I get asked sometimes (actually never) “should I crimp my ammo or not?”
That’s a complicated question. To crimp ammo is to simply apply pressure around the case mouth and squeeze the case against the bullet jacket. Some reloaders say it helps accuracy, and some say it deteriorates accuracy. The theory is that crimping ensures uniform neck tension with each crimp being the same from bullet to bullet. So did it make a difference?
All I can do is share my results so you can come to your own conclusion.
Using my go to accuracy testing load, Hornady 53 ELD match, and a Lee Factory Crimp Die… I loaded and crimped ten ELDs and then left ten un-crimped.
As we can see, there are definitely more flyers in the crimped ammo. The group is far more spread out and the mean radius expanded from .36 MOA to .58 MOA.
The crimp on my Lee is set very light. I don’t have a good measure of how much crimp is present, but the wings of the LEE FCD just kiss the cartridge. Even with such a “small” crimp, the group size opened up substantially.
Take it for what its worth, but if you found any interesting factoids about crimping that you have personally observed, sound off below!
I never crimp any of my ammo. Full length sizing is all and the bullet seats nice and snug.
Only ammo that needs crimping is for a revolver as the case seats on the rim, not the neck like a pistol..
Not exactly true. We can’t use such a definitive proclamation on the subject of crimping. Granted, ‘to each his own’ but when you consider the VIOLENT “bullet trip” that a semi-auto round takes in chambering…from the magazine all the way into the chamber, it WILL open your eyes for sure. Ask Patrick Sweeney. I can’t recall WHICH (there’s actually more than one in which it’s discussed) volume of the AR-15 books he’s published and the description he offers leaves nothing to be desired, and violent again, is a great word. More on Patrick Sweeney: I can honestly say with ALL the publications, helpful knowledge and advise from so many sources, specifically for AR’s…nobody comes close to what he has to offer the AR/firearms/gunsmithing world (certainly applies to me anyway). Consider the extraction FROM the mag where the bolt STRIPS the round then to be slammed in to the chamber at FULL STOP. All in HOW fast? As fast as you can pull the trigger, and we’re just talking about SEMI-autos ha ha ha…
It is worth noting that if you are reloading a cartridge with fairly stout recoil, a crimp is likely necessary to prevent the bullets from working forward under recoil and binding in the magazine, inducing feeding problems. Even if there is a slight loss of accuracy, reliability is still the most important feature of any firearm.