AR-15 guys, please help

[Mudburner]

Please see the photo.

I recently got these two AR-15 parts kits (everything included except the lower receivers). Both are the same length barrel, but the position of the gas block is different.

How do you call these? (ie what are the proper terms for these different length gas systems?). Barrels measure (from chamber to end of flash hider) 17.25" The top one is marked 5.56x45 1:9, and is "unknown manufacturer". The bottom one is not marked for chamber size anywhere, and is an Anderson manufacture. Both were clean, and new or like new condition. The Anderson upper appeared brand spanking new with absolutely no wear marks on it. I lubed each bolt/bolt carrier quite a bit. The top buffer weighs 5.06 oz, the bottom one weighs 2.94 oz.

I put each upper, with its own bolt/bolt carrier & buffer/buffer spring on the full stock lower at the bottom (from one of my other guns) to test fire & zero.

The top one choked; failed to feed, failed to extract, had to be mortared to unlock the bolt, about every 3rd round... I had to rod the bore to extract spent casings, and they had damaged rims.

The second one in the photo went on the exact same full length lower, and performed well, quickly zero-ing. I was using my own handloads, which function well in my other, full-size 20" guns.

-why does the top upper receiver/barrel combo choke? FTF/FTE, bolt gets stuck? I didn't try other ammo, or store-bought ammo yet. I have some steel case I could try, or I could buy some mfg. ammo.

I intend to get two identical lowers and assemble these parts kits to complete rifles. Not a problem there. All the other little parts/springs/etc were in the box.

-can I put the adjustable stock/buffer combo on the top one?

 

[Gasgun]

Top one is called carbine length gas.
Bottom is called mid-length gas.

As far as the malfunctions you are having, “unknown manufacturer“ and low end stuff tends to give problems.
Can’t help you there.

 

[Mudburner]

Roger. Thanks, I appreciate the terminology. It was pretty inexpensive, so I took a chance.

 

[Compooky]

I’m interested in how the top one had malfunctions yet the bottom one functioned fine with a carbine buffer and spring in an a2 tube.

 

[Mudburner]

Yeah, that's why I'm asking questions, cuz I dont have any experience with anything but full size Army issue stuff. I would like to switch & put the full stock on the mid length upper, and it seemed to function OK. If not, I'll assemble it with the adj. stock.

 

[Old Man with Gun]

Where did your kits come from? Dealer or a guy with a box of parts. If it was the second, it could be a clean out of parts bins and the parts are not all compatible.

If you had a working rifle, changed something and now have a problem, we can help.

But saying I assembled a Franken-rifle and it doesn't work doesn't have a starting point. We don't know if it is possible to assemble two functional rifles with the parts you have.

Try to find a local mentor.

 

[Mudburner]

Gunbroker. Seller "Gunbusters SE".
Gunbusters (there are several) (Gunbusters SE, Gunbusters NE, Gunbusters 63005, Gunbusters 32257, Gulfcoast GB) take firearms legally required to be destroyed, disassemble them, and destroy the serial numbered parts. In this case, the lower receiver. All other parts for that gun are removed and put in bags/sold at auction as a parts kit. So these were assembled rifles, sold separately. "As far as I know" all the parts for each were kept together. But good question. All I did was put the uppers as I got them, with their own buffer/spring/bolt onto a lower I already had. As I mentioned, one appeared brand new, the other (problem child) like new, with VERY little wear.

Is there anything I can inspect for? Buying used guns off the internet has never presented this sort of challenge. I've bought lots of Gunbuster stuff over the years. This is the only one ever didnt work well. Do new ARs tend to be finicky? "Unknown" manufacture could be anything, good, bad or middling. Roll of the dice. Ima go back & clean it & play with it until it runs right.

But my main question I wanted to know has to deal with swapping the buttstocks between the two, and the buffers/weight/spring combos... vs the barrel length/gas system length. I dont know jack about that.

So, assuming they were properly assembled/properly functioning rifles, what is the proper weight buffer, buffer spring, for the carbine length barrel? And again, for the mid-length barrel? How does a guy measure springs?

I agree, no telling who built the no name gun, no telling what quality parts, etc. But it was not expensive, so no sweat-ey-da.

 

[S197]

I would try the bcg from the assembly that ran properly. if it still has feeding problems then I would say something is out of spec. Post pics of the feed ramps of the upper that is failing.

