Brass Trimming problems

[Tex3030]

I trimmed some brass the other day and measured each case after trimming. I found that the trimmed brass was off by +.003 to -.005. The -.005 case came out in the middle of the batch (other than that one case it was +-.003) The lengths were not restricted to long at the beginning and short at the end, it varied on each case.
I am using a Lyman manual trimmer. All of the primers were removed for the trimming and for the measurements. I am using remington brass.
Does case length usually vary this much?
Does the length of the case matter if there is no crimp on the bullets?

 

[kraky2]

Some people think length of brass does matter. For your normal hunting rifle I would say not much. (of course you should be in safe spec for your rifle.) I have read articles where people have said that over trimming can cause bullet deforming as the bullet leaves the case because of the big gap between it and going into the barrel. Perhaps some of the really experienced long rangers here can comment.
Getting back to the trimming. If your hardware on your trimmer is set so nothing slips and you are applying the same amount of pressure during trimming you have me baffled.

Only last comment I can make is did you take measurements AFTER DEBURRING that trimmed brass? This is important because burrs.....raised edges....etc etc can easily affect your measurements untill they are removed.

 

[kraky2]

BTW Sinclair offers an insert tool that is cheap and lets you figure out how much room you have in your chamber (in your particular gun) before you have to trim. I have them for most all calibers and it's amazing how much over factory specs alot of guns are. I have several factory mag rifles that never need trimming for the life of the brass. They really have saved me a ton of time and trimming over the past few years.

I am very curious if some of the really experienced guys here can chime in on the "bullet deformation" idea and whether its valid for a big gap between the case mouth and the lead into the rifling.

 

[Gene]

Excessive trimming can cause a build up of carbon in the barrel, between the end of your case and the leade in the chamber. The carbon ring can be difficult to remove. I try to stay about .010 under SAMMI when I trim. Minor variations in the length are acceptable. However, the carbon ring is not terribly important in a hunting rifle. Normal brushing with a good solvent will remove most of it.

 

[J E Custom]

I trimmed some brass the other day and measured each case after trimming. I found that the trimmed brass was off by +.003 to -.005. The -.005 case came out in the middle of the batch (other than that one case it was +-.003) The lengths were not restricted to long at the beginning and short at the end, it varied on each case.
I am using a Lyman manual trimmer. All of the primers were removed for the trimming and for the measurements. I am using remington brass.
Does case length usually vary this much?
Does the length of the case matter if there is no crimp on the bullets?

Tex

I had similar results and found I was not applying the same amount of pressure
each time and this flexed the base of the trimer,so I took the handle off and
chucked a cordless screwdriver to the shaft and solved the base flexing issue.
because your pushing inline with the cutter.(Plus it is faster).

And yes trim length does matter so try not to trim any more than you have to
to be consistant (I like .010 less than the chamber length).

J E CUSTOM

 

[boomtube]

"I am using a Lyman manual trimmer. All of the primers were removed for the trimming and for the measurements. I am using remington brass. Does case length usually vary this much? Does the length of the case matter if there is no crimp on the bullets?"

First, length is only "critical" for maintaining consistant crimps. Well, wiithin rational limits. Don't cut off a quarter inch.

A length spread of .010" is "normal" for rifle cases.

I too have Lyman trimmers, both the "Universal" and "AccuTrimmer". With the Univerasal, my lengths are very consistant IF I don't quit turning too soon. The AccuTrimmer is somewhat more variable because it indexs off the front edge of the rim, making finished length dependant on the thickness of the rim.

Those trimmers that use "draw-in" collets see lengths vary somewhat due to differences in the actual diameter of each rim and how tight the user turns the locking handle.

Only the Lyman Universal and Willson trimmers, as far as I know, index the case heads on a solid steel stop so lengths actually can be consistant if the user is careful.

 

[MontanaRifleman]

Tex, I use an RCBS Trim Pro Power Case Trimmer and my cases come out within .001

On a side note for everyone else, SAAMI spec for my 300 WSM case length is 2.10. My new Norma brass is running about 2.09. After firing and neck sizing the brass seems to actually shrink in length and I keep having to trim them shorter to keep them uniform. The neck sizing does seem to stretch them on aversge about .001 I have some 3 and 4 times fired cases that are down to about 2.08 which is .02 shorter than spec. I'm hoping that whe I get some a custom FL die They will get stretched back out. It almost seems that as the walls of the cases are stretched it draws the neck downward?

Anyone else have this issue?

 

[lever-hed]

tex3030, I heard the lymans tend to vary consistency, though I don't have any experience with these trimmers. I use a Wilson trimmer and once its zeroed in it trims to within .001" and most of the time less. I would say it does make somewhat of a difference in performance but not much.. for my 25-06 cases I concentrate more on neck size and chamfering and primer pockets as far as case prep. My cal spec says max 2.494" case oal, and min trim length is 2.484", I try to stay in between this range at about 2.490". My chamber is 2.520" measured and they say if you go over max case length do not go closer then .024" of your chamber length. There is the argument though that case length is directly affecting bullet release where the bullet contacts the neck surface. I'll leave that discussion out of this post. Good luck.

 

[kraky2]

I wonder why anyone would say to keep a trim length .024"? I've never had a problem using nearly the full dimension once it's measured in any of my guns. Any more input on this?? (I think we have the original question answered re inconsistant trim length)

 

[lever-hed]

..as I indicated, my case oal max is 2.494, chamber is 2.520, if I back away .024 from my chamber length, I'll be at 2.496, .002 over the max SAAMI. I assume there is a safety factor involved and how this number was arrived at I couldn't say. If the case neck expands and there is debris, dirt, sand brass shavings, powder etc etc, stuck in the chamber, and if you don't clean your chamber for say many many rounds (or never)and use it in the field the end of the chamber can get bogged up with crud.. If the case neck cant expand enough to release the bullet (and all the gas) will create excessive pressures, obviously could blow up the gun, and maybe a finger or hand or elbow. For persons who use primarily at the bench and/or don't have custom chambers, I could see how this 'safety factor' could be objectionable. If it's a hunting gun (ie factory bbl) its typically assuming one will use it in the field, which most are made to be abused to a degree. Bottom line, if you know your chamber length and assume 3 to 4 thousands case growth, then you're fine, but if you're just shootin hogs, safety's built in.. like tom cruise said, I just drive, I don't know nuthin 'bout cars…

 

[Tex3030]

I found the problem I was having with the trimmer. When clamping the case in I would slide the neck of the case onto the pilot so that the case would be true to the cutting head. When I was clamping the the case in the case would rotate, and at times it would grab the cutting head and unscrew it. I tested it by trimming 10 cases and all were within +-.001. Thank you for the responses.

 

[lever-hed]

I'm glad you were able to find the problem. The wilson is similar, it hold the shell in a steel bushing and if the twist the bushing while cutting it will sometimes rotate the set screw and mess up the trim length. Happy hunting/shooting.

 

[anachronism]

You did size your brass before trimming, didn't you? If you trim your brass & then size it, you're going to get different readings before and after sizing...

 

[davewilson]

the best case length trimmer out there is the Lee. it's also the cheapest, most accurate and easiest to use. i have a Wilson and will sell it for 1/2 price if anyone wants it.