Too tight crimp would affect accuracy?

[Buddhabelly]

I've started on my 9mm loads. Made 40 counts of the 124 Montana Gold at 1.135 with 4.3 Gr of W231, much like many of the people here from another thread. I shot the 40 rounds this morning. Functioned fine. Kinda hot. I shot them through my CZ75 SP-01, BHP, and G19.

I noticed that the accuracy was fairly disappointing.

I pulled apart one cartridge using a bullet puller and noticed that there is a VERY prominent line across the bullet, where the case mouth us crimped onto it. I thought such an indentation may in fact affect the flight of the bullet, hence causing it to fly erratically thus resulting in wider group size. Am I being paranoid, or I did indeed crimp it too tight?

[CSACANNONEER]

A line in the bullet due to crimping is not going to do a thing to affect accuracy or precision. Many bullets come with canullars straight from the manufacturer. If the crimps are too tight, you might experience over pressure and/or inconsistant pressures due to differences in the rigidity of the brass. That could cause inconsistant velocities which will affect precision and possibly accuracy as well.

[bruceflinch]

The middle of the road powder charges tend to be more accurate, that the hotter loads.

[Buddhabelly]

A line in the bullet due to crimping is not going to do a thing to affect accuracy or precision. Many bullets come with canullars straight from the manufacturer. If the crimps are too tight, you might experience over pressure and/or inconsistant pressures due to differences in the rigidity of the brass. That could cause inconsistant velocities which will affect precision and possibly accuracy as well.

Ah, I see. The wise man has spoken.

Thanks

[Audredger]

The middle of the road powder charges tend to be more accurate, that the hotter loads.

This Man is wise too!!!

[huckberry668]

Crimp on a non-cannelure bullet does affect accuracy. I've done many tests with both pistol and rifle bullets (w/o cannelure) and heavier the crimp worse the accuracy. Light crimp (around 0.002") most of times doesn't affect accuracy much tho. tell me how a heavily deformed bullet from its original shape will shoot accurately especially from a reloader whose cases are not uniform?

Think about it, why is there a need for cannelure if a line in the bullet doesn't affect accuracy? Cannelure is to allow crimping w/o deforming the bearing surface. Cannelure is for cartridges that don't headspace on the case mouth. I don't think I've used or seen 9mm auto bullets with cannelure.

9x19 headspaces on the case mouth and therefor the cannelure makes for a dangerous situation. You'd see cannelures mostly on revolver bullets due to need to keep the bullet in the case during heavy recoil. Rifle bullets with cannelure are mostly FMJs or solid copper. FMJs needs to be rigid and not for accuracy. Solid copper needs lessen the bearing surface so the pressure doesn't increase due to the harder core.

For straight wall pistol cartridges that headspace on the mouth, if you crimp it too much there may not be much of a mouth to headspace on and the bullet maybe pinched creating even higher pressure and causing catastrophic failure. that's why they don't make 'roll crimp' dies for these.

Try these for more accurate 9mm ammo:
1. measure the case length and use only .750" long (resized & deprimed) cases. this is the single most important factor in 9x19 besides bullet quality.
2. try a lighter load, middle of road for example. make sure powder charge is consistant.
3. crimp only .002" at the mouth. use your dial caliper carefully, it's achieveable.
4. try different bullets

[1lostinspace]

I don't know about hand gun but for my .223 yes it effected accuracy dramatically.

[RaymondMillbrae]

A cannelured boolit is one thing. But if you are crimping so tight that it is imbeddig a line in the boolit...then that is a totally different story.

For pistol rounds, you should only SLIGHTLY crimp - just enough to take off the bell and place a super slight crimp on the case mouth. This prevents the case mouth from catching on anything when getting stripped from the magazine and getting chambered.

Another thing...over crimping plated or lead boolits (regardless of what anyone tells you), will cause key-holing. (The boolit will tumble). This is pretty basic reloading knowledge. Dont take my word on it, try it yourself, and see ut with your own eyes.

In Christ: Raymond

[XDRoX]

I'm with these last couple posts saying it's a bad idea to over crimp. If you're denting a jacketed bullet you're over doing it. All you really want to do is remove the bell. There's no need crimp past that. IME over crimping will hurt accuracy.

[Buddhabelly]

I'm with these last couple posts saying it's a bad idea to over crimp. If you're denting a jacketed bullet you're over doing it. All you really want to do is remove the bell. There's no need crimp past that. IME over crimping will hurt accuracy.

I've taken a caliper and carefully measured the line on the bullet, over and over under a loop light.

The deepest part of the line/indentation is .006" less than the nominal diameter of the bullet. So it's only .003"crimp.

Not so bad, right?

[huckberry668]

I've taken a caliper and carefully measured the line on the bullet, over and over under a loop light.

The deepest part of the line/indentation is .006" less than the nominal diameter of the bullet. So it's only .003"crimp.

Not so bad, right?

Doesn't sound too bad but you can try less and see if that does anything for accuracy. Try 'no crimp', or just crimp enough to remove the 'bell'.

[JagerDog]

Crimp on a non-cannelure bullet does affect accuracy. I've done many tests with both pistol and rifle bullets (w/o cannelure) and heavier the crimp worse the accuracy. Light crimp (around 0.002") most of times doesn't affect accuracy much tho. tell me how a heavily deformed bullet from its original shape will shoot accurately especially from a reloader whose cases are not uniform?

Think about it, why is there a need for cannelure if a line in the bullet doesn't affect accuracy? Cannelure is to allow crimping w/o deforming the bearing surface. Cannelure is for cartridges that don't headspace on the case mouth. I don't think I've used or seen 9mm auto bullets with cannelure.

9x19 headspaces on the case mouth and therefor the cannelure makes for a dangerous situation. You'd see cannelures mostly on revolver bullets due to need to keep the bullet in the case during heavy recoil. Rifle bullets with cannelure are mostly FMJs or solid copper. FMJs needs to be rigid and not for accuracy. Solid copper needs lessen the bearing surface so the pressure doesn't increase due to the harder core.

For straight wall pistol cartridges that headspace on the mouth, if you crimp it too much there may not be much of a mouth to headspace on and the bullet maybe pinched creating even higher pressure and causing catastrophic failure. that's why they don't make 'roll crimp' dies for these.

Try these for more accurate 9mm ammo:
1. measure the case length and use only .750" long (resized & deprimed) cases. this is the single most important factor in 9x19 besides bullet quality.
2. try a lighter load, middle of road for example. make sure powder charge is consistant.
3. crimp only .002" at the mouth. use your dial caliper carefully, it's achieveable.
4. try different bullets

What he said.

[NotEnufGarage]

This "no crimp" or "light crimp" practice would only apply to tapered crimps, right? If you're using a Lee factory crimp die, the crimp would not effect accuracy, correct?

[damndave]

I can't comment on the crimp as BamBam31 set up my dies for me

I also use the same bullets and powder. I tried it with 4.3g, but very much like 3.9g. They are loaded at 1.132-1.135 due to inconsistencies in the bullet lengths. Cycles fine in my G34 and the felt recoil is soooo minimal. Try and few and see what you think.

[NotEnufGarage]

I can't comment on the crimp as BamBam31 set up my dies for me

I also use the same bullets and powder. I tried it with 4.3g, but very much like 3.9g. They are loaded at 1.132-1.135 due to inconsistencies in the bullet lengths. Cycles fine in my G34 and the felt recoil is soooo minimal. Try and few and see what you think.

Can you post some closeup pictures of a few rounds you've loaded? It might be obvious from those if they're crimped excessively.