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  • Double Diamond .40cal to 9mm Conversion Barrels for Glock Gen1-4

Double Diamond .40cal to 9mm Conversion Barrels for Glock Gen1-4

$149.99 to $239.99
SKU: 1007
$149.99 to $239.99

SAVE MONEY ON AMMO! Reduce Recoil!
Easily convert your .40 Caliber Glock to shoot 9mm in seconds!

Designed to allow shooters to change calibers by simply dropping in the Double Diamond conversion barrels in conjunction with the appropriate caliber magazine. The barrel is cut to fit in the ejection port of the intended slide. Basically, it's a .40 caliber barrel on the outside chambered in 9mm ... brilliant!

Swapping out recoil guide rods, ejectors, extractors, or strikers is not necessary.

Twist rate for the Rifling in all Double Diamond barrels:

9mm - 1/10" Right Hand

10mm/.40 - 1/16" Right Hand

.45 ACP - 1/16" Left Hand

Please note: Will work in Gen 1, 2 & 3 Glock handguns. Threaded Conversion Barrels will NOT work with most compensators.

Looking to convert your .45ACP to 10mm?
Click here!

Got a 10mm and want to shoot .40 S&W?
Click here!

Convert your .40 caliber to shoot 9mm in seconds by replacing the factory barrel with our high performance Double Diamond conversion barrel.

Double Diamond match grade replacement barrels are manufactured in the USA from the highest grade 416R stainless steel forgings. CNC machined and heat treated, providing a life time of service and better-than-factory accuracy at an affordable price.

The standard groove and land rifling make this an excellent choice for those who wish to shoot lead, plated, or jacketed bullets. Can be used in "C" model (compensated) Glocks, in addition to standard Glocks.

Special features include:
• Ready to use, pre-fit, drop-in
• No gunsmithing required.
• Precision machined from heat treated 416R stainless forgings
• Oversized lock-up area produces greater shot-to-shot accuracy
• Tighter than factory spec dimensions
• Polished feed ramp, bore and chamber
• Match grade, broach cut rifling and target crown
• Compatible with all Glock generations
• Maximum chamber support
• Improved feed ramp design
• Diamond turned exterior
• Okay to use lead, plated or jacketed bullets
• Made in the USA

Match grade broach cut rifling and target crown. Okay to use lead, plated, or jacketed bullets. Lifetime warranty. GlockStore will replace any of its barrels or barrel accessories which are found to have manufacturing or material defects. Customer modifications or the use of reloaded ammunition will void this warranty.

Please note: Threaded barrels use standard 9mm threads.

Barrels may only be returned if they are unused and in resellable condition. If the item is defective — i.e., does not function — we will accept a return within the 30-day period only.

Not available for export outside the United States.

Order Online or Call Toll-Free: 1-800-601-8273
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Ratings & Reviews

15 reviews

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Great barrel and very accurate to convert to 9mm


Received one of the last generation barrels recently for my Glock 23. What a difference. The .40 barrel would throw rounds in a varied grouping but once I got this sighted in, shoots a very nice group at 25 feet. Would recommend highly. Sidenote, threaded DOES come with a thread protector already. Add a little blue loctite to keep it in place.

Double Diamond Perfection


600 rounds through it so far and zero problems. I did replace the extractor and ejector with Glock 19 oem parts. No FTF or FTE problems at all. Also no problem with brass hitting me in the face. Beautiful fit and finish. Thank you Glockstore!

Sweet swap


Got to take this for a walk at charity event shoot for 4 days.
Threw this in my G22 Gen3 and fed it S&B 115gn fmj. The barrel was machined true, could ragged hole at 7yds. Good enough for my eyes.

Downside: In 800 rounds I had 14 Type 3s. Could be a lot of things including the ammo, however, my G19 Gen2 ate the same amount of the same ammo and got 1 Type 3. In this case, maybe not the ammo. Could have been tired hands.

Take Away: I wouldn't use it for carry, but for range work I think it's awesome. Besides, Type 3s are my favorite. Finger magic.

Buy with confidence great product


I'm completely satisfied with this conversion barrel and with the CustomerService I received from the glock store. I waited for a sale and got the barrel for 116 bucks with free shipping and after ordering I live chatted with Conor An he told me it ship towards the end of the week I ordered it on a Tuesday it shipped on Thursday and got it Friday... since installing (in my glock 35 G4) i have put about 100 rounds through it no problems great fit and finish and very accurate... I have nothing negative to say if you are thinking about buying this barrel you wont regret it

Works like a charm.


Since I converted my Glock - 23 from a 40 cal to a 9 mm it works like a charm. At first I had a feed problem because of the new Gen 3 lower but it went away after a few rounds

Fantastic 9mm barrel


Great quality, perfect workmanship. Accuracy on par with Glock factory barrels. As good ( maybe better?) than my Glock 26.

40-9 conversion


Very nice barrel but needed a little fitting around the top lip over the chamber to fit into my slides. Otherwise happy with the purchase



I purchased this conversion barrel for my G23 and I can confirm that the pistol functioned FLAWLESSLY!!! The only other amendment was the addition of G19 magazines. I experienced no FTF, FTE, no malfunctions whatsoever!!...I was originally going to purchase the 9mm specific extractor just to be safe, but never got around to it. Went to the range this morning for yearly quals, and brought my MCK with the G23 (9mm convert) and it shot beautifully!!

40 to 357 sig


I carry a Glock 27 and I also have the 40 to 357 sig conversion barrel. both perform flawless with standard 40 cal mags!

Excellent for 9mm range FMJ Ammo.


I have these very 9mm conversion barrels in both my Glock 23 and 35, and they work great. Be aware through that the dimensions are tight in the chamber and my carry ammo won't readily cycle through them. Apparently my carry ammo is just a thousandth or two wider than the range ammo I use. Speaking of range ammo, I can use 9mm to the extent of my budget and FMJ range ammo runs through the barrels perfectly, saving me a ton of money. Good accuracy too, when I do my part.

Great product


Love the conversion barrel for my glock 27. No problem so far.