Bushmaster upper ejection issue

[Hoot]

Somewhere, I have a diagram of what the port opening measurements should be. But I’m gonna have to hunt for it. I’m not at home where I can get into my archives.

Unfortunately, I can't find the master of the image I posted that got lost to greed via TinyPic. Its got to be around here somewhere. I lost a lot of time that 'll never get back, to TinyPic.

Hoot

[Texas Sheepdawg]

Somewhere, I have a diagram of what the port opening measurements should be. But I’m gonna have to hunt for it. I’m not at home where I can get into my archives.

Unfortunately, I can't find the master of the image I posted that got lost to greed via TinyPic. Its got to be around here somewhere. I lost a lot of time that 'll never get back, to TinyPic.

Hoot

I’ve got it on my server at the house. But I can’t access it remotely anymore. Turned that function off last year.

[Texas Sheepdawg]

Of all the annoying causes of friction, an unpolished hammer face riding under the BCG is one of the most common causes. It’s also one of the easiest to hone and polish out. Always look for causes of friction during cycling. From rough hammer faces to raspy buffer springs. I have this hammer well on its way to becoming smooth as a mirror. Look at those ridiculous milling marks!

E21F0AB7-4C6F-4F33-94F5-DB01FD11EA61.jpeg (73.26 KiB) Viewed 10598 times

[Texas Sheepdawg]

Almost there.

B34C7E89-57B0-4624-9A80-92A81F790D50.jpeg (65.68 KiB) Viewed 10597 times

[acekc]

OK, I finally had a chance to make it back out to the range. A couple of things have changed:

1. The more I've shot the gun the more I suspected that the magazine was at least partly to blame for my troubles. I decided to spring for a Lancer 10 round mag (a/k/a 4 round 450BM) and a Tromix follower. I used this magazine today.

2. Those 250gr FTX bullets are expensive! I switched to 225gr FTX's for today's testing. Starline Brass, CCI magnum primers, 38gr of LIL GUN and a COAL of 2.13" or so. The powder charge and COAL were chosen because multiple people had good things to say about the accuracy of this load. Crimp was taper crimp with the same crimp I'd used on the 250's (0.473" I believe).

3. Today's testing used the stock buffer spring and the Spike's T-2 buffer. I've used this before but

So how did it go? Not perfectly but a lot better. I loaded as many as four rounds into the magazine at a time and fired a total of ten rounds. The gun cycled properly every time and there were no jams.

There were a couple of issues: Ejection still seemed pretty weak and somewhat inconsistent to me. Also, I shot the magazine empty three times and the bolt failed to lock back on the empty magazine in all three tries.

I know that an earlier post said that these uppers were typically overgassed but is it possible that something is causing it to be undergassed? I know that 38gr of LIL GUN is (according to Hodgdon) minimum charge for the 225gr FTX but it seems like lots of others have used this load without cycling issues.

As for the hammer and buffer spring: I've oiled the buffer tube and spring previously so I don't think they're the issue, and the trigger is an aftermarket all-in-one CMC trigger with a VERY smooth hammer face.

[Bmt85]

Your 225 FTX load should cycle. Under gassing might be an issue, but I don't think so. Usually when undergassed, the brass will fall at your feet, or maybe not make it out of the upper. You're having inconsistent ejection.

Have you checked to see if the brass is hanging up on the extractor? I thought it was mentioned, but it doesn't look like it was. If your extractor has burrs or sharp edges, it can bite into the brass, causing ejection issues. Easy to check and fix.

I'm curious to the gas port size, or if there is a burr in the gas port. However, those don't usually lead to inconsistent ejection. Also, those uppers can be a pain to dismantle. I say, again, send it in and let them figure it out.

[viper_51]

new build 18” heavy barrel mid length gas tube with a carbine receiver extension so i also have same issues !
1 weak ejection or no ejection
2 slight gouges were extractor possibly catching case rim
3 inconsistent ejection angle (2:00-4:00 oclock)
4 bolt fails to lock open on a single round magazine but will manually
5 tried h2 buffer ..made it worse !
ive have new magazine ordered lantec with tromac follower


ANY ADVICE WOULD BE HELPFUL THIS IS A BIT AGGRIVATING

[jbullock78]

are you me? I had the exact same issue this saturday with my 450- Anxiously awaiting any info.

[Texas Sheepdawg]

Just an observation. Originally the 450 bushmaster was engineered with a carbine length gas tube. Not a medium length or long length.

Carbine length gas tube.

Published reloading data in the Hornady manuals were also established on a barrel with the carbine length gas tube and a 1:24 twist barrel.
Think about this as you’re trying to work out your issues on a barrel with a mid-length gas system.
Timing will have changed on a mid-length gas system. Factor in a different twist as well and you have even more variables to contend with.
Hope this helps.

[Slayer]

I also bought a 20" Bushmaster upper from midway back in January. At first it ran through a box of Hornady factory ammo fine.
But I noticed the extractor was really chewing the rims up. When I got to my reloads it wouldn't eject at all. Jamming constantly. I triple checked my reloads and they were in spec. Case length was shorter at 1.692, but thats not too bad really.
Bolt wouldn't lock after last shot... many of the same symptoms you guys had.
So... i ordered a thumper extractor from windam weaponry, a new extractor spring kit as well. I took the O ring out, as well as the little rubber part that rides inside the spring and threw them in a box.
With just the spring in the windam extractor it runs flawlessly.
If you compare the windam weaponry extractor to the Bushmaster there's a major difference in the geometry of the 2 extractors.
You will see it right away. I also trimmed a coil off the bottom of the magazine spring. So far its been a Cheap fix for me, windam is getting stuff out fairly quickly considering whats going on right now.
This may help you guys, may not. Not a costly what I would call upgrade at any rate. Worth a shot! Also tweaked and polished feed lips on the bushmaster clip. Thinking that fixed my bolt not staying open issue. The bullet does have to rest at the proper angle in the mag.
Shouldn't have to mess with a new gun like that, but the price at midway is certainly right.
Give it a try, so far mine hasn't jammed since doing those 3 "mods"