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SOLVED: Cycling Issue with AR

F

FrozenRopes

Sergeant
Full Member
Minuteman
Jul 11, 2011
132
0
45
MA, USA
I'm new to ARs.
Just got a BCM upper 14.5 with mid gas system.
It works fine for 30 rounds on a clean gun then won't pick up the next round or hold open on empty mags. I've tried Federal 62gr Mil-surp, Rem UMC, handloads.
Am I doing something wrong? ie. not lubing correctly/enough
Is the ammo I'm using crap? I always here people say "My AR eats everything."
Do ARs need break-in time?
Should I send it back?

(This also happened with an AR I had last year. I didn't keep it long. So I'm thinking operator error not the upper)
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ropes</div><div class="ubbcode-body">Do ARs need break-in time?</div></div>No.
 
Re: Cycling Issue with AR

Which buffer are you using in it? Carbine or rifle? Sounds like for whatever reason your bolt isnt cycling all the way back. If not it wont lock back on empty or go far enough back to pick up the next round.
 
Re: Cycling Issue with AR

Suggest you Check what ric44 suggested and run it very wet initially ... "lots and lots of oil"

RJ
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mm128</div><div class="ubbcode-body">Try FACTORY ammo if you havent.

Your handloads MAY be the issue.

</div></div>

I've tried Remington UMC 223, and they didn't take.
I have some Match Ammo I'll give that a go tomorrow.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ric44</div><div class="ubbcode-body">Which buffer are you using in it? Carbine or rifle? Sounds like for whatever reason your bolt isnt cycling all the way back. If not it wont lock back on empty or go far enough back to pick up the next round. </div></div>

It's a carbide buffer, spring, and stock. I checked twice.
I can manually cycle dummy rounds fine.
I can only move about 1/4 inch past the mag catch. Is that normal?
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: richardj</div><div class="ubbcode-body"> Suggest you Check what ric44 suggested and run it very wet initially ... "lots and lots of oil"

RJ </div></div>
Will do!
I'm going to lube the snot out of it.

ETA: I actually just checked the BCG and it was dry as a fart.
The cheap oil I used must have burnt off.
Hopefully M-Pro 7 Gun Oil will do the trick.
Any oil suggestions?
 
Re: Cycling Issue with AR

Yeah that part is ok I think. Just sounds like you have something binding or perhaps its not getting enough gas on the bolt to do its thing due to gas leakage or misalignment....Im no whiz on these things but do own 2 or 3 and manage to keep them all running. Maybe someone with more know how will chime in.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ric44</div><div class="ubbcode-body">Yeah that part is ok I think. Just sounds like you have something binding or perhaps its not getting enough gas on the bolt to do its thing due to gas leakage or misalignment....Im no whiz on these things but do own 2 or 3 and manage to keep them all running. Maybe someone with more know how will chime in. </div></div>

Nothing binding. I'm going to try extra lube, factory ammo, and a quick cleaning (even though I cleaned it 60 rounds ago).
Does a buffer with a H3 on it mean anything?
 
Re: Cycling Issue with AR

Make sure that your gas block hasn't shifted. If you think that you might have bumped it, you may have shifted it ever so slightly causing the holes in the barrel and the gas block to not match up perfectly.

Check to make sure the gas key bolts haven't broken. Mine were staked correctly so they wouldn't back out but one of the bolts cracked/sheared off allowing gas to escape under/around the gas key; preventing it from picking up the next round or staying open on the last round. The head of the bolt didn't come loose until I put an allen wrench in it.

Make sure your buffer and spring match the lower that you have. Carbine/collapsible or rifle/fixed stocks need their specific buffer and springs.

Also, I use CLP for my lube. Mobile 1 is good too.

Good luck
 
Re: Cycling Issue with AR

Well, start cheap first.
OIL. Mine all like to be wet.

Next, check to make sure that your gas key on top of the BCG has not backed out at all. Make sure it is a really solid staking job (can you do pics? That could help on the staking job). If has backed out, I would take it to a competent gunsmith and have them restake it.

How new/old are the mags? Could have too much tension against the bottom of the bolt carrier. Does it happen with 15 rounds as well as 30 in the mag?

H3 buffer (to my recollection) is the carbine buffer. Sounds right.

How much of the rifle is new? Or is it a used rifle that is new to you? Just curious.
 
