Crimping in all its glory and ugliness

[iracecars4fun]

So i have been reading through the forums and have a fairly good idea but looking for a little confirmation.

I have been reloading for about 2 years now and have just read that crimping gave an improvement in accuracy, due to suspected increased bullet tension consistency now my questions are two fold

1. Bolt guns: now if i turn the case neck and seat the bullet precisely measured to .002" or so behind the lands and grooves of my rifling, i find it hard to believe that a normally seated crimped bullet will be more accurate than that. generally speaking, there are always exceptions!

2. Semi's : i just recently started to reload for my AR for hunting purposes. when i purchased the dies and ammo i forgot about a crimping die, so i do not have one. i have also been reading on the forums where people have been saying that crimping isnt exactly necessary even for semi autos. just keep an eye out for any shots that feel different.

im hoping that my understanding is accurate and that someone, with many years of reloading experience, can shed some light on any areas of misconception.

[E4for2]

If I ever crimp a rifle round,,this is what I use,,but lightly !!

[Snake Plissken]

I have used the Lee FCD which is a collet-type crimping die and at most it's a rather light crimp only because I have had setback in a trial run. You just have to try and see on your own if it's necessary. If you're loading for a bolt gun I see no reason to crimp. Just chamfer the mouth a tad and seat with good neck tension and a clean neck (I use a bronze brush).

[GunnutAF]

iracecars4fun
It really depends.

Bolt gun- is it a hard kicking Magnum? Or a mild recoiling caliber? Some bullets don't like crimping- I found match bullets in .224 hate crimping so I don't. Where non canleared bullets of .308 on up like it?

Semi auto's -My 30-06 I crimp as recoil will set the bullets back, 30-30 I crimp cause of mag spring and recoil will set bullets back. In My AR's it depends if it has a crimp groove -crimped, match bullets no.

[iracecars4fun]

well my bolt gun is a .30-06 but the bullets i use have no grove for crimping

[30 cal slut]

bolt gn...i don't ctimp

spicy AR loads...dillon taper crimp. i am told that you're less likely to get ino an over pressure situation with the taper vs roll crimp.

[GunnutAF]

iracecars4fun
Then it depends on what you want to do! If your cases give you plenty of tension press on. Though I've found some powders perform better with some crimp even with non grooved bullets. Granted I was only concerned with hunting accuracy- not match accuracy or super long range performance. :D

[iracecars4fun]

See thats where it can get interesting i use the same load, at least for now, for both hunting and long range shooting (600) yards, and perhaps long range hunting. so i am concerned with exceptional accuracy as well as durability (no loss in accuracy due to bumping the ammo or rifle or repeated shots.)

[markm]

iracecars4fun
It really depends.

This is absolutely it. You need to know your neck tension. There is no absolute answer for you based on someone elses experience.

It depends on your brass and dies. For bolt gun ammo, I don't need to crimp because I use a neck bushing die to get the right neck tension for the brasss.

Our most accurate ammo is a MatchKing in .223 that has a light LEE factory crimp on it. It'll hold half MOA or less out to 200 yards on low wind days.

[nineteenkilo]

This is absolutely it. [...]
Our most accurate ammo is a MatchKing in .223 that has a light LEE factory crimp on it. It'll hold half MOA or less out to 200 yards on low wind days.

This is nearly identical to some of my better loads. The Matchking is a hell of a bullet (along with everything else Sierra makes) and the Lee FCD is all I use for the most part.

[markm]

Yeah... I was thinking the crimp my be bad... but I wasn't going to take my FCD die out of my progressive to run matchkings... so they get the same crimp as every other bulk load...

Turns out to be really accurate ammo.

[iracecars4fun]

so whats the most effective way of determining if a crimp is needed? check the COAL of a few random rounds in a magazine after a few shots?

[markm]

so whats the most effective way of determining if a crimp is needed?

The most appropriate way is to use dial calipers to measre the OD of the empty case's neck. Then seat the bullet and measure again.

I'd say that the diff should be at least .002" for a gas gun... maybe .003"-.004"....

Too much more than that and you start deforming shit and getting bullet runout.

If you only have .001" in neck tension, the bullets might start moving back into the caseneck.

[tb-av]

The most appropriate way is to use dial calipers to measre the OD of the empty case's neck. Then seat the bullet and measure again.

I'd say that the diff should be at least .002" for a gas gun... maybe .003"-.004"....

Too much more than that and you start deforming shit and getting bullet runout.

If you only have .001" in neck tension, the bullets might start moving back into the caseneck.

Thanks for this... I knew there was something I didn't understand about crimping but couldn't figure what to ask.

[markm]

Run several cases to make sure you don't make adjustments off of one sample.