Impact of Trim Length

D.B. Cooper · Jul 17, 2022

What is the real world, actual impact of trim length? Specifically, trim length longer than spec?

I'm loading up some 243 Win for hunting season, and noticed that my brass is running .010-.013 longer than spec, even after hand trimming with a Lyman hand case prep tool.

I load .10 grains below maximum charge. (Which is probably why they're elongated.) What impact to safety, loading/extracting (bolt gun), and accuracy will this have?

Walkalong · Jul 17, 2022

If it gets long enough to pinch the bullet because it's past the chamber (Brass neck out further than chamber "neck"), pressure can skyrocket, even with a "light" load.

Trim it.

Blue68f100 · Jul 17, 2022

The problem with the brass being to long is that you can pinch the bullet increasing pressure like it's jammed into the lands.

Walkalong beet me to the punch.

Kaldor · Jul 17, 2022

Like those guys said, trim them back. Some times some rifles will allow you to get away with it. But sometimes it wont and it will drive pressure up, sometimes catastrophically.
I would just trim trim them back to 10 thou under SAAMI spec in batch. Then you can very likely shoot the entire batch twice without needing a trim. Then trim again after the 2nd firing.

Disclaimer!! Its still prudent to take a check to ensure they are still under SAAMI max length after the first firing. If you have 100 pieces of brass, taking a random sample of 10 or 10% is probably adequate. It very likely the brass isnt growing 10 thou in a single firing, but if it is, you need to have the rifle checked for headspace.

AJC1 · Jul 17, 2022

To short isn't a problem but to long is trouble. You know better....

D.B. Cooper · Jul 17, 2022

AJC1 said:
...You know better....

I do. That's why I asked. I just wasn't sure how much lee way was there. That, and there are no automated case prep kits available locally, so I have to do it by hand.

Thanks, everyone.

Rule3 · Jul 18, 2022

D.B. Cooper said:
What is the real world, actual impact of trim length? Specifically, trim length longer than spec?

I'm loading up some 243 Win for hunting season, and noticed that my brass is running .010-.013 longer than spec, even after hand trimming with a Lyman hand case prep tool.

I load .10 grains below maximum charge. (Which is probably why they're elongated.) What impact to safety, loading/extracting (bolt gun), and accuracy will this have?

Which "spec" Max or trim to?? You are measuring after sizing yes? Your Lyman tool is not adjustable??

murray brook · Jul 18, 2022

You can purchase chamber length gages from Sinclair. Not expensive but very useful in finding out your chamber length. Can save you a lot of needless trimming, and keeping close to chamber length can help avoid carbon rings. JMO
SINCLAIR INTERNATIONAL Sinclair Chamber Length Gage | Sinclair Intl

D.B. Cooper · Jul 18, 2022

Rule3 said:
Which "spec" Max or trim to?? You are measuring after sizing yes? Your Lyman tool is not adjustable??

Trim to. Yeah, after neck sizing. The Lyman tool isn't really for trimming; it's for deburring and primer pocket cleaning/reaming.

Varminterror · Jul 18, 2022

D.B. Cooper said:
trim length longer than spec?

How are you defining “spec”?

What SHOULD be happening, rather than trimming to any book value: reloaders so concerned with exactly appropriate trim length SHOULD be measuring their actual chamber necks, and trimming accordingly to produce a desired clearance at the neck. We do not want the neck to make contact on the chamber neck, but also do not want unnecessarily excessive clearance.

CoalCrackerAl · Jul 18, 2022

Also the bolt could be harder to close as well.

Rule3 · Jul 19, 2022

Varminterror said:
How are you defining “spec”?

What SHOULD be happening, rather than trimming to any book value: reloaders so concerned with exactly appropriate trim length SHOULD be measuring their actual chamber necks, and trimming accordingly to produce a desired clearance at the neck. We do not want the neck to make contact on the chamber neck, but also do not want unnecessarily excessive clearance.

I asked him that on post #7 and he answered it on post #9
But of course there is the more convoluted explanation.

Sounds like he is not trimming at all.

Rule3 · Jul 19, 2022

D.B. Cooper said:
Trim to. Yeah, after neck sizing. The Lyman tool isn't really for trimming; it's for deburring and primer pocket cleaning/reaming.

Sounds like you need a trimmer of some sort. The come in all sizes, shapes and prices,
If you just need hunting loads a basic trimmer for a hundred rounds should be good enough.

Laphroaig · Jul 19, 2022

murray brook said:
You can purchase chamber length gages from Sinclair. Not expensive but very useful in finding out your chamber length. Can save you a lot of needless trimming, and keeping close to chamber length can help avoid carbon rings. JMO
SINCLAIR INTERNATIONAL Sinclair Chamber Length Gage | Sinclair Intl

If you have a bore scope you can chamber a brass of known length and scope the chamber from the muzzle to see where it stands. You would need some longer brass to get an exact length but can easily get a ballpark idea if your chamber is short or long.

