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Frequently Asked Questions

I am submitting this lower under a Form 1 to the ATF, what do I put as the model and serial number?

The Model is either going to be “GSF”, “GLF”, or “CLT9MM.”
The Serial Number will be “GSF #####”, “GLF #####”, or “CLT9MM #####” exactly as shown, no dashes, with space.

Which Lower Parts Kit will fit in your lower?

Any standard lower parts kit will work fine in our lowers.

When will you have more of _______ in stock?

If you like us on Facebook we will post when we list new stock on our website. We are running at full capacity to get lowers ready to ship.

We are not currently allowing back orders. We are working at full capacity to keep a steady flow of inventory available for customer orders.

Please note: your order for any of our lowers REQUIRES an FFL. Please email or fax your FFL license to us as immediately as possible once you place an order. We do not contact the FFL for you – when you make the arrangements for the transfer be sure to have your FFL send a copy of their license with each order you place. Please do not assume that an FFL is “on file” already with us.

What condition are your blems in?

Quarter Circle 10 Blemished Lower Receivers may have one or more minor cosmetic defects including, but not limited to dents, scratches, dings, discolorations or any other aesthetic imperfection, none of which affect functionality or performance.  Quarter Circle 10 Blem Receivers maintain the full manufacturer’s guarantee on functionality, but do not include a warranty on the finish.

Why do I need a special bolt to fire your Glock style magazines?

The feed lips of a Glock style magazine are smaller than the feed lips of the standard Colt style magazines. Single feed vs Double feed. There needs to be material taken off in order for it to feed the rounds into the chamber.

How can I track my order?

When we ship an order we will ship it USPS priority flat rate. We will send an email notification of shipping with tracking number to the email you have listed under your information.

Do you have a build tutorial?

We do not currently have a build tutorial but here is a great source for putting together a Quarter Circle 10 lower receiver. AR9 Pictorial

Do you ship to California/Are your lowers California Compliant?

Yes, we do ship lowers to California, although we do not install bullet buttons. The CLT9MM model will accept a bullet button as it uses a standard magazine release. The Glock model lowers can be shipped to California with the installation of a Raddlock magazine lock kit; we do not install these either.

My Glock Last Round Bolt Hold Open is not working, How can I get it to run?

If you are using a DDLES style BHO bar (characterized by a hole at the end of the bar that the finger of the bolt catch runs into) we recommend using our revised BHO bar (where it is flat on the end and lifts from under the bolt catch. Bolt Hold Open

DDLES Version

DDLES Style 

QC10 Version

QC10 Style 

If you are using having issues with the QC10 Version please work through the following steps to ensure proper action. If you are still unable to get it running please contact technical support at technical@quartercircle10.com

  1. Ensure you have installed the replacement spring that we sent with your lower. It should be flush against the shoulder of the bolt catch detent. Ideally leaving 2 to 3 coils of the spring off the end.
  2. Review the BHO bar with no magazine installed and no upper on. While manually engaging the bolt catch the BHO bar should move freely up and down.
    1. If the BHO bar does not move freely apply a drop of lubricant to the slot with roll pin
    2. If the BHO bar continues to have issues with movement disassembly may be needed (an 1/8th inch punch will be needed to remove the roll pin holding the BHO bar and shim) clean all debris and residue from the BHO shim along with the BHO bar
  3. Now Review the “L” part of the bar and that it is resting flat within the channel. Without a magazine inserted, the bar should be in the recessed slot, laying underneath the bolt catch.
    1. If the BHO bar does NOT sit flat in the channel you will have to adjust the bar so that the “L” piece will sit flat. This is rare, but it has to be flat in this channel.
  4. Insert a magazine and check the BHO bar magazine follower catch. With the magazine inserted, it should push up on the BHO tab, causing the BHO bar to lift upwards out of the recessed channel, therefore allowing the Bolt Catch to rotate upwards. Check this first without an upper on then place the upper on.
    1. If you are not getting the required lift ensure that Glock magazines are being used as some aftermarket magazines very in spring stiffness.
    2. See step 1 to ensure the replacement spring is installed correctly
    3. Further modifications can be made to the detent spring if required lift is not be obtained and all other conditions are met. Please contact technical@quartercircle10.com before modifying the replacement spring
  5. If the BHO system is working during all these steps but fails to work under live firing, ensure the bolt is traveling far enough past the bolt catch to engage.
    1. This check can be done by holding down the bolt catch while firing, if the bolt catch fails to catch when manually holding it down the dwell of the bolt must be adjusted. Please contact technical@quartercircle10.com to discuss this as it can vary from trigger issue to buffer and spring weight.