450 Bushmaster AR15 magazines

[rbernie]

What will (and will not) work?

 

[mcb]

Most shorter magazine (20rd or less) will work unmodified. Straight 20rd works great for me. I did buy some 458 SOCOM followers from calegalmags.com and put those on some old NHMTG magazines. Found that makes loading the first round easier.

I have found 30rd magazines are a bit more finicky and sometimes will cause feeding issues when full.

The most important thing is be sure the feed lips have no sharp edges or corners. They dig into the side of the cartridges. I break the edges with a jeweller's file if needed and hit them real quick with a felt wheel and polishing compound.



My modified straight 20 next to a factory 450 BM magazine.

ETA: The rib down the front of PMAGS cause issue with many loads.

 

[Flintknapper]

The most important thing is be sure the feed lips have no sharp edges or corners. They dug into the side if the cartridges. I break the edges with a jeweller's file if needed and hit them real quick with a felt wheel and polishing compound.
.

^^^^^ Good advice. Same holds true for the mags I use in my 458 SOCOM. Good idea to slick up the magazine feed lips and also 'scallop' the front of the mag.

 

[Rembrandt]

The biggest problem I've found were the followers. Even the factory Bushmaster mags didn't get it right. The pics below will illustrate what part of the problem is. Some of the manufacturers use the same follower for both the 450 and 458. Both cartridge cases are not the same diameter, one has a taper and the other does not.

I found the Tromix followers to be shaped correctly to cradle the 450 cases. Photo below illustrates the difference, left is a Tromix...right is a Bushmaster. https://tromix.com/product/center-feed-followers-for-lancer-mags/

The best 450BM magazine is the one you make yourself. We use Lancer magazines, prefer the 10 round for hunting because they don't hang down below the lower receiver as far. We like the 20 round mags for the range. Take the magazine apart and snip off the plastic round limiting protrusion on the base plate. This will allow for an extra round to be inserted. Cup out the front of the magazine where the round will be pushed forward. Not doing so can cause the round to be pushed upward when feeding into the chamber. With that removed the round will make a smooth transition forward as the round is fed. We also like the Lancer semi clear mags and the ability to see how many rounds it's holding.

 

[gotboostvr]

@Rembrandt

Those Lancer mags look real slick. And how did Bushmaster get the followers for their own cartridge wrong? Good call on Tromix's part. Great info.

 

[Rembrandt]

The second photo down is a factory Bushmaster magazine, note how much space (or light) is under the cartridge. That's because the channel is too narrow (and tapered), cartridge doesn't get cradled properly like in the third photo down. The Tromix followers have a wider channel contour which allows the round to be fully supported front to rear.

 

[mcb]

I have never had an issue with the factory 450 Bushmaster magazine follower I have. Yes the follower does not have the correct radius but the 458 SOCOM follower I am using in my home built magazines only contacts the round on the two ridges molded into the follower and they work fine too. For that mater I have never had an issue using the 223 followers but I wanted dedicated 450 Magazine so I made my mods.

The scallop cut on the front of the magazine is not strictly needed, the nose of the round should hit the feed ramp before the round can hit the front edge of the magazine but it sure makes loading them easier and less likely to scratch up you rounds while loading.

 

[Rembrandt]

mcb, we have three AR 450 Bushmasters between the boys and myself, two worked fine with the factory Bushmaster magazines, the third one constantly had feeding problems. All are the same manufacturer uppers, only difference was brands of lower receiver. Can't explain why the one jams and the others don't. When we went with the Lancer/Tromix units they all perform flawlessly.

 

[jmorris]

I used regular old Colt 20 round mags with mine, didn’t change a thing.

 

[mcb]

I played with converting 10rd Magpul magazines but was not happy with the results. The 10rd magazine bodies are short enough you can easily use a good file to remove the rib from the inside front.


Left: Rib Removed, Right: Factory

I also filed the follower flat too though that was not strictly needed bit did makes it easier to insert with four rounds loaded under a close bolt.



Unfortunately with it being single stack and the rounds coming up in the center have a pretty good mechanical advantage over the feed lips and they spread badly in this case. It seems to function fine in the gun but when the magazine has even just one round in it the feed lips spread enough to make insertion difficult and it will not drop free.

To date I have used four different magazine in my 450 Bushmaster.