Re: Cycling Issue with AR

Dude, H3 buffer is WAY too heavy of a buffer. With midlength gas you're not overgassed like lots of other carbines. You should just run a plain carbine buffer, not even an H buffer.

Heavier buffers will slow the cyclic rate. You're short stroking.
 
Re: Cycling Issue with AR

Check your gas rings for misalignment. That's been my #1 cause of short stroking without a doubt.

 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BESpain</div><div class="ubbcode-body">Make sure that your gas block hasn't shifted. If you think that you might have bumped it, you may have shifted it ever so slightly causing the holes in the barrel and the gas block to not match up perfectly.

Check to make sure the gas key bolts haven't broken. Mine were staked correctly so they wouldn't back out but one of the bolts cracked/sheared off allowing gas to escape under/around the gas key; preventing it from picking up the next round or staying open on the last round. The head of the bolt didn't come loose until I put an allen wrench in it.
</div></div>
Gas block hasn't moved. It's a low profile gas block under the rail.
Just checked the key bolts with an allen wrench and both were good to go.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ogreshooter</div><div class="ubbcode-body">Well, start cheap first.
OIL. Mine all like to be wet.

Next, check to make sure that your gas key on top of the BCG has not backed out at all. Make sure it is a really solid staking job (can you do pics? That could help on the staking job). If has backed out, I would take it to a competent gunsmith and have them restake it.

How new/old are the mags? Could have too much tension against the bottom of the bolt carrier. Does it happen with 15 rounds as well as 30 in the mag?

H3 buffer (to my recollection) is the carbine buffer. Sounds right.

How much of the rifle is new? Or is it a used rifle that is new to you? Just curious. </div></div>

Just oiled it all up.

The gas key is solid. It's a new BCM, both nuts are stacked well on both sides.

Mags are new with fresh springs. I did try a new ar-stoner 10 round in there to with no change.

The lower is only 1 year old. Got it last year with the first upper I tried.
The upper is only a few months old, I was just waiting on a BCG from BCM to finish it up.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Dude, H3 buffer is WAY too heavy of a buffer. With midlength gas you're not overgassed like lots of other carbines. You should just run a plain carbine buffer, not even an H buffer.

Heavier buffers will slow the cyclic rate. You're short stroking. </div></div>
I'll try a standard carbide buffer
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: p951951951t</div><div class="ubbcode-body">Check your gas rings for misalignment. That's been my #1 cause of short stroking without a doubt.
</div></div>
Checked them, two of the gaps were close but not the third. I shifted them around a bit.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Dude, H3 buffer is WAY too heavy of a buffer. With midlength gas you're not overgassed like lots of other carbines. You should just run a plain carbine buffer, not even an H buffer.

Heavier buffers will slow the cyclic rate. You're short stroking. </div></div>

^^^This would be my first guess since you provided the H3 info
<span style="text-decoration: line-through">Second would be try different mags
Also check gas block and gas key, could be.</span>
ARs do like lube, a few drop on a soft brush, I use a shave brush at home, and lightly coat everything that moves, I've used breakfree CLP without issue.
That M855 should be high enough pressure to say its definitely a problem with the gun.
 
Re: Cycling Issue with AR

Gas ring alignment causing issues in the AR platform is a myth. You can have more gas escape out around the tail of the bolt where it meets up with the bolt carrier than through the tiny gap in the gas ring.

LMT's enhanced carrier has multiple holes in the carrier that will vent gas before the bolt has exited out of battery.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Gas ring alignment causing issues in the AR platform is a myth. You can have more gas escape out around the tail of the bolt where it meets up with the bolt carrier than through the tiny gap in the gas ring.

LMT's enhanced carrier has multiple holes in the carrier that will vent gas before the bolt has exited out of battery. </div></div>

I thought it was a myth too, but I didn't want to crap on any one trying to help.
 
Re: Cycling Issue with AR

I guess it doesn't hurt to check it, but really I've heard way too many people perpetuate this. Ammo, mags, buffer, loose gas key and shifted gas block have been the main culprits(or things to fix) in the failures I've seen.

