ProWin M4 Mag BB's fail to move up magazine

[Greenworks]

I am having this weird issue where the BB at the top of the mag loads, but the BB's beneath it stay in place, as if they're catching on something inside the magazine!

I've disassembled the mag so that the spring popped out and there was no obvious obstruction, although I couldn't see all the way into the compartment that holds the BB's. Any ideas on why this might be happening, or is a complete disassembly of the mag my only option ?

I've attached some images incase I haven't described it well. I'm really quite confused, since there are around 20 rounds loaded into the mag and the spring is exerting quite a lot of pressure on the BB's. 

View attachment 37581

View attachment 37582

 

[Wo1f]

Either:

the B.B. channel is dirty and is being stopped by friction (I’ve had this happen on mp9 gas mags)

the bolt lock piece is deformed in some way that it isn’t finding the whole cleanly and getting stuck (edit: only applies on pistol/ mp7 style mags)

the channel is a tiny bit too wide and the bb’s have sat a bit wider than their usual double stack nature. (Can be tested by getting something small like an Allen key or screwdriver and pushing down on the second bb from the top)

 

[Greenworks]

Either:

the B.B. channel is dirty and is being stopped by friction (I’ve had this happen on mp9 gas mags)

the bolt lock piece is deformed in some way that it isn’t finding the whole cleanly and getting stuck (edit: only applies on pistol/ mp7 style mags)

the channel is a tiny bit too wide and the bb’s have sat a bit wider than their usual double stack nature. (Can be tested by getting something small like an Allen key or screwdriver and pushing down on the second bb from the top)

Click to shrink...

Thanks for the reply wo1f. Pushing down on the 2nd BB from the top does sometimes release the stack from being stuck and bring the BB to the top of the channel. 

However the same problem occurs when the next BB is loaded into the gun. The last 6 or so rounds tend to feed better than when the mag is full. I'll take another look for dirt but I have a feeling it's the third point, channel being too wide. How would I deal with this?

Edit:

When there are more than 2 BB's in the channel, they suffer from this issue and get stuck fairly consistently. The spring itself is slightly warped but doesn't look like enough to cause such a big issue.

 

[Wo1f]

Thanks for the reply wo1f. Pushing down on the 2nd BB from the top does sometimes release the stack from being stuck and bring the BB to the top of the channel. 

However the same problem occurs when the next BB is loaded into the gun. The last 6 or so rounds tend to feed better than when the mag is full. I'll take another look for dirt but I have a feeling it's the third point, channel being too wide. How would I deal with this?

Edit:

When there are more than 2 BB's in the channel, they suffer from this issue and get stuck fairly consistently. The spring itself is slightly warped but doesn't look like enough to cause such a big issue.

Click to shrink...

I’d start by stripping the mag and cleaning the B.B. grove (or whatever it’s called where the bb’s sit). If the spring is warped, perhaps rotating it will help. Are the BB’s held in a plastic tube or is is part of the metal on the mag?

 

[Greenworks]

I’d start by stripping the mag and cleaning the B.B. grove (or whatever it’s called where the bb’s sit). If the spring is warped, perhaps rotating it will help. Are the BB’s held in a plastic tube or is is part of the metal on the mag?

Click to shrink...

The BB's are held in a subsection of the magazine which is part of the metal. 

I'll take a crack at the mag tomorrow then, not much I can do but go for it I guess!

 

[Marcsparks]

Hi, did you sort your mags,  I think you will find it is the follower getting stuck, the tube the bbs run in curves around under the gas resovoir into a plastic section, the plastic follower gets stuck down there, I stopped putting more than 40 rounds in mine and it fixed it.. I also found the mags dont like some bbs, caused similar problem, it actually preferred cheaper Zero One ones..good luck

 

[Seven]

Not an M4 mag but I noticed the exact same thing on my Hi-capa prowin mags.

Solution was to ensure the BB's stacked perfectly.

If there was a gap in the stack it would almost always stop pushing the BB's into the lips at that point.

Without a gap in the stack it feeds the lips without fail every time.

I just figured that the way and amount of pressure the follower and spring applies upward to the BB's caused them to essentially pinch the unbalanced BB's against the casing, but that's just me taking a very uneducated guess.

Tldr; Ensure the BB stack is perfectly balanced, no gaps in the stack.

Edit: just realised how bloody old this thread is. *Facepalm*

 

[Phil]

The bb follower might be installed backwards?