Rule3 · Jul 19, 2022

Take your pick, depends on how much you want to spend. If only for one caliber it's not to expensive.

https://ads.midwayusa.com/case-trimmers-and-prep-centers/br?cid=8935

Walkalong · Jul 19, 2022

Varminterror said:
We do not want the neck to make contact on the chamber neck, but also do not want unnecessarily excessive clearance.

This, which, for most people, means trimming to minimum case length and never going over max case length.

Varminterror · Jul 19, 2022

Rule3 said:
I asked him that on post #7 and he answered it on post #9
But of course there is the more convoluted explanation.

Sounds like he is not trimming at all.

My question stands - how does he choose to define “spec?” Trim-to length is an arbitrary subtractor from a SAAMI max length, meaningless for an individual rifle chamber. It’s an option, and it almost always does produce “safe” ammo, as is the objective of the processes described in reloading manuals, but it doesn’t suit the actual rifles we’re holding.

We find the shoulders to set our sizing dies, we find the lands to set our seating dies, we also should be finding the neck to set our trimmer - otherwise we just have to accept that we’re making ammo undersized in any or all of these dimensions to ensure generic fit (like checking ammo in gauges rather than your actual firearms), and we would NOT be making dimensionally tailored ammo. Pretty straight forward.

Hugger-4641 · Jul 19, 2022

I have two 30-06"s that have totally different neck tolerance.
My Rem 700cdl sf will take a few thousandths over max case length with no problem.
My Howa 1500 will take 2.496 without resistance on the bolt handle and not a pinch more.

Walkalong · Jul 19, 2022

Varminterror said:
What SHOULD be happening, rather than trimming to any book value: reloaders so concerned with exactly appropriate trim length SHOULD be measuring their actual chamber necks, and trimming accordingly to produce a desired clearance at the neck. We do not want the neck to make contact on the chamber neck, but also do not want unnecessarily excessive clearance.

How to get max length for your chamber.

D.B. Cooper · Jul 20, 2022

Varminterror said:
My question stands - how does he choose to define “spec?”

The trim to length stated in the Lyman reloading manual.

D.B. Cooper · Jul 20, 2022

Rule3 said:
Sounds like he is not trimming at all.

I haven't been. I was getting acceptable results just neck sizing and watching for splits in the neck and primer issues, of which I've had none. I recently started loading maximum loads to get really high velocities, so I'm checking more things more often now.

I just bought a Hornady trimmer and will be setting it up soon.

cfullgraf · Jul 20, 2022

Generally speaking, the maximum case length specification is the case length that will fit "any" chamber. The "trim to length" is shorter than maximum length.

Whether you full length size or just neck size, the cases should measure less than the "maximum case length". If your rifle chamber is cut to SAMMI specifications, the case should fit the chamber without any interference.

Chambers are cut with some kind of tolerance. There are measurements that can be taken to determine what the maximum case length for a particular rifle the chamber is cut for. The operator can determine this dimension or not.

Bottom line, one should determine cases fit the chamber without any interference. Any interference will cause a rise in pressure when the round if fired.

There are a variety of trimming systems available. Some parts of the globe have some limitations on receiving material orders, they just need to be accounted for in life.

At one time I worked for a nickel refining company with facilities in the Pacific rim area. We had extensive machine capabilities in the Pacific rim to make parts that could not be easily be delivered from producers in the "real, manufacturing" world.

Rule3 · Jul 20, 2022

cfullgraf said:
Generally speaking, the maximum case length specification is the case length that will fit "any" chamber. The "trim to length" is shorter than maximum length.

Whether you full length size or just neck size, the cases should measure less than the "maximum case length". If your rifle chamber is cut to SAMMI specifications, the case should fit the chamber without any interference.

Chambers are cut with some kind of tolerance. There are measurements that can be taken to determine what the maximum case length for a particular rifle the chamber is cut for. The operator can determine this dimension or not.

Bottom line, one should determine cases fit the chamber without any interference. Any interference will cause a rise in pressure when the round if fired.

There are a variety of trimming systems available. Some parts of the globe have some limitations on receiving material orders, they just need to be accounted for in life.

At one time I worked for a nickel refining company with facilities in the Pacific rim area. We had extensive machine capabilities in the Pacific rim to make parts that could not be easily be delivered from producers in the "real, manufacturing" world.

A voice of reasonability.

Rule3 · Jul 20, 2022

Just the basics! Steps #8 and #9

https://www.rcbs.com/rcbs-how-to-reload/rcbs-step-by-step-reloading.html

D.B. Cooper · Jul 28, 2022

CoalCrackerAl said:
Also the bolt could be harder to close as well.

You jinxed me. That started happening yesterday at the range.

Impact of Trim Length

Member

Moderator

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Moderator

Member

Member

Moderator

Member

Member

Member

Member

Member

Member

Similar threads