Bushmaster upper ejection issue

[acekc]

I recently dipped my toe in the 450BM waters with one of the Bushmaster uppers from Midway. Mine has a 20" barrel and came with a magazine.

I loaded up some rounds and headed to the range. The lower has a stock buffer and spring. Ejection was very spotty and I gave up trying to load more than one round at a time into the magazine. The brass would occasionally eject between 1 o'clock and 2 o'clock (flying around ten feet away) but more often would either barely make it out of the ejection port or stay in the gun, laying on top of the empty magazine.

Since this is a Bushmaster upper chambered in 450 Bushmaster it does have the ejection port opened up already. Basically the portion rear of the dust cover detent measures around 0.51" (doesn't appear to have been touched) while the area forward of the detent is a uniform 0.55" or so. Is this sufficient or does it possibly need to be opened up more? I would think that Bushmaster would open it up enough from the factory but perhaps not.

I don't suspect the loads but just in case:

Starline Brass
250gr GTX bullets
2.25" COAL
CCI SRP
LIL GUN (four rounds each with a charge range of 36.4 to 38.2 in 0.2gr increments)
0.478 taper crimp

The problems occurred regardless of the powder charge.

[Bmt85]

I don't have my Bushmaster upper anymore, so maybe someone else can give their ejection port opening sizes. It sounds ok to me, though.

My personal opinion, it's a new, recently purchased upper, so send it in now. Let them figure it out. Also, IIRC, Bushmaster is being shut down (along with a couple other brands owned under Remington), so who knows when they will stop accepting returns. I would also send a note with the upper stating the issues, and to double check the ejection port opening.

As to the erratic ejection, it really sounds like it could be 2 problems. One, it sounds like you're overgassed, which isn't surprising with the 20" barreled Bushmaster uppers. They run a carbine length gas system, and usually too big of port. Best way to fix that is run more weight in the buffer, and/or add weight to the bolt carrier. Hoot did a write up on the added weight to the bolt carrier years ago. If you have heavier buffers, you can try those. I actually run a Slash's XH buffer in a couple of my uppers. It's very heavy! Another issue could be that the extractor or buffer is weak. You could try installing a new buffer and spring, or even try the o-ring that is available.

[Texas Sheepdawg]

I’ve found it’s best to run your new upper a little wet until it breaks in. I used duralube and gave the BCG a generous coating. Plus I sprayed some in the buffer tube as well. But speaking of buffer tubes. Have you inspected your buffer spring? Carbine springs belong in carbines and rifle springs belong in rifles. Also. The milspec buffer spring is not a very smooth operator. If you pull out your buffer and spring, also inspect the spring to see if it’s rough or polished. A milspec buffer spring may feel like a 1000 grit emery cloth if it’s a cheapy. Pull the spring, wipe it down. If it’s dull, run your fingernail along the spring. If it’s feeling more like you’re scratching a honing stone and it’s not polished to a reflective surface that’s smooth as glass, that’s going to affect your cycling. I’ve replace ALL of my buffer springs with the JP polished springs. They cost under $20 a piece but you will notice a huge improvement in action. They come in both carbine length and rifle length.
Check this first then tell us what you discovered.

[acekc]

To be clear the only reason I suspected the ejection port opening was because of the problems I'm having. I didn't realize that these uppers were typically overgassed, so I'll probably start my troubleshooting there.

I have a couple of buffers (stock and T2) and a small variety of springs (stock, Sprinco red and blue). I'll try some combinations of those and see if I can get it to operate reliably. I found the thread on Hoot's CCW but I don't have the equipment necessary to melt lead so it's probably not an option for me.

[acekc]

I checked the lubrication and it seemed sufficient, it arrived pretty wet from Midway to be honest. I had previously lubricated the buffer tube on the lower.

Went back out today and put another 30 rounds through the upper. I took along the two buffers and three springs that I'd talked about before and swapped in various combinations:

3 oz. carbine buffer
4 oz. Spike's T2 buffer
Stock spring
Sprinco blue spring
Sprinco red spring

I saw a few different scenarios:

1. Relatively strong ejection in the 2:00 area.
2. Relatively strong ejection in the 3:00 area.
3. Very weak ejection (brass flies 1-2 feet) in the 2:00-3:00 area.
4. Brass does not exit the gun and winds up laying on top of the magazine.

Strangely I honestly couldn't tell much difference in behavior between the various buffers and springs.

I've uploaded a picture of the ejection port in case it would be helpful. I'm somewhat out of ideas at this point.

[Hoot]

Check your ejector plunger to make sure its not binding. You can remove your BCG, hook a case rim under the extractor and rock the case into position to get a sense of the spring's power. Coax some oil down into the spring well. Some times they bind with brass shavings. I say this because it should sling the brass a lot further than a couple of feet unless you've removed some of the spring. I have a light spring in mine since I use a catcher bag rather than have the brass get all dinged up as it hits the concrete pad on our rifle range. Doubly so if you're shooting in a field, so you don't have to hunt for them. The ejection port cut out looks adequate, assuming the case isn't dragging on the next unfired round in the mag. Try chambering a round, drop the mag out and shoot the single round. See if it flies differently as a means of determining whether its dragging on some part of the mag.

Hoot

[acekc]

I checked the plunger, didn't seem to be binding at all. I put a drop of oil on top of/around it and worked it in just to be sure.

I definitely haven't messed with the ejector spring at all, I've done nothing to this upper other than put rounds through it.

As far as dragging on the next unfired round, that's definitely not the issue. I've been loading rounds one at a time in an attempt to figure out this ejection issue. On the few occasions where I haven't then the brass sticks in the action, the next round gets jammed up and the whole thing turns into a giant mess.

I admittedly haven't yet tried your suggestion of firing without the magazine in place. I'll give that a try next. The mag already has two strikes as far as I'm concerned because if I load the rounds to the back of the mag then the top one catches on something and cants up at a crazy angle. The Lancer mags with Tromix followers are looking more and more attractive...

[Texas Sheepdawg]

Maybe this will help.

82A79F9F-1203-47F4-863C-F4F697143A7E.jpeg (77.41 KiB) Viewed 12412 times

[Texas Sheepdawg]

057A4644-2800-46A9-BFB1-FD9131860362.jpeg (11.92 KiB) Viewed 12412 times

[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.