.308 Trim Length

[yukonal]

I've had carbon rings in 2 different 223's, and a 6 BR. Are those cartridges overbore?


Original post, 2nd paragraph/question...

 

[6BRinNZ]

I've had carbon rings in 2 different 223's, and a 6 BR. Are those cartridges overbore?


Original post, 2nd paragraph/question...

Using a bore scope I have seen carbon rings forming up in the .308. I scrub them out before they become an issue ~300 rounds or so.

 

[USMCDOC]

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.

Had the same problem with some .223 brass i had, a lot of it was so short, i felt that it would have proved to be inconsistent to use. I am talking about 5,6 and 7K short.

 

[XTR]

I just stumbled on this one.

So I have a 6SLR and I was wondering if I needed to think about trimming, but since it's a wildcat there isn't any set value. Some time back I got 6 and 30 cal chamber length checkers from Sinclair but never got to using them.

Checked the 6SLR... um, yea, that's never going to need trimming. My once fired brass is still over .030 short of the end of the chamber..... Now I thought, hmmm... what about my F-TR rifles?

All are chambered with a 2013 FTR reamer.

yea, 2.037.

All these yrs of trimming at 2.015 and initial trims at 2.005. Yea, that's behind me now.

 

[T-shooter]

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.

The manuals say the "maximum" trim length is 2.015". I'm sure there is some safety room there. Only problem going too long is if the neck contacts the step in the chamber possibly causing it to pinch/crimp against the bullet and increase pressure. I just trim to 2.005" and not worry about it. My neck turning tool is also set to work from that length. I don't think I've ever had any grow to the 2.015" length.

 

[SheepDog]

Actually the manuals list the maximum case length at 2.015 which is the SAAMI specified length. The maximum trim to length would be the length of your chamber from bolt face to the end of the chambers neck minus about .003" to .005" and yes, as long as you can accurately measure that distance it provides better bullet support. If you use the listed overall cartridge length (loaded) that is listed in the book you won't get any extra room for powder. I have never found a problem with fitting a case to the chamber unless someone else wants to use your ammo.

 

[dcali]

As long as the case fits, you are good. Just pay attention. Cases often grow erratically, varrying by several thousandths within the same batch. So you want to keep a margin for safety's sake. The end of the chamber is angled- turning it into a makeshift crimp die if you let the cases get too long. 10-20 thousandths of clearance is fine.

 

[johnfred1965]

I don't remember where I read this theory, but it claimed that the more clearance from the neck to the end of the chamber allowed the bullet to obturate(?) up to the neck diameter, then get squeezed back down going through the throat. Supposedly this would round the neck/throat junction, and cause more copper fouling when the bullet is squeezed back to size. This sounds feasible, but weather it really affects your accuracy or not is open for debate. Just some more fuel for the fire. John