Do you trim pistol brass?

[KUHIO]

I've been loading 9mm and I've been getting inconsistant OAL's. I'm usually getting +/- .002 I believe this is due to varying case lengths. I wasn't too concerned with it when I started building this load, but now I've worked it up a bit. Because of this I'm using a OAL with 'room for error' where small deviations will not cause a danger to me or my firearm. These are just target loads, so accuracy isn't paramount. Is this cause for concern, do I need to start trimming cases or what? Help, I'm a noob

 

[rjrivero]

I have never measured my pistol brass, much less trimmed it.

 

[KUHIO]

So you're saying I shouldn't worry about it? How do you load to a specific OAL then? very confused

 

[PDshooter]

N E V E R .......:barf:

 

[KUHIO]

Any one have HELPFUL insight? Just stating that you never trim your brass does not help me.

Can anyone tell me how you load to specific cartridge lengths, with brass of varying lengths, without trimming?


I've randomly measured dozens of my 9mm brass with lengths from .743''-.756''. Though most of them are measuring in the .748''-.751'' range.

 

[Unclenick]

Trimming serves two purposes. First is to prevent a case from getting so long that it jams the case mouth into the throat of your barrel, which can cause very high pressure, especially in a rifle with a ball throat that tapers from the freebore straight into the lead. The second is to level the distance from the casehead so that your crimps apply consistent pressure.

Many pistol cartridges keep their length or, especially in lower pressure rounds like the .45 ACP, they can actually shrink with each load cycle. Unless you have a high enough pressure cartridge to grow the case with each shot, as some heavy magnums can, you have no need to trim for the first reason. If you are roll crimping, uneven case length can affect the crimp strength significantly. If you are applying a taper crimp, though, the case length is less critical since the crimp occurs over greater distance and so case length variation is a lower percentage of that total crimp distance. Unlike a roll crimp, the purpose of the taper crimp is not so much to grasp the bullet hard as it is simply to prevent the bullet from backing up into the case under recoil.

With jacketed bullets crimping is usually unnecessary except to remove the flare from the case mouth after the bullet is seated. If you are putting a roll crimp into a bullet cannelure, that is the only instance in which you might find case length critical. For that purpose you can trim them once and if you subject them all to the same loads the same number of times, they should continue to have matching length throughout their useful life.

If you think about COL, you will realize that because the reloading press ram pushes the case up from its base, the depth the bullet is pushed in on seating is with respect to the base, not the mouth of the case. So, the case length doesn't affect the COL. The case mouth will just be higher up on the bullet in some rounds and lower on others, bu the bullet nose will still be the same distance from the casehead. What is critical is the distance from the base of the seated bullet to the casehead because that controls how much space the powder burns in and that, in turn, controls pressure. If you seat a bullet deeper in, the pressure goes up.

 

[Sparkies02]

9mm Cases

I have been reloading for quite a while and I definately check and trim all of my pistol and rifle cases. I don't see how you can get consistent cartridge lengths without doing so. I have also had a lot of trouble with jamming in my semi-auto pistols when I don't trim my cases. I use the Lee case trimming system and it is quick and gets the job done.

 

[Unclenick]

Depends on the load. My .45 ACP cases lose almost half a thousandth per load cylce firing target loads. The Lee trimmer I bought for them back before I had much experience has never been used because it has never been able to touch the brass. The case mouths just keep getting farther away from its cutter. I once tracked a batch of cases through 50 light target reloadings, and they were all about 0.020" shorter when I retired them.

What grows a case starts when the firing pin pushes the cartridge forward by whatever amount the headspace is loose. The primer then ignites and pressure builds to the point the brass sticks to the chamber wall. But because the case head is forward by the amount of the looseness in the chamber, there is an air gap between the casehead and the breech face. The casehead is too thick to stretch under normal pressure, but with the case walls stuck to the chamber, the only way the pressure can push the casehead against the breechface is by stretching the brass next to it.

