Disengrating AR Buffers and Short Stroking 18 Inchers

[Kommander`]

I don't post here allot but I do lurk and learn and the signal to noise ratio here is much better than other sites that shall not be named, even if they are allegedly dedicated to the topic at hand.

Today at the range I ran into two AR-15 issues, one with my 11.5 inch barreled AR Pistol and one with my Fathers 18 inch barreled rifle. The pistol is a Aero upper and BCG with Aero lower but with a PSA parts kit and buffer tube/buffer/spring. The 19 inch rife is all Aero except it's built on a Spikes lower. Both guns have carbine buffers/buffer springs. The issues are thus;

My fathers rifle is brand new but seems to be short stroking. The only issue we can find with the gun is that there appears to be a burring around the back edge of the notch in the bottom of the BCG. This is in turn causing a bit of damage to the face of the buffer. Sadly I missed the obvious step of trying my BCG in my fathers rifle so that and other parts swaps are going to be conducted later to try to isolate the issue. Does anyone know of the common causes of short stroking, this is the first time I've run into this problem.

After we got home I started pulling other ARs apart to compare parts and discovered that the plastic end cap on my pistols buffer was cracking and falling apart after about 2k rounds. The pistol runs just fine and ejects where it should (3 to 4:30ish) so I am wondering if I should just purchase a higher quality carbine buffer, PSA parts being what they are, or if I should purchase an H-1 or H-2 buffer that the internets allege a 11.5 inch barrel needs.

Thanks.

[Lon]

Ditch the PSA crap. Get a good buffer and spring and I’d be surprised if the problem didn’t go away. I’ve had some 11.5” uppers that needed a heavy buffer and others that haven’t. You can always add weight to the buffer if you need to. They make buffer weights you can buy.

As far as your dads rifle, pics would help. But the first thing I’d do is switch out BCG and see what happens.

[Kommander`]

I have included the best pictures I can of the issue on the 18 inch rifle. The burr is hard to see but its the shiny spot around the edge of the slot in the BCG. The impression its leaving in the buffer is much clearer.

As for the pistol it runs properly, it just seems that the buffer is falling apart either due to poor workmanship or hitting the back of the buffer tube too hard. If its just because PSA is crap I can just get a better carbine buffer and spring. However I am wondering if I should go with a heavier buffer.

[DDTSGM]

Please explain what is occurring when the rifle short strokes - location of rounds/brass/bolt, etc.

Short-stroking can be caused by insufficient gas. The barrels gas port could be too small (unlikely). The gas tube could be improperly installed - someone may have left the gas tube roll pin out when they installed the gas tube. Check this by visual inspection and pulling on the gas tube, if it comes out of the gas block there's one problem.

The gas key (on top of the BCG) may not be sealing properly with the gas tube - to check this I take the bolt out of the carrier and let the carrier slide forward - it shouldn't bind when the gas tube enters the gas key. The gas tube should have a slight bell at the end, consistent around the tube, look and see if there are signs of uneven wear.

The gas key may also be leaking. This is most often indicated by carbon fouling at site of the leak. Look for this in particular at the front of the gas key, ahead of the gas key screws, where the gas key mates with the BC. While you are at it, give the gas key a tug or two to make sure it is tight and check to see if the gas key screws are properly staked.

An AR may also short stroke because the gas rings are worn. A quick and dirty way to check the gas rings is to extend the bolt from the carrier and then set the BCG nose down on a table. If the BC descends or collapses under its own weight, the gas rings need replaced.

Short stroking can also be caused by too heavy of a buffer or recoil spring, as well as any binding/rubbing as the BCG travels to the rear.

Have you ran the buffer back and forth in the receiver extension (buffer tube) to ensure it isn't binding? Was the rifle well lubed?

There is nothing wrong with you taking a stone and smoothing the burrs off the end of the BC, and the face of the buffer. That's what I would do if I had that problem.

Carbines should run with a carbine buffer. I've found that mine feel smoother and function fine with an H buffer, which is also commonly called an H1. Although, if the rifle is actually short stroking an H1 buffer won't fix it.

