Currently, the 357 Sig is our most popular build. The main question that we get is: “Can you rechamber my 9mm blow back to 357 Sig?” or “What is the price and delivery for a 357 Sig barrel for my 9mm AR?”
Our Sig builds are gas operated and take a customized 6.8 SPC BCG and custom Gas system. These are NOT blow back barrels that can be swapped on to your 9mm lower. This makes the build much more expensive than just a barrel swap.
There is a reason you can’t find 357 Sig Blow Back barrels any more: They Blow Up! They cause case head separations and can damage you and your upper.
We can tell you how to modify your glock mag lower to use with our gas operated 357 Sig Upper. However, we recommend using the new CMMG 9mm Pmag conversions and standard lowers. These mags have less drag and are smoother operating for the gas operated uppers.
Because gas operated pistol caliber uppers have such short gas systems, be prepared to clean your upper on a shorter cycle than a carbine or rifle length system.