In a shrinking round the pressure never gets to the level needed to stick the brass to the chamber. Instead, the whole case backs up like a piston, stops at the breech and fattens to seal and fills the chamber. That shortens it slightly more than the sizing die can recover it from.

9 mm runs right on the boarder line of enough pressure to stick brass. It can therefore happen or not happen or just depending on the recipe or how smooth your chamber is? Whether you've got case growth or not is easily determined by running the Lee cutter in. It nothing comes off, then it didn't need sizing, and vice versa.

 

[cgaengineer]

Your OAL has nothing to do with case length, think about it for a sec. If your case is in your press and it is sitting on shell plate waiting on a bullet and the case is short is the press arm stroke longer or shorter...no? Only the distance between the bottom of the die and top of empty case is different, the distance between the bottom of die and bottom of case is exactly the same, case length has nothing to do with this distance. If the case is short the seating depth of the bullet is less only because there is less metal, if the case is longer the seating depth is greater because there is more metal...OAL will be exactly the same.

What you are experiencing is slightly different bullet lengths. The difference you mentioned is well within working range and is actually very good. I have seen BTHP Match .308 bullets with more variance then that.

 

[DaveInPA]

Case length has nothing to do with your OAL.

 

[KUHIO]

Thank you for the clarification guys. I was obviously thinking about this way too hard. So does any one have any idea why I'm getting inconsistant COL's or how I might remedy this issue?

 

[floydster]

I never trim pistol cases and have been loading for 54 years.
Peace, Floyd

 

[RidgwayCO]

Having your COL's vary by plus or minus .002" is normal (actually it's pretty good). It's most likely caused by the bullets themselves varying in length or nose shape, especially with a generic "round nose" or "SWC" bullet seating plug.

I have found that a custom seater plug made for the exact bullet I'm working with (made by RCBS, Lee, and perhaps the other die manufacturers) helps me minimize the plus or minus on my COLs.

 

[Hook686]

Why the variance in COL ? For me I concluded I do not pull the press lever exactly the same each time aned there are variations in the friction between bullet and case wall with each loading.

 

[rwt101]

This might be over kill but I rotate the case 1 or 2 times and run it back into the seating die. It seems to help in the oal consistency. Of course I am using a lee turret in single stage load. I am not interested in speed. But I thonk within .002 is real good.
Bob T

 

[zxcvbob]

You're using cast bullets, right? The plug in your seating die probably does not match the bullet nose profile. (It doesn't seem to matter so much with jacketed bullets.) Probably not worth fixing unless you have a different seating plug already.

That's my guess anyway

 

[FrankenMauser]

I rarelly measure my pistol brass. I attempted to trim once... the pilot wouldn't fit .... I never tried again.

I understand that it might make a difference for competition shooters, of folks that may not have the time to deal with a malfunction during a shooting trip.

I simply load, fire, tumble, reload, fire, tumble.... In each step of the process, I am inspecting for defects. If I see anything I don't like, the case gets scrapped. The only cases I have ever found to be over-length were a few A-Merc, once fired. (The headstamp, alone, was enough to scrap them.)

 

[Don H]

I've been loading 9mm and I've been getting inconsistant OAL's. I'm usually getting +/- .002

FWIW, you'll find more variation than that in a box of new, name-brand premium cartridges.

 

[Selfdfenz]

DonH beat me too it. I was going to suggest checking a 100 round Value Pack of WWB.......

s-

 

[M1911]

Any one have HELPFUL insight? Just stating that you never trim your brass does not help me.

Can anyone tell me how you load to specific cartridge lengths, with brass of varying lengths, without trimming?

You can decide whether my insight is helpful or not. I've never trimmed or measured my pistol brass.

OAL is a function of how deep your seat the bullet, not the length of the cartridge case.

It is my understanding that you do need to measure and trim rifle cases. But straight-walled pistol cases behave far differently than bottle-necked rifle cases.