cast bullets and crimping

[303carbine]

What affect does a heavy crimp have as opposed to a light crimp on a 45-70 cast bullet.?? Is accuracy affected to any degree?? Thanks,John............:coffeecom

[leftiye]

The crimp is there to stop a lever or auto from pushing the boolit back unside the case (causing high pressures), or a revolter from pulling the boolit out and jamming the gun.

As far as ignition, recent threads have said that crimp isn't a big factor, but that how heavy case grip on the boolit is, and how consistent it is are the big factors.

If a repeater (lever), then the ctg. length is about functioning through the action, and as long as the boolit stays where it should be, there is no effect (exept some bolt guns which will allow seating the boolit into the rifling). Single shots should be seated into the rifling and can be shot with little or no crimp and neck tension.

[cbrick]

Yes, what leftiye said.

Why crimp a 45-70 hard enough to deform the bullet? But in answer to your question, no, it shouldn't effect accuracy as long as it's not crimped enough to damage the bullet, it's just not necessary to crimp that much.

Rick

[Bass Ackward]

What affect does a heavy crimp have as opposed to a light crimp on a 45-70 cast bullet.?? Is accuracy affected to any degree?? Thanks,John............:coffeecom


John,

Depends. Crimp appears to be a pressure phenomenon and not a cartridge specific one. It is also magnified by powder speed obviously. It also is bullet design related. A light crimp over the end of a wadcutter can be much stronger than trying to crush brass into a lead drive band no matter how much crush you attempt. Then eventually you deform the bullet. But if that bullet has a long crimp groove, a heavy fold WILL make a significant difference " if " it is needed to improve ignition.

From my testing crimp "can have" significant effect on pressures up to 20,000 psi. From 20,000 to 24,000 moderate and above that very minimal results with case neck tension having more of an affect on ignition.

So if you are shooting a trapdoor, crimp might mean everything to you. But if you are cranking a Marlin to 460 Wby velocities, bullet movement is more the concern.

[303carbine]

Just back from the range with some very good results. I used a lesser crimp on the latest batch of 420 grain GC cast bullets and accuracy improved over the heavy crimped ones.The load was the same just the crimp was different and that tells me the crimp has something to do with accuracy, at least in my Marlin GS.8-)
The load I'm using is 40 grains of H4198 under a 420 GC cast bullet lit up with a Federal LR primer, I got to chrony this load and it clocked in at 1635 fps out of the stubby barreled Marlin.

[cbrick]

I used a lesser crimp on the latest batch of 420 grain GC cast bullets and accuracy improved over the heavy crimped ones. The load was the same just the crimp was different and that tells me the crimp has something to do with accuracy, at least in my Marlin GS.8-)

Sure, if the crimp is hard enough to damage the bullet. Damaged bullets will definitely affect accuracy. Just enough crmp to keep the remaining bullets from moving under recoil in the magazine. Any more crimp than this will not only hurt accuracy but will shorten brass life by over working it.

Rick

[303carbine]

Anyone who can post a target pic for me ,I would really appeciate it. Email me at :coffeecom deerslayer@shaw.ca:brokenima
Thanks a bunch

[drinks]

Just get a Lee collet type crimp die.
Makes a very narrow crimp ring at the case mouth, requires no crimp groove or canelure and is not critical as to case length.