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Posted: 1/18/2021 12:41:15 AM EST
Hi all!

I've been looking everywhere for a 10mm conversion barrel for my Glock 21.  They used to be everywhere now I can't find one for love or money.  Is this yet another government / BLM / ALIEN conspiracy?  All I want to do is shoot 10mm out of my freaking G21!

All joking aside - has anyone seen one for sale anywhere?
Link Posted: 1/18/2021 12:57:30 AM EST
In for answers. Been looking everywhere too. According to Midway, the storm lake one is discontinued and the one on the GlockStore has been out of stock forever.
Link Posted: 1/18/2021 5:44:20 AM EST
What I learned is...

Any Glock 20 - 10mm barrel will work.

Haven't figured out which weight recoil spring to use.
Link Posted: 1/18/2021 11:14:31 AM EST
Isn't the muzzle end of the 45 larger?  Wouldn't the barrel just bang around in the slide collet?
Link Posted: 1/18/2021 11:24:21 AM EST
I can't believe how stupid I am. Seriously. I took the barrel out of my G20 and it dropped right into my G21. Solid as a rock!

Off to buy a G20 barrel. Thanks dude!
Link Posted: 1/18/2021 4:58:59 PM EST
Well that right there is good to know.
Link Posted: 1/18/2021 6:51:07 PM EST
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Originally Posted By _disconnector_:
I can't believe how stupid I am. Seriously. I took the barrel out of my G20 and it dropped right into my G21. Solid as a rock!

Off to buy a G20 barrel. Thanks dude!
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Link Posted: 1/18/2021 8:11:48 PM EST
I feel stupid too. Then what's the difference between a 20 and a 21 or a 40 and a 41 slide? You'd think aftermarket slides would be marketed as works for both. The outside diameters of the barrels are the same. I just measured them.

Suddenly I need a threaded 21 barrel to go in my P80 frame 20 with tall sights, a 20 barrel to go in my 21, and a 41 barrel to go in my 40.
Link Posted: 1/18/2021 9:09:16 PM EST
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Originally Posted By _disconnector_:
I can't believe how stupid I am. Seriously. I took the barrel out of my G20 and it dropped right into my G21. Solid as a rock!

Off to buy a G20 barrel. Thanks dude!
View Quote

If this is true, I’m going to kick myself for not buying a Glock 20 barrel long ago...
Link Posted: 1/18/2021 10:45:37 PM EST
The diameter of the barrel at the point where it goes through the slide is identical for both barrels according to my calipers.

I need to measure the barrel hoods and stuff tomorrow.  But according to my Mark 1 eyeball it looks good.
Link Posted: 1/18/2021 11:06:08 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By _disconnector_:  Isn't the muzzle end of the 45 larger?  Wouldn't the barrel just bang around in the slide collet?
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Wait - you have a 10mm slide, and a 10mm bbl - but you want to shoot 10mm out of your .45?
Link Posted: 1/18/2021 11:22:00 PM EST
KKM
Link Posted: 1/19/2021 12:01:25 AM EST
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Originally Posted By backbencher:


Wait - you have a 10mm slide, and a 10mm bbl - but you want to shoot 10mm out of your .45?
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I want a second 10mm for my son to use as a hog hunting sidearm.
Link Posted: 1/19/2021 12:01:44 AM EST
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Originally Posted By GMZ:
KKM
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Out of stock everywhere . .  .
Link Posted: 1/19/2021 1:37:51 PM EST
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Originally Posted By _disconnector_:
Out of stock everywhere . .  .
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You put it in a Gen3 21sf correct? Hovering over the order button for a factory G20 barrel to drop in my 21sf...
Link Posted: 1/19/2021 1:39:01 PM EST
[Last Edit: 1/19/2021 1:39:55 PM EST by Dolomite]
Another question:  How reliable is .40 out of such a set-up?

ETA:  G21SF is best G
Link Posted: 1/19/2021 2:47:20 PM EST
I just tried my G40 and G20 KKM barrels in my 21 slide, made by Rock Slide. Then the Wilson Combat G21 barrel in the LWD 10mm slides. None would slide into battery. The 10mm barrel hoods are about 0.427" wide at the back. The .45 ACP is about 0.480" measured at the same spot.

Still might pick up a couple barrels and fit them to have 2 caliber guns.

Attachment Attached File


Link Posted: 1/19/2021 6:09:22 PM EST
[Last Edit: 1/19/2021 6:12:49 PM EST by _disconnector_]
That's weird.  I have a bone stock G40.4 and a bone stock G21.4  Here are the measurements of the barrel hoods -

Attachment Attached File


They aren't perfectly identical but it's so close that it could simply be manufacturing tolerances or a bit of wear.  Lockup feels tight as a normal Glock which is a tiny bit rattly since it's a Glock . . hahahaha.

I would confidently shoot the G40 barrel in the G21 with hunting loads.

Maybe this is a gen4 thing?

Link Posted: 1/19/2021 6:21:08 PM EST
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Originally Posted By _disconnector_:
That's weird.  I have a bone stock G40.4 and a bone stock G21.4  Here are the measurements of the barrel hoods -

https://www.ar15.com/media/mediaFiles/40889/IMG_3538_JPG-1787038.JPG

They aren't perfectly identical but it's so close that it could simply be manufacturing tolerances or a bit of wear.  Lockup feels tight as a normal Glock which is a tiny bit rattly since it's a Glock . . hahahaha.

I would confidently shoot the G40 barrel in the G21 with hunting loads.

Maybe this is a gen4 thing?

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That's probably it. All my Glock stuff is Gen 3.
Link Posted: 1/20/2021 7:42:19 AM EST
[Last Edit: 1/20/2021 7:43:30 AM EST by Falconpunchjr]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By _disconnector_:
That's weird.  I have a bone stock G40.4 and a bone stock G21.4  Here are the measurements of the barrel hoods -

https://www.ar15.com/media/mediaFiles/40889/IMG_3538_JPG-1787038.JPG

They aren't perfectly identical but it's so close that it could simply be manufacturing tolerances or a bit of wear.  Lockup feels tight as a normal Glock which is a tiny bit rattly since it's a Glock . . hahahaha.

I would confidently shoot the G40 barrel in the G21 with hunting loads.

Maybe this is a gen4 thing?

View Quote


Yeah its a gen 4 thing, 20,21,40,41 same frame and 20/21 same slide just different number/extractor but my 45 extractor works great for 10. You don't happen to have a 41 do you? I'm trying to see if my kkm 10mm barrel or factory 45 will fit in a 21 slide.
Link Posted: 1/20/2021 9:33:39 AM EST
[Last Edit: 1/20/2021 9:34:39 AM EST by _disconnector_]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Falconpunchjr:


Yeah its a gen 4 thing, 20,21,40,41 same frame and 20/21 same slide just different number/extractor but my 45 extractor works great for 10. You don't happen to have a 41 do you? I'm trying to see if my kkm 10mm barrel or factory 45 will fit in a 21 slide.
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No G41 here but I'd bet that it would work.  The G40 barrels external dimensions are pretty much identical to the G21 except for length.

Wait - does that mean that the breech face for the G21/41 isn't larger?  If so I might grab a G41 barrel for my G21 . . . time to break out the calipers to check.
Link Posted: 1/20/2021 11:08:20 AM EST
[Last Edit: 1/20/2021 11:39:55 AM EST by Falconpunchjr]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By _disconnector_:
No G41 here but I'd bet that it would work.  The G40 barrels external dimensions are pretty much identical to the G21 except for length.

Wait - does that mean that the breech face for the G21/41 isn't larger?  If so I might grab a G41 barrel for my G21 . . . time to break out the calipers to check.
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Show me where you want measurements at and I'll let you know. I'm hoping my kkm 10mm 41 conversion barrel will fit a G21 slide since they are cheaper then the G20. I found a used G41 threaded barrel, so that's why I'm going all through this lol. I'll need the barrel OD mostly, but the breech face helps too.

I don't know about the 21/41, I know people are saying 20/21 breech face is the same. I can measure my stock 45acp barrel, kkm 10mm breech and OD. I think the kkm 10mm is a little wider to help feed.
Link Posted: 1/20/2021 3:11:10 PM EST
[Last Edit: 1/20/2021 4:39:47 PM EST by _disconnector_]
OK - the breech faces are the same but the barrel hood *is* different.  On the G21.4 (.45ACP) barrel it's 12.23mm and on the G41.4 (10mm) it's 10.86mm.  Because of this the G21/G41 barrels would not fit the G20/40 without modding the barrel or the slide.

TL;DR?  G20.4/40.4 barrels fit the G21.4/41.4 guns but the reverse is NOT true.  You can shoot 10mm out of a G21.4/41.4 with just a stock Glock barrel but shooting .45 out of the 10mm will require either slide/barrel mods or a conversion barrel.  Personally I'm just going to buy a G41.4 barrel and knock a .75mm off of each side of the barrel hood extension with a file.  It's not part of lockup or timing.  The tiny gaps on the sides of the barrel hood are irrelevant for shooting the gun since the barrel is constrained by the slide for side to side motion.

In a nutshell - eric is right.  But in a G4 you can use the 10mm barrel in the .45 with no mods.

I'll post pictures of what I'm referring to later when my dang phone finishes updating . . . it's taking forever today.
Link Posted: 1/20/2021 7:30:41 PM EST
So will a G20 barrel fit a Gen 3 G21?  I keep going back and forth on whether to go the 10mm or .45 Super route.  I already have a Storm Lake ported G21 barrel so case head support isn't an issue.  I'm leaning a bit towards 10mm just because I don't have to worry about ammo mix ups.
Link Posted: 1/20/2021 8:48:45 PM EST
[Last Edit: 1/20/2021 8:50:10 PM EST by _disconnector_]
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Originally Posted By Brandi:
So will a G20 barrel fit a Gen 3 G21?  I keep going back and forth on whether to go the 10mm or .45 Super route.  I already have a Storm Lake ported G21 barrel so case head support isn't an issue.  I'm leaning a bit towards 10mm just because I don't have to worry about ammo mix ups.
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Sorry dude - I have no idea about a Gen3.  All of the stuff that I have to work with is gen4.

A gen4 10mm barrel will fit into a gen4 45 slide.  That I do know.

.45 Super is pretty awesome and why I bought a G21.  But if you want decent factory ammo get the 10mm.

Or, in true ARFCOM fashion - "buy both".  With politics the way they are moving your window of opportunity is closing.
Link Posted: 1/20/2021 9:04:28 PM EST
I asked KKM if their 10mm 41 conversion barrel would fit in the 21 and they said no. Its made more for the 30s slide. I guess I'll just have to get a g40 and pair it with my 41. I need to have everything threaded, they don't make their 10mm threaded anymore for the 41.
Link Posted: 1/22/2021 10:11:18 AM EST
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Originally Posted By GMZ:
KKM
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I emailed KKM last year about getting a conversion barrel, or using the G20 barrel in a G21 slide. They said they will not make any more conversion barrels, and "We cannot advise anyone to use a G20 barrel in a G21, even if it drops on and functions, we do not consider the fitment correct."
Link Posted: 1/22/2021 4:35:48 PM EST
For what it's worth, I've heard that 10mm conversion barrels in G21's have been historically problematic.   I would suggest either buying a G20 or if you want more power, buy a good .45 barrel and shoot .45 Super.  You could also get a 460 Rowland setup for it, both of which are more powerful than 10mm.
Link Posted: 1/24/2021 8:29:58 AM EST
Related question: will any G30 barrel work in a G29? I'd like to get a threaded 45 ACP for silencer use.
Link Posted: 1/24/2021 9:05:41 AM EST
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Originally Posted By TacticalGarand44:
Related question: will any G30 barrel work in a G29? I'd like to get a threaded 45 ACP for silencer use.
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Also would like to know about any threaded .45 ACP barrels to fit a gen 3 G20.


Link Posted: 1/24/2021 4:13:57 PM EST
I found a used storm lake conversion bbl. I can’t find any 10mm ammo to test it that isn’t over $1/rd. I plan on trying it with .40 later if I can’t find any cheaper 10mm.
Link Posted: 1/25/2021 6:03:39 PM EST
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Originally Posted By castlebravo84:


I emailed KKM last year about getting a conversion barrel, or using the G20 barrel in a G21 slide. They said they will not make any more conversion barrels, and "We cannot advise anyone to use a G20 barrel in a G21, even if it drops on and functions, we do not consider the fitment correct."
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They have a G41 barrel in 10mm on their site now. Maybe they changed their mind. I bought a G40 .40 S&W barrel and will ask about .45 ACP and .357 Sig barrels for the G40.
Link Posted: 1/25/2021 10:11:28 PM EST
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Originally Posted By eric496:


They have a G41 barrel in 10mm on their site now. Maybe they changed their mind. I bought a G40 .40 S&W barrel and will ask about .45 ACP and .357 Sig barrels for the G40.
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Originally Posted By eric496:
Originally Posted By castlebravo84:


I emailed KKM last year about getting a conversion barrel, or using the G20 barrel in a G21 slide. They said they will not make any more conversion barrels, and "We cannot advise anyone to use a G20 barrel in a G21, even if it drops on and functions, we do not consider the fitment correct."


They have a G41 barrel in 10mm on their site now. Maybe they changed their mind. I bought a G40 .40 S&W barrel and will ask about .45 ACP and .357 Sig barrels for the G40.


Interesting about the G41 10mm barrel...

A G40 357sig barrel is a likely possibility, but from what I understand, .45acp is wider than the breech face on a G40 slide.
Link Posted: 1/26/2021 6:25:52 AM EST
[Last Edit: 1/26/2021 6:45:52 AM EST by eric496]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By castlebravo84:
Guess I need to order more slides.

Interesting about the G41 10mm barrel...

A G40 357sig barrel is a likely possibility, but from what I understand, .45acp is wider than the breech face on a G40 slide.
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Originally Posted By castlebravo84:
Originally Posted By eric496:
Originally Posted By castlebravo84:


I emailed KKM last year about getting a conversion barrel, or using the G20 barrel in a G21 slide. They said they will not make any more conversion barrels, and "We cannot advise anyone to use a G20 barrel in a G21, even if it drops on and functions, we do not consider the fitment correct."


They have a G41 barrel in 10mm on their site now. Maybe they changed their mind. I bought a G40 .40 S&W barrel and will ask about .45 ACP and .357 Sig barrels for the G40.
Guess I need to order more slides.

Interesting about the G41 10mm barrel...

A G40 357sig barrel is a likely possibility, but from what I understand, .45acp is wider than the breech face on a G40 slide.


You're correct and I knew that. I should have thought about it for a minute before emailing KKM. Now they'll probably think I'm too stupid to sell a conversion barrel to. Hope they will make the .357 Sig barrel though. Guess I need to think about ordering more slides for now.
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