450 Bushmaster AR15 magazines

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Here's the follower that I printed yesterday at a cost of about $2.00. An injection molded part would be way cheaper but the tooling would cost some money depending on how many cavities, etc. The follower is very smooth inside the Lancer magazine tube and it works well, in fact it feels smoother than the Lancer follower. I've made a couple of small changes such as moving the boss with the hole for the spring .075" further forward, and I gave the spring a bit more clearance as it compresses by moving the two inside radii .100" further apart. I'm going to change the surface that the cartridge sits on, the .500" cylinder, from a straight cylinder to a tapered cylinder with .500" at the rear and .482" at the front to better support the cartridge. The rear "leg" could be shorter like the Lancer follower but leaving it longer provides more support for the spring as it compresses. This follower appears to be an improvement over running the BM follower in the Lancer magazine and it's a lot easier to print parts compared to filing. So at this stage I'm going to use the Lancer springs with ABS printed followers in five of the Lancer mags and call it good.

Underside of printed follower
450bm_hybrid_follower_2.jpg

Bushmaster follower on left, printed ABS follower on right, both in Lancer 20-round magazines
450bm_hybrid_follower_3.jpg
 
Very nice!! Any recommendations for 450 BM followers that are available on the retail market? Do the plastic ones on eBay work? How about the follower inserts that lay on top of original 556 followers?
 

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Thanks!! I’ll check them out. I’m new to the 450BM but been using AR’s in many other calibers. I’ll put these on my list. I’m testing several options right now. • I may even have a 15 round option. I need to get it in the field to confirm reliability.
 
The 450 Bushmaster cartridge is a poor design for use in a standard AR-15 5.56 magazine body....here's why.

All AR-15 5.56 mag bodies are much wider at the rear than in the front for use with the bottle necked 5.56 rounds. When you stick a relatively straight walled case in there, the back end of the cases will start to scissor tail apart in a semi-double stack.....kinda like a stack-and-a-half. The front of the case is supported by the much narrower ribs in the front, so the front part of the case single stacks with one round directly above/below the other. So you end up with a semi-double stack at the rear and a single stack in the front. That in turn causes the entire column to grow taller and taller at the front compared to the shorter double stack at the rear. So the rim of the case sinks low and tail drags, while the front of the case goes skyward. Couple that with the fact that the round isn't large enough in diameter, it tries to squirt out between the feed lips especially at the front end. Bushmaster never should have released the cartridge in the AR-15 until they made dedicated magazines. Instead they tried to jury rig the thing with a follower bandaid that simply can't fix the stacking problem inside the mag body.

Tony Rumore
Tromix
 
The 450 Bushmaster cartridge is a poor design for use in a standard AR-15 5.56 magazine body....here's why.

All AR-15 5.56 mag bodies are much wider at the rear than in the front for use with the bottle necked 5.56 rounds. When you stick a relatively straight walled case in there, the back end of the cases will start to scissor tail apart in a semi-double stack.....kinda like a stack-and-a-half. The front of the case is supported by the much narrower ribs in the front, so the front part of the case single stacks with one round directly above/below the other. So you end up with a semi-double stack at the rear and a single stack in the front. That in turn causes the entire column to grow taller and taller at the front compared to the shorter double stack at the rear. So the rim of the case sinks low and tail drags, while the front of the case goes skyward. Couple that with the fact that the round isn't large enough in diameter, it tries to squirt out between the feed lips especially at the front end. Bushmaster never should have released the cartridge in the AR-15 until they made dedicated magazines. Instead they tried to jury rig the thing with a follower bandaid that simply can't fix the stacking problem inside the mag body.

Tony Rumore
Tromix

I sort of agree and yet we manage to do it with regular 556 magazine bodies all the time. My 450 BM (a Bushmaster factory upper kit) has been 100% with my converted (use 458 SOCOM follower from CALegalMags) straight 20rd magazines. After a quick debur and and polish of the feed lips my factory magazines have been 100% also. I just don't use them much since they are artificially limited to 5rds and my conversion hold 7rds.
 
I sort of agree and yet we manage to do it with regular 556 magazine bodies all the time. My 450 BM (a Bushmaster factory upper kit) has been 100% with my converted (use 458 SOCOM follower from CALegalMags) straight 20rd magazines. After a quick debur and and polish of the feed lips my factory magazines have been 100% also. I just don't use them much since they are artificially limited to 5rds and my conversion hold 7rds.

And you'll completely agree when you try and put 10 rounds in a 30 round 5.56 body, of which the 458 SOCOM runs perfectly.

Tony
 
I guess I should change my story since January.

I have always used regular old Colt 20 round mags with my 458 socom. So that’s what I used with my 450 BM and all I really did with it was sight it in and hunted with it and it ran fine.

A buddy really wanted the upper so I sold it to him before I “played” with it much.

I have another now and did discover that it wouldn’t feed the last round out of the mag, don’t guess I made it to that point on the last one. As others have pointed out it was due to the follower.

I found one on thingiverse that dropped in over the regular .223 follower, printed it, that cured the problem.
AC0D8B9F-0732-4FE2-BB13-37388D1E9AF1.jpeg 31844B2F-0A72-40AB-9373-3769D597B082.jpeg

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As a follow-up:

I could not get 100% function over time out of any 450 Bushie magazine / follower combo that I tried, I suspect mostly for the reasons that Tony pointed out above. No combination of body and follower worked flawlessly for me until I broke down and tried a Duramax 450 Bushmaster magazine. It has an appropriate follower, and single-stack guides built into the body to keep the roundstack, well, stacked properly. I'm not pleased with the cost, but in every other way consider it a win.

https://dura-mag.com/product/duramag-ss-450-bushmaster-stainless-steel/
 
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