Magazine capacity and ammunition type

[Blackstone45]

I've been told by a few people that the number of rounds you can squeeze into a magazine is affected by the ammunition as well. For example, I've been struggling to get more than 16 rounds of .40S&W into an IPSC standard legal magazine, when others with the same setup report they can get 17 reloadable, and even 18 in. They told me it depends on the ammunition itself. So is it OAL of the cartridge that might affect this?

 

These are also relatively new magazines so maybe they need to be fully loaded and unloaded a few times?

[Matt1911]

I would guess it has to do with the followers and springs that are used. 

[xrayfk05]

I fail to see how the ammo makes (that much) of a difference, it's a combination of tube, guts and basepads.

What tubes and springs/follower are you using? 16 is in the low end of IPSC legal magazines.  

How long is the spring? A standard 140mm spring in a 120mm mag will take up space, I usually shorten the springs to be only a few cm longer than the tube. 

Even the cheap SPS mags will do 18 out of the box.

 

This is assuming a 2011, a CZ TS has 17 round standard IIRC.

[THS]

Some of this may be due to using reloaded ammo.   The tiniest bulge at the base can add up over 16 rounds to change capacity.

[RJH]

Most of it will end up being spring, follower, base pad combo. But sometimes roll sizing things might get you an extra round if you are already close.

 

 

Edited to add: I'm pretty sure the SPs mags are more blocky like the para mags which will allow an extra round or so over standard 2011 style mags. Not going to guarantee that, but I think that's correct

Edited May 9 by RJH

[shred]

6 hours ago, RJH said:

Edited to add: I'm pretty sure the SPs mags are more blocky like the para mags which will allow an extra round or so over standard 2011 style mags. Not going to guarantee that, but I think that's correct

They are not.  SPS are STI clones.

[RJH]

1 hour ago, shred said:

They are not.  SPS are STI clones.

 

 

Is it the bul mags I am thinking of then? I'm almost positive one of those Euro guns have slightly different mags

[Blackstone45]

19 hours ago, xrayfk05 said:

I fail to see how the ammo makes (that much) of a difference, it's a combination of tube, guts and basepads.

What tubes and springs/follower are you using? 16 is in the low end of IPSC legal magazines.  

How long is the spring? A standard 140mm spring in a 120mm mag will take up space, I usually shorten the springs to be only a few cm longer than the tube. 

Even the cheap SPS mags will do 18 out of the box.

 

This is assuming a 2011, a CZ TS has 17 round standard IIRC.

I'm running a gun that uses Tanfo LF mags. One of the top Euro shooters told me they can easily get 17 in their mag, and if they cut a couple of coils from the spring, they can even squeeze in 18 (not reloadable). We're using the same gun and magazines.

 

I've cut a few coils as well as recommended by them, but I'll take a look at the actual spring length vs tube length as you suggested.

I probably just need to do some more full load and unload cycles to 'set' the spring.

Edited May 10 by Blackstone45

[Joe4d]

12 hours ago, RJH said:

 

 

Is it the bul mags I am thinking of then? I'm almost positive one of those Euro guns have slightly different mags

rescomp,, whays the Beeze knees back in the day for USPSA Limited. I have 2,, they are a bit blockier and thinner metal, combined with Bolen guts, and base pad a 140mm and a 40 U die. you had a 23 round start... Talking STI eagle here.
I only ever used them for 22-and 23 round stages.. Freeked a few RO's out and had them gauged more than once.
Back to the OP ? Id look into after market springs and followers. 

Edited May 10 by Joe4d

[Blackstone45]

39 minutes ago, Joe4d said:

rescomp,, whays the Beeze knees back in the day for USPSA Limited. I have 2,, they are a bit blockier and thinner metal, combined with Bolen guts, and base pad a 140mm and a 40 U die. you had a 23 round start... Talking STI eagle here.
I only ever used them for 22-and 23 round stages.. Freeked a few RO's out and had them gauged more than once.
Back to the OP ? Id look into after market springs and followers. 

The magazines were supplied by the gun manufacturer with the correct springs and followers. I don't know the make of the springs and followers though.

[Joe4d]

3 hours ago, Blackstone45 said:

The magazines were supplied by the gun manufacturer with the correct springs and followers. I don't know the make of the springs and followers though.

well then you deal with lower capacity..
OEM tend to be concered with function and longevity.. So they err on side of caution with larger sturdier followers, and stronger springs that last longer.. A gun that doesn't run in bad PR.
When trying to squeeze best performance competitors trade some of that to get an edge,, lighter thinner followers, and smaller wire shorter springs.. Knowing full well these springs will wear out faster and followers wont take the beating.. Mags may need to kept cleaner ,, etc..
 

[Matt1911]

4 hours ago, Blackstone45 said:

The magazines were supplied by the gun manufacturer with the correct springs and followers. I don't know the make of the springs and followers though.

Yeah that’s why others are getting better capacity. 
You are playing the game with stock parts, others are swapping things out to get race cars. 

[zzt]

On 5/9/2024 at 4:18 AM, Blackstone45 said:

These are also relatively new magazines so maybe they need to be fully loaded and unloaded a few times?

 

Give it a shot.  The original MBX springs needed to take a 'set' before they would load to capacity.  I'd load as many as would fit and let them sit for a week.  Unload and reload.  Usually, two weeks was enough, but sometimes I had to go to three.  After conditioning the mag springs, you can fill to full capacity and they are reloadable.