For your pistol's buffer nose, you can buy a replacement here: https://www.kakindustry.com/ar-15-pa...r-bumper-black They offer multiple colors which you can use to differentiate different weight buffers.

Someone mentioned that you could add weight to your pistol buffer, creating an H buffer. This is done by replacing one of the steel weights from the carbine buffer with a tungsten weight. the resulting buffer should weigh around 3.8oz. https://www.kakindustry.com/ar-15-pa...eight-tungsten

I've also bought from these guys several times: https://www.tungstenman.com/Tungsten-Buffer-Weight

Hope this helps.

[Andy T]

Was the short stroking rifle properly lubricated?
Who assembled the uppers?

[HCM]

Was the short stroking rifle properly lubricated?
Who assembled the uppers?

This ^^^

Plus what is the gas system length on the 18” ?

Do you know the Gasport size on either of the barrels?

The size of the gas port and the length of the gas system affect how much gas is coming back to push the bolt carrier key and that’s the bolt carrier assembly. The cycle of operation requires a balance between the amount of gas coming back and the buffer weight and strength of the spring.

18 inch barrels can be had in mid length intermediate and rifle length gas systems…

[Kommander`]

Both guns were properly lubricated. The 18 inch rifle has a rifle length gas system with a carbine buffer and spring. It is a complete Aero build, aside from the stock. Both uppers were assembled by the factory and I assume/hope that they have the correct size gas ports but I have not checked them. The rifle hand cycles just fine, with no noticeable hang ups. I will conduct the checks Dan Lehr suggested but I didn't notice anything obviously amiss when I inspected it. We only got about 20 rounds out of the rifle before giving up on it. Usually the bolt simply overrode the next cartridge in the magazine and went into battery. However a few times it got hung up, once actually partially stripping a round from the magazine and putting a bit of a dent/scratch in the top of it. It ejected just fine every round.

The pistol has been 100% reliable, even with the damaged buffer. I didn't want to use PSA parts in my pistol to begin with but since I built it during the pandemic that's where I ended up. I have pretty much decided to replace the PSA buffer and spring on my pistol, I just don't know if I should stick with the carbine weight or go with an H buffer. A replacement buffer bumper from KAK would be great, but ten dollars shipping on a one dollar part isn't cost effective. However I could buy a whole recoil set up from them and then it would be worth it just to have the PSA buffer as a back up. I don't know how good of a reputation KAK Industry has though.

[Andy T]

What ammo were you shooting? I like using cheapest ammo (Wolf, etc) possible. However, it does cause short stroking in some guns (DD MK18 and DD barreled 14.5) I have as the guns get dirty. This is usually because the ammo is not loaded to spec.
You could try some M193 or another decent ammo to rule that out.
Also inspect and post photos of the carrier key staking and the carrier key fit to the carrier. Beyond that, consider contacting Aero. They could have messed up with the gas port/gas block install.

[DDTSGM]

Both guns were properly lubricated. The 18 inch rifle has a rifle length gas system with a carbine buffer and spring. It is a complete Aero build, aside from the stock. Both uppers were assembled by the factory and I assume/hope that they have the correct size gas ports but I have not checked them. The rifle hand cycles just fine, with no noticeable hang ups. I will conduct the checks Dan Lehr suggested but I didn't notice anything obviously amiss when I inspected it. We only got about 20 rounds out of the rifle before giving up on it. Usually the bolt simply overrode the next cartridge in the magazine and went into battery. However a few times it got hung up, once actually partially stripping a round from the magazine and putting a bit of a dent/scratch in the top of it. It ejected just fine every round.

The pistol has been 100% reliable, even with the damaged buffer. I didn't want to use PSA parts in my pistol to begin with but since I built it during the pandemic that's where I ended up. I have pretty much decided to replace the PSA buffer and spring on my pistol, I just don't know if I should stick with the carbine weight or go with an H buffer. A replacement buffer bumper from KAK would be great, but ten dollars shipping on a one dollar part isn't cost effective. However I could buy a whole recoil set up from them and then it would be worth it just to have the PSA buffer as a back up. I don't know how good of a reputation KAK Industry has though.