Left to Right: 10rd PMAG converted to 450 BM (hold 4 rds of 450BM), 5rd 450 Bushmaster Magazine made by DPMS*, 5rd 450 BM Bushmaster factory magazine**, Converted NHMTG 20rd magazine with calegalmags.com 458 SOCOM follower (holds 7rds of 450BM).

*I am assuming DPMS since that is on the floorplates. Wish I had more of this magazines. I only have two Not sure where it came from (I got it from a buddy that doesn't know where he got it from) but they are awesome. Nice and short, holds 5 rounds, with machined Delrin followers and have fed flawlessly for me. They were my hunting magazine this year.

** Not sure why Bushmaster put the dent in the corners near the bottom of the magazine body? This stops the follower early and thus the 5rd capacity. With that length of the magazine body it should hold 7rds like my converted 20rd magazine next to it.

 

[Rembrandt]

** Not sure why Bushmaster put the dent in the corners near the bottom of the magazine body? This stops the follower early and thus the 5rd capacity.

I wondered about that also, appears to be a cheap way to limit the follower. Prevents follower removal for servicing.

 

[mcb]

I wondered about that also, appears to be a cheap way to limit the follower. Prevents follower removal for servicing.

In retrospect is for limiting capacity in states that have a 5rd limit when hunting. Ohio where I grew up was slug only and has a 3rd limit. That 3rd limit is now by the honor system now that they have allowed rifles with straight wall cartridges to be used also. I currently do all my hunting in Tennessee now and it has no magazine limit. I should have thought of that. You can get the follower out but its a real pain in the butt to work that follower past the stops.

 

[MCMXI]

I ordered a 16" Faxon .450 BM barrel today along with an adjustable gas block from Superlative Arms, and after looking at this thread a few weeks ago I'd like to try some Lancer magazines. A coworker bought one of his 5.56 Lancer mags to the office and I like the way the feedlips interact with the .450 BM cartridge compared to the BM magazines. I'm curious if anyone has tried the 20 round Lancer magazines with .450 BM which Tromix advises against. Why does the 450 BM cause feeding problems with 20 round magazines but the .458 SOCOM doesn't? I've had zero feeding issues with the five BM magazines that I have, and that includes two 9-round and three 5-round. That said, I'm thinking about buying five Lancer magazines and swapping followers with the five BM magazines. The dimples at the corners are annoying but I'll check my five tonight to see if they have them. The 9-round might not.

".375/.458/450BM/12.7×42 Center-feed follower for Lancer 5.56 magazines. CNC machined from 6061-T6 solid aluminum bar stock. This follower used in a 20rd 5.56 Lancer magazine, will hold 7 rounds of big bore ammunition. In a 30rd 5.56 Lancer magazine, it will hold 11 rounds (11+0) of big bore ammunition. We only recommend using the short 4 round magazine for the 450BM. Longer magazines can cause feeding problems with this cartridge."

https://tromix.com/product/center-feed-followers-for-lancer-mags/

 

[MCMXI]

How important is the follower? It's only in contact with the last round in the magazine.

 

[Gtscotty]

I wonder how hard it would be to print a functional follower optimized for the .450 BM on a 3D printer?

 

[MCMXI]

@Gtscotty , not hard at all, in fact I printed two followers today but not for a .450 BM mag. I do that sort of thing regularly using a Dimension 1200, and ABS plastic will hold up to compression loading very well. It's nowhere near as good as nylon 6,6 in terms of abrasion resistance but it would be easy to print up a bunch and swap out if wear is an issue. For me the follower is the easy part of the problem, the magazine tube on the other hand is a much bigger issue. When I got my .450 BM and mags I set about cleaning up the inside edges of the feedlips to reduce the amount of gouging, but the Lancer feedlips are definitely an improvement. That's why I'd like to use the Lancer tubes with BM followers.

 

[Gtscotty]

Very interesting, that's a fancy machine. I bought a Prusa i3 MK3s about a month ago, for experimenting with designs and general fun at home. I've been thinking about what gun related designs I might like to try, followers seem like an interesting idea, no real heat load, and most of the force is compression. Have you ever used PETG for followers and whatnot? It would be much easier to print with my setup than ABS.

