Any AR experts here?

[Tweety Bird]

If this needs to go in another place, somebody feel free to move it. But though it's about a rifle, it's not a Ruger, so I'm going to at least start with it here.

We have a neighbor who spent all of his high school graduation money on a custom-built AR15 last spring. I don't know who built it (some "custom" gun builder in Florida somewhere but I don't remember the name). Poor Riley has had nothing but trouble with it.

First of all, it's an M4 length gun, chambered in .300 Blackout rather than .223 or 5.56. I know absolutely nothing about the 300 Blackout round other than it's a shortened .223 case with the neck stretched to 30 caliber.

When he first got it, the darn thing wouldn't extract or eject the empty brass. He brought it up to me and I found the extractor spring was extremely weak. We put a new spring in it and that problem went away.

Since then, he's had another issue that he's finally asking me about. It seems to be short-cycling. It'll fire the first 2 rounds fine, but won't pick up the 3rd round from the magazine. Loading the magazine full, or with only a few, doesn't seem to make a difference. He's tried 3 different magazines (2 Magpul and 1 GI style) and they all do the same. He listened to some internet ninja who told him to cut his buffer spring, so he did (cut about 1 turn off the spring). No help. He's also tried removing weights from the buffer but again, it didn't help.

I let him borrow the buffer spring out of Mrs. Tweety's carbine-length AR, and that didn't help at all.

Today he brought it up to me and we went to shoot it. It's back to all of its original parts, including the "modified" buffer spring. Sure enough, the first 2 rounds went fine but it just would not pick up the 3rd round from the mag. The bolt was fully into battery but no round in the chamber. That's why I think it's short-cycling.

I took the bolt out of my Rock River and dropped it into his gun and it ran perfectly with my bolt in his gun. So just for fun, I put his bolt in my rifle and it ran fine, as well.

I helped him take the gas tube out of his gun and told him to take it home and clean it well. It feels like some coked-up oil on the outside of the rear end of the tube so I'm guessing some oil got in there. The tube seemed clear enough when I blew through it, though.

So this one has me stumped but then I'm certainly not an AR expert.

I'm thinking the 300 blackout round is a lower pressure round than the .223, which makes me think it's a gas-delivery issue. I know the carbine-length (his) and rifle-length (mine) have different size openings in the gas block. Would a standard M4 gas block have too small a gas port for a lower pressure round like the 300 blackout? I don't know. So I'm looking for input so I can help him.

Summary on Riley's gun:
Won't fire more than 2 rounds in a row.
Extracts and ejects spent brass just fine.
Different magazines and buffer spring no help.
His gun (carbine-length) runs fine with my bolt carrier group
My gun (rifle-length) runs fine with his BCG.
His gas key seems to be staked well and secure.

Ideas?

 

[TRanger]

Get rid of it and buy one from a reputable maker. "Custom built" is always a red flag.

 

[Tweety Bird]

Riley can't afford that. He's a college kid and just wants to get this one working.

 

[Dan in MI]

I'm not fully up to speed on the Blackout but it can run in many variations fro mild to wild. Original design was slow heavy bullets. Now they've made light bullet hunting rounds out of it. So I'd guess pressures vary. I would see if you can find out what type of round it made for. It may well have been designed for type and A and you are shooting type B.

If cleaning the gas tube doesn't get it. Maybe just get a BCG and call it day.

 

[JohnBoy]

I agree with 'Dan in MI', ammunition for this chambering can vary greatly - but that doesn't really explain the 'two and done' problem. I'd first reach out to the builder and explain the issues - ask for his recommended load.

Additionally, I'd mess around with a varying number of rounds in the magazine, I'd shoot one at a time with no magazine in the rifle, I'd also shoot a round - let the firearm rest a few minutes - shoot again - repeat.

It almost seems like heat (minimal) buildup is causing a problem with cycling - or pressure is somehow being affected.

Again, as 'Dan in MI' states, 'Maybe just get a (new) BCG and call it a day."!

Good luck with this - never fun when a pile of cash is dropped on a gun that is unreliable.

 

[Tweety Bird]

I was wondering if it's heat-related, myself. I don't know if it's possible for any coking in the gas path to expand or be more restrictive after a few rounds or not.

One thing I did notice is that with the bolt removed from the gun, his didn't operate as smoothly as mine. I took it apart and the rings and bore looked pretty good but that's not a very scientific investigation. I told him he might want to put a very LIGHT coat of oil on the rings but to not let oil of any amount get into the gas areas. I have a feeling that if he gets it real clean, it'll run well, but "wait and see" is the order of the day now.

He told me his father bought some subsonic rounds for it but it wouldn't even eject the empties with that one (no surprise there). The ammo he was using appeared to be factory loads from Remington but he said he has some reloads (unknown origin, at least to me) that act the same. Again, I know absolutely nothing about this round. Too bad he didn't just stick with the more common stuff, as I'm sure he's learning the hard - and expensive - way.

Again, Riley's a college freshman and doesn't have a lot of $$ to drop on this, so a BCG is probably out of the question for him. He was likely wondering if a trade (mine for his) BCG would work but he's polite enough not to ask. I wouldn't trade a Rock River part for one of unknown origin anyway.

