Case Length And OAL measurement

[Eric1234]

Hey guys,

This might be a dumb question but I haven't been able to find a good answer. I'm a long time gun enthusiasts but fairly new to making hand loads..

My question is how important is it to trim all your cases to the same length if you're seating your bullets based off the OAL measurements?

I'm trimming. 308.. I have case variences of 2.35 to 2.65. I'm playing around with different setting depths of .020 -.005. So far .005 is the most accurate with 178 grain AMAX & H4895. Lapua brass, Shooting a Savage 10 FCP, Shilen Match Barrel 26" 1/10 twist.

 

[Patch700]

My question is how important is it to trim all your cases to the same length if you're seating your bullets based off the OAL measurements?
.

The simple answer is that it isn't... Being that you're measuring from base to bullet tip you are leaving a possible .050" variance in your rounds.. So as long as you are not too long with your brass you won't see a difference accuracy wise.

 

[Eric1234]

The simple answer is that it isn't... