.308WIN Actual Chamber Length vs SAAMI

[roscoe53]

This is my go-to site for technical questions so here's what I'm trying to determine. SAAMI spec for .308Win shows a maximum length of 2.015". I used a Sinclair Chamber Gauge and found that my chamber measures 2.0465". If I trim .010" off the case length will exceed SAAMI spec of 2.015" vs 2.0365". The trim length in manuals call for 2.005". Two questions: 1) Is there any advantage to not trimming all the way back to the 2.005" and trimming .010" less than the actual measured length and 2) Is there an issue with exceeding SAAMI spec even though my chamber seems longer. I figured out how to measure for overall length with bullet, but didn't know if I was missing something on the actual cartridge / chamber length. Thanks guys!

 

[FLIGHT762]

Your chamber doesn't seem longer, it is longer. I bought the Sinclair tool and checked my two 308 bolt guns. One was 2.040" and the other 2.045". I started laughing since I had been so anal about trimming everything getting close to 2.015" thinking I would blow myself up if I went past 2.015".

No need to trim until you get close to your measured chamber length. Let them grow and pick a length you want to trim back to. 2.030" ? It's your choice.

 

[918v]

Trimming short results in less bullet pull. Depending on the bullet and how far your lands are and your jump, trimming long may be better.

 

[roscoe53]

Thanks guys, that's helpful. I'm trying to optimize every way that I can and just wasn't sure about this - as you stated, I didn't want to long and possibly crimp the neck thus creating increased pressure. I had no idea of trimming longer would be positive or negative. As it stands now, using Sierra 168gr. HPBT MK w/ 43gr of Varget seated .005" jump repeatedly produced .250 or less at 100 yards. Now, wanting to work up to 600 yd I'm looking for every little thing I can that might make a difference. Appreciate your input.

 

[GhengisAhn175]

Ensure youre velocities are stable (low ES/SD) before
continuing.

Small groups doesnt mean stable load

 

[roscoe53]

ES Ave 21 / SD Ave 9. Trying to use up the rest of my CCI 200 and try some Fed or CCI BR to try and bring the ES down.

 

[GhengisAhn175]

Looks like you can tweak seat depth or neck tension if you want to try and get it down but 21/9 is NOT bad, actually very good.

Unless you're shooting at 1500+ yards you can't say that a 21/9 is what caused you to miss an MOA sized target

 

[roscoe53]

LOL, I have plenty of excuses for missing at 1500! My range is only 600 yards but here Georgia has some 1,000 yard ranges. Question: is there any advantage to maximizing neck length so long I keep under my chamber dimension? I will take a look at neck tension as you suggest - thank you!

 

[GhengisAhn175]

More neck length = can seat bullet longer w/ better support.

Only desireable if you're single feeding to go past mag COAL.

Its not bad to have a longer neck BUT you want uniform neck length with all your cases so just trim to match lengths