Just a note from personal experience.
I had a 70% failure to fire rate on two different ARs with the JP spring kit and some cheap steel ammo from Cabelas. MFS was the brand. I had a 100% failure to fire rate with Monarch brand from Academy. Putting a milspec hammer spring back allowed both to shoot the crap ammo but cost at least 1.5 lb. of increased trigger pull over the JP springs. The JP springs worked just fine with name brand ammo and my reloads with CCI 41 primers.
I had a 70% failure to fire rate on two different ARs with the JP spring kit and some cheap steel ammo from Cabelas. MFS was the brand. I had a 100% failure to fire rate with Monarch brand from Academy. Putting a milspec hammer spring back allowed both to shoot the crap ammo but cost at least 1.5 lb. of increased trigger pull over the JP springs. The JP springs worked just fine with name brand ammo and my reloads with CCI 41 primers.