For a while there it seemed like everyone and his brother had loose carrier keys. (Right after the ban sunsetted, tons of new AR manufacturers who didn't stake properly.) Then everyone's gas blocks were moving. (Because people were getting rail systems and adding low profile gas blocks that used setscrews into non dimpled barrels.) During the ban, nearly every failure was mag related. (old shitty mags)

Now it seems that each manufacturer has slightly different gas port settings (and maybe chamber dimensions) which change dwell time, resulting in trying to unlock too soon or too late. The fix is a different buffer weight. Also it's good to double check your spring to make sure it isn't a Rifle spring. (I dunno if this would even cycle fully though.)
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Gas ring alignment causing issues in the AR platform is a myth. You can have more gas escape out around the tail of the bolt where it meets up with the bolt carrier than through the tiny gap in the gas ring.

LMT's enhanced carrier has multiple holes in the carrier that will vent gas before the bolt has exited out of battery. </div></div>

Well, if you say so. I had a problem with a larue stealth short stroking, took out bolt, fixed gas rings, problem solved. Experienced the same thing with a DD rifle I built too. I'm not calling BS on you but I will in fact test my theory next time I'm at the range.
 
Re: Cycling Issue with AR

Here is one more thing to check. If you are running it with a used PRS or UBR stock then someone might have used the wrong size screw that holds the stock onto the buffer tube. If that screw is too long it will stop the buffer short and keep the bolt from locking back on an empty magazine. This happened to me with a used UBR. I had to cut that screw, also vented it like a factory Magpul screw. Gun cycles fine now.

You also might think you have the right buffer spring and you don't. Count the coils if you haven't already. That also has happened to me with used gear
 
Re: Cycling Issue with AR

Sounds like an overweight buffer, to me. H3's are for highly overgassed guns (ie. suppressed), and a 14.5" Midlength is going to be undergassed, if anything. Put a standard buffer in and you should be good to go.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ropes</div><div class="ubbcode-body">Do ARs need break-in time?</div></div>No.
</div></div>

AR's deffinitely need break in. Those parts usually come with a slightly rough finish. some of the parts need to smooth up from normal wear. If you happen to have an AR with tight tolerances, this will be very evident.


It sounds like it might be short stroking and not coming all the way back during operation. Most of the time, it's due to new, dry parts not moving smoothly. Oil usually fixes it.

I agree with richardj, lots of oil. Run it wet (with oil) for the first 150 round or so. Once the parts wear in a little, it will cycle smoother.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: redirt78</div><div class="ubbcode-body">Here is one more thing to check. If you are running it with a used PRS or UBR stock then someone might have used the wrong size screw that holds the stock onto the buffer tube. If that screw is too long it will stop the buffer short and keep the bolt from locking back on an empty magazine. This happened to me with a used UBR. I had to cut that screw, also vented it like a factory Magpul screw. Gun cycles fine now. </div></div>

That's a subtle one!
 
Re: Cycling Issue with AR

- magazine does not feed as it should
- magazine not in proper position (height)
- Gas key loose or blocked (something inside, primer etc)
- Gas rings leaking
- Gas tube blocked or not sealing/touching gaskey properly
- Gasblock allignment not correct (remove it, carbon marks on barrell tell)
- Gashole too small
- Ammo too mild (for buffer)

IMHO healthy, clean AR15 should work without oil.
 
Re: Cycling Issue with AR

I had that problem with 16" barreled Larue OBR 556. Called Larue and they said before sending it back see if it cycles fine with Federal Gold Metal match ammunition. I single load each round and the bolt always locked open.

The problem is I was reloading with insufficient power charge. I was following reloading manuals. The ones I've been using are just why to low on max loads.

Once I got the right load I've had no more problems. Rilfle has a Wylde chamber and sami specs are for 223, I think Wylde chamber can take pressure of 556 chamber.
 
Re: Cycling Issue with AR

The H3 buffer is way too heavy--put in a standard or maybe H.

Mobil 1 engine oil will not burn off near as soon as many "gun" oils, plus it makes it very easy to clean carbon from the gas ring area. Be sure to give the rings etc a good soaking. Carry some oil in a small squirt bottle and put a couple drops in the vent holes on the side of the bolt carrier from time to time til this thing has a few hundred rounds through it. CLP or whatever will do for this.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Dude, H3 buffer is WAY too heavy of a buffer. With midlength gas you're not overgassed like lots of other carbines. You should just run a plain carbine buffer, not even an H buffer.

