How many parts can be made compatible


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Skribs
October 27, 2011, 06:29 PM
I'm just wondering from a hypothetical standpoint, that if I wanted to design a semi-automatic pistol to interchange between 9mm and .45 ACP as easily as possible, how many parts can be the same?

Could I use the same frame, and design thicker magazines for the 9mm version?
Could I use the same slide, and just use a thicker barrel on the 9mm? Or are there other parameters I would be missing by doing this?
What other parts could be the same, and what would be required to be different?

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rcmodel
October 28, 2011, 11:29 AM
In general a .45 slide is not going to work with a 9mm.

The two cartridges are worlds apart in case rim size.

So unless you can get around how to make a .45 extractor & breach face work with the .086" smaller 9mm rim, it isn't going to work.

Guns that easily interchange those two calibers have two or more complete slides & barrels fitted, and also use different magazines for each caliber.

rc

ATLDave
October 28, 2011, 11:55 AM
There are a number of guns that have interchangeable slides (including barrels) and keep the same frame for both calibers. The EAA Witness line includes a number of guns where the same frame will run 9mm, 38 super, .40 SW, 10mm, and .45 ACP. Separate mags needed for each caliber, of course, but otherise just swap the tops and keep the frame the same. That means the trigger/sear/hammer stays the same. That's a good thing, if you tend to sink money or effort into impoving the triggers on your pistols.

CWL
October 28, 2011, 01:52 PM
To fit the same frame, your slide weight will differ greatly between .45ACP and .9mm NATO. This weight will affect the 9mm more since the recoil forces necessary to operate a heavier slide (unless you want to get even more complicated with gas operated) may affect reliably. Given that, your springs set will need to be calculated and changed between calibers.

ATLDave
October 28, 2011, 03:08 PM
CWL, I guess that's why many of the guns that have interchangeable slides have a recoil guide rod and recoil spring that "lives" on the slide.

Skribs
October 28, 2011, 04:18 PM
So basically what I would do is design a frame around a .45 slide and magazine, and then design a 9mm magazine and slide around that frame?

rcmodel
October 28, 2011, 04:23 PM
Or buy a 1911 frame with both slide sets.

http://www.brownells.com/.aspx/pid=12448/Product/2011-SLIDE-FRAME-KIT

rc

ATLDave
October 28, 2011, 04:28 PM
Skribs, I think it is true that you have to design around your largest and your most powerful cartridge (not always the same thing), and then size down barrel, slide (including recoil spring), and mags.

1SOW
October 28, 2011, 08:43 PM
rcmodel +1

See last month's American Rifleman for an STI with two uppers, using the same mags for 40cal and 9mm. Interesting.

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