 adjustable block (all the way open)
Spikes ST2 buffer/unknown spring
Full auto BCG from Hells Canyon Armory

Rifle 2:
Seekins lower and Vltor Mur upper
Daniel Defense S2W 18" mid gas length barrel
PRI .750 adjustable gas block (all the way open)
Unknown buffer and spring
Full auto BCG from Hells Canyon Armory
Any ideas would help greatly.
Thanks

 

[Maestro Pistolero]

Weak magazine springs? It's the magazine follower that locks the bolt open.

 

[wvlapua]

Try adjusting the gas block the other way (less gas). Sounds to me like the bolt is cycling too fast/hard.

 

[BLDTYLRY]

Make sure you run them wet for the first 100 rounds. And make sure you have a carbine buffer and buffer spring.

 

[Eagle1899]

What ammo are you using?

 

[TheGerman]

Either magazine or ammo, but most likely magazine.

 

[kimberseries1]

Sounds to me like your buffer is WAY too heavy. You are running an H2, which is 2 sizes above a carbine weight. You aren't cycling far enough back because the weight is too heavy for rifle length gas, and looks like too heavy for middy, if its the same buffer weight.

Unknown springs can be replaced with a carbine buffer kit from BCM. Rifle #2 unknown buffer and springs problem solved.


At least that's my $0.02


Edit: I just swapped my H buffer to an H2 in my 11.5" barrel......

 

[nso123]

Are you by chance shooting Wolf ammo?

 

[bhart89]

Is your gas tube in backwards or upside down?

 

[kimberseries1]

And what length buffer tube in your rifle-length gas rifle? Shouldn't it be rifle length buffer tube? Not a carbine-length? The rifle-length tube is longer, with a rifle-length spring. I've only run middy's and carbines, but I assume if you're running a carbine tube and spring in your #1 rifle, your spring is WAY too heavy as well. I would assume to run a rifle length gas with a carbine buffer tube, you would need a much lighter spring. Someone with more experience can tell you for sure.

Sounds like you are very under-gassed.

 

[kimberseries1]

Weak magazine springs? It's the magazine follower that locks the bolt open.

If he can't run the mag 'till it's empty, this can't be the problem. Unless he's using GI-issued mags from the early '90's that were used for 20 years-with original springs-I doubt it's a mag problem. With the components he's running, I'd assume he has a PMAG or similar in it.

Also, if it's under-gassed, it won't travel far enough back to catch the bolt catch.

 

[BDHershey]

I'd bet heavy buffers and weak ammo.

 

[SeaBassHWD]

Sounds lime you have gas problems. Either the gas block isn't properly installed or it's letting too much gas escape. Check the gas adjustment first before re-aligning the block.

 

[Lead Heads]

All good suggestions. Let me touch on a few. The magazines I am using are PMags and I know they work. Ammo is 62grn Black hills match. Gas blocks fit tight to the barrel and I checked for obstructions using pipe cleaners. I also did the same for the gas tube and reassembled them and blew down the gas tube to make sure air was flowing. The buffer and spring might be the cause because when I put the other lowers on to see if it was the spring or buffer they were both carbin lowers. Might try changing the springs and buffers. Any other ideas？

 

[pawprint2]

if after changing buffer and springs, same problem: remove the gas block and physically check size of gas port in barrel, and in gas tube, triple check alignment of port and block. Double check the alignment of tube and block. It sure sounds like you have a gas problem.

 

[Crosshair]

Since you are running adjustable gas blocks (and all the way open) I'd opt for the lightest (carbine) buffers for both of them. Then, as long as you are reliably locking back, even with weaker .223 loads, you can tune the blocks to run the best recoil-wise. Like mentioned above, sounds like too heavy of buffers in both. The T2 is about in between H and H2. I like to err on the side of too much gas, rather than not enough, for reliability sake.
Just curious, are the BCGs phosphate coated or NiB, or Cerraplated?

 

[R.Walters]

I had the same problem. My buffer was too heavy.

 

[Lead Heads]

Both BCG are phosphate. I am running them way wet.

 

[Shooter McGavin]

If he can't run the mag 'till it's empty, this can't be the problem. Unless he's using GI-issued mags from the early '90's that were used for 20 years-with original springs-I doubt it's a mag problem.

