Gen 1 STI mag tubes - difference between .40 and .45?

[matteekay]

So, for reasons beyond even my own comprehension, I built an open gun in .45 ACP. Runs great and fun to shoot, but I'm capped at around 16 rounds if I want reliable feeding (140 tubes, Dawson SNL basepads, Grams guts). 

 

I've been wondering if I could retrofit a 170mm .40 tube to work; they use the same followers, and obviously the basepads are the same. Where do the tubes differ? Is it just the lip dimensions (in which case I can simply open them up a little) or is the taper at the top of the mag totally different as well?

[ChuckS]

i went the other way when I was shooting open and used a .45 170mm tube for .40. The only difference that I know of is the depth of the ribs on the sides of the tubes. If you look at your .40 tube, you will see that one side is deeper than the other. On a .45 tube, the ribs are shallow on both sides.

[shred]

The side-to-side space inside is larger on a .45 mag.  You could use a .40 mag but won't get as many rounds in as you would a .45 mag.  The danger with using a .45 mag for .40 is you can get rounds stuck side by side on a bad day.

 

The very earliest STI 40 mags had one side flat and one side ribbed (two sides flat = 45, two sides ribbed = 38 Super).  Then they went to varying ribs per side for .40 and then to the same ribs both sides per caliber.  (All of these people call "gen 1" for some reason.)

Either way, a .45 mag is going to have zero to minimal ribs.

 

[ChuckS]

26 minutes ago, shred said:

- snip - The danger with using a .45 mag for .40 is you can get rounds stuck side by side on a bad day. - snip -

No bad days in 12 years! But then. the mag was tuned by Beven. My .40 tubes would hold 26 rounds and the .45 tube held 26.5. I used that mag for reloads on the clock

[matteekay]

5 hours ago, ChuckS said:

i went the other way when I was shooting open and used a .45 170mm tube for .40. The only difference that I know of is the depth of the ribs on the sides of the tubes. If you look at your .40 tube, you will see that one side is deeper than the other. On a .45 tube, the ribs are shallow on both sides.

 

3 hours ago, shred said:

The side-to-side space inside is larger on a .45 mag.  You could use a .40 mag but won't get as many rounds in as you would a .45 mag.  The danger with using a .45 mag for .40 is you can get rounds stuck side by side on a bad day.

 

Okay, really good to know. I might see if I can grab a tube on the cheap to experiment with; the extra length might still hold more than the wider 140 tube. At the very least, the same capacity but easier to reload would be worth it.