Printable View
How far is generally acceptable to trim back a case from its specified original factory case length? say for a case of specified L=2.015" (.308winchester) would trimmed L=2.00" be acceptable?
what are the general guide lines for case trimming?
in Freedom
atr
Get a Lyman reloading manual. It calls it out for every cartridge listed. It’s also the best loading manual available. It will save you a lot of “guessing” on questions that you might have.
Virtually every reloading manual I've read calls for a trim-to length .010" under case length max. Some of my manuals will even state a case length minimum. I have seen a few odd cartridges that have a .020" trim but I can't quote one off the top of my head.
And it's pretty consistent across manuals over time and publisher. My manual collection starts in 1941 and ends probably 2 years ago. And stretches almost 5 feet long.
Did I mention I collect old reloading manuals?
1952 Belding and Mull is pretty cool.
Most chambers are often considerably longer than listed maximum case length. I like to find out, and then trim about .005" under that. I keep my chamber stats in my die box. The only problem with my method is that my reloads might be too long for someone else's gun. jd
When I was shooting M-14’s I trimmed my cases to2.00”. That way when they grew to the max length it was time to trash them with the load I was using. Boltgun cases I trim to .010” under max. BP cases are at max length.
I measure chamber length before trimming, my Marlin's and Savage 99's, military 8mm's, most others have chambers that are longer (MUCH LONGER) than 'specs' in the manuals and SAAMI. For rifles I measure the lot of cases, usually 50-100 and trim to the shortest case or .005" shorter than chamber length. I have spent little time measuring handgun cases, most 45 ACP, 357, 44 Special and 38 Special have been shorter than specs, I guess I should check my 40's and 9's but they have functioned just fine without trimming. Uniformity rather than actual length is important as long as the case is NOT TOO LONG, causing high pressure or malfunction in the semi-autos. I use a decent stainless steel DIAL caliper for measurement, with a Wilson case trimmer, consistency is about half a thou (.0005"), same with the Lee Hand trimmer, with my old Forster - .003" seemed to be the best I could get. Crimping for lever guns requires good uniform case lengths, though the Lee Factory Crimp can help.
I generally trim .010" under max length. Years ago I bought a couple of inserts from NOE which indicated the max. length of the cartridge and trim accordingly.
thanks guys...I've been using 0.01 under as my cutoff...just needed some reassurance that it was still a good number to hold to
best
atr
https://saami.org/ Look at cartridge drawings for the difference between them.
Some pistol cases that headspace on the case mouth, may get little to no trimming.
Headspacing can be by case mouth, shoulder, belt, or rim.
I usually trim cases to .005" below max length, but there's a caveat: I only do this for bolt actions where I neck size only. I check case length often when reloading, and trim the cases when necessary. If the cartridges are for a semi-auto I full length resize and trim the necks back to 0.010" below max length.
Generally speaking, manuals give “trim-to-length” specifications that equal ten thousandths under published maximum allowed length. This will work but, each firearm is different and simply trimming to book may result in a case that is well under optimum length. This is when a chamber cast becomes useful, because it allows you to choose a case length that works within the parameters of your chosen specifications, in your firearm. Ammunition made this way may not be safe to use in a firearm belonging to someone else!
I trim to specs unless it's for my military bolt rifles. For them, I trim 0.005" below chamber length so seated bullets can touch the rifle lands and I can test for accuracy by seating depth and distance from the lands.
I have some 308 cut back to 1.8 but it's also blown out to 45 cal so there's that .
The more important question is how long from bolt face to case mouth step is your chamber . I had a 45 Colts that's speced at 1.285 that had a 1.305 chamber and a little 6.5×50 that's .050 , all neck not headspace, longer than book, so it happens.
I think I have a few 45 Colts that are headstamped 308 Win so that's almost an inch hacked off and a healthy neck turn too .
I am also a member of the "-0,10" club" with a slight (?) twist. It takes a few minutes longer but I use a set of vernier's to check each case's length. Finding the shortest, assuming it is in this minus-.010 range -- I trim this one (if needed) first -- and then trim ALL in the lot to (hopefully) exactly the same length. E.g., whatever it turns out to be of lesser importance than actual measurement. Why??? I reckon that when I come to the crimping stage, each different length might produce a different crimp.. Maybe 'good'? Maybe not? Anhoos -- what I do :).Quote:
Originally Posted by atr
I have trimmed about a third of the neck off a fired case and made an insert to go in the case mouth. It is a firm slip fit in the case with a small step at the end the same size as the OD of the neck. Leave it out too long and chamber it, hits the end of the neck and gives you your max length. It might seem to be too much trouble but I like to tinker around in my cluttered shop, it ain't work.
If you happen to have a Teslong bore scope just chamber a case and run the scope down the muzzle, have a look and trim to fit. It's hard to believe useful how the bore scope is, cheap compared to the rest of this hobby.
Dave
I trim more to get uniform length for crimping. Trim to shortest case.