450Bushmaster.net

No worries Jim, I had to proof-read my post as I had switched the two of them a couple times myself. It's easy to confuse the two, but the difference is important as they provide two different functions that work together for ejection.

I'm having these problems still. I've just made the mods to one of my mags that Hoot recommended but haven't been to the range yet to test if it helps. I've been looking at the ejection port in the receiver. It seems very tight and not much bigger at all than the cartridge. Has anyone opened it up slightly and do you guys who know what you're doing recommend it? I was thinking of just filing it a very little bit top and bottom.

Jeepejeep wrote:I'm having these problems still. I've just made the mods to one of my mags that Hoot recommended but haven't been to the range yet to test if it helps. I've been looking at the ejection port in the receiver. It seems very tight and not much bigger at all than the cartridge. Has anyone opened it up slightly and do you guys who know what you're doing recommend it? I was thinking of just filing it a very little bit top and bottom.

For a 450b upper made by the factory, you should never need to adjust the ejection port size. Their functionality does depend up the extracting case not colliding with the next round coming up from the mag. As long as you relieve the top of the front wall of the mag in a semi-circle and squeeze the lips closer together, any steel after-market 5.56 mag should be able to be adapted to work. Obviously, there are other problems that can arise, affecting cartridge handling, but if you have to machine the ejection port, you are band-aiding a different problem.

Hoot

Thanks, Hoot, I guess I'm just looking for anything to get this thing to work. Why the hell do we have to tweak and file and modify the mags anyway? Why can't they work from the factory? Is this too much to ask? It works perfectly with the .223 upper, why not with the 450? OK, rant over

Jeepejeep wrote:Thanks, Hoot, I guess I'm just looking for anything to get this thing to work. Why the hell do we have to tweak and file and modify the mags anyway? Why can't they work from the factory? Is this too much to ask? It works perfectly with the .223 upper, why not with the 450? OK, rant over

The .223 is a staggered stack round. The 450b is a single stack round. With a staggered stack, the rounds sit off to the sides of the mag, under the lips, so lip gap can be wider with no impact. In a single stack, they run straight up the middle and the gap between the two lips is critical to their behavior. Too loose and they ride too high, ride angled incorrectly, even spew out. Too tight and the bolt will not pass between them to catch the face of the next round and strip it. In the case of the upper lip of the front of the mag wall. A .223 has much narrower neck and a shoulder to allow it to ride up and over that wall during stripping. The 450b obviously does not and the lip of the case catches the lip of the mag if you don't relieve it. Put a factory 450b mag next to a .223 mag and it all leaps out at you.

Hoot

Yup, I see that and again, thank you for your knowledge. What I don't get is why doesn't Bushmaster have this perfected and done before the mags are sold? This is their cartridge and so I'd think they would make all modifications right out of the box. That's assuming the problems I'm having are truly mag related. Even so, they claim it's a direct swap, upper for upper so no matter what, it should work. I guess I'm spoiled by my dead reliability of my Glock and even my Hi-Point Carbine! . More of a rant about Bushmasters quality control than anything, I guess.

Just an update, I sent back the gun to Bushmaster< got it back in four weeks, brought it to the range and it ejected every shell flawlessly. I shot about 50 rounds, and got it dialed in.
I have a one inch group at 50 yards and a 2.5 inch group at 100, all with Hornady factory ammo- couldn't be happier . Wish I knew what the problem was- Bushmaster didn't say.
Thanks for all your help guys. Takin it out opening day- Saturday, hopefully will have pics and stories to tell.

Glad to hear it worked out, enjoy your rifle.

FirstARinNY wrote:Just an update, I sent back the gun to Bushmaster< got it back in four weeks, brought it to the range and it ejected every shell flawlessly. I shot about 50 rounds, and got it dialed in.
I have a one inch group at 50 yards and a 2.5 inch group at 100, all with Hornady factory ammo- couldn't be happier . Wish I knew what the problem was- Bushmaster didn't say.
Thanks for all your help guys. Takin it out opening day- Saturday, hopefully will have pics and stories to tell.

got mine working well by following the advice here and modifying the mags. I'll be out there on Sat. morning too. Here's hoping I have some pics and a good story.

I shot a little video yesterday on the factory 450 bushmaster mag and how to do a mod that may help reduce jams and at the same time, increase capacity. As soon as I edit and upload it to You Tube, I will post it here.