Thread: Crimping and it's effect on accuracy.

Have a new rifle that already shoots 3/4" with a variety of 130gn loads, including one type of factory ammo (.270 dontcha know....). The Lee die set I acquired has a crimp die, I have always wondered if it would actually average out neck tension and runout, therefore improving accuracy.

Thought I'd toss the idea on here and see what pops up.......

Could maybe work, but you would need every case trimmed to the exact same length, otherwise you would have varying degrees of crimp, which would give more variation not less.

@Tentman

Hmmm I'm not an accuracy guru (maybe a nut but thats diffrent). There's a quite a few things that would possibly improve the accuracy of a particular load (case sizing technique, seating depth, runout etc) before I'd worry about neck tension, unless its a cartridge that is know for sensitivity to neck tension like 300BLK.

Having said that, if we're talking about the Lee collet crimp die, it doesn't need cases trimmed to length, its a smart design where the collar that does the crimping is pushed up by the case holder, there is zero thrust on the case itself. The neck size collet die works the same way, but against a mandel instead of the bullet

I wouldn’t crimp any bolt action rifle loads there is no point and it is in my experience slightly less accurate works the brass harder and therefore decreasing case life
I would crimp rifle loads for semi auto rifles
I would/do crimp pistol/ pistol cartridge loads for rifles
I put a very light crimp on my bpcr loads as the brass is not sized at all so the bullet is simply placed in with little or no neck tension
The light crimp is to just stop the bullet from falling out but can still be pulled out by hand if you wanted

https://youtu.be/wnZWv38cNKw

poohseventy shooting 3/4" now.......DONT CHANGE A THING..... one thing to try (if you dont do it already) as you are seating projectile rotate case 180ish degrees and continue seating projectile,by turning it you conteract any runout tendency of the press....had many try this then measure it with good results,as for crimping,it MIGHT improove ES by controlling burn but not something I would muck around with myself.

A lot of yanks swear-by-it, when all else fails, and it does seem to be about the Burn. But as Mickey Duck says, why bother, you've already attained what most hunters want

Hey, it's a hunting rifle. Don't try and fix what is not broken. A 2" group is fine for hunting out to 400 metres (further than most people shoot). Quit while you are ahead.

just adds more variables to fret about imo ... and 0.75 moa sounds just fine & dandy

Originally Posted by gundoc

Hey, it's a hunting rifle. Don't try and fix what is not broken. A 2" group is fine for hunting out to 400 metres (further than most people shoot). Quit while you are ahead.

Thanks Gundoc, my dear old Oberndorf Mauser Kurz (Sporter, made in 1921 but recently rebuilt) may not be as out of date as I thought, since it only shoots 1.5" groups (albeit with 125 partitions which are pretty hard to get to shoot in lots of rifles) Tee-Hee.

I have never crimped anything tho I have crimping dies.

With no experience in crimping anything...from what I have read it can be beneficial for accuracy in rounds that have to jump a long way to the lands(like a lot of factory ammo does)
If you are loading close to the lands probably no benefit.

Or at least that is my understanding of it haveing never crimped any of my ammo to test.

I have never noticed any difference with crimping high pressure cartridges (.308, .270, .30/06 etc). I have read about the potential of crimping, negative and positive, but never observed any difference myself in my experiments. I usually end up seating my bullets just touching the lands or just off, and I theorise that seating the bullet this way would over power any kind of mild effect crimping would have.

The only noticeable difference with crimping I have observed is with lower pressure pistol-type cartridges like the .44 magnum and .44-40 WCF, or the old .45-70. In these cases the higher pressure of a good crimp gives a more complete burn on certain powders (AR2205 and AR2207)
(The exception is black powder in the .44WCF and .44-70, in which crimping seems to have no effect, in fact you can slip-fit the bullet and it gets the same velocity.)

So I don't bother with crimping except for these last cartridges, for which it is mandatory.