Glock 21 - Conversion to 10mm

A friend of mine ran 10mm fairly successfully from his .45 with just a barrel swap. He occasionally had some ejection problems. That's all I've seen with my own eyes.

I run a heavy duty 10mm extractor for both calibers in my G21.3 with a KKM barrel for 10mm and OEM barrel for 45 has worked fine for years

PM member GRT45 and he can point you to everything he has written on the subject.

He is expert on the topic, probably forgotten more on the subject than many will ever learn.

Thanks! :cheers:

I've gone the opposite direction and converted my G20 to a G21. Has worked flawless since I did the conversion (Lone Wolf slide and barrel assembly) 10 years ago.

Most of the time for conversions you only need the magazine change. Sometimes to get to 100% you need a ejector and extractor for the caliber change, and even more, you may need to change recoil springs, usually down in weight, and or go with a heavier load (conversion barrels are heavier because of the thicker wall, ie, same OD, smaller ID).

Toni77 said:

My apologies if there are already existing threads about this topic but...

I'm planning my next purchase and looking for using 45ACP and 10mm.
What would be the best option? Glock21.4 with conversion barrel?
Do I need to replace some other component?

Other premises to consider?

Thanks for your advise!

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Hi Toni77,

The article linked below will give you information about the conversion process. It covers your alternatives and the issues that come up. It should answer most, if not all, of your questions.

Converting the Glock 21 to 10mm Caliber

For a G21 conversion to 10mm, I prefer Gen4. In my experience, the stock Gen4
dual-spring RSA can handle a broader range of ammo choices extending higher into the full-power range before it becomes necessary to use an aftermarket RSA with stronger springs. Incidentally, Glock, Inc. claims the Gen4 dual-spring RSA has a longer service life compared to the Gen3 single-spring RSA. I appreciate the more aggressive texture of the Gen4 grip to maintain a secure grasp of the pistol when shooting the hottest 10mm loads. You may like one of the Gen4 backstrap adapters with a beavertail for the same reason. I often add one when shooting 460 Rowland.

My current preference for a barrel supplier is KKM Precision.

9x45 said:

Most of the time for conversions you only need the magazine change. Sometimes to get to 100% you need a ejector and extractor for the caliber change, and even more, you may need to change recoil springs, usually down in weight, and or go with a heavier load (conversion barrels are heavier because of the thicker wall, ie, same OD, smaller ID).

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Careful with ejector and extractor changes. Some conversion bbl makers take those factors into account and hedge the manufacturing specs to account for the new caliber with old calibers ejector/extractor. You then change to new parts they were not expecting..and things get wonky. Call the specific manufacturer.

That said my Glock 30 gen 4 tan fine with a lone wolf barrel. Frankly more reliable than 2 Glock 20’s I’ve had.

All the Gen3 and Gen4 Glock 45ACP and 10mm pistols use the same ejector (S-shaped and marked 8196-2) so that is not an issue for the conversion to 10mm.

I have a Glock 20 and what I did was just buy a complete slide and barrel from a Glocks 21 off of GB at a reasonable price.. This allowed me to have separate sighting arrangement for each caliber. I know it is more expensive than just the barrel swap from the G21, but later on I could add a frame for a Glock 21 slide and still be at a good price point. I use the 20 top end for outside activities and the 21 top end for home duty when I think about it.

Sent from my SM-T818V using Tapatalk

I did what Pikepole20 suggested, except went from a 21 to 20. Bought a new Gen 3 upper off of this site at a reasonable price ($250). Am completely satisfied.

Church Key

I have a Gen 3 G21SF. Was going to get a 10mm conversion barrel, but decided to buy a complete G20 upper and mags off of Gunbroker. Couldn’t be happier. Both calibers run 100%. I occasionally use the 45 in IDPA and winter-time carry, and use the 10mm as a sidearm when hog hunting.

Ranger357 said:

Careful with ejector and extractor changes. Some conversion bbl makers take those factors into account and hedge the manufacturing specs to account for the new caliber with old calibers ejector/extractor. You then change to new parts they were not expecting..and things get wonky. Call the specific manufacturer.

That said my Glock 30 gen 4 tan fine with a lone wolf barrel. Frankly more reliable than 2 Glock 20’s I’ve had.

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I quoted Ranger357, but this is an open question to anyone who can give me a somewhat definitive answer.

So basically if I do this conversion, I should be good to go on a Gen 4 G21 with just a barrel swap and some G20 mags?

For reference, I am looking at a stock length Storm Lake 10mm barrel. I decided to go with a stock length instead of extended because it's going to be my woods gun when I'm doing things around the farm. I want to be able to get it out of the holster faster if I needed it, and am only going to occasionally hunt with it.

I know this is an old thread and say thanks in advance for any input.

6Actual said:

I run a heavy duty 10mm extractor for both calibers in my G21.3 with a KKM barrel for 10mm and OEM barrel for 45 has worked fine for years

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who makes a heavy duty 10mm extractor that works with both cartridges and does it require a different spring?

Borg Warner said:

who makes a heavy duty 10mm extractor that works with both cartridges and does it require a different spring?

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I use the same spring, If I remember correctly I believe it was Apex or Wolf 21 extractor Has worked fine with 45 and 10mm for a very long time

I have a 10mm conversion barrel I run in my old G30
I just use 10mm magazines and she runs as reliable as it does with oem .45 barrel.

I ordered a Storm Lake conversion barrel for a G21 and it's on the way. I also have 4 G20 mags ordered.

I'll shoot it when I get it all in and see if I need to do anything with my extractor.

6Actual said:

I use the same spring, If I remember correctly I believe it was Apex or Wolf 21 extractor Has worked fine with 45 and 10mm for a very long time

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So if I am reading this correctly, you did change your extractor?

Edited to add. Disregard, I saw where you said that you changed yours out.

buster55 said:

I have a 10mm conversion barrel I run in my old G30
I just use 10mm magazines and she runs as reliable as it does with oem .45 barrel.

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How many rounds do you think you have put through it? And I assume you have not changed out your extractor?