.308 Trim Length

[yukonal]

If my reamer print shows my case mouth at 2.045", and reloading manuals say trim length for .308 is 2.015"...is there any problem with moving my trim length out to 2.020" or longer?

Or even 2.030? Is there any benefit to be gained by leaving the trim length longer?

I'm annealing and trimming after every firing.

 

[Blackthorn]

I would buy a Sinclair chamber length gauge and double check your chamber length. The Sinclair instructions say to trim to no less than .010 less than chamber length. I don't know if there is any benefit to the longer length. Personally I trim my cases to 2.005 every time just for the sake for consistency and my rifle seems to like it.

 

[savagedasher]

What ever the reamer print says you should alway trim shorter . How much shorter depends on how often you trim . Larry

 

[Shynloco]

What ever the reamer print says you should alway trim shorter . How much shorter depends on how often you trim . Larry

TRUE! Remember (yukonal), a .308 has historically always had a significant JUMP, UNLESS you buy a custom reamer where you specify bullet seating depth. I also trim to 2.005 in my "across the counter" .308's and that's what most of my Reloading Manuals recommend. Only in my custom built/reamer, have I tightened the jump factor down.

Alex

 

[jsudduth]

If my reamer print shows my case mouth at 2.045", and reloading manuals say trim length for .308 is 2.015"...is there any problem with moving my trim length out to 2.020" or longer?

Or even 2.030? Is there any benefit to be gained by leaving the trim length longer?

I'm annealing and trimming after every firing.

Good luck with finding cases that long. I've never seen a new case over about 2.006 to 2.008.

In my rifles it would take 10 or more firings for a case to grow that long.

JS

 

[YEW PLUCKER]

I trim mine to 2 inches.

 

[yukonal]

I understand that JS. Just wondering if it would hurt to let them "grow" a little bit, then keep them trimmed. I've had a few carbon rings in the past...for whatever reason...and it seems to me it'd be easier to deal with the carbon/fouling farther out. Maybe it's a non issue.

My cases are at 2.012" after a couple firings. Barrel was chambered with a 2013 F-TR reamer, so it has a longer throat.

Also, I have a chamber length gauge, and I guess I better dig it out of the corner of the drawer and use it!

 

[SheepDog]

The only thing you need to be concerned about is letting the case get too long and pinching the neck on the bullet. As long as you are willing to trim the case after each firing you can have the case within a couple of thousandths of the end of the chamber.
Whether there are any advantages or disadvantages the only way to find that out is to test it. It might help with throat erosion but that is debatable.

 

[Richard Jones]

http://bulletin.accurateshooter.com/2015/06/how-to-craft-your-own-chamber-length-gauge/

 

[yukonal]

Actual neck is 2.057". So I have alot of room to let them stretch a bit. Might help having a little more neck tension, as 185's are way out in the neck with that reamer...

 

[DRNewcomb]

It would be interesting if a good brass company made a .308 long case, one that was over maximum out of the box and had to be trimmed before use. The Lapua Palma .308 I recently bought were pretty short, out of the box.

 

[yukonal]

That's a good idea. Taylor your neck length/tension to your to your individual rifle/chamber.

 

[boltgunluvr]

What ever the reamer print says you should alway trim shorter . How much shorter depends on how often you trim . Larry

Exactly this. Don't overthink it and don't try to fix what's NOT broken.

 

[seymour fish]

Exactly this. Don't overthink it and don't try to fix what's NOT broken.

Perhaps the OP is wondering about some theoretical slowing of formation of a hard carbon ring. Any thoughts ?

 

[Someoldguy]

Not sure this is worth getting 'wrapped around the axle' over.

Try 10 cases or so. Shoot 3 - 10 shot groups. If there is no accuracy difference, for better of worse, then the upside is you don't have to trim them as often.
If the accuracy improves with longer necks, then you can determine if you want to continue to monitor them closely as a case neck too long will likely result in an overpressure event.
If the accuracy remains the same or decreases, then I would wonder why use long case necks when you are getting nothing out of it?

Edit to add - Why are you annealing and trimming after every firing? There is a spec for when to trim, and what length to trim to, for SAAMI spec chambers. Most shooters I know anneal to extend brass life. Perhaps you have observed something that has caused you to follow this regimen? Is the carbon ring you speak of causing problems? How have you observed this ring, and how have you determined that you can 'move' it with the length of the brass neck? Is this carbon ring easier to remove or non-existent if you allow the necks to grow longer? Otherwise, you may be subjecting yourself to a lot of trouble for naught. (?)

Or am I missing something?

 

[yukonal]

Perhaps the OP is wondering about some theoretical slowing of formation of a hard carbon ring. Any thoughts ?

Yep, that and a longer neck possibly giving the bullet more/better support and alignment in the chamber.

As the neck grows, I just don't see any reason to let that brass go to waste, if it's not causing any issues. So, I was just wondering if anyone had any results or experience with trying this.

 

[yukonal]

Edit to add - Why are you annealing and trimming after every firing? There is a spec for when to trim, and what length to trim to, for SAAMI spec chambers.

Most shooters I know anneal to extend brass life. Perhaps you have observed something that has caused you to follow this regimen?

Is the carbon ring you speak of causing problems? How have you observed this ring, and how have you determined that you can 'move' it with the length of the brass neck?

Is this carbon ring easier to remove or non-existent if you allow the necks to grow longer? Otherwise, you may be subjecting yourself to a lot of trouble for naught. (?)

Or am I missing something?

Annealing and trimming (if at all) every time for consistency and brass life.

I've had carbon rings form on two other rifles right at the mouth, creating drag on bullets while chambering the round. The bullet literally touched the ring (scratch marks on extracted bullets) while it sat in the chamber.

I have observed these rings with a Hawkeye Bore Scope, and am wondering if the carbon in general will be easier to deal with closer to the throat.

 

[Dos XX]

I trim to 2.005 every time. I SS tumble then anneal every firing. The trimming also takes care of any case mouth peening from the SS tumbling. I also want it to be the same every time so that neck length growth can't change my neck holds, using about 1.5 holds. I don't know that it would change it, but I do know that by trimming every time it won't.

That said, I have a Giraud trimmer which makes it way too easy to trim for me to think about letting it grow. If I had to trim 300 or 400 rounds by hand every time, I might be inclined to test it and see what I could get away with.

I have never had a carbon ring, and I have shot out a couple of barrels on my .308's. I am not afraid of the bore brush, though.

 

[6BRinNZ]

Yep, that and a longer neck possibly giving the bullet more/better support and alignment in the chamber.

As the neck grows, I just don't see any reason to let that brass go to waste, if it's not causing any issues. So, I was just wondering if anyone had any results or experience with trying this.

As someone else mentioned the brass probably won't grow that long. The one thing you will find is that the brass will grow at uneven rates so the longer you want the brass to grow to the greater the discrepancy between pieces of brass. Which IME is worse than the not having much bullet in the neck...and a .168 - .170 FB leaves more than plenty in the neck.
IME letting it grow much past 2.010 is when the larger discrepancies show up.

 

[boltgunluvr]

Perhaps the OP is wondering about some theoretical slowing of formation of a hard carbon ring. Any thoughts ?

Seriously? How many of us 308 shooters have issues with carbon rings? After multitudes of 10K rounds, none for me. That's usually an issue with overbore cartridges.