How Much is To Much Crimp?

[joestefano]

Can you apply a factory crimp to much? I am using a Lee Factory crimp Die on my 40sw. the case measures at .423 my crimp is at .414. what if any is the danger of to much crimp?

[GrumpyOne]

Too much crimp will undersize the bullet, causing it to skip down the barrel. Accuracy will suffer, you might even start seeing soem keyholing. When crimping an auto round, crimp only enough to remove the bell/flair that you put into the case when seating the bullet. It should be straight walled, not squeezing into the bullet.

[Action Pistolero]

The rule of thumb is measure the case thickness and double it. Add bullet diameter. Crimp the case mouth .002 to .003" less than your figure. This will fix most feeding problems and not deform the bullet in any way.

[Sarge]

I will add that too much crimp can actually lessen neck tension and lead to setback.

[joestefano]

I will add that too much crimp can actually lessen neck tension and lead to setback.

What is "setback"?

[Jman]

helpful links I found with a simple search..

http://www.brianenos.com/forums/index.php?showtopic=97653&st=0&p=1117163&hl=%20setback&fromsearch=1entry1117163

http://www.brianenos.com/forums/index.php?showtopic=98108&st=0&p=1121663&hl=%20setback&fromsearch=1entry1121663

http://www.brianenos.com/forums/index.php?showtopic=63951&st=0&p=743289&hl=%20setback&fromsearch=1entry743289

HSMITH's posts in the last link are excellent.

[G-ManBart]

Can you apply a factory crimp to much? I am using a Lee Factory crimp Die on my 40sw. the case measures at .423 my crimp is at .414. what if any is the danger of to much crimp?

.414" is way too much crimp. That will likely cut/mar the jacketing and can cause poor accuracy. It can also allow the case to move too far forward in the chamber. .40S&W headspaces on the case mouth, so you need some of it to be available to contact the front of the chamber.

Setback is when the bullet is pushed deeper into the case when it hits the feedramp (being pushed by the slide). Setback increases pressures and, in some combinations, can cause them to exceed pressure limits, blow out cases etc...it's a bad thing.

.420" is pretty much the magic number for .40, give or take a thousandth or two for different thickness brass and/or chamber dimensions. R,

Edited June 7, 2010 by G-ManBart

[G-ManBart]

Too much crimp will undersize the bullet, causing it to skip down the barrel. Accuracy will suffer, you might even start seeing soem keyholing. When crimping an auto round, crimp only enough to remove the bell/flair that you put into the case when seating the bullet. It should be straight walled, not squeezing into the bullet.

Yeah, not so much

If you run a heavy crimp and then pull the bullet, you'll find that it's simply got a line where it was squeezed by the case. That one tiny area will be undersized, but the rest will be the same, so it's not going to cause the bullet to "skip down the barrel".

If the crimp is so heavy that it cuts the jacket, it won't be an undersized bullet, but accuracy will still suffer, and it's also possible to get inconsistent headspace (likely actually) because the case mouths aren't making contact with the front of the chamber.

All of that adds up to poor accuracy, but the bullet isn't skipping.

The last time I pulled a factory bullet (AA&A 147gr JHP, 9mm) it had a very heavy mark on the bullet from the crimp they used. They also happen to be the most accurate in my M&P, so I'm pretty sure it's not undersizing the bullet...but it's not heavy enough to cut the jacket. R,

[Putty]

i run .418 as I was getting vertical spread with MGB's. Recrowning the barrel may have had something to do with the fix also.

[GrumpyOne]

Too much crimp will undersize the bullet, causing it to skip down the barrel. Accuracy will suffer, you might even start seeing soem keyholing. When crimping an auto round, crimp only enough to remove the bell/flair that you put into the case when seating the bullet. It should be straight walled, not squeezing into the bullet.

Yeah, not so much

If you run a heavy crimp and then pull the bullet, you'll find that it's simply got a line where it was squeezed by the case. That one tiny area will be undersized, but the rest will be the same, so it's not going to cause the bullet to "skip down the barrel".

If the crimp is so heavy that it cuts the jacket, it won't be an undersized bullet, but accuracy will still suffer, and it's also possible to get inconsistent headspace (likely actually) because the case mouths aren't making contact with the front of the chamber.

All of that adds up to poor accuracy, but the bullet isn't skipping.

The last time I pulled a factory bullet (AA&A 147gr JHP, 9mm) it had a very heavy mark on the bullet from the crimp they used. They also happen to be the most accurate in my M&P, so I'm pretty sure it's not undersizing the bullet...but it's not heavy enough to cut the jacket. R,

Bart, I pulled some plated bullets that I had bought for the brass (38 super). They were crimped so heavy, that the tail end of the bullet was sometimes as small as .348. I would think that this would be undersized. I don't know what machine they were made on, but the way they were made, the only part of the bullet that remained .355 was from the crimp up (they were Trun Cone bullets, and there was maybe 1/8" or less of .355 diameter from the case to the start of the cone), they looked like a mushroom when pulled, bigger at the top than the bottom. I did shoot a couple, couldn't hit the broad side of a barn with them. And, I didn't really mean "skip" and you know it! I meant more like bounce or wobble!

I'll see if I can't find some of them and take some pics...I gave most of them away, as some were ok to re-use.

Edited June 7, 2010 by GrumpyOne

[G-ManBart]

Bart, I pulled some plated bullets that I had bought for the brass (38 super). They were crimped so heavy, that the tail end of the bullet was sometimes as small as .348. I would think that this would be undersized. I don't know what machine they were made on, but the way they were made, the only part of the bullet that remained .355 was from the crimp up (they were Trun Cone bullets, and there was maybe 1/8" or less of .355 diameter from the case to the start of the cone), they looked like a mushroom when pulled, bigger at the top than the bottom. I did shoot a couple, couldn't hit the broad side of a barn with them. And, I didn't really mean "skip" and you know it! I meant more like bounce or wobble!

I'll see if I can't find some of them and take some pics...I gave most of them away, as some were ok to re-use.

I should have been more specific since the OP didn't say what he was loading. Jacketed won't turn into undersized. With lead and plated (essentially the same) I guess it would be possible to squeeze them enough to undersize them a bit, but I'd think they'd have to be pretty soft. R,

[GrumpyOne]

The ones I'm talking about were very soft!