450 BM mags

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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450 BM mags

Postby Forgotten man » Mon Oct 30, 2017 2:53 pm

getting into the 450 BM and ready to buy an upper, question about the mags are they 5.56 std. or are they 450 mags specific built for them?
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Re: 450 BM mags

Postby Al in Mi » Mon Oct 30, 2017 3:52 pm

Pattern is 5.56 but feed lips a little closer and have a single shot follower.

Bartz has about the best one I've used.
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Re: 450 BM mags

Postby Hoot » Mon Oct 30, 2017 10:13 pm

+1 on the Bartz mag.

5.56 rounds stack in a zigzag, staggered pattern. When the spring in the mag pushes straight up, the 5.56 rounds push about 50% up and 50% (over-simplified) outward against the lips. That makes them hold against the normally spaced lips pretty snug until they are each stripped by the bolt moving forward. The 450b rounds stack almost vertical and the majority of their uplift goes straight up with only a small percentage of the energy vectoring out toward the lips. Consequently, they may squeeze their way up through the gap between the lips at the most inopportune times. As Al explained, you need to squeeze the lips just far enough toward each other so that the upward force of the spring can not overpower the gap. Removing excess spring tension is a Big Help by removing just enough turns so that the last round is positively forced up against the gap. That's all the upward force you really need the spring to provide, assuming you're not rolling around in the muddy jungles of Vietnam. Most of us don't let our mags get mud in them after all.

Here's how I do it:

Slide the mag floor plate part of the way off off and look at where the bottom of the spring is originally cut. Mark that end of the mag body with a sharpie so you dont forget where to cut the winding's you will be removing later. Finish removing the floor plate the rest of the way and push the spring and follower out. If you are modding a 556 mag, you really should replace the stagger stack follower with a single stack one. Some folks just grind off the 556 follower where the mock cartridge molded into it exists, to get it mostly flat. There's "good enough" and then there's best engineering practice. The latter costs more. So does your hunting trip! With the follower and spring removed, first thing I do is polish the underside of the lips, where the cartridge drags along with a small piece of crocus cloth or use a dremel felt polishing fob and some of the polishing compound they gave you with it. Both work.

Then, using either a dremel rotary stone or fine rat tail file, remove some of the magazine at the top of the forward wall, creating a crescent cut down into it. Figure about 1/3 - 1/2 a 450b round depth crescent. There's pictures of the mags around to serve as a visual guide, if you dont understand what I'm talking about. Once the metal is removed, debur the cut so there are no sharp edges remaining. Blow out the residue left behind and wipe the inside clean with a rag lightly moistened with mineral spirits to get any debris still remaining, Wait a minute for it to dry. Don't oil the inside of the mag body despite it sounding like a good idea. They're designed to run dry.

Push the follower and spring back in (the right way) all up until the single stack (or modded stagger stack) follower reaches the stopping point, while allowing any excess spring to push out the bottom as far as it wants. Place one 450b round in the mag and push in against the spring jutting out of the bottom until it is pushing the round lightly against the lips. At that point, using a sharpie, Mark the winding of the spring where it still juts out,+ 1 turn more, + whatever amount it takes to round off that turn at the end of the mag body that you (hopefully) first marked, after partially removing the floor plate.

Cut off any excess turns past the mark you made on the spring. Once again, push the spring back in compressing any excess still jutting out and reinstall the floor plate (the right way). Now its time to check the lips spacing. Stuff the mag full of 450 rounds and see if they stay down in the mag. If they do, tap (not slam) the full mag down on the bench top a few times to make sure they don't change their mind. If they stay put, the battle has turned in your favor. At that point, hand cycle all the rounds through the action by easing the bolt back and forth, not slamming it into battery each time. That way, the rounds don't needlessly pull their bullets. Reload the mag and repeat until you're left with the impression that it's stable. If the rounds do not stay down in the mag when fully loaded, then you will need to bend the lips inward a little at a time, retesting, until they do. If the rounds stay put but hand cycling does not go according to plan, then we need to go back and do some fine tuning of the lips as well. We'll address both in the next installment.

To be continued...

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Re: 450 BM mags

Postby buckeye3405 » Mon Nov 20, 2017 10:18 am

I bought 2 Bartz magazines when I completed my build. Best decision I made during the build process. Absolutely ZERO feeding issues.
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Re: 450 BM mags

Postby Jmeier1981 » Tue Nov 21, 2017 10:11 pm

Where can you get Bartz mags? I dont see them listed on their site.
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Re: 450 BM mags

Postby Hoot » Wed Nov 22, 2017 5:43 am

Jmeier1981 wrote:Where can you get Bartz mags? I dont see them listed on their site.


Generally, they sell through distributors. There is contact information for their distributors on their web page, or call Bartz and ask. They're good people to talk to.

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Re: 450 BM mags

Postby buckeye3405 » Thu Nov 23, 2017 9:10 am

Jmeier1981 wrote:Where can you get Bartz mags? I dont see them listed on their site.



Try these guys. They aren't listed on the website but I emailed them and was able to order 2 from them shipped to Ohio.

https://www.notjustguns.com/contact_us.php
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Re: 450 BM mags

Postby plant_one » Thu Nov 23, 2017 9:56 am

jays sporting goods carries them too, amongst other places. unfortunatly they dont list them on their website.

give em a ring, they might be able to help ya out too
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Re: 450 BM mags

Postby giannid » Sun Dec 17, 2017 11:41 am

My Tromix upper is having feeding issues with the Bartz Magazine so these magazines don't work well with all builds. My upper went back to Tromix and Tony says not to use this magazine because it has too much spring pressure. Say's the 20 round modified Colt magazine I sent in with the upper is the one to use. I'm going to try the bartz magazine with a new spring and see if it works better. Or I may just cut the spring in the Bartz mag. It does have a lot more spring pressure than the other colt magazine.
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Re: 450 BM mags

Postby Jim in Houston » Sun Dec 17, 2017 4:05 pm

giannid wrote:My Tromix upper is having feeding issues with the Bartz Magazine so these magazines don't work well with all builds. My upper went back to Tromix and Tony says not to use this magazine because it has too much spring pressure. Say's the 20 round modified Colt magazine I sent in with the upper is the one to use. I'm going to try the bartz magazine with a new spring and see if it works better. Or I may just cut the spring in the Bartz mag. It does have a lot more spring pressure than the other colt magazine.


There's a thread here somewhere that talks about the problem of having magazines with springs that are too strong. As I recall, if you have this situation, start cutting the spring at the bottom one coil at a time until the spring has just enough tension to get the last round in the magazine firmly against the feed lips on the magazine.

Personally, I use standard AR magazines like those from Brownells, which are metal, or polymer P-mags. They seem to work, even if you don't change out the follower. However, use the 20 round straight sided-ones, as the BM rounds don't handle the curve in the 30 round mags well.
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