Try an 18 1/2 recoil spring. If it locks your slide back on the last round, it's the right one. The 17 main spring will probably reduce your trigger pull to around 4 1/2, maybe only five, but at least it'll help a bit. If it was my gun, I'd probably try a 20 pound recoil spring first, to see if it locked the slide back and if so, that's it. If you have any friends who know much about the 1911, I'd much rather you have him show you how to tweak that leaf spring and keep the 23 pound mainspring with the hardball loads. In that case, the 18 1/2 would probably be just right. By that I mean it would be better balanced for recoil.