10 rnds in a 10 rnd Mag?

[Rocketrob]

Having problems with 10 rnd mags. These are 450 bushmaster 10 rnd mags yet I can only get the gun to strip and load properly if I only put 4-6 rounds in the mag.
If I load more than 4-6 rounds the rounds go nose high and the rim of the case hits the bolt release when inserting the mag. If I pull the rnd forward so it misses the bolt release it is so nose high it hangs up in the breech.
Ist photo shows my 3 mags - one on left has 10 rounds, middle has 6 rounds and right has 4 rounds.

[Hoot]

Welcome Aboard Rob!
Getting the banana style mags to play well, is a long standing battle around these parts. Not sure why they even sell them.
Take all the rounds out and feel the spring tension. If its strong, try removing one turn by removing the floor plate off of the bottom and diking or cutting one off with a Dremel cutoff wheel. Retest the number of rounds you can get to cycle. If they do better, consider removing another turn. Point being, the spring tension is going to be real high as you add more rounds and the upward pressure makes the top ones ride nose up. Find a balance where the shortened spring will still feed the last round reliably. That will reduce the upward pressure when the max number of rounds are pushed in compressing that spring. While you have that floor plate off of one of them, try "ironing out" that dimple they press into the corner down near the bottom. Dimples are a source of performance problems in every capacity mag they make.

Let us know where the sweet spot winds up being. IE, how many turns you had to remove to reach that compromise. I will put that information in my repository of useful knowledge sub-forum.

Hoot

[Rocketrob]

10 rnds mag being inserted in mag well case rim hangs up on bolt release

10Rnds-BoltRelease copy.jpg (114.23 KiB) Viewed 7627 times

Hoot, Thank you for the very detailed and practical response.
I was thinking the spring pressure was to high. I asked the vendor how do they get 10 rounds to function even suggesting cutting off a few coils and was told they do not have to do a thing - works great!. When the mag is loaded to 10 rnds, the top round pitches up and in doing so the case rim rotates counterclockwise about it's centerline and the top moves rearward and is caught by the bolt release upon inserting the mag which causes it to rotate nose high even further.

[Rocketrob]

Not wishing to start trimming spring coils just yet I pulled the spring through the mag floor to the shortest length that barely holds the first round in. I get a slight reduction of the nose up angle on the 10th round. Second photo is with 8 rnds loaded - not sure I will ever get functioning 10 rounds out of these mags.

[commander faschisto]

If that's still happening with minimal spring pressure, need to look at tweaking the feed lips closer together...lots of us have done that to other metal mags especially early on in the production runs for the 450b, and the discussions should still be in the files here somewhere. If you can search them, you'll see pics of the proper orientation. Basically, you want to achieve a slightly nose-up orientation for the top round. We've also found that holding the rounds perfectly level is not a good thing for this caliber, as is also the case as with your example, when the cartridge is held too much nose-up. Your examples in the pics are wildly off, and I can see why there's a feed problem, to say the least.

Closing the gap between the feed lips can be done by placing the mag feed lips top-down on a hard surface, like a bench top, and then gradually pressing the mag firmly but carefully downward to bend the feed lips closer toward each other. Do it a step at at time until you get the top cartridge being held slightly, but clearly, nose-up. Check the position of the feed lips left-to-right to make sure they are bent equally on each side, so that they look "level" across the mag. Load up a few rounds and test each tweak amount for feed reliability. Repeat as needed...

This has been done by lots of us before, and should work for your set of mags, theoretically. See how it goes and let us know.

[Rocketrob]

Thank you Commander!