 

[hittman]

I'd first reach out to the builder

Me too.

Why try to gunsmith it if they already know a solution or are willing to make it right?

 

[Tweety Bird]

I told him to talk to the builder. That's all I can do; it's really hard to force a 19-year-old to do anything.

He keeps asking me for help, I suppose, because I only live 2 miles from him. Apparently he doesn't realize that I'm a mechanic but NOT a gunsmith. He's a good kid, though, so I'll help him all I can.

 

[krw]

The only firearms I am married to are the ones my Dad gave me. In saying that, sell it and buy a 5.56 upper. It will be cheaper, and ammo cost a LOT less. I have a 300 Blkout carbine length upper I shoot fully suppressed and it is a Rosie O'Donnell. I am using a YHM Phantom can. And if you don't have a suppressor they are basically a 7.62x39. I have been told to open up the gas hole and also been told 300 Blkouts run a lot more reliable suppressed through a pistol length upper but I don't have a SBR stamp yet. If your not shooting this rd suppressed your spinning your wheels. Get a 5.56 upper and move on.

 

[RSIno1]

If it works fine with your bolt carrier group compare the 2 and see what the difference is - size, weight, surface texture etc.

 

[Mobuck]

Here's my suggestions: First start with a clean gun. I'm not sure why(or how) you "took the gas tube out of the gun" for cleaning BUT make sure you replaced the gas tube/block in proper alignment with the gas port in the barrel. Lube the bolt gas rings, cam pin, and bolt locking lugs with appropriate lube(I use wheel bearing grease on the cam pin & locking lugs and CLP or RemLube on the rest of the bolt. Load ONE round in the mag and chamber that round leaving the mag in place. Fire that round and see if the bolt locks open. Repeat 3-5 times. If the bolt locks open EVERY time, there's adequate gas being vented to the bolt. If not, there's a lack of gas(mis aligned gas block/improperly installed gas tube or improperly sized gas port) or gas is being lost in the system(loose gas key, missing/damaged gas rings, loose gas block).
While making these checks, see where the empty brass is landing. I don't have the AR ejection chart handy but basically, if the brass is landing in the 1-2 o'clock area(muzzle being 12 o'clock), there's more than optimum gas. If brass lands in the 5 o'clock area, there's less than optimum gas.
An adjustable gas block/heavier buffer can remedy an oversized gas port and a lightened bolt carrier can help with an under sized gas port.
These suggestions are very general but fairly basic to the AR platform.

 

[Tweety Bird]

I mean, I took the tube out. Simple to do, the gas block was fixed in place with 2 set screws and the tube to to the gas block by a spring pin. An Allen wrench and a roll pin punch had the tube out in less than a minute. It'll go back just the reverse. Other than clocking the gas block, it's aligned fore-aft by a machined shoulder on the barrel. Yes, the holes will be aligned when we re-assemble it. I'll check the location of the gas block hole against that of the barrel hole and shoulder when I put it back together.

The only thing I could tell, when comparing the two BCGs was that the bolt was stiffer to move in and out of his carrier than on that of mine. The bottom of my carrier was more polished than his, but mine has a lot more rounds through it and the trigger groups are different so the hammer might ride differently on them.

The facts that both BCGs work fine in my rifle, my BCG runs well in his but his BCG won't work well in his gun steer me to a gas problem.

The brass is going to the 4-5 o-clock position. I had a piece of cardboard taped to the right side of the shooting bench for the brass to hit. Most of them hit the cardboard and bounced behind the bench, indicating that they were being tossed rearward. A few even went far enough rearward to miss the cardboard wall entirely. So again it points to a slow movement of the BCG.

We'll get it figured out. I've told him to keep oil out of the gas tube because of the coked-up mess on the rear of the gas tube. Maybe if he can get that all cleaned up and keep it that way, it'll work for him, we'll see.

 

[Tweety Bird]

The only firearms I am married to are the ones my Dad gave me. In saying that, sell it and buy a 5.56 upper. It will be cheaper, and ammo cost a LOT less. I have a 300 Blkout carbine length upper I shoot fully suppressed and it is a Rosie O’Donnell. I am using a YHM Phantom can. And if you don't have a suppressor they are basically a 7.62x39. I have been told to open up the gas hole and also been told 300 Blkouts run a lot more reliable suppressed through a pistol length upper but I don't have a SBR stamp yet. If your not shooting this rd suppressed your spinning your wheels. Get a 5.56 upper and move on.

Again, it's not mine, it belongs to a college kid who can't afford $300 or more for a new upper.

But he did say that when he spoke to the builder, it was tested with a suppressor so maybe you're onto it here.

I know the M4 gas blocks have a smaller gas hole than the M16 because of the location of the port in relation to the chamber. So if he has a normal M4a gas block, the port might be too small for 300 Blackout. I offered to try my M16 A2 style FSM but his barrel isn't machined for a pinned gas block so we couldn't do that, either.

Fellas, suggestions for dumping a lot more dough into this rifle aren't helpful because he can't afford it. And he's too honest of a kid to sell it if it doesn't run right. Fixing it, hopefully cheaply, are what we are seeking for him.

 

[Mobuck]

it was tested with a suppressor

That would account for some extra deposits in the gas tube. It might also indicate that the maker expected the use of a suppressor and sized the gas port specifically for that use. If so, the most economical solution would be returning it to have that port enlarged. I have bolt carriers and buffers in 3 weight ranges to allow "adjustment" w/o having to swap gas blocks. Just a suggestion: don't "remove the gas tube for cleaning". If it's cruddy, take a syringe and squirt some Hoppes in the tube and let it soak muzzle down. Then take one of the pipe cleaner thingies sold by several places and swab the tube gently(don't want to ram that cleaner in the tube and stick it or twist it off or you will have to pull the tube to remove). Generally speaking, if that stuff is loosened somewhat by the Hoppes, the next shot will eject it from the gas tube(right into your bolt group but that's easily cleaned). While on the subject of removing the gas tube & block, those parts should be fairly snug and not something that just popped off "in under a minute". Done properly, it takes as long or longer to assemble, align, and secure the gas block as it does to seat the barrel and tighten the barrel nut.

 

[DeletedMember275]

The diameter of the gas port in the gas block is pretty much irrelevant, as long as it's aligned with the actual gas port in the barrel. The hole in the gas block is generally quite large, to allow for some minor misalignment anyway. The diameter of the gas port in the barrel is a major concern. Carbine-length gas systems need a larger gas port than a rifle-length system; pistol-length needs to be larger than carbine-length. Don't go drilling the gas port any larger until you eliminate all other possible causes, though. The fact that his rifle runs well with your bolt is a huge red flag! **SOMETHING** is likely amiss with his bolt carrier group.

Gas tubes do NOT require cleaning!!! Wipe down the part that protrudes into the upper receiver, and then you're DONE!

 

[wolfsong]

A great and enjoyable thread. Thanks to all the participants.

 

[Kevin]

Oh yeah. I don't have anything to add. I'm not familiar with AR platforms at all. But I just learned a whole lot. Very interesting!

Tweety Bird, please keep us updated if Riley solves the problem (or you of course)

 

[Racer9]

I assume you tried different magazines?
AR15.com might be more help.

 

[Rabon]

If this needs to go in another place, somebody feel free to move it. But though it's about a rifle, it's not a Ruger, so I'm going to at least start with it here.

We have a neighbor who spent all of his high school graduation money on a custom-built AR15 last spring. I don't know who built it (some "custom" gun builder in Florida somewhere but I don't remember the name). Poor Riley has had nothing but trouble with it.

First of all, it's an M4 length gun, chambered in .300 Blackout rather than .223 or 5.56. I know absolutely nothing about the 300 Blackout round other than it's a shortened .223 case with the neck stretched to 30 caliber.

When he first got it, the darn thing wouldn't extract or eject the empty brass. He brought it up to me and I found the extractor spring was extremely weak. We put a new spring in it and that problem went away.

Since then, he's had another issue that he's finally asking me about. It seems to be short-cycling. It'll fire the first 2 rounds fine, but won't pick up the 3rd round from the magazine. Loading the magazine full, or with only a few, doesn't seem to make a difference. He's tried 3 different magazines (2 Magpul and 1 GI style) and they all do the same. He listened to some internet ninja who told him to cut his buffer spring, so he did (cut about 1 turn off the spring). No help. He's also tried removing weights from the buffer but again, it didn't help.

I let him borrow the buffer spring out of Mrs. Tweety's carbine-length AR, and that didn't help at all.

Today he brought it up to me and we went to shoot it. It's back to all of its original parts, including the "modified" buffer spring. Sure enough, the first 2 rounds went fine but it just would not pick up the 3rd round from the mag. The bolt was fully into battery but no round in the chamber. That's why I think it's short-cycling.

I took the bolt out of my Rock River and dropped it into his gun and it ran perfectly with my bolt in his gun. So just for fun, I put his bolt in my rifle and it ran fine, as well.

I helped him take the gas tube out of his gun and told him to take it home and clean it well. It feels like some coked-up oil on the outside of the rear end of the tube so I'm guessing some oil got in there. The tube seemed clear enough when I blew through it, though.

So this one has me stumped but then I'm certainly not an AR expert.

I'm thinking the 300 blackout round is a lower pressure round than the .223, which makes me think it's a gas-delivery issue. I know the carbine-length (his) and rifle-length (mine) have different size openings in the gas block. Would a standard M4 gas block have too small a gas port for a lower pressure round like the 300 blackout? I don't know. So I'm looking for input so I can help him.

Summary on Riley's gun:
Won't fire more than 2 rounds in a row.
Extracts and ejects spent brass just fine.
Different magazines and buffer spring no help.
His gun (carbine-length) runs fine with my bolt carrier group
My gun (rifle-length) runs fine with his BCG.
His gas key seems to be staked well and secure.

Ideas?

If an AR does not lock the bolt back after the last round in fired it is short stroking. If his gun works with your bolt I would check the Key for tightness and replace the gas rings on his bolt (simple cheap and readily available) or if your gun cycles fine with his bolt, I would probably just trade him bolts.