The mainspring housing that came with the magwell is 1/4" longer that the factory msh on the gun. Also the mainspring from the factory is 1/4" shorter than the one I ordered from Wilson combat. When I installed the spring and guts into the dawsons, then installed it onto the gun, I was able to get in installed but the gun was locked up, nothing would work. I changed parts from the factory msh to the dawsons msh, same thing. I can install it but the gun locks up. I tried with the factory retainer and cap and also the set I bought nothing worked.