That's funny! I am still running mags from 1990 that I got form my Uncle Sam and never had a problem. Crap I think I need to take a pic so some one believes me, lol.

 

[Lead Heads]

Asked about the stocks. On rilfe #1 I have a Magpul UBR. Rifle #2 I have a Magpul STR. I believe both are carbine length tubes. I did run a UBR on the 20" rifle length gas BCM with Rock barrel I built and it ran great. HmmM

 

[smschulz]

I would start by ordering a Wolff spring set, extra/std/reduced power.
Different weight buffers too would help find the right combo.
However, you will end up with some extra parts but it is the only way.
You should also try different ammo.
My money is on the spring buffer combo.

 

[kimberseries1]

Asked about the stocks. On rilfe #1 I have a Magpul UBR. Rifle #2 I have a Magpul STR. I believe both are carbine length tubes. I did run a UBR on the 20" rifle length gas BCM with Rock barrel I built and it ran great. HmmM

UBR is rifle length: I think. I think I remember you do have to add a rifle tube for this stock. Been a while. You just need a carbine buffer. I would buy a rifle length spring just to be sure. I'm pretty sure BCM would have the spring/buffer combo.

Do you mean CTR instead of STR? The CTR should be a 6-position carbine stock. #2 just needs a carbine buffer. I would just get the combo from BCM to be sure you don't have some kind of Extra Power spring or something.







Shooter McGavin: Do you still eat pieces of shit for breakfast?

 

[AvsFan]

I have two AR15 builds doing the same thing. They will not cycle and pick up the next round or lock the bolt back. Bolt will lock back manually. I pull the trigger and the rifle goes bang for the first round and ejects the case, shot two the rifle just goes click. One rifle was able to do two shots every now and then. I checked the gas blocks and gas tubes for obstructions and they are all clear. Triple checked the blocks for alignment, perfect. I switched out the lowers and bolts with ones that I know work, same problem. I am out of ideas. Please help. Any ideas would help greatly. Below is a main components build list for the rifles.
Rifle 1:
Seekins billet lower and IMR upper
Rock 18" rifle gas length barrel
Seekins .750 adjustable block (all the way open)
Spikes ST2 buffer/unknown spring
Full auto BCG from Hells Canyon Armory

Rifle 2:
Seekins lower and Vltor Mur upper
Daniel Defense S2W 18" mid gas length barrel
PRI .750 adjustable gas block (all the way open)
Unknown buffer and spring
Full auto BCG from Hells Canyon Armory
Any ideas would help greatly.
Thanks

Perhaps, I'm off base here but, I noticed a common denominator "Full auto BCG from Hells Canyon Armory"?

1) Have you checked to insure the gas key is screwed down onto the bolt tight & flush w/o any gaps whatsoever all the way around?
2) Are the gas keys staked properly?
3) Does the bolt collapse into the carrier (with the gas rings installed) when you extend the bolt out and allow the weight of carrier to rest on top?
4) Have you double checked to make sure the gas rings aren't lined up?

 

[Lead Heads]

Stock on #2 is a MagPul STR and it is carbine length. I will try different buffer/spring combos. Rifle #1 has a Spikes ST-2 which weighs 4.05 oz. Spikes ST-1 weighs 3.0 oz.. Is that lite enough?

 

[Tack425]

Im going to throw something out there too, but suggest that you tackle and eliminate one variable at a time. It sounds like your systems are short stroking as others have stated. I would also agree that its probably the buffer/spring combo. Now in reading the posts the one thing I was looking for was the buffer tube itself and the UBR from Magpul. I run a Magpul PRS on my POF and it has their proprietary vented screw in the rear. If you don't install this particular screw the buffer compresses the air in the buffer tube and it won't compress all the way "short stroking" the system. Now not being totally familiar with the UBR, does it have a vented screw like the PRS? But either way check your buffer tube and make sure the vent hole isn't occluded.

Again I may be way off, but its worth a shot and its a free fix if it works.

Stay safe

 

[LawnMM]

Its short stroking by the sound of it. Buffer spring is too weak or the buffer is too heavy, or both. You said 'unknown' spring? Put a brand name buffer spring and buffer in there and see if it works, then you can start re-introducing your more custom/swanky heavy buffer and such.

