When we talk about crimping straight wall rimless pistol cases* many think that it is necessary to crimp the case into the bullet in order to hold the bullet securely in place. While crimping can give some security to the 'hold" it is not necessary and correct resizing will allow the bullet to be held snugly by case tension alone. Remember straight wall pistol cases 'headspace' off the case mouth and too much crimp may allow the cartridge to seat too deep so that the bullet engages the rifling. This can prevent the slide going fully into battery leading to failure to detonate or potentially dangerous detonation while the slide has not fully closed.
In addition to feeding issues and dangerous detonation over-crimping coated bullets (non jacketed) will lead to poor accuracy as the relatively thin coating is partially scrapped off the bullet during its exit from the case during firing causing the bullet to loose its integrity and perfectly spherical shape. Further, now that the coating cannot protect the lead core, lead will be deposited in the barrel during firing with successive shots stripping more coating and building up the lead fouling even further.
To properly seat your bullets turn down your crimp die so that it just straightens out the bell/flare and if you really feel the need to, give it only a light 'kiss' of crimp. It's pretty hard to look at the finished cartridge and tell if its crimped too much so it's necessary to check
Check Your Crimp
To check your crimp use a bullet puller to pull a loaded round and look to see if it has evidence of an indentation in the bullet. A correctly seated bullet will show no sign of indentation.
|An over-crimped bullet showing pronounced indentation|
|A pulled bullet correctly crimped showing no evidence of indentation|
Now once you have it just right you need a further test to make sure it chambers well in your pistol. Remove the barrel and drop the cartridge in to the chamber. If it fits well you'll hear it "clunk" and it will sit just flush or just under the barrel hood. Alternatively use a case gauge to check your loaded rounds are in spec.
Now clean the all the crap out of your barrel and hit the range with a batch of well made rounds and enjoy.
*Same principle for 357SIG but the case head-spaces on the shoulder.