 

[Makinchips208]

Sounds like multiple problems, maybe isolating them will help.
For example, If you have to mortar it and or use a rod down the bore to extract a spent case? That has nothing to do with any part of the rifle, EXCEPT the internals of the barrel and/or chamber issues (including headspace), and possibly ammo.
Failure to feed is another problem altogether with many other possible causes.

 

[Old Man with Gun]

If you have a functional rifle, keep the good lower and swap the upper you are having trouble on to it. If it runs the problem is the other lower, if not it is this upper.

You should be able to swap working upper with working lowers, no problem.

It sounds like you have a bad upper. It could be the barrel, gas system, BCG or your ammo. Try factory brass case ammo first, then swap BCG.

On the lower, the stock and everything inside it goes together. Do not mix up the buffers and springs.

 

[Old Man with Gun]

Take pictures at range of damaged brass, jams, etc.

 

[hlee]

Also of note is that the buffer length is dictated by the receiver extension. The rifle buffer (long one) is required for the A2 stock. Using the carbine buffer (short one) with the rifle receiver extension will result in damage to your lower receiver. Using the rifle buffer with the carbine receiver extension will prevent proper cycling of the firearm.

 

[Mudburner]

If you have a functional rifle, keep the good lower and swap the upper you are having trouble on to it. If it runs the problem is the other lower, if not it is this upper.

You should be able to swap working upper with working lowers, no problem.

It sounds like you have a bad upper. It could be the barrel, gas system, BCG or your ammo. Try factory brass case ammo first, then swap BCG.

On the lower, the stock and everything inside it goes together. Do not mix up the buffers and springs.

This is what I wanted to know. Thanks.
I will do this:
-keep same buffer/spring combo in the gun that it came with.
-clean it thoroughly, try bad upper on known good lower.
-try bolt/carrier from one that ran in the bad upper.
-buy store-bought ammo. My handloads are suspect.

 

[Mudburner]

Thanks for the advice. I appreciate y'all.

 

[erik72]

The top one choked; failed to feed, failed to extract, had to be mortared to unlock the bolt, about every 3rd round... I had to rod the bore to extract spent casings, and they had damaged rims.

The fact you had to "mortar" the gun to remove spent cases is is where I'd focus. Obviously matching the buffer with the correct buffer tube is important but I'm trying to understand your experience here. Is the spent case stuck? Or did the bolt lugs not disengage? Drop a resized piece of brass into the chamber by hand. It should drop right in and fall out freely. If that's not the issue then you've got a gas issue or something is wrong with the bolt. Does the bolt have gas rings on it? Does it move freely by hand?

 

[Mudburner]

I suspect my handloads here. We'll see if mfg. ammo runs or not, as above.

Spent cases were stuck. Had damaged rims, so extractor claw engaged.

Bolt is like new, has perfect gas rings. I actually lubed one magazine full of ammo with clp and it ran better, bit eventially choked. Again, I suspect my handloads.

 

[bill_van]

Regarding your handloads.... if not full length resized, they will get stuck in the chamber as described. You are on the right track trying factory ammo. If that does not work start troubleshooting the rest of the carbine as mentioned.

I don't recommend lubing the inside of a mag. Lube on a case could lead to over pressure and possible damage to you and your weapon. Keep lube off chamber and bullets at all cost!

 

[Bantam1]

The chamber on the barrel could be out of spec also. This can cause feeding and extraction issues if the chamber is too tight.

 

[Mudburner]

Range report:

Problems solved. Bought some PMC ball ammo and bang, bang, bang, bang. I am happy to report that both uppers functioned flawlessly on that A2 lower.

Ejection pattern for both uppers were 3:30/4:00 at about 6 feet. Thanks for all who responded. I appreciate ya. Case closed. Cheap or not, they both work. Was hitting the 200 yard gong easy. The Anderson even went through a 30rd mag of my dirty brass handloads with no problems. Ima hafta step up my reloading game.

 

[bill_van]

Glad it was an easy fix! Enjoy.... they are a lot of fun!

 

[hlee]

Yeah, reloads being the only source of ammunition is what kept me off the AR “wildcat” track n for a long time. Availability of quality factory ammunition is a godsend when troubleshooting a firearm.