Moved from old YW site:
gschwertley
veteran member
Posts: 260
(1/22/05 8:16 pm)
Reply | Edit | Del All
Trimming Brass
--------------------------------------------------------------------------------
Once again, most of you will know the following, but just in case for some new guy, here goes.
I had been interested in guns for many years before I started reloading. I don't know why the long gap, but I didn't start reloading until around 1983. Just didn't know the joys of the hobby before I got involved, I guess.
Anyway, very early on, I learned about trimming cases. I hadn't been reloading long when I was invited to go on a shooting trip up into the national forest above Los Angeles. One of our party had a Ruger Mini-14 that he was shooting his own reloads in. Every once in a while, he would get one that wouldn't chamber and he'd throw it away. I picked these up and took them home with me.
At that time, I was acquainted with a man who was a commercial reloader (he had his own factory) in Orange County, Calif. This was before the days of the OC TV show. I showed these rounds that wouldn't chamber to him, and he immediately said, "cases not trimmed." At that point, he proceeded to explain why they should be trimmed.
The reason why cases need trimming is because with each firing, the brass "flows" a bit; it lengthens in the direction of the burning gasses of the propellant. Also, in spite of SAAMI standards, case lengths vary with different manufacturers, particularly foreign ones. Some brass is softer than others and needs trimming more often.
Now, there are several reasons for cases to be trimmed, or at least checked, for length. These reasons can be placed in two categories: Production and Shooting.
Reloading is all about uniformity and consistency. In producing your reloads, trimming cases to a uniform length ensures that you do not have problems with bullet seating, particularly if you are crimping the bullet. If the case is too long when the bullet is seated using a crimp, the mouth of the case can contact the seating die and get crushed down before the ram meets the end of it's travel. This happens when you adjust your seating die to a certain crimp on one case length, and then a longer case comes along (for which the die is now out of adjustment). What happens on necked- down cases typically when this happens is the shoulder collapses. You may not be able to see it with a passing glance, but when you go to chamber the round, it won't go in all the way.
If you have cases of varying lengths, this also changes the neck tension (bullet "pull") on the bullet from cartridge to cartridge. This is because the more brass you have gripping the bullet, the more friction to hold it in place. The bench-rest shooters can tell you more about this one.
So on the production side, having uniform case lengths just makes the job easier. You don't have to stop and re-adjust the die.
On the shooting side, the reason I explained above dealing with chambering applies, also the comments about uniform bullet pull. Also there is the possibility of high pressures. This can come about when the case length is so long with a seated bullet, that the case mouth actually gets jammed into the leade of the rifling. When a shot is fired with this condition, the excess brass has a wedging effect on the bullet and bullet release is slightly delayed. This results in what the reloading books call "erratic ignition" -- and high chamber pressure what with all that burning gas behind the bullet delayed in its release.
So to check your case length, you first study up on the cartridge using a good reloading book, which will give case maximum length and maybe "trim to" length as well. Even some of the free loading data pamphlets printed by the powder companies sometimes have this info. To determine this length, you can use a dial caliper. You can also buy case length gauges, which I like but are "spendy". There is also this graduated template-like thing, having a step for each popular cartridge but I don't like these much. One of these would be better than nothing, however. Lee trimming tools have the gauge built in; more on these below.
To actually trim the cases, you have several choices. There are a bunch of trimmers on the market, these are miniature lathes, to turn down excess material. I have one of these, an old Hornady made on Pacific tooling. You can also get trim dies which you put in your press and run one case into the die at a time and trim it manually.
A more sophisticated method would be to use one of the fancy motorized trimmers, but I have not used on of these yet so can't comment much on them.
Lee makes a little gadget called a "Zip Trim" which is interesting. You use a shell holder and mandrel, this last part you screw onto a cutter. When placed in the turning cartridge case, it cuts to the exact trim length. After trimming, you can leave the case in the Zip Trim and do the chamfering process. I have to admit, I didn't expect much out of the Zip Trim. It is just a little plastic do-dad with a string on it. I asked myself, "how good can anything be that is string-actuated?" Well, I have been pleased with mine and I now alternate its use with my older lathe-type trimmer just to vary the repetitive motion. Plus, if it breaks, send it back to Lee and they will fix it. Different shell holders and mandrells are required for different calibers.
I mentioned chamfering the case mouth above. This is required after case trimming because of the brass that "flashes over" and leaves a ragged edge on the case mouth. You just use one of those little "rocket ship" shaped chamfering tools to do this.
Much of the above information applies to necked-down rifle cases; straight-walled cases like those used in most pistols do not seem to "grow" much with multiple firings. This is because there is no shoulder for the burning gasses to push forward on during ignition. While this is generally true, you still need to pay attention to this problem with handgun cartridge cases. Most revolver cartridges headspace on their rims, and have a gradual ramping-up in the bullet end of the chambers. This is not so with most automatic pistol cartridges, which tend to headspace on the case mouth. Excess case length with auto pistols can prevent the action from going into battery because the case head is too far to the rear. With those few revolvers that fire auto pistol cartridges (like Smith & Wesson Model 625-2 in .45 ACP, or Model 547 in 9mm, for examples), excessive case length will prevent the cylinder from closing.
Of course, not paying attention to case length in straight-walled cases may still leave you with production problems like die adjustment.
yockey5
Owner
Posts: 3733
(1/22/05 9:24 pm)
Reply | Edit | Del
Re: Trimming Brass
--------------------------------------------------------------------------------
Thanks GS, very informative and I'm sure appreciated by those that stop by and read.
Don
Yesterdays Weapons forums
http:pub151.ezboard.com/bsteyrmannlicher
Why did I leave that 1901 m95 8x50r sporter in Nashville?
mikmarjon
Administrator
Posts: 2729
(1/22/05 10:49 pm)
Reply | Edit | Del
Re: Trimming Brass
--------------------------------------------------------------------------------
I still read anything I can find about reloading.I'm still new enough at it to read anything new that comes along.The only thing I can add is that most lee dies come with a great setup sheet in the container that will tell you how to set up the dies for the way you want to load.and even have some recipes for several different powders and bullets.
come visit us and discuss the weapons of yesterday
yesterdays weapons forums
pub151.ezboard.com/bsteyrmannlicher
TNGunsmoke
Moderator host
Posts: 1972
(1/22/05 11:45 pm)
Reply | Edit | Del
Re: Trimming Brass
--------------------------------------------------------------------------------
Glad to see this. I haven't been reloading for long, and had wondered why it was such a big deal. Now I know. Thanks for a great post.
Come visit us and discuss the Weapons of Yesterday Yesterdays Weapons Forums
txpete
contributing member
Posts: 40
(1/23/05 1:04 am)
Reply | Edit | Del
Re: Trimming Brass
--------------------------------------------------------------------------------
midway sells a case lenth gauge for $8.95 and I have one for each of the handgun cal's I reload for.
as you resize the case just slip it in the gauge and if it doesn't seat flush it's to long and needs trimming.
www.midwayusa.com
pete
Edited by: txpete at: 1/23/05 1:05 am
gschwertley
veteran member
Posts: 261
(1/23/05 1:13 am)
Reply | Edit | Del
Re: Trimming Brass
--------------------------------------------------------------------------------
One thing I left out. Case trimming is my least popular chore in reloading. It is the equivalent of "breaking rocks" on the rock pile in prison. It's boring a repetitive but often must be done.
Login
Register
FAQ
