Case trimming

Reloading equipment, methods, load data, powder and projectile information.

Case trimming

Post by Sergeant Hartman » 13 Jul 2018, 7:12 am

Hey guys got a question wnot how much to trim brass. I have looked at thre different sources and all are slightly different. So question is which one, or it doesn't matter.

Eg 308w

ADI is 2.005
Saami is 2.015
Lee manual says 2.020

I aim to wait till size grows to 2.015 then trim to 2.005. Should I do this or trim to 2.015 if it goes over 2.015
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Re: Case trimming

Post by SCJ429 » 13 Jul 2018, 8:24 am

For the 308 Win, the maximum length is 2.015 and the trim length is 2.005. If some of your cases are approaching or at 2.014 trim the whole batch to 2.005. There will be a little margin but the long necks will eventually hit the end of your chambering, effectively crimping the projectiles and can lead to dangerously high pressures. How long are your necks? I have seen some Federal brass that was at 2.017 after firing the factory loaded ammo.
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Re: Case trimming

Post by Cooper » 13 Jul 2018, 8:36 am

I alway trim back back to the minimum length. But wait til it is near maximum before I trim.

I started using the Nick Harvey manual first which has the trim length written millimetres which I find works for me. When I am looking for a trim length I usually refer back to the Nick Harvey and I find it easy to find. This is probably only because I started with it first.

But it pays to check other manuals as you have done.

Nick Harvey
Max case lenght 51.18mm
Trim to lenght 50.92mm
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Re: Case trimming

Post by sungazer » 13 Jul 2018, 8:39 am

It can be worth finding out where that point is. I mean the point at how long the cases can get in your chamber then keeping them just a bit shorter say 5 thou. If they are a lot shorter carbon and hot gases are exposed to that part of your chamber as well. Some also believe it helps to support the projectile more it can certainly give a bit more length to help seat them if your cases or throat is a bit on the long side.
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Re: Case trimming

Post by Sergeant Hartman » 13 Jul 2018, 8:43 am

Thanks sjc, that's what i was doing set the vernier at 2.016 and if i find it hard to fit in the callipers jaws then trim to 2.005.

Some don't increase but I am doing load dev and run different qty powder. But next visit could basically end the load dev cycle
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Re: Case trimming

Post by Sergeant Hartman » 13 Jul 2018, 8:46 am

Hmm how to find out, I did the empty cartridge slightly neck sized with a projectile to find the lands hack.... ies a ruger precision so assuming the tolerances are going to be on the tight side
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Re: Case trimming

Post by straightshooter » 13 Jul 2018, 9:03 am

SAAMI standards have the chamber length at 2.020 and case length at 2.015.
I would suggest trimming to 2.015 when the cases reach 2.020 or more.
Note carefully what Sungazer says.
One reason for trimming is to prevent the over length case being crimped into the projectile by the chamber throat and possibly causing dangerously high pressures.
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Re: Case trimming

Post by sungazer » 13 Jul 2018, 10:26 pm

Always good to check your empty cases in the chamber or at least a sample before and after reloading. If any feel tight investigate the cause.
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Re: Case trimming

Post by madang55 » 18 Jul 2018, 12:15 am

sungazer wrote:Always good to check your empty cases in the chamber or at least a sample before and after reloading. If any feel tight investigate the cause.

Exactly right. I reformed, trimmed etc some 223 to 300AAC, they chambered ok but after I loaded them up, not ok. I think the shoulder was wrong so I pulled them and chucked em out.
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