450 BM .. every shot FTE
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://www.flickr.com/photos/130728319@N05/]
450 bm fte issues by [url=https://www.flickr.com/photos/130728319@N05/]
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.
UPDATE
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.
Any help here would be greatly appreciated.