Crimping and neck tension

[justinp61]

If the rifle I'm loading for was a bench gun, I wouldn't try the crimp. This rifle is my magazine fed coyote/groundhog gun and will get beat around. Currently loads are running .004" interference fit on the necks but not much of the bullet bearing surface is in the case.

If I have time to shoot today, I'll shoot a couple groups with crimped and uncrimped.

 

[schooney57]

Loaded up 50 rounds for the 22-250 and set up my Lee crimp die for a light crimp

Crimp on the left, no crimp on the right.
View attachment 417355

 

[Mikecr]

In my mind mind, mere shaping of outer case mouths to counter their chamfering is not crimping into bullets or changing bullet hold.
That is, if the loaded case mouth ID does not rest below cal diameter, then the neck ID is not crimped.
So that outer shaping, apparently coined a taper crimp, seems but another reloading misnomer.
Like referring to loaded ammo as 'bullets', or a cartridge as 'caliber', or a nose datum point as the 'ogive', or neck interference as 'tension', etc..

It's nowhere near the same as actual crimping of mouths into bullet grooves, where bullets are then hooked into position until necks expand enough to clear that. The purpose of this being to keep bullets in seated position throughout recoil and hard chambering.
And this would delay bullet release for sure.

I wouldn't suddenly crimp necks into bullets while at a max charge.
But taper crimping as described would likely have no affect, as the neck ID is the same whether outer mouth shaping is applied or not.

 

[Mikecr]

I threw this pic together to illustrate tapering mouth onto bullet bearing -vs- an ugly lack of taper.

I guess it wouldn't hurt anything, provided this action does not interfere with precision setting of CBTO.
But I doubt that you could see a result of this across a chronograph.
The reason I say that is because case mouths are thinner and wouldn't grip with significant force relative to the rest of full thickness neck.
Also, the down-shaping of case mouths would not hold over time, as this sets an outward springback bias to the mouths.
Brass counters last sizing direction over time (a few days, few weeks, few months), some percentage, where it is free to do so.

 

[Mikecr]

In contrast, an actual crimp, into bullet groove, is a whole different game. Yeah, I'm bored at the moment..

Here, tension is still overcome by pressure to release, but the bullet is also hooked by the crimp.
Instead of the bullet swingin in the breeze with ANY neck expansion, it cannot release until the neck has expanded enough to release the hook. That's a delay of release, and you would see it across a chronograph.

 

[Pdvdh]

When I crimped bullets for use in my AR-15, the bullets were also deformed inward under the crimp. How do I know? I pulled bullets and could see the deformation in the bullets.

These crimped bullets still shot with much better precision than the same exact shell, load, and bullets, that were not crimped.

Call it anything you want, in some instances, precision improved 40%.

Gotta ask the question Mikecr. Have you ever crimped a bullet and compared the precision of the crimped bullet in your rifles, to the same axact load uncrimped?

More than one knowledgeable reloader has, and they typically state crimping never degraded precision. Hammer bullets experimented with crimping in the past, for example. And have stated they found that crimping caused no degradation to precision.

 

[338 dude]

This is for a 6mm arc in an ar platform. I have bushing dies and I crimp, didn't know if I would mess up neck tension and mess up my loads.

Running a six arc in my AR and I don't crimp

 

[Dmagna]

Running a six arc in my AR and I don't crimp

I just started doing it, might go back to not crimping.

 

[Varmint Hunter]

Gotta ask the question Mikecr. Have you ever crimped a bullet and compared the precision of the crimped bullet in your rifles, to the same axact load uncrimped?

I have made direct comparisons on several occasions. I have also compared crimping (FCD) in a relief groove vs against the bullet shank. The only thing that I have found, definitively, was that the outcome was not predictable. I shoot all loads for group at 400yds and checked SDs with a LabRadar. Some loads improved with crimping, some noticeably degraded and others stayed within the realm of normal variabilities. Most of the time I completely avoid crimping because it introduces another variable. I do crimp 458SOCOM and 45-70 ammo. I do not crimp any .223 ammo for my AR because it didn't prove to be necessary. I have found that there is more than sufficient neck tension to keep bullets in place and crimping didn't seem to improve anything. However, mileage varies and we all tend to load based on our past experiences. Crimping is just another of the many variables that may, and may-not, improve the performance of reloads.

 

[Mikecr]

Gotta ask the question Mikecr. Have you ever crimped a bullet and compared the precision of the crimped bullet in your rifles, to the same axact load uncrimped?

More than one knowledgeable reloader has, and they typically state crimping never degraded precision. Hammer bullets experimented with crimping in the past, for example. And have stated they found that crimping caused no degradation to precision.

No, I don't crimp case mouths.
But when someone explains HOW/WHY 'taper crimping' offers potential, I will consider it. That's for sure.
Until then, I'm left with my own reasoning.

You see I don't care at all about what people do.
Instead, I seek truths -regardless of what people do.
So when someone says [this helps], with [this is how & why it helps], then I'm all ears. And I always appreciate that.
Otherwise, I only notice to try and figure out what's going on. To close in on truths.

 

[bamban]

If crimping helps precision, every benchrest shooter will be all over it. I tried crimping on hammers, not going there any longer. To have any crimp consistency, cases must be trimmed to the same length. The nature of the beast.

My story I am sticking to it. YMMV..

 

[justinp61]

I set up and did a little shooting this afternoon. Two three shot groups each of crimped and uncrimped. I shot one round that was crimped a lot, the first one I crimped, after crimping it I backed the die off and snuck up on the crimp. After the waste load I shot the rounds alternating between crimped and uncrimped, waiting three minutes between each shot. The shooting was done at 200 yards off a bulls bag and rear rest, the rifle is in a factory plastic Savage stock, ready to shoot it weighs nine pounds three ounces.

The two uncrimped groups averaged just over 2 1/8" c to c, the two crimped groups averaged 1 3/8" c to c. I'll revisit this later and see if the results repeat.

 

[Lefty7mmstw]

It sounds like a lot of crimping is done to settle down bad loads. I've played around with the 300win and 338win using Hornady pills (rem pills also in the 300win) and the only thing it did was make me trim every firing as otherwise after a firing or two I'd bulge the crimp. The 1/2 moa accuracy on the Hornady pills and slightly sub moa accuracy on the remmy pills remained the same.

I will crimp on my 405 and 375 as there's enough recoil to move bullets otherwise, plus I've got to get rid of the bellmouth on the 405. I also crimp pistol rounds mainly for the same reason but with the 40s&w you have to have certain dimensions or you aren't going to feed and go into battery. I decent taper crimp combined with sizing accomplishes that well.

 

[Pdvdh]

No, I don't crimp case mouths.
But when someone explains HOW/WHY 'taper crimping' offers potential, I will consider it. That's for sure.
Until then, I'm left with my own reasoning.

You see I don't care at all about what people do.
Instead, I seek truths -regardless of what people do.
So when someone says [this helps], with [this is how & why it helps], then I'm all ears. And I always appreciate that.
Otherwise, I only notice to try and figure out what's going on. To close in on truths.

Thanks for responding.

Ideas, notions, theory, conjecture, and speculation about cause and effect subject matter remain hypothetical in nature until tested. By definition. Truth generally requires confirmation through testing. Which is why I asked.