Does Crimping effect bullet runout?

Muir

Well-Known Member
The short answer is No. It doesn't appear to.
I spent Christmas day loading 100 rounds of 300 AAC Blackout with Speer TNT 125 grain bullets. Using a Hornady Bullet Run out Gauge I ran the run out on each cartridge before and after crimping. The average runout was +/- .001 to .0015 inches. This didn't change with moderately heavy crimping -Which is to say it neither got worse nor improved with crimping. I used shortened Federal 5.56 brass that was FL resized, trimmed, had the case mouth flared to accept the bullet base, and then seated. The Dies were Lee and the press was my Forster. A Lee FCD was used to crimp.

As a further aside on the necessity of crimping properly, I read an astoundingly unscientific article on reloading for the 300 AAC Blackout by the NRA here in the US. The author reported poor accuracy using a taper crimp from the Redding dies he was pimping for the piece; writing off poor accuracy with bullets such as the Nosler 125 gain Ballistic Tip to the lack of a crimping groove. I have loaded these same bullets with identical loads as his but used a Lee FCD and got half MOA. Save the taper crimp for light loaded 45 ACP or 44 Special gallery loads...~Muir
 
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I use the Lee FCD on all my reloading, I load 300aac using a subsonic load of 3.4gr of Viht N310 with a 168gr cast boolit and it produces almost single hole accuracy (at 25m). Same with the 44magnum, my "indoor range" subsonic load of 4.8gr of TiteGroup or 6.5gr of NobelSport GM3 and a cast 200gr gives a very accurate load. I haven't any way of measuring runout but I'm very happy with the results from the FCD :)
 
My own findings are no, runout is not improved, nor particularly changed by use of the Lee Factory Crimp Die. Other techniques are used to maintain low case sizing & bullet seating runout. .... But, it does even out neck tension and that in simple terms aids pressure consistency. So all other brass and brass prep being carried out diligently, the nett result is usually improved consistent accuracy...and that is what I find, so I'm happy to continue using the Lee FCD.
 
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I should have premised the post by saying that I have heard both; that crimping somehow 'straightens' the bullet and improves run out and the opposite, that it ruins concentricity. Whether it is a benefit or not is a whole 'nuther subject. While the use of crimping is gaining acceptance, it is still frowned upon by a lot of people as something that destroys accuracy and ruins the cartridge case.:rolleyes:~Muir
 
I should have premised the post by saying that I have heard both; that crimping somehow 'straightens' the bullet and improves run out and the opposite, that it ruins concentricity. Whether it is a benefit or not is a whole 'nuther subject. While the use of crimping is gaining acceptance, it is still frowned upon by a lot of people as something that destroys accuracy and ruins the cartridge case.:rolleyes:~Muir


I have done a lot of testing with crimped and uncrimped rounds and have found the crimping to half my es and sd. I use a device to reduce runout to under a thou. Then I will crimp the round afterwards. The runout does not change at all- I check every round. I crimp all my loaded rounds as I find my groups are smaller and the consistency gets better.
 
I have done a lot of testing with crimped and uncrimped rounds and have found the crimping to half my es and sd. I use a device to reduce runout to under a thou. Then I will crimp the round afterwards. The runout does not change at all- I check every round. I crimp all my loaded rounds as I find my groups are smaller and the consistency gets better.
Holy Smokes! You check every round you load?? That's devotion! I just checked these because it was a -8F cold, snowy Christmas day and I had five pounds free time and a half an ounce of curiosity. That concentricity gage hangs on the wall of my reloading room and I just happened to look up and see it there!

I agree with you about the reduced ES and SD 100%. I have gone to great lengths to prove it, with a number of weapons, though ammo makers have always known this; which is why they put some form of crimp on their ammunition. I also crimp everything. I will have crimp dies custom made if Lee doesn't already offer it. Two of the greatest myths hovering around the bullet seating aspect of reloading: You must seat to X-thou from the lands, and crimping has no value. ~Muir
 
Holy Smokes! You check every round you load?? That's devotion! I just checked these because it was a -8F cold, snowy Christmas day and I had five pounds free time and a half an ounce of curiosity. That concentricity gage hangs on the wall of my reloading room and I just happened to look up and see it there!

I agree with you about the reduced ES and SD 100%. I have gone to great lengths to prove it, with a number of weapons, though ammo makers have always known this; which is why they put some form of crimp on their ammunition. I also crimp everything. I will have crimp dies custom made if Lee doesn't already offer it. Two of the greatest myths hovering around the bullet seating aspect of reloading: You must seat to X-thou from the lands, and crimping has no value. ~Muir


My home made concentricity guage / straightener is very quick. About 5-10 seconds does each round. I only handload 223 so it isn't all that time consuming. This machine is set up for 223 only. There's maybe only one in ten rounds that actually need straightened. The rest I just go through and any over a thou of runoff I give them a go. I also use fairly light neck tension (1 thou) which leaves stress on the neck to the minimum. Here's a picture of the device:
9023155796f140a76f35dfc8d01cef2c.jpg
 
Muir and I had a discussion about this last year. I am a big believer in the crimping, and the Lee Factory Crimp die.

