B&T APC9 PRO SIG P320 Lower Receiver Group and SIG Sauer P320 Magazine Compatibility.
Based upon multiple inline manufacturing and generational changes instituted by SIG Sauer on its P320 magazine feeding devices, B&T USA feels compelled to provide our customers with the below guide outlining SIG Sauer P320 magazine compatibility with our P320 lower receiver groups. B&T engineered its lower receiver to function specifically with the United States Army’s chosen M17 magazines produced for them by Mec-Gar NSN: 1005-01-665-3062 (17 rd.) & NSN 1005-01-665-4553 (21 rd.). This magazine is slightly different than the magazine offered commercially by SIG Sauer and produced by Checkmate and/or SIG Sauer proper. This fact coupled with generational and inline manufacturing changes by SIG Sauer has created tolerance and functionality complications with some of its magazines and their differing components, inclusive of the magazine body, follower, spring, and baseplate.
B&T has received several inquiries regarding P320 magazine compatibility. As such, we have conducted extensive testing and evaluation with known P320 magazine generations. The primary complication discovered is P320 magazine compatibility with our APC9 PRO lower receiver Bolt Hold Open (BHO) feature that may not properly function. While it was discovered it may be possible for some magazines to sit slightly higher within the lower receiver; increasing engagement of the BHO did not effectively remedy the issue. Measurements of magazines from Mec-Gar, Pro Mag and Sig Sauer USA (CheckMate) revealed that the distance from the magazine catch notch to the BHO shelf on the magazine follower varied. A longer distance from the top of the catch to the top of the BHO shelf indicates a more positive engagement with the BHO in the lower.
Pro Mags offer the most engagement with a measurement of 1.519 inches. When Inserted into an APC9 PRO lower receiver, there is no discernable play in the BHO mechanism. In test firing, BHO engagement was 100% when Pro Mags are utilized.
Mec-Gar magazines provide less engagement than Pro Mag, measuring 1.440 inches. When inserted within an APC9 PRO lower receiver, there is some head room in the BHO mechanism, but this does not affect function. In test firing, BHO engagement was 100% when Mec-Gar magazines were used.
SIG Sauer magazines (marked Made in USA) provide the least engagement of any magazines tested, measuring 1.399 inches. When inserted into an APC9 PRO lower receiver, the BHO mechanism is barely engaged. In test firing, BHO engagement was approximately 20% when Sig Sauer USA magazines were used.
Based upon our testing and evaluation, B&T USA we recommend our customers utilize Mec-Gar magazines based upon their ability to properly engage the BHO and reliability function.
As a complimentary service, B&T USA is offering to adjust customers APC9 PRO lower receivers designed to accept and function with P320 magazines. This adjustment includes modification to the magazine well and over insertion tabs if the customers lower is not functioning properly with approved magazines. Please contact [email protected] for further details.