KAK is okay as far as I'm concerned, I've built a lot of buffers using their components.

I'm assuming the rifle has a carbine buffer tube, correct?

What were you using for magazines - how old were they, how were they loaded? What ammo? Weak mag springs can allow the bolt to outrun the magazine.

A rifle gas system shouldn't be short stroking with a carbine buffer. The TDP gas port size for a rifle length system should be around .0995 the carbine gas port is smaller at .0625. The carbine buffer weights 3 oz and the rifle buffer weighs 5 oz. So, there is a possibility that rather than short stroking you are outrunning the magazine.

Very hard to diagnose w/o the rifle in hand.

As to PSA, I've used a lot of their components with no problems. Very few rifle manufacturers make their own springs, I doubt there is an OEM supplier that has a sign out front that says 'we specialize in shitty recoil springs for PSA.' If the carbine spring is between 10 and 10.5 inches it is probably GTG. If you look at ATF reports, PSA puts out a lot of rifles. I would say their biggest problem is QC on completed rifles versus shitty LPK's etc. All that to say, I don't think I'd junk a functioning LPK just because it is PSA. I think of PSA as the Volkswagen of the rifle world - a rifle everyman can afford.

I've built about a dozen or so rifles for folks plus the eleven in my safes, and haven't had any complaints. What I generally do is start with an H, shoot it to see how it feels and whether it is reliable with generic ammo - I use ARMSCOR .223 to vet them for function before I give them to someone. I have enough supplies to make a carbine buffer into an H through H3 to tune if needed. I don't mess with recoil spring to adjust.

So, TLDR I'd try a heavier buffer.

[HCM]

Both guns were properly lubricated. The 18 inch rifle has a rifle length gas system with a carbine buffer and spring. It is a complete Aero build, aside from the stock. Both uppers were assembled by the factory and I assume/hope that they have the correct size gas ports but I have not checked them. The rifle hand cycles just fine, with no noticeable hang ups. I will conduct the checks Dan Lehr suggested but I didn't notice anything obviously amiss when I inspected it. We only got about 20 rounds out of the rifle before giving up on it. Usually the bolt simply overrode the next cartridge in the magazine and went into battery. However a few times it got hung up, once actually partially stripping a round from the magazine and putting a bit of a dent/scratch in the top of it. It ejected just fine every round.

The pistol has been 100% reliable, even with the damaged buffer. I didn't want to use PSA parts in my pistol to begin with but since I built it during the pandemic that's where I ended up. I have pretty much decided to replace the PSA buffer and spring on my pistol, I just don't know if I should stick with the carbine weight or go with an H buffer. A replacement buffer bumper from KAK would be great, but ten dollars shipping on a one dollar part isn't cost effective. However I could buy a whole recoil set up from them and then it would be worth it just to have the PSA buffer as a back up. I don't know how good of a reputation KAK Industry has though.

Regarding the 18 inch, rifle length gas with a carbon length buffer tube and a carbon buffer is problematic.

A VLTOR A5 buffer tube / system appropriate for rifle gas would definitely help. Rifle length gas systems were developed for use with rifle length buffer tube / spring and rifle buffers. Besides the weight difference in the buffer they use a longer buffer tube. The VLTOR A5 uses a longer carbine type tube and modified buffer to mimic a rifle length system. This allows a longer stoke by the BCG.

The A5 was developed when the Marine Corps was looking at upgrading their 20 inch rifle length gas M16A4s to a collapsible buttstock as the M16A5. As they do with many things the armies Picatinny Arsenal ripped it off as the collapsible buttstock for the M-16 A2/A4.

For your 11.5 I would want at least an H buffer, H2 or H3 if the gas port is oversized. I would also consider using a different buffer spring.

In my experience the parts arrow makes them selves, receivers handguards and There ballistic advantage barrels are pretty good. The downside to their complete guns is they seem to use the cheapest springs and small parts they can find and their assembly is hit or miss.

KAK stuff is decent.