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To trim or not to trim. That is the question

TJV

The reloading manual has two values for case length; maximum case length (in this case 1.760) and case trim length (in this case 1.750).

I have fired this brass twice. I have measured the cases and they average 1.752.

Should I trim the case back to 1.750 or is it OK to forego the trimming AND if I should trim to 1.750 why is it important to trim for .002?

Thanks for your advice.
 
IMO...You should be fine at 1.752. I have 3 factory 223's, and measuring with the Sinclair chamber length gauge pictured below. One requires a trim where you are now, but the other two I can let it grow to 1.770 or a fuzz more if I want.

clgauge04s.jpg
 
Reloading manuels are wrong in this regard. When you get more advanced in reloading ypu learn to measure your chamber and find your own barrel specific brass length and forget what a manuel says.

These numbers in manuels are junk. Not even worth referencing.

You measure your chamber. Then measure all your brass. And move on accordingly.

Jmo, do as you wish.
 
You need to know the "actual measured length" of YOUR chamber. And my guess is, the Sinclair Chamber length Gauge (plug) WILL work in your chamber. I use one for each caliber chamber I have.
Measure your chamber, write that measurement down and refer to it before you start trimming.
Bump dies will keep the brass from growing to the point that you may not have to trim for a looong time. Got BR brass with 25 to 30 resizes and still no need to trim. Most chambers are cut about .020 longer than the Max trim length.
You could get carbon buildup at the end of the chamber (ahead of the case neck) so plan on keeping your chamber clean. One step at a time.:)
 
Reloading manuals are using Factory specific cartridge drawing
So they are correct on the factory numbers
Trim lingth is normally what you should trim to
It is normally has a ten thousand safety margin
 
Trimming brass to SAAMI specs is for people who would prefer not to experience blowing up a rifle; due to the excess length causing your loaded round being crimped when you chamber it and pull the trigger. I watched an AR-15 disentegrate when a guy who told me that SAAMI chambers were waaaaay too long to bother trimming cases.
 
IdahoSharpshooter said:
Trimming brass to SAAMI specs is for people who would prefer not to experience blowing up a rifle; due to the excess length causing your loaded round being crimped when you chamber it and pull the trigger. I watched an AR-15 disentegrate when a guy who told me that SAAMI chambers were waaaaay too long to bother trimming cases.
Click to expand...
Agree , to each his own... Myself I am not chancing it... I clean any gun after shooting it anyway I have done it that way for fifty years with no problems... I hate trimming but it's not the end of the world... A gun blowing up in my face could be though...
 
I stick to the values in the manual, and they have worked VERY well. I would, however, add that it may even be more important that all the case end up the same length, even if that is a few thousandths different than the book trim length value. If your cases are growing longer as they usually do during the firing/re-sizing cycle, I can almost guarantee they won't all end up the same length after a couple firings or so. So trimming isn't solely to brings cases to some exact book value length, it also to make them all of uniform length.
 
OK, for you experts out there, what is the point to trimming cases to fit to the end of the chamber? Is it only to help prevent build up of carbon rings? Or is there a substantial consistency gain?

I too have seen first hand what can happen when an otherwise hot load suffers a bullet pinch due to improper trimming methods. No one hurt, and the gun didn't blow completely to bits, but it did suffer damage.
 
Case trimming is primarily a safety issue, just to ensure that you don’t wind up crimping a case mouth on a bullet via the end of the chamber. Bad ju-ju follows if it's severe enough, not something I’d recommend. The “Trim To” lengths found in the manuals are actually somewhat arbitrary, in that they’re normally just SAAMI or CIP Maximum lengths, minus ten thou. This is the mid-range between Min and Max, with Minimum length normally being .020” under the specified Maximum. In cartridges that NEED to be crimped (which I don’t recommend except in a few specific cartridges) uniformity also helps ensure equal neck tension and accuracy. Seems like a gear many folks have wound up with waded panties over trimming in the recent past, and it's not really something that should cause, this much consternation. Safety issue, first and foremost.
 
Some manuals also list the SAAMI "Minumum Case Length". This is usually .010" shorter than "Trim-to Length".

Most new brass arrives at or slightly longer than "Trim-to Length". But Nosler 223 Rem brass comes actually shorter than Minimum! I mean almost .015" shorter than Trim-to length. I kid you not.
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How do you accurately check the chamber length to establish the max case length for trimming purposes?

How does the Sinclair Gage fit into the chamber to measure it when it's larger in diameter than the neck?
 
K22 said:
How do you accurately check the chamber length to establish the max case length for trimming purposes?

How does the Sinclair Gage fit into the chamber to measure it when it's larger in diameter than the neck?
Click to expand...
It's only slightly larger than the case neck, about halfway between case neck OD and chamber neck ID (SAAMI specs, not custom tight neck, may have to turn down the slug for those.)

I've made a couple of homemade chamber length gauges (adaption of the Hornady L&L "headspace" [sic] gauge) as described here:

http://forum.accurateshooter.com/threads/headspace-gauge.3875237/#post-36585857
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K22 said:
Thanks. Learn something new even after 50 years at it. :)
Click to expand...
If you tell me the caliber in question, I will measure the appropriate Sinclair slug for you. Then if you know the ID of your chamber neck ...

PS I only have 22, 6mm, 25, and 270 slugs.
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