450 BM .. every shot FTE

[alclark2]

I did several tests this weekend on my .450 bushmaster. As the title states, every shot was a failure to extract. I took several pictures to show what's going on. I've built a few ARs but diagnosing issues like this isn't exactly my forte. I'll start with what I did...
I cleaned the barrel thoroughly
I left the bolt very wet with Rem oil
I used a Franklin armory and a bushmaster mag
I used both Remington green tips and Hornaday factory loads

Here are some pictures of the ammo and mags

450 bm fte issues by

[URL="https://flic.kr/p/NRiG92"] 450 bm fte issues by

[URL="https://flic.kr/p/NRiG8F"] 450 bm fte issues by
450 bm fte issues by Aaron Clark, on Flickr
450 bm fte issues
And a picture of my 100 yard setup just for fun.

I have heard several things... I may need an adjustable gas block. Also/or, I may need to change the weight of the buffer tube.

Any help to steer me in the right direction would be appreciated.


-Aaron

 

[SEIndSAM]

Are you sure the gas block is centered over the hole in the barrel??

 

[indiana hillbilly]

I had to install a spikes T2 buffer in mine. Mine would stovepipe on ejection. With the heavier buffer, it slowed the action down just a bit. Also I opened up the lips on the magazine just a bit.

 

[halfmileharry]

Are you sure the gas block is centered over the hole in the barrel??

My first thought as well. Definitely check for hole alignment, clogged gas tube, block, etc.
Barrel length? Tube length/ dia, etc?
My last build gave me gas trouble. I used one of the cheap "Palm Tree" gas blocks and it kept stopping up.
I changed it out to a better gas block and haven't had any more issues from it.
Sure you've heard it before but "Part's ain't Parts"

 

[alclark2]

Are you sure the gas block is centered over the hole in the barrel??

The upper was built by Franklin Armory so I have no way to tell...

 

[alclark2]

My first thought as well. Definitely check for hole alignment, clogged gas tube, block, etc.
Barrel length? Tube length/ dia, etc?
My last build gave me gas trouble. I used one of the cheap "Palm Tree" gas blocks and it kept stopping up.
I changed it out to a better gas block and haven't had any more issues from it.
Sure you've heard it before but "Part's ain't Parts"

I'll check the gas tube first. Its a 20" barrel with rifle length gas tube.

 

[M67]

I'll check the gas tube first. Its a 20" barrel with rifle length gas tube.

Rem oil kinda sucks for an AR

But, a rifle length gas system on a 450? That could be the issue right there

 

[oldpink]

Dunno if excessive pressure could be an issue with a gas-operated gun, but I spotted in your third and fourth photos something that looks suspiciously like an ejector impression on the case head, specifically around the "P" of the "R-P" head stamp traditionally used with Remington-Peters brass.
The only time that I've ever seen an ejector pin hole impression on a case head was with over pressure reloads.

 

[halfmileharry]

Dunno if excessive pressure could be an issue with a gas-operated gun, but I spotted in your third and fourth photos something that looks suspiciously like an ejector impression on the case head, specifically around the "P" of the "R-P" head stamp traditionally used with Remington-Peters brass.
The only time that I've ever seen an ejector pin hole impression on a case head was with over pressure reloads.

I saw that too. I didn't think that would cause the problem but it could very well be relevant.

 

[Spear Dane]

That green tip is the most half assed looking garbage I've ever seen for a gun.

 

[rvb]

you haven't really given a description of the failure other than "fails to extract." that can mean lots of things.

is it actually leaving the brass in the chamber while trying to feed the next round? extraction failures are often called double feeds.
what does it do when you cycle by hand?
does it lock back on an empty mag?
can you watch while it's being shot and see if the bolt is fully opening or just a little or not moving at all?
is it trying to feed the next round while not clearing the empty case?

while the primers look good, there is evidence of high-pressure brass flow into the ejector. are you sure it's an extraction failure and not an ejection failure? could be some brass shaving hanging up the ejector. you should be able to remove the bolt, stick a spent casing under the extractor hook and hold it in line with the bolt, then when you let go the ejector should 'fling' the case in the direction of the extractor.

finally, does the extractor look good? have good spring to snap over rim? no brass shavings keeping it from grabbing rim of case?

you need to better describe how it's failing to start to narrow down the issue.

I'm not familiar enough w/ the oddball AR calibers to know what gas system length, port size, etc is needed, but can only assume it 'should' work being a factory upper. experimentation with buffer weights might be a bandaid solution, depending on whether it's undergassed or even possibly over gassed..

-rvb

 

[BiscuitsandGravy]

I would do a simple check to see if you can blow air thru the gas system. I appears at first glance that your gas system is plugged. The 450BM should have a very stout kick with stock buffer spring/buffer/etc.

Try a single round at a time w/o mag to see if it cycles any. Have a friend watch the BCG while you fire.

 

[oldpink]

rvb had all kinds of excellent suggestions.
I'll just add that the one occasion that I encountered over-pressure ammo was with some .30-06 reloads that I had assembled with a maximum charge of IMR4831 behind the 165 grain Barnes X-Bullet (the first iteration, not the later XLC or the current TTX or TTSX), I had extreme difficulty getting the third one to extract at all from my Ruger M77 bolt gun, necessitating me repeatedly rapping the bolt handle to get the bolt to rotate enough to unlock and extract/eject the third round, which had a totally blown primer and primer pocket and ejector indentation on the case head.
The preceding two over-pressure rounds didn't quite have blown primers (close, though), but they were also very difficult to extract/eject, both with clear evidence of the ejector indentation on their case heads, along with flattened and cratered primers.
I have every reason to believe that loads that are above the specified pressure in an AR platform would cause similar problems, and that ejector indentation on the case head just about guarantees that those loads are a might over what they should be.