Heavier buffers will slow the cyclic rate. You're short stroking. </div></div>

Hmmm. I have to disagree here... Heavy buffers will generally <span style="font-style: italic">stop</span> a rifle from short-stroking... Not cause it... because its the inertia of a heavier moving object that compresses the spring more than a lighter buffer and allows the BCG to travel further back. An object in motion tends to stay in motion. Therefore a heavier buffer set in motion will travel further against the same buffer spring than a lighter buffer... Unless the loads are just really weak... FWIW.
I'd be more inclined to think its the buffer spring. Or one of the other things mentioned above.

A heavy buffer will slow the cyclic rate but that does not translate to short-stroking. Quite the opposite. A fast cyclic rate generally means the BCG is not traveling as far back... Short-stroking... Or, the rifle has been tuned to run faster by matching the spring tension to the proper buffer weight and load.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ronas</div><div class="ubbcode-body"> Rilfle has a Wylde chamber and sami specs are for 223, I think Wylde chamber can take pressure of 556 chamber. </div></div>

That was my first thought. BCMs are normally chambered in 5.56 instead of .223 unless its a Wylde chamber. Maybe the .223 ammo ain't hot enough to cycle the bolt back?

I'd check with the manufacurer about the chamber and ask about recommended ammo.
 
Re: Cycling Issue with AR

H3 buffer is too heavy. Swap to an H and the problem will probably correct itself.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: oneshot onekill</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Dude, H3 buffer is WAY too heavy of a buffer. With midlength gas you're not overgassed like lots of other carbines. You should just run a plain carbine buffer, not even an H buffer.

Heavier buffers will slow the cyclic rate. You're short stroking. </div></div>

Hmmm. I have to disagree here... Heavy buffers will generally <span style="font-style: italic">stop</span> a rifle from short-stroking... Not cause it... because its the inertia of a heavier moving object that compresses the spring more than a lighter buffer and allows the BCG to travel further back. An object in motion tends to stay in motion. Therefore a heavier buffer set in motion will travel further against the same buffer spring than a lighter buffer... Unless the loads are just really weak... FWIW.
I'd be more inclined to think its the buffer spring. Or one of the other things mentioned above.

A heavy buffer will slow the cyclic rate but that does not translate to short-stroking. Quite the opposite. A fast cyclic rate generally means the BCG is not traveling as far back... Short-stroking... Or, the rifle has been tuned to run faster by matching the spring tension to the proper buffer weight and load. </div></div>

It takes more energy to get a heavier object into motion, mid length operates at lower peak pressure and with less time pressurized, it may not be enough pressure and/or time to accelerate the buffer to the point where inertia is suffecient to continue rearward travel. Just a thought.
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: oneshot onekill</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Dude, H3 buffer is WAY too heavy of a buffer. With midlength gas you're not overgassed like lots of other carbines. You should just run a plain carbine buffer, not even an H buffer.

Heavier buffers will slow the cyclic rate. You're short stroking. </div></div>

Hmmm. I have to disagree here... Heavy buffers will generally <span style="font-style: italic">stop</span> a rifle from short-stroking... Not cause it... because its the inertia of a heavier moving object that compresses the spring more than a lighter buffer and allows the BCG to travel further back. <span style="font-weight: bold">An object in motion tends to stay in motion.</span> Therefore a heavier buffer set in motion will travel further against the same buffer spring than a lighter buffer... Unless the loads are just really weak... FWIW.
I'd be more inclined to think its the buffer spring. Or one of the other things mentioned above.

A heavy buffer will slow the cyclic rate but that does not translate to short-stroking. Quite the opposite. A fast cyclic rate generally means the BCG is not traveling as far back... Short-stroking... Or, the rifle has been tuned to run faster by matching the spring tension to the proper buffer weight and load. </div></div>

Good point, but don't forget, an object at rest tends to stay at rest. Inertia works on both positive and negative acceleration. You have to remember that a standard buffer will have a higher velocity than an H3, all other things equal. It does make sense that given the same amount of energy, the buffers should travel back the same, independent of weight, but my experience with AR's says that an H3 can cause short stroking. Changing the buffer spring would be the logical next step.

A fast cyclic rate does not mean the BCG isn't traveling as far. It means the buffer is moving back extremely quickly and "bouncing" off the back of the buffer tube. A properly functioning AR should have the buffer traveling to it's most rearward position with every shot. That's why the buffer is there in the first place and padded on the back.
 
Re: Cycling Issue with AR

I almost don't want to break up this tread, I'm getting a lot of good info on this topic. But good news...