Most people would think that with the huge pressures, that the resistance of the crimp would be miniscule, but it is not, and here is why:

In the first few microseconds of powder burning, the pressure spikes, then decreases as the bore volume increases with the acceleration of the bullet, because pressure decreases directly with the volume increase ( linearly ). And pressure is the force on the bullet which is accelerating it down the bore.

If one bullet is loose, it will be pushed out by the primer ignition, into the lands, changing the case volume and moving the pressure spike in terms of time and position in bore travel. Then the tight one will be closer back. Result = more variation in MV shot to shot, larger ES and larger groups.

Accuracy and precision of the rifle and loads means consistency, repeatability. In ammunition, that means consistent and uniform brass of the same volume, the same primers, the same lot of powder charged to the same weight, bullets seated to the same depth in case necks of the same tension. The easiest means of getting close to identical neck tension is a proper Lee Factory Crimp.
 
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Southern is100% correct. While this is going on, and as a part of this, the burning rate of the charge in that particular case is being established, which also influences pressures.~Muir
 
Have you measured run out of the bullets themselves?
I can't see how a narrow banded crimp would affect the run out of a seated bullet in any way

if it was crimping along a much wider range of the neck I could see it.
 
Agreed. That is what I have told people, myself. Unless the crimp was the ONLY thing holding the bullet into the neck, it won't defeat the alignment, or misalignment held by the neck. If it does, it's really not to a measurable degree. As to the bullet runout, do you mean an eccentricity of the bullet proper around it's center line? Oh God! What a nightmare of measuring and fussing that would cause!!:scared: I don't unless they are cast bullets dropped from a two piece mold. Otherwise I trust to The Almighty. (or Hornady, Speer, Berger, Barnes, Sierra, etc...:D)~Muir
 
I've got s question that needs answering.you could try it out for me having the kit.seat a bullet in the case.take out and check runout.put case back in the seater exactly how it came out. Spin it 180 degrees and and run frew the die again and check the runout and see if it's halved.i had a tip about doing this when seating the bullet.i do it all the time now as my ammo seems really really consistant.would like to here your findings.regards swaro.
 
Swaro; I did this already. The results were inconclusive and dependent on the set up used. I ran this last fall through a Lee "O" frame, my RCBS A1 and the Forester Co-ax. Shell holder fit to the rim was important except in the Forster... in fact, the Forster had the least run out of all of them to start; which is their claim to fame. My old A1 had the largest effect but I think this was due to the unit being 40 years+ old and at the time I had the press set to tilt rearward. Now, all that said, I shot very fine groups with ammo produced in that press and still do. My 7-08 is consistently half MOA accurate and I use that old RCBS exclusively -tho now set vertical.

As to concentricity: A buddy of mine related to me accidently tipping over a factory 338 Lapua round and as it rolled across his kitchen table the bullet tip woggled, visibly out of round. On further inspection, most of the ammo was out of round yet he was banging an 24x36" steel plate at 1600 yards with it. My own story centers around my 9.3x57. When I got my Husqvarna 9.3 I ordered some Hornady (shudder!**) dies and got to work. I made up 40 rounds and went to the range. Imagine my surprise when half the rounds refused to chamber. On close inspection, these rounds had the bullets set at such an angle that they refused to fully seat in the chamber. In fact, all the rounds had visibly canted bullets. The ones that chambered, i shot. The others i took home and pulled the bullets. So how did these crooked bullets shoot? At 50M with open sights, all the 6, three shot groups I fired were ragged holes or near it. I shoot for concentricity, but I no longer go too crazy about it. I started flaring case mouths with a Lee Universal Case Flaring die when seating bullets in the Hornet. There was no longer any bulge from a mis aligned flat-base bullet in that thin neck. I later continued it to all my loads because the bullets -boat tail or flat base- seated very smoothly with little effort. I think that helps over all. but I've done no real definitive tests. Like rotating the case, It probably helps so I stick with it.~Muir

(** These dies were horrible. The tapered expander was drilled far off center which caused the necks to be pulled out of round as the case was withdrawn from the die.)
 
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Hi muir, please could you try this method Ive mentioned again, I got this tip off one of 1967 spuds videos on youtube, I assume spud did try this out himself to know this, whatever the results I wont change my system now as my ammo shoots superb groups
 
Hi muir, please could you try this method Ive mentioned again, I got this tip off one of 1967 spuds videos on youtube, I assume spud did try this out himself to know this, whatever the results I wont change my system now as my ammo shoots superb groups
Sure. I'm loading 308 tonight. I'll give it a run. I won't flare the case mouths as I normally to. Flat base or boat tail?? I can load either. Not to diminish Spud's contribution to your small groups, but the technique is well known and has been for decades. I used it when I was a kid tho I had no way of measuring the run out.~Muir
 
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Bolt tail,6.5 cal 140gr amaxs or 30 cal 168gr amaxs or 155gr smk (2156) palma, I would imagine the longer the bulket the more run out you get.
 
View attachment 64807 had a quick zero check.168gr amaxs in my 308.its a 3 shot group at 100yds . just Wasting ammo if I fire anymore.photo is on its side.was a left to right wind.0.256 of an inch.centre to centre.who needs a 6mm br :D
 
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