Our uppers are designed and milled to match the profile of the Vltor MUR 1 upper receiver. As such, the MUR 1 will have a very tight fit, but our lowers will be compatible with almost any upper receiver your choose to use in your build. Our blowback bolts do not have machined grooves for the use of a forward assist, and we recommend the use of a “slick-side” upper receiver. We can report proper function with the following upper receivers:
Vltor Modular Upper Receiver
GIBBZ Arms G4 Side Charging Upper Receiver
X-Products X-15 SCU Billet Side Charging Upper Receiver
The following triggers have been tested by us and function properly:
Our CLT9MM lower receiver is compatible with our 9mm bolt, which offers superior machining tolerances and engineering, and is designed specifically to work flawlessly with our barrels. Both CMMG and JP offer 9mm bolts that will also function right out of the box.
Because of the narrower feed lips in a Glock magazine as compared to a Colt-style magazine, our Glock Small Frame lower requires the use of a bolt that has the “Glock Cut” feature. Because of this, we also offer our Glock-cut bolts in all calibers. This is our proprietary bolt, built from the ground up to function with the Glock magazine, rather than simply modifed from existing 9mm bolts. JP also offers a bolt with the Glock Cut.
Buffer weight and spring combination in sub caliber blow back AR platforms is critical. They will not function reliably or safely with standard AR-15 carbine buffers and springs. Standard 5.56/.223 buffers are typically on the light side ranging from 2.9-4.5oz. With the straight blow back systems a heavier buffer and spring combination is essential. We have found best results with the buffer weights listed below and a Wolff or Sprinco extra power AR-15 carbine spring. Depending on your barrel length and ammunition type used, a standard carbine spring may be used. Below are links to a few buffers and springs that typically work well with our our GSF/GLF lowers and mil-spec carbine length buffer tubes. If firing with a suppressor installed a heavier buffer is typically required for best function, felt recoil and sound suppression.
9X19: 5.0-8.5oz buffer
.40 S&W: 6.0-10oz buffer
.45 ACP: 7-12.5oz buffer
When Using a Suppressor
9X19: 7.0oz-12.5oz buffer
.40 S&W: 8.0-12.5oz buffer
.45 ACP: 10oz-12.5oz buffer
Any stock or arm brace that is compatible with a Mil-Spec buffer tube will work with our lowers.
For the Colt 9mm lower receiver we recommend the Metalform Magazine.
For the Glock Lowers we have found that the Glock OEM Magazines work best. We do not recommend the use of Korean aftermarket magazines, as they are inconsistent in quality and fit. We have had good initial results with ETS Group and Magpul polymer magazines, and will be conducting further testing.
Any other parts or accessories that are manufactured to true Mil-Spec standards should be compatible. Unfortunately, we cannot test or even list every accessory that is compatible with our lowers, and common sense and product measurements should be consulted before the purchase of parts. If at all possible, try to find your desired part locally to verify a perfect fit, or check back with our constantly growing list of verfied compatible components and accessories.