I was gifted a new Glock 20. I am a huge fan of 10mm and intend to shoot many rounds of 10mm through this gun. However, my supply of 10mm is not great while I have over 30,000 rounds of .45acp stockpiled. Can I put a factory 21 slide/barrel/recoil spring assembly/magazines on the 20 frame and expect it to function reliably or is there something unique about the 20 frame that I’m not aware of?

I just received a new Glock 20 Gen 5 MOS and the ejector is marked 65577.   The previous generation Glock 10 mm, 45 ACP and 45 GAP used the same ejector.   I copied this info out of an older Glock armorers manual.   I’d say if you have a Gen 5 Glock 20 with ejector 65577 you should be able to use a new Gen 5 Glock 21 slide.   If you have an earlier gen Glock 20 looks like the 10 mm and 45 ACP frames use the same ejector.






Ejector only - 10mm, .45 Auto, .45 GAP (marked 8196-2) replaces 4340-marked ejector - ref only / not for sale. Use 8203 Trigger Mechanism Housing




Glock 20.5 ejector 65577 in my MOS 20.5.

For as cheap as G21’s are just buy a complete gun.

This. If you price out all the parts I am thinking you will be near the cost of a used Glock (you know they don't really wear out?) .

To my way of thinking Two Glocks are way more valuable than a Golck and a pile of parts

To me a Glock is nothing more than a bullet slinger. They’re shit. I don’t want the one I now have, let alone two. It would be more useful if it could sling .45acp.

No. You need a whole new slide assembly

The breech face is not wide enough for .45ACP … it’s sized for .40/10mm

I read too fast.  Yes, if everything’s the same generation. I’ve swapped slides and frames around.

PD trades are in the 350-450 range on Gunbroker. Most likely itll be harder to find a complete slide and mags for better than that price.

ETA: Talking G21 Gen4

If your not eligible for blue label this is a very good price for a Ges 3 Glock 21 SF, $369.  Standard Glock 21 is $399 at Aim Surplus.   I’d rather have a whole gun as just swapping slides.




https://www.aimsurplus.com/products/leo-trade-in-gen-3-glock-21sf-short-frame-45-auto-handgun

Why spend money on what you view as shit?

Sell your G20, take that money and put it towards something you will enjoy shooting.

I agree with this.

  ^^ This! It makes no sense whatsoever to sink more money into a handgun you hate.