 

[Temp9]

I had the same problem when switching to a Magpul PRS (rifle buffer system). Turns out it was my buffer spring that was too strong. I swapped out the cheapo DPMS spring for a JP spring and problem solved. I'm pretty sure any proper strength spring would've worked, but the DPMS spring was noticeably stronger (probably about 15-20%) than the JP, which is supposed to be 8% stronger than a standard spring.

 

[BobD]

I have two AR15 builds doing the same thing. They will not cycle and pick up the next round or lock the bolt back. Bolt will lock back manually. I pull the trigger and the rifle goes bang for the first round and ejects the case, shot two the rifle just goes click. One rifle was able to do two shots every now and then. I checked the gas blocks and gas tubes for obstructions and they are all clear. Triple checked the blocks for alignment, perfect. I switched out the lowers and bolts with ones that I know work, same problem. I am out of ideas. Please help. Any ideas would help greatly. Below is a main components build list for the rifles.
Rifle 1:
Seekins billet lower and IMR upper
Rock 18" rifle gas length barrelF
Seekins .750 adjustable block (all the way open)
Spikes ST2 buffer/unknown spring
Full auto BCG from Hells Canyon Armory

Rifle 2:
Seekins lower and Vltor Mur upper
Daniel Defense S2W 18" mid gas length barrel
PRI .750 adjustable gas block (all the way open)
Unknown buffer and spring
Full auto BCG from Hells Canyon Armory
Any ideas would help greatly.
Thanks

Are both rifles not locking back?
Here's a few things to check-

1) Measure buffer and spring length. Weigh buffer. Count spring coils.

Here are a few specs I dug up. I'm not certain each is exact but should give a good starting place. Can always public check the figures.

Carbine spring ~ 37- 39 coil, 11.25" length (compressed 2.808")

Carbine buffer (H tungsten weighted and specialized) 3.25" length
Standard ~ 2.96 - 3.0 oz
H-1 ~ 3.8 oz
H-2 ~ 4.1 - 4.6 oz
H3 ~ 4.8 - 5.4 oz
Specialized go higher


Rifle length spring ~ 41- 44 coil, 12.75" length (compressed 3.168")

Rifle buffer 5.905" length
Standard ~ 5.2 oz
Specialized go higher


2) Remove any attached bolt release (eg. Bad lever)

2) Fire several rounds manually loading, look for carbon deposits where they shouldn't be (ie. gas block). Also, look for direction of ejecting cartridge. It can help troubleshoot how far through the cycle there is a problem. If your showing signs of being under gassed here you know where to look. If you're throwing properly then can likely eliminate any questions on the front end.

3) Inspect bolt and carrier's contact areas for rough surface (burs), undue friction or deformity (make sure it's gliding smoothly through full cycle)

4) M16 bolt is heavier, try swapping either a regular SA or lighter bolt. May work just fine in most rifles, especially carbine length but could indicate there's not enough pressure


Good luck-

Sent from my iPad using Tapatalk HD

 

[smschulz]

UBR is rifle length: I think. I think I remember you do have to add a rifle tube for this stock. Been a while. You just need a carbine buffer. I would buy a rifle length spring just to be sure. I'm pretty sure BCM would have the spring/buffer combo

No, the UBR is not rifle length and it comes with it's own buffer tube.

 

[tylerw02]

On rifle-length 18", the T2 is too heavy. But with a gas block fully open, it should be working. I'm going to bet you have the gas block misaligned. Did you ensure there is the "gap" between the block and the contour change? This gap is to allow for handguard endcaps. Many will try to run the gas block up against the shoulder without leaving the gap.

 

[Lead Heads]

Gas block hole and barrel port hole line up. Triple checked. I did try a couple of different bolts that I know work. The only things I did not try is the buffer/spring. I did switch lowers that I know work but they were carbine lowers. I am ordering a couple sets of springs and lighter buffers. I will let you know how it goes.

 

[Sugarbug]

Sounds to me like your buffer is WAY too heavy. You are running an H2, which is 2 sizes above a carbine weight. You aren't cycling far enough back because the weight is too heavy for rifle length gas, and looks like too heavy for middy, if its the same buffer weight.