Changing out the H3 buffer for a standard buffer worked.
Not to mention adding some M-Pro 7 Gun Oil to the right spots.
Just popped out 120 rounds of M855 without skipping a beat.

My reloads, however, were under-powered. I kind of figured they would be weak because I used a mild charge.
 
Re: Cycling Issue with AR

"Cycling Issue with AR"

I don't always cycle, but when I do, I prefer a bike.
 
Re: Cycling Issue with AR

Fantastic! Looks like I was wrong though... Not the first time and certainly not the last!
As I think about it I've always gone in the opposite direction with buffer weight and had positive results. I'd get an AR with a crappy factory buffer and swap it with something heavier if it didn't function 100%. I learn something new every day!
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: oneshot onekill</div><div class="ubbcode-body">Fantastic! Looks like I was wrong though... Not the first time and certainly not the last!
As I think about it I've always gone in the opposite direction with buffer weight and had positive results. I'd get an AR with a crappy factory buffer and swap it with something heavier if it didn't function 100%. I learn something new every day! </div></div>

The main reason that most likely worked is because your carbine was over gassed. When it's overgassed and has a short gas system, the dwell time is shorter and the excess gas will actually try and unlock the action before chamber pressures have fully subsided. The brass will still be compressed into the chamber walls and the bolt will try and extract that "sticky" case. This will result in a slowing of rearward movement of the carrier and short stroking. Many times there will still be enough inertia for the carrier to fully cycle, but the case won't fully extract. Usually a sign of this is bent rims, torn rims and ejector swipes. This is when people start adding really heavy extractor springs and o-rings under the extractor. Ultimately it is better to use a heavier buffer to delay the unlocking until after the chamber pressures have subsided.

Normally overgassing is the culprit in carbine systems for short stroking. And the best fix is a heavier buffer. This was an instance where it just wasn't. I based my assessment more so off of experience vs. an understanding of physics. It's a pretty delicate balancing act.

Here's an interesting chart. Notice that a standard rifle buffer is pretty much the same weight as an H3 buffer. I think the difference really lies with the distance the spring compresses and how much the spring is precompressed in the carbine vs the rifle. I've also noted that many carbine's that have cycling issues will run great with a rifle length buffer/tube/spring. This is why a couple manufacturers like Vltor have come up with slightly longer carbine buffer tubes.
BufferTable-1.jpg
 
Re: Cycling Issue with AR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: oneshot onekill</div><div class="ubbcode-body">Fantastic! Looks like I was wrong though... Not the first time and certainly not the last!
As I think about it I've always gone in the opposite direction with buffer weight and had positive results. I'd get an AR with a crappy factory buffer and swap it with something heavier if it didn't function 100%. I learn something new every day! </div></div>

The main reason that most likely worked is because your carbine was over gassed. When it's overgassed and has a short gas system, the dwell time is shorter and the excess gas will actually try and unlock the action before chamber pressures have fully subsided. The brass will still be compressed into the chamber walls and the bolt will try and extract that "sticky" case. This will result in a slowing of rearward movement of the carrier and short stroking. Many times there will still be enough inertia for the carrier to fully cycle, but the case won't fully extract. Usually a sign of this is bent rims, torn rims and ejector swipes. This is when people start adding really heavy extractor springs and o-rings under the extractor. Ultimately it is better to use a heavier buffer to delay the unlocking until after the chamber pressures have subsided.

Normally overgassing is the culprit in carbine systems for short stroking. And the best fix is a heavier buffer. This was an instance where it just wasn't. I based my assessment more so off of experience vs. an understanding of physics. It's a pretty delicate balancing act.

Here's an interesting chart. Notice that a standard rifle buffer is pretty much the same weight as an H3 buffer. I think the difference really lies with the distance the spring compresses and how much the spring is precompressed in the carbine vs the rifle. I've also noted that many carbine's that have cycling issues will run great with a rifle length buffer/tube/spring. This is why a couple manufacturers like Vltor have come up with slightly longer carbine buffer tubes.
BufferTable-1.jpg
</div></div>
MAN!... That's great information!!! I'm just sorry it took me this long to get back to this thread. Thank you for sharing all of this.

John
 
Re: Cycling Issue with AR

This is why I love this forum. I was having the same issue with my BCM. Same upper. I'll have to try this and see how it works.
 
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