 

[MCMXI]

@Gtscotty , I've only used ABS-P430 (black and blue) that we buy from Stratasys. I have no experience with PETG. I might model an improved .450 BM follower and print it to see how it works compared to the BM followers. Like I mentioned earlier, the follower is only in contact with the last round in the magazine so it doesn't affect the other rounds.

 

[Rembrandt]

How important is the follower? It's only in contact with the last round in the magazine.

This may illustrate why, magazine on the left is a Bushmaster brand follower that does not cradle the cartridge properly. As a result the round is tipped upward. This is even more pronounced when if using standard military type followers. May or may not feed properly into the chamber.

Magazine on the right is a Tromix follower in a Lancer magazine. Round lays level and is in line with chamber.

 

[MCMXI]

I don't think the angle of attack is due to the follower but rather the feedlips since Bushmaster feedlips tend to splay apart. Lancer feedlips are hardened steel so they don't splay apart. Load a bunch of rounds in both mags and take another photo and you'll see the same condition. I ordered seven Lancer mags yesterday and removed a Bushmaster follower this morning. I'll post a photo of a Lancer mag with a Bushmaster follower next week.

 

[mcb]

I believe you also have the problem that the curvature of a curved 556 magazine is not correct for the taper of a 450BM cartridge and this contributes to the nose up issue as you fill up a longer 30 rd magazine.

ETA: some numbers

223/556 has just a shade over 1° of body taper resulting in just over 15° of rotation of the stack in the 15 rounds down one side of the double stack in the 30rd magazine. 450 BM only has a touch over 3/4° of body taper and with ~ 11 rounds firing in a 30rd magazine that is only ~8.4° of rotation in the single stack.

 

[MCMXI]

I received seven Lancer magazines this morning (5 10-round and 2 20-round) and was able to fit a .450 Bushmaster follower to one of the Lancer magazines. I still need to clean the follower up a bit but it wasn't technically difficult to do and it appears to work just fine. I plan on putting the Lancer 5.56 follower in the BM magazine and will repeat this process four more times for the other .450 BM mags that I have.

The feedlip spacing is different for Bushmaster and Lancer magazines so the top round rides a bit higher in the Lancer magazine

BM rear > .424" front > .436"
Lancer rear > .450" front .465"

Also, the angle of the feedlips is different with the BM feedlips being virtually horizontal relative to the cartridge. As the photos show below, the feedlips do affect the presentation of the cartridge to the chamber which will be more exaggerated as the number of rounds in the magazine increase due to increased spring force. The feedlips limit upward movement of the cartridge which is independent of the follower. The BM feedlips flex whereas the Lancer feedlips appear to show no flexing at all. Also, I don't see the need to remove material from the front of the Lancer magazine since the cartridge easily clears the tube during feeding.

Bushmaster follower on left, Lancer follower on right


Bushmaster magazine top, Lancer magazine bottom, both with BM follower


Lancer magazine left, Bushmaster magazine right, both with BM follower


Lancer magazine left, Bushmaster magazine right, both with BM follower


Lancer magazine left, Bushmaster magazine right, both with BM follower

 

[MCMXI]

I tested feeding from the Lancer mag with BM follower this afternoon and it works great. I think I'll add the relief cut to the front of the magazine tube like the one shown on the BM magazine above. When the round goes up the feedramp the rear of the cartridge drags over the top of the tube at the front. It doesn't seem to adversely affect feeding but it will subject the plastic tube to unnecessary stress and wear. The Lancer follower drops into the BM magazine tube without any issues and goes past those ridiculous crimps at each corner with ease. The BM spring seems to be a little different compared to the Lancer spring so I'll need to play with it a bit to get it to fit on the Lancer follower.

 

[MCMXI]

I created a model of a hybrid Bushmaster/Lancer follower with a profile that better matches the .450 BM cartridge and am printing it tonight. This follower should drop right into the Lancer magazines and work with the Lancer spring. The springs in the Bushmaster magazines have a narrower winding which means that they don't work with the Lancer follower or base plate without modification. The Lancer follower and spring work just fine in the Bushmaster magazines.

Hybrid Lancer/BM follower for Lancer magazine


Bushmaster follower on left, Lancer follower on right, both in Lancer 20-round magazines

 

[xds45]

10 rounds of .450 in stock Sig .556 30 rounds mags works well for me.