Unknown springs can be replaced with a carbine buffer kit from BCM. Rifle #2 unknown buffer and springs problem solved.


At least that's my $0.02


Edit: I just swapped my H buffer to an H2 in my 11.5" barrel......

Sounds like a too-heavy buffer. It's cycling enough to eject the spent cartridge, but not enough to strip the next round from the magazine.

Also, you might try closing up your gas block and slowly opening it in the event it is cycling too fast (which I don't think).

Just realized there's a ton of response to this thread I didn't read and it may already be resolved.... :shrug:

 

[tylerw02]

Gas block hole and barrel port hole line up. Triple checked. I did try a couple of different bolts that I know work. The only things I did not try is the buffer/spring. I did switch lowers that I know work but they were carbine lowers. I am ordering a couple sets of springs and lighter buffers. I will let you know how it goes.

Did they work on the other lowers you tried? If so, then you know its the buffers and springs. If not, you know its the gas block.

 

[Lead Heads]

They did not work on the other lowers. However one lower had a H2 Buffer and the other had a H3.

 

[Sugarbug]

Nevermind... wrong thought.

 

[Crosshair]

They did not work on the other lowers. However one lower had a H2 Buffer and the other had a H3.

Which, of course, are both heavier than the T2 : ) I'm pretty sure you're on the right track with ordering some carbine buffers and some fresh known-weight springs.
Though, I would say it'd be nice if your gas ports were spec'd a little bigger so it'd cycle heavy buffers with the blocks dialed fully open.

 

[Lead Heads]

Which, of course, are both heavier than the T2 : ) I'm pretty sure you're on the right track with ordering some carbine buffers and some fresh known-weight springs.
Though, I would say it'd be nice if your gas ports were spec'd a little bigger so it'd cycle heavy buffers with the blocks dialed fully open.

Hell. I have a drill and I am willing to try anything to get these things working.
Anyone know where I can get some reduced power springs？ Wolff is on back order and I can't find the listing for the spring pack from BCM as mentioned.
If you have a link that would help greatly.
Thanks

 

[Crosshair]

Hell. I have a drill and I am willing to try anything to get these things working.
Anyone know where I can get some reduced power springs？ Wolff is on back order and I can't find the listing for the spring pack from BCM as mentioned.
If you have a link that would help greatly.
Thanks

I'd say once you get a carbine buffer in there and a fresh spring, try shooting some weakish pmc .223 or something, comparing it to full house 5.56 stuff and see how it does. If it still occasionally doesn't lock back with the lightest buffer, then I'd look at gas port size, and/or reaming/enlarging it. I'd want a really good drill press setup with the perfect bit size though, to consider doing it myself...and I'd still be nervous that I would screw myself. Since there is no "spec" on anything other than m-4 barrels, the manufactures may use any thing from .060" to .085" -- depends on the maker.
If you had the money and patience, it'd be interesting to see how a JP low-mass BCG and spring setup would be in there!

 

[tylerw02]

Pretty sure there is a spec on other barrels and it isn't lack of a spec that makes manufacturers choose other port sizes. They choose the largest ones because they want their guns to work with crummy ammo.

 

[kimberseries1]

Hell. I have a drill and I am willing to try anything to get these things working.
Anyone know where I can get some reduced power springs？ Wolff is on back order and I can't find the listing for the spring pack from BCM as mentioned.
If you have a link that would help greatly.
Thanks

AR-15, M16, M4, Stocks

all you need is on this page.

 

[Tack425]

OP any update?

 

[biggin69]

I hope this isnt a repeat. You said the gas block was installed up against the shoulder of the barrel. My experience is that the gas block must be moved forward the thickness of the original front hand guard holder (metal plate). Check that measurement beacuse this might cause an offset in the holes between the barrel and the gas block.

 

[insight3b]

i hope this isnt a repeat. You said the gas block was installed up against the shoulder of the barrel. My experience is that the gas block must be moved forward the thickness of the original front hand guard holder (metal plate). Check that measurement beacuse this might cause an offset in the holes between the barrel and the gas block.

^^^^^this^^^^^