.45 vs. 9 capacity in various brands

[Skribs]

This is not a .45 vs 9 thread. Rather, I am curious as to why different brands have different ratios of 9-to-.45 capacity in their guns. For example:

FN FNP, 17 vs. 15. (13% more in 9)
Glock or Springfield XD, 17 vs. 13. (30%)
Springfield XDm, 19 vs. 13. (46%)
S&W or Ruger, 17 vs. 10. (70%)

Why is it different from one to the other? Do those with a higher ratio have skinnier .45s? Or do those with a lower ratio have better engineering in their .45s?

I know the common idea is to compare 15 or 17 rounds of 9 (in the M9/G19 or G17) vs. 7 rounds in the 1911, but that's not what I'm looking at. What I am curious is why some guns have a significantly bigger gap than others when transitioning from 9 to .45.

 

[PabloJ]

The FNP .45 is a monstrosity of a gun with sheet metal magazine unlike the Glock which is polymer over sheet metal shell?

 

[Skribs]

But is the FNP .45 magazine constructed differently than the FNP 9? What about Glock 21 mags vs. Glock 17 mags?

 

[holdencm9]

Well, in a single-stack, you should theoretically be able to hold 23% more 9mm's than .45's just due to the difference in diameter (I average base and neck diameter of both cartridges).

However, say you have 3.5 inches of space in a magazine, between follower and feed lips.

.45 auto: 3.5" / .4745" = 7.38 ---> 7 Rounds
9mm: 3.5" / .3855" = 9.08 ----> 9 rounds, or nearly 29% more

So the rounding off of the rounds (pun intended) can have an effect.

Also the incline of the stacking of the double-stacks. Say you have 3/4" wide magazine just for example. The .45 is more of a stagger, you can fit 8 rounds in the same 3.5" depth. The 9mm is almost a true "double-stack" and can fit 13, which is about 63% more rounds.

(See picture attached.)

The combination of the rounding off of the rounds as well as the stagger and magazine construction can all affect the number of rounds various magazines hold.

 

[JTQ]

The Ruger SRs and the S&W M&P's in 45ACP are probably pretty close in size with their 9MM family members, thus they have lower capacity.

The FNP 45 and Glock 21 are both a whole lot bigger than their 9MM brethren.

 

[Skribs]

Holdem, you're saying it's likely that skinnier pistols have a higher ratio of 9-to-45, and the fatter pistols allow the 45 to bulk out more? Because the pistols I mentioned all have a similar capacity in 9mm.

JTQ that's kinda what I was thinking.

 

[holdencm9]

Holdem, you're saying it's likely that skinnier pistols have a higher ratio of 9-to-45, and the fatter pistols allow the 45 to bulk out more? Because the pistols I mentioned all have a similar capacity in 9mm.

I think it would be the opposite. All else being equal, double-stacks will give even more advantage to the thinner bullet, because as shown in my picture, they will zig-zag a lot steeper angles. You get the benefit of the smaller diameter in two directions instead of just one. But that's all else being equal. Sometimes two guns that you'd think are identical aside from caliber, the .45 is a bit bigger. The M&P 9c for instance is a bit smaller than the m&p 45 compact. So it isn't comparing apples to apples.

 

[Skribs]

What I was thinking is that if you make it a little wider, the 9s are still double-stacked and won't stack much more efficiently, but the .45s will stack better.

The apples-to-apples comment makes sense. I think JTQ's explanation is probably the answer I was looking for: that those with a high ratio (like the M&P going from 17 to 10) there is only a small difference in width (looking on their site, it has the same width of 1.2") whereas those with a lower ratio have a bigger difference (G17 is 1.18", G21 is 1.27").

 

[tahunua001]

walk into a gun store and ask to see a 45ACP and 9mm bullet up next to each other. the 45ACP is a much larger bullet than the 9mm meaning that less rounds will fit in the same amount of space. the 9mm leaves less empty space in the magazine being more compact and therefore uses the limited mag space more efficiently.

as for the larger difference in XDMs over XDs, the XDM uses a steeper grip angle than the XD in in their 9mm and 40 cal options allowing for slightly longer magazines, however this steeper grip angle creates problems with 45ACP so they had to keep the same angle and magazine style as the XD45 meaning that they can take the same magazines and have the same mag capacity.

 

[hAkron]

I have a Sarsilmaz K2-45 imported by EAA. It's a full sized gun, but not a monster. It's based on the CZ 75 platform. It is a 45 and It has a 14 round magazine!!