Position of crimp in crimp groove

[thegreatdane]

Gentlemen,

In a generous crimp groove, what OAL. Do you crimp to? More specifically, I mean, do you crimp to the shoulder or to the rim?

Here's a picture:
http://i25.photobucket.com/albums/c66/drobberson/Forum/20121210_202459-1.jpg

I'm curious as to how this effects consistency.

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[Harter66]

Pick a place that fits , feeds, and is accurate shoot them up.

[thegreatdane]

I have been. They shoot nicely; however, I am chasing increased consistency over the chrony. Trying to bring down the extreme spread and standard deviation. Does anyone have a crimp position theory?

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[brassrat]

That crimp looks too heavy to me, is that bullet crimp groove that deep to begin with? What weight bullet?

[thegreatdane]

It's a really deep groove. 130 gn 38 special. The crimp is admittedly firm, but will be fired in a snubby.

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[geargnasher]

Ok, my experience has been that consistency comes from having first CONSISTENT and secondly ENOUGH case tension holding the boolit. Crimp is just icing on the cake, not the meat and potatoes of a solid, repeatable revolver load.

As far as where to crimp, for revolvers I crimp what looks like about halfway between the two shown in your pic, and roll it tight against the boolit to minimize split mouths from over-worked brass. For tube-fed rifles, I tend to just tuck the case mouth right under the "top" of the crimp groove, and don't worry about folding it all the way to the bottom, since it has to hold against compression in the magazine rather than pull in the cylinder as is the case with revolvers.

For pistol-caliber rifles that share ammo with the revolvers, I have had custom-designed boolits, or in one notable case use a Lee boolit, all having very shallow crimp grooves so that I can fold the brass tightly to the bottom of the groove AND have the case mouth under the very top to prevent telescoping in the tube mags, the best of both worlds. The shallow crimp groove designs prevent overcrimping and overworking the case mouths. Many of the typical revolver boolit designs have crimp grooves that are, in my opinion, excessively deep and attempting to roll the mouth all the way to the bottom and keep the brass tight against the bottom of the groove can damage the boolit upon launch, cause inconsistencies in pressure required to break the crimp, and wears out the brass.

Gear

[williamwaco]

For revolvers only, I seat the bullet to the exact top of the crimp groove. Just slightly deeper than the bullet on the left.
I would then crimp about half as much as you did.

I have not seen a bullet with a crimp groove that deep, I think it is too deep. My crimp method would not allow the case rim to contact the bullet. I don't think that would accomplish anything but shortening the case life. I am not sure exactly what I would do with that bullet.

I might even do something like the bullet on the right. I don't like the looks of it but you could place a modest crimp just into the bottom of the crimp groove.

like geargnasher said, less crimp means longer case life.

PS: firing it in a snubbie? The cartridge and or the crimp doesn't know the difference.

.

[hithard]

That's alot of crimp...hope you never have to pull any of those boolits.

Only thing you have to do is just break the plane of the boolit diameter when crimping. If the boolit tries to slip down it will get hung on the lip of the crimp groove. This takes alot of pressure, make a dummy round and then try and push the boolit into the case past the crimp groove. You'll see what I mean. Then just take a hammer and try and whack it in there. Just remember to do this with a dummy round.


Oh, and the boolit on the left is the way to go.

[geargnasher]

One more thing to note, the case on the right in the pic looks like it buckled a bit from too much crimp pressure after the mouth "grounded out" on the crimp groove's shoulder. Like I said, I'd split the difference between the two and give JUST enough crimp to have brass contacting lead firmly with no air underneath. In other words, just like the cartridge on the left but with the boolit not seated as deeply. Be sure and seat/crimp in two operations or it will be impossible to get the brass to fully contact the shoulder of the groove with a modest crimp.

Gear

[runfiverun]

i'd seat the one on the right a little deeper and keep just that little bit of roll.
i do like gear does and crimp up top with the lever guns and just enough to allow my finger to drag the case without a hitch.
i will stay on the long side in a revolver,if i am not sharing ammo with my leverguns.

i will go so far as to champher pistol cases to make thing go smoother [i clean primer pockets,wash and tumble my brass, and cast for 22 caliber rifles too]

the crimp is not the answer to evening out velocity deviations.
neck tension,and consistent ignition is.

[44man]

I am going with Gear 100% on this.
Way too much crimp. I see no case tension at all and crimp will not help at all.
Boolits too soft and the wrong expander. You will do nothing but ruin the boolit trying to escape that crimp. I will bet fired cases still have crimp on them. Brass makes a nice size die!

[gwpercle]

I seat mine like the one pictured on the left, so the bullet can't be shoved deeper into the case .

[**oneshot**]

I use a light roll crimp just above the bottom of the crimp groove.

[thegreatdane]

Thanks for your responses fellas.

Previously, I've gone with the left one. The reason there is so much crimp is that I was reaching for the bottom of the groove. I won't load 'em that way.

Interestingly enough, I found a good way to achieve the best of both worlds. I seated a boolit to the length pictured on the left, applied a medium/light roll crimp, and used light taps on an inertial boolit puller. This brought the boolit forward until the crimp met the contours of the generous groove. I'm hoping this satisfies both intentions: 1) eliminating recoil elongation 2) consistent ignition. I do understand that there are other contributing factors to consistent ignition; but a little extra consistency can't hurt. Also, I was more concerned with growing OAL than setback due to lightweight revolvers.

I'll let you know if my theory plays out.

[cbrick]

This is something I have tested extensively. Gear - R5R and 44man are right on the money.

The crimp will do nothing to improve the standard deviation or extreme spread as was your stated goal. The crimp will only "aid" in preventing bullet creep. What will help you acheive your goal is very consistent neck tension. That means all brass from the same lot and fired the same amount of times.

I have posted this in several threads in the last few years, seems it could be a benefit to post it again.

Rick

Crimp testing

FA 357 Mag 9”
RCBS 180 GC Silhouette @ 192 gr. (WW HT @ 18 BHN)
H-110
Winchester brass
CCI 550 primer
Temp 70 Humidity 38%
All chrono tests 10 shots

1> My normal profile crimp, second firing of WW brass, Carbide die sized
E.S. 30
A.V. 1518
S.D. 9

2> Roll crimp, second firing of WW brass, Carbide die sized
E.S. 30
A.V. 1520
S.D. 9

3> No crimp, second firing of WW brass, Carbide die sized, very slight bell
E.S. 30
A.V. 1528
S.D. 9

4> Light profile crimp, virgin WW brass, not sized, not expanded, slight bell only
E.S. 26
A.V. 1532
S.D. 8

5> My normal profile crimp, virgin WW brass, not sized, not expanded, slight bell only
E.S. 26
A.V. 1536
S.D. 8

[stubert]

Do you have a photo of just the boolit?

[cbrick]

Do you have a photo of just the boolit?

55735

Rick