Sylvan Arms AR-15 to 9mm Conversion Block for Glock Pattern Magazines – GCB100

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UTG GL933 33 Round Polymer Glock 9mm Magazine


UTG GL933 33 Round Polymer 9mm Glock Compatible Magazine

Easily Convert Your AR-15 Lower to Accept Glock Magazines

The Sylvan Arms AR-15 to 9mm Glock Conversion Block – GCB100 is a drop-in addition that converts your AR-15 lower to a 9mm Lower for use with Glock magazines. This accessory is designed to install in Mil-Spec lowers almost exactly like a standard rifle magazine, without resorting to buying a separate lower receiver exclusively for Glock mags.

This fantastic conversion kit from Sylvan Arms is one of the best accessories on the market today and increases the modularity of your AR-15 pattern rifle.

Takes Your AR Build to the Next Level

The Sylvan Arms AR-15 to 9mm Glock Compatible Conversion Block is designed to fit into the magazine well of your standard AR-15 and reduces all the extra space and allows Glock 17 and 19 pattern magazines to fit. The fit and function of this adaptor are exceptional and genuinely ingenious which makes it one of the best AR-15 accessories on the market today.

It is machined from black oxide steel and 6061-T6 aluminum coated with a black anodized finish for extreme durability and wear resistance. This adapter promotes easy installation and swap-out when needed and takes your AR build a step further to switch that big 5.56mm-sized hole into a 9mm-sized one to fire your favorite 9mm ammo.


  • Easy to install and swap out
  • Accepts popular Glock 9mm magazines
  • Designed to work with Mil-Spec lowers
  • Does NOT include last round bolt hold open
  • Works with Glock® 17 and Glock® 19 mags
  • Built of 6061 aircraft-grade aluminum
  • Does not include last round bolt hold open


  • Material: Steel and 6061-T6 Aluminum
  • Finish: Black Anodized
  • Weight: 4.2 oz.

DISCLAIMER: This product is not manufactured, authorized, endorsed, or warranted by GLOCK. GLOCK does not warrant or represent that this product is compatible with GLOCK pistols.

Have Questions About this Product?

The AT3 Tactical store has a 90 day no-hassle return policy for products in good condition. You can view the full details of our return policy here.

If you encounter an issue or defect with a product after 90 days of your purchase, you can refer to the manufacturer for a warranty claim. Their policies are below.

Sylvan Arms Warranty

We stand by our products!

If you are experiencing an issue with a Sylvan Arms product, please contact us at your earliest convenience so we can address the issue. Our goal is to make it work for you so please give us all details possible. Not every product is 100% compatible, with variations in build, but we will do our best to make it work with your components.

We have a 30-day hassle-free return policy. If you would like to make a return please request an RMA number from our customer service department. We reserve the right to deny return requests if the item has been intentionally damaged beyond repair.

Contact Details:

  • Telephone: 888-256-5632
  • Email:

Disclaimer: Manufacturer’s warranty is subject to change without prior notice.

Customer Reviews

Based on 9 reviews
Scott Goad
Works great

Works great does what it's supposed to do.

Thanks for sharing your feedback! We're glad you're satisfied with your purchase.

9mm conversion block

These work very nice. I just wish they could come up with a last round bolt hole open. Other than that they're great.

Thanks for sharing your feedback! We're glad you're satisfied with your purchase.

Grant B.
Sylvan 9mm block

I added this block to my PSA AR/multical lower and tested it with Glock, Magpul and ETS 32rd magazines. I had zero failures to feed with all magazine brands. The Glock and Magpul magazines were positive engage on insertion and "drop-free" upon mag release actuation. The ETS mags needed "firm" seating and were not drop-free. The conversion block works as advertised and I highly recommend.

Thanks for sharing your feedback! We're glad you're satisfied with your purchase.

It Depends

I've used the Conversion Block on 7 builds. The $100 for the CB still outweighs the cost and difficulty in obtaining a dedicated 9mm lower. The converted lower can be converted back and used with other uppers which is an advantage. It's incredibly easy to install. So the only real question is, does it work? The answer is "it depends". On some lowers it fits like a glove. On others, Anderson Manufacturing in particular, it has up to 3/16 of an inch in upward shift.The set screw and the normal magazine catch prevent drop down but nothing in the design prevents the upward movement. The shift or up and down wobble causes a variety of malfunctions and will ruin an otherwise enjoyable day of shooting. Anderson is just one example I mention because many budget minded builders use Anderson because they are readily available locally and because they are reasonably priced. It seems that all mil spec receivers are not the same when it comes to accepting Sylvan CB's. I can tell you that the receivers that work with the CB work fantastic. Your 9mm build will function as well as it would with any dedicated 9mm lower. If you get a bad match you can Smith your way to perfection but you will have to make adjustments and do some work.

Daniel Swierczynski
Great Glock Block....

This block is a nice alternative to a dedicated 9 mm lower. Allows you to remove and use other calibers in the same rifle. Works well, easy to install and remove, no last bolt hold is easy to get used to. I highly recommend. AT3 has fast shipping and great customer service, highly recommend them as well.

Thanks for sharing your feedback! We're glad you're satisfied with your purchase.