Case Trimming & Chamfering Clarified

[ryan richards]

Dear CBOs

I've got new pistol brass from "Starline" in 380 ACP, 38 Super, and 38 Special.

Does this brass have to be chamfered before its first reloading? I read that it helps in seating the boolit.

Is brass trimming necessary for the above calibers while new or old?

Is it best just to buy this inexpensive equipment from Lee and use it if the opportunity presents itself?

Thanks

[docone31]

I am not that competitive. I just take new brass, use an expander die, and load it to fit the chamber.
I have almost never trimmed my brass. Mostly, by the time I am about ready, I trade the rifle in for another one. Even with rifles I have used for long term, I never trimmed the brass. It always seemed to work.
I do use mostly under peak loads also.

[Doc Highwall]

You do not have to chamfer straight cartridge cases like your .380. When you load it it gets belled slightly to allow the bullet to enter and then crimped after the bullet is seated. Also cartridges like yours head space on the case mouth so you have to be careful not to over crimp or trim too short. With a rimed cartridge like 38-357, they head space on the rim and crimp is only important to keep the bullets from moving during recoil.

[.38 Special]

I occasionally chamfer new handgun brass, if it's for "special" purposes. Mostly I don't. And I can't ever tell a difference.

I've completely given up trimming handgun brass. Folks will say that if you don't trim you will get uneven crimps. I am convinced that those people have never experimented with it. I did, and trimming makes zero difference. I do, though, shoot brass as a lot so each piece always has the same number of loadings. If the brass grows or shrinks, it all does it at the same rate.

[DLCTEX]

I figure chamfering is a good investment of time if it helps prevent shaving lead on my boolits. I think it worthwhile, but I am not anal about it, if I have time, I do it, if not, ok. Case length is easily checked and a sampling of a lot is sufficient to tell me if I want to trim. Bottleneck cartridges are sometimes stretched in the process of sizing the neck with a neck expander ball. In my 22-250 and 220 Swift reloading I prefer the Lee collet die, and will be adding one for 243. No stretch. DALE

[Bass Ackward]

If the brass grows or shrinks, it all does it at the same rate.




I went downstairs to test this statement. I measured 1 of 10 of my Starline Auto Rim brass that has never been trimmed yet. I picked this cartridge because pressure is not supposed to be an issue. Or I should say that is shouldn't be. And the first case varies .007 for OAL around the mouth. When I shoved 10 up in the trim die, 9 were not marked and 1 was a partial. This brass has been shot and reloaded 9 times so far. Bad news is my unfired Starline aren't perfect either. So how does this affect crimp?

I trimmed two on the lathe trimmer. One trimmed, and one not, were reloaded. One set was both crimped in the same step with bullet seating and two reloaded crimping in separate steps. Run out was measured on all, at the front of the drive band. These were .260 LBTs with a wide front band that will exaggerate the run out with more distance from the crimp. Bullet run out is less than .0005 so subtract that from these rough measurements.

Crimped during seating: .004 for the trimmed. .006 for the not trimmed.

Crimped separately: .002 for the trimmed. .005 for the not trimmed.

These are among my better set of dies too. Will it make a difference on the target? The crimp is my last chance in the reloading process to correct my mistakes and those of my equipment. After all the time and expense I have invested, I feel that it is better to have this habit / step than not to whether it does in this specific situation or not.

[mooman76]

Camfering will help some when loading cast boolits. If the case length is off it will effect crimping aand loading to a small degree but depending on how much. The lee chamfering will do the job but I lie a little steeper angle on the inside to help keep lead from shaving especially on bottle necked carts since they don't bell.
I don't always do this but I do do it when I trim. Might as well do it while already into the trim proccess, it doesn't hurt none.

[Firebird]

Chamferring will remove the roughness left by the factory trimming to length. This can "grab" your expander when belling the case mouth and cause problems when seating flat-based bullets.
Having uneven case lengths when taper crimping doesn't matter; having uneven lengths when roll-crimping does affect the tightness of the roll crimp. Setup the roll-crimp die with a shorter then normal case and the longer cases will bulge at the neck and you lose the neck tension that is a large amount of what holds the bullet in the case. Setup the crimping die with a longer than average case and the shorter cases won't be properly rolled into the crimping groove of the bullet.

[mike in co]

You do not have to chamfer straight cartridge cases like your .380. When you load it it gets belled slightly to allow the bullet to enter and then crimped after the bullet is seated. Also cartridges like yours head space on the case mouth so you have to be careful not to over crimp or trim too short. With a rimed cartridge like 38-357, they head space on the rim and crimp is only important to keep the bullets from moving during recoil.


technically the rounds headspace on the case mouth, in reallity they are held against the back of the chamber/breech face by the extractor.

to prove this point to some doubting thomases..i recently took a 9x21cz 85 pistol to the range with both 9x21 ammo and 9x19( std 9mm/9 luger)n ammo. there is aprox 0.078" difference in case/chamber length between 9x19 and 9 x21..2mm.
the firing pin of the 9x21 gun should never touch the primer of a 9x19 round IF they actually chamber on the case mouth........every round of 9x19 fired and cycled the 9x21 gun...feeding from the mag.

the real concen on the crimp is an over crimp may bell the case causing a failure to chamber.

crimp controls burn..it is important to consistancey. for consistant crimps, you need consistant case length...so yes trimming is a good idea, required no, improtant if accuracy is a concern.

a chamfer is good if using cast as it does help boolit feed into the case.

if using a coated bullet burrs on the inside of the neck will scrape the coating away.

a reloader or an ammo crafter.....your choice

mike in co

[454PB]

I have found that the higher the pressure, the more likely that straight wall cases need trimming. I load .45 Colt to mild pressures, and the cases never seem to lengthen. My .454 Casull cases are generally loaded to very high pressures, and require trimming to keep the crimp consistent. When I buy a new batch of brass, I give it a visual inspection, and if the case mouths are rough, I do a light chamfer. I then run them into the expander die and load them.

[S.R.Custom]

You don't chamfer brass that gets belled with an expander ball in the sizing/seating process.

[mike in co]

You don't chamfer brass that gets belled with an expander ball in the sizing/seating process.


well here is an issue....i use no factory bell dies. most have very radical angles. ( your statement looks like a rifle reference not pistol...which dont have bell functions). taking brass more than 1 thou over bullet/boolit dia is detrimental to the brass life. i use some lyman m dies and in some cases chamfer rather than bell.

the single most popular case failure ( revolver) is neck splits.....cause brittle brass, from over working...bell/crimp, bell/crimp. bell/crimp.................

avoid things that cause failure.

mike in co