 

[BStarkey 46947]

I have a Bushmaster 16" upper on a PSA complete lower. I only shoot Hornady ammunition. The LGS told me a few years ago there were original issues with the Bushmaster extractor design and it was re-designed to overcome FTE issues. It does create distinctive marks on the case rim. I have never experienced this issue, no help.

 

[phylodog]

I may have missed it but I didn't see a recommendation to make sure the gas carrier key is not loose on your bolt carrier. That is always the first thing I check for a suspected gas issue.

 

[alclark2]

Just to elaborate... The brass is staying in the chamber. It will eject properly when cycled by hand.

We took a video of the action... We now see that the bolt is not coming back far enough.

https://youtu.be/_O1xVAGVcpw

I took the buffer and spring out of 4 ARs last night.

450 BM 120 grams + (Spring is 1/2-3/4" longer than all of the other ARS)
Sig 84 grams
PSA 87 grams
Unknown 87 grams

I shot the rifle with the most flexible spring and lightest buffer from the Sig AR. We did get enough action to get the brass to stovepipe once.

I looked down the gas tube and barrel with my LED flash light and I can see its transmitting a very clear ring of light. It appears to be wide open.
There is plenty of fouling on the tube. The rifle is definitely flowing. The next step in the gas department is to disassemble and inspect the gas block. We thought there could be a potential leak at that point. This would allow us to check the alignment of the holes. Also, we thought about running a chrono to see what the ammo is actually doing.

The rings on the bolt are misaligned properly. That didn't seem to be an issue.

I've emailed Franklin Armory to ask about any issues with these uppers.

 

[alclark2]

Guy on another forum....



Welcome aboard Al.

In the video, it look like it's get some gas, just not enough to get the bolt all the way back. The fact that you can hand cycle the spent round tells you what you already probably have determined. The spent cases are not seized in the chamber, though they some times do. With incomplete extraction, the expanded cases can some times jam back into the chamber on the forward stroke. I have an upper built with a Franklin barrel. From the factory, the barrel would not fully extract either. I found the gas sampling hole had to be enlarged slightly to get it to cycle reliably. I must stress that I did not buy a complete upper, just the barrel. That having been said, I'd be po'd if I bought a complete upper they didn't test it at the factory before they shipped it.

Somethings to try: Chamber a round, remove the mag and see if it extracts when fired. If it does and you have one, try it on a known-good, different lower. It should run like a top on a regular rifle spring and buffer. I have no personal experience with telescopic lowers however.




Looks like I may see the issue from the factory barrel

 

[BiscuitsandGravy]

IMO- its either very under gassed- consider all comments above. This sounds like a dumb question but its not and I have seen it done... Are you using the correct length gas tube? Take a picture of the upper from underneath without the BCG so you can see the length of the gas tube and if it lines up with the casting/machining marks inside. I've seen short gas tubes cause a light cycle just like that.

Or, change buffer/buffer spring to a known working setup. An easy test would be to change out your lower with one that you know works.

And try some Hornady.

I'm betting gas issues. I have a friend that built a Franklin 20" setup and it kicked and cycled like stock buffered 450's should- a mule.

 

[alclark2]

IMO- its either very under gassed- consider all comments above. This sounds like a dumb question but its not and I have seen it done... Are you using the correct length gas tube? Take a picture of the upper from underneath without the bolt so you can see the length of the gas tube and if it lines up with the casting/machining marks inside.

Or, change buffer/buffer spring to a known working setup. An easy test would be to change out your lower with one that you know works.

And try some Hornady.

I'm betting gas issues. I have a friend that built a Franklin 20" setup and it kicked and cycled like stock buffered 450's should- a mule.

I'm not crazy about that Remington ammo. I received it as a gift.
I've provided enough time to Franklin to respond. I'm going to call them and ask. I tried three different springs and 3 buffers of varying weights. I feel like its under gassed personally.


BUT .. I did look up that Spikes T2 buffer and I see it weighs in at 42 grams. The others I tried are 84, 87, 120+ (wouldn't register on my scale). I don't want a "bandaid" fix but if it is simple as swapping the buffer... That could be the issue? I don't know.

Correction...

T2 = 85 grams
T1 = 115 grams

That won't fix anything.

 

[BiscuitsandGravy]

I'm not crazy about that Remington ammo. I received it as a gift.
I've provided enough time to Franklin to respond. I'm going to call them and ask. I tried three different springs and 3 buffers of varying weights. I feel like its under gassed personally.


BUT .. I did look up that Spikes T2 buffer and I see it weighs in at 42 grams. The others I tried are 84, 87, 120+ (wouldn't register on my scale). I don't want a "bandaid" fix but if it is simple as swapping the buffer... That could be the issue? I don't know.

Correction...

T2 = 85 grams
T1 = 115 grams

That won't fix anything.

Just to humor me... Take a quick look at the gas tube length as it extends into the upper. See if it ends at the middle of the semi circle cut out. I've emailed my friend about his 20" Franklin because I think he had the same issue at first. A short gas tube. If the length is right you can rule that out.