So, bare with me on this one. I realize I could ask this on glocktalk or some such place but I trust the info and experience here much more.

As I understand it, the G21 and G20 frames are identical, as far as trigger parts, locking insert, ejector etc. (this correct?)

That being the case, I should be able to slap a complete G20 g3 or g4 upper on my G4 G21 frame, get some 10mm mags and I'm good to go to shoot 10mm.

With that said, I've noticed that there are conversion barrels out there to take a G20 upper to either .40 or .357 sig...as the 10mm case is the same base dimensions as the 40 and 357 (obviously outside of the necked down portion on the 357), the 10mm mags should work for either the 40 or the 357...right?

I'm really only interested in the 10mm conversion for right now, but would also like to be able to go to 357 down the road, and a lone wolf barrel is cheaper than a whole new gun.

Obviously I wouldn't be counting on the 357 conversion for defensive purposes until I'd ran enough rounds through to be confident, but wondering if that all makes sense.


Cliff notes: Have Gen 4 G21...can I a.) use either g3 or g4 G20 upper or does it have to be G4? b.) once the G20 upper is on, does the 357 sig feed out of the 10mm mags at least semi-reliably, since they make conversion barrels?

No help on most of your question, but I'd think the shorter OAL of the 357Sig as compared to 10mm would potentially be an issue?


I'm not at all Glock expert, or even a Glock novice; just a bit of assumption.

quote:

Originally posted by P250UA5:
No help on most of your question, but I'd think the shorter OAL of the 357Sig as compared to 10mm would potentially be an issue?


I'm not at all Glock expert, or even a Glock novice; just a bit of assumption.

That's one thing I wondered also, but there are no large frame 357 or 40 mags for glocks...it's got the same COAL as the .40 which there are also conversion barrels for...

Will be interesting to find out though. I know the 20/21 have been long touted as the best choice re: caliber conversions (11 conversions I think I saw somewhere?) so if I can scratch these oddball caliber itches with one pistol, it'd save me quite a bit of coin.

I have the 40 and 357 barrels for my 20's. Not a single problem. They feed fine from the 10mm magazines.

o5

It seems to me that with converting pistols, as long as the back end of the cartage is compatible everything should work with the correct barrel.

quote:

Originally posted by FenderBender:
It seems to me that with converting pistols, as long as the back end of the cartage is compatible everything should work with the correct barrel.

I think that's it...breech face size and firing pin location, ejector location and functionality, and then mag/follower compatibility (would be worried about necked cartridges on a follower that's not made for them)

Not exactly the info you're looking for, but... I have a 40 barrel for my G20
that I use for IPSC. No malfunctions to date.
I plan on getting a 357 barrel soon.
BTW: 40 out of the G20 is super soft. I need to get a set of barrels for my G40 as well.....

Have Gen 4 G21. Can I...

a.) use either g3 or g4 G20 upper or does it have to be G4?

The recoil assembly for your Gen4 will not work in the Gen3 slide. You'd be better served with a Gen4 slide and not have to work with adapters. However, changing spring rates with a Gen3 slide and guide rod is a lot easier to do than changing springs in a Gen4 rod.

b.) once the G20 upper is on, does the 357 sig feed out of the 10mm mags at least semi-reliably, since they make conversion barrels?

the 357 Sig should feed with no issues as most bottleneck cartridges rarely have issues.

Not a big help but I also shoot 40 out of my 20. I do it with a stock gun with the factory 10mm barrel.

I believe the issue will be the G3 slide on the G4 frame. I believe going the other way leaves a gap at the end of the frame. I use a KKM 10mm conversion barrel with a different extractor they sent with the barrel and have had no issues. This is in a G4 21. I also bought a G3 recoil spring and guide rod with adapter to have a stronger spring for 10mm. I have both 40 and 357 Sig barrels for my G29 and they function fine. The 357 Sig point of impact is different than the other 2 calibers.