Neck Crimping

[baydog]

Hello. does anyone crimp the neck of the case to the bullet to help get a more consistent pressure build / bullet release or does everyone crimp because you own a semi auto or a lever action type gun?... I'm finding that it's helping me tighten my groups a bit and the only thing i can figure is that by crimping it is giving the bullet a more consistent release because the pressure is more even on each bullet release??

Thanks

baydog

 

[Bullet bumper]

It can work like that but in many cases the improvement is also related to lack of neck tension to start with. If the bullet is not secure , crimping will help make it more secure .
Sometimes bad projectile seating can be made better by the crimp die .
In an auto it is a good idea due to the greater slamming inertia of the bolt and more fierce feeding .
In a big recoiling rifle it may be required to prevent projectile movement of the rounds in a magazine .
However generally in bolt actions with smaller cartridges it is not required if an adequate neck tension is applied by the dies in the first place .
Once you crimp a non cannelured bullet you put a groove in the jacket which can upset the lamina flow and cause a slight extra shock wave on the bullet which will increase drag .
So in a long range bolt action with custom dies , custom chamber and expensive high BC jacketed bullets that give excellent concentricity to the seated bullet why would you then crush the bullet jacket ?
Slaming away with an auto at 100 yards at watermelons , well it would not be an issue .
Crimping has it's place and in certain circumstances can fix a few reloading problems but not the best way to load precision target ammo for a single fed bolt action .

 

[Lefty7mmstw]

As bullet bumper has said, crimping has it's purpose.
That said, it is one more variable to contend with when assembling ammo. If your necks aren't perfectly concentric, it can accentuate run-out; if your case lengths aren't perfectly equal, it can enlarge bullet pull variations.
Basically do it if you have to... 44mag., 405 win, 416 rem, etc. would get a crimp. 9mm, 45, 40 s@w would get a mild taper crimp. Most bottleneck cartridges that won't detach a retina used in a bolt or single shot need no crimp. Some are on the bubble like the 375; I've crimped ammo and left some un-crimped; it makes little difference unless I'm holding on to lead bullets. The lead pills need a crimp.

 

[baydog]

Thanks Bumper and Lefty. I tried it on my 7 mag that i have a lot of brass for and it seems to tighten the groups up a bit at 100 yards but thats a gun that i have a lot of brass to monkey with. This 300 rum, new nosler brass can be almost $2 a piece. i don't think i want to be sacrificing a lot of brass to find out that it isn't that much difference in crimping or not crimping. I'm in the same boat with my 240. I found out that it was cheaper to buy loaded factory weatherby ammo than it was to buy brass only...Didn't quite understand that one but thats the truth...Thank ya'll for your help..Oh yea Lefty, suppose to go pick up my 300rum today from having muzzle brake installed. It took longer to have that installed then t did to save the money to buy it and have it shipped. I bought it a month or more ago and haven't been able to fire it yet because of having brake installed...Still know what it feels like to be a kid waiting for Santa Claus !! gun)

 

[Bullet bumper]

If crimping is improving groups and you don't actually need to crimp then I would look at increasing neck tension from your neck sizing die or if that is already quite adequate , changing powder to a slighly faster powder .
Also I would check the bullet runout after seating to see if the seater die is doing a good job .
Another thing I don't like about crimping , especially factory type crimps is it works the end of the case more and work hardens it . That increases the chance of neck spliting . I always find that softer necks shoot bettter than hard necks in my bolt guns but that does not mean for sure it wiil do the same thing in all .

 

[morcey2]

I crimp the hand loads for some of my rifles and find that it does help. The caveat is that most of the rifles I shoot are sporterized milsurps that have the original military barrels. They usually have "generous" chambers and leades that are long enough that I can't seat the bullets anywhere near the lands.

For example, I have an M44 Spanish Mauser (8x57) that my dad gave me that would shoot 3" 5-shot groups uncrimped, but that dropped to 1" crimped. I get the same type of results with 2 7x57 surplus rifles, one Mexican 1910, the other Dominican republic. The DomRep one has a slightly under-length chamber (almost closes on the Go gage) but still has on oversized throat. To get new brass to chamber easily, I have to resize it with a 0.005" feeler gauge between the case head and the shell holder.

Lever action (or anything else with a tubular mag): Get a bullet with a cannelure and roll or factory crimp in the cannelure.

Semi-Auto: Probably should be crimped, but I know quite a few people who don't and it works fine.

For a bolt-action rifle with a normal chamber and leade length, crimping shouldn't be necessary with proper neck tension and a reasonable jump to the rifling. I have a 257 roberts that I had built on a Yugoslav mauser receiver that does 1" groups at 200 yards with 115 gr Nosler BT uncrimped and 0.020" off the rifling, but that group size more than doubles with the crimp. That's what I expected, but I wanted to experiment with it anyway.

Matt

 

[Bullet bumper]

The thing is that if you work up a load with a crimp and then don't crimp , it is going to change things. If you work that load back up without a crimp it may shoot better than the original crimped load .
Just swapping back and forth between a crimp and no crimp is not the best way to compare the two because the load has been tuned for only one .
The only good way is to work up two separate loads , one crimped and one not and get them shooting the best you can and then see which one shoots best . You could still end up with no clear winner though as far as accuracy goes . However if the use of the ammo does not require a crimp and the accuracy is equal or better in the non crimped round then I would prefer the non crimped ammo for reasons other than accuracy. Avoid a crimp if you can .
I don't think it's got anything to do with the type of action or the chamber . I think it is related to changes in neck tension , pressure curve changes and seating concentricity changes . I have a Mauser that shoots well with uncrimped ammo but then again I have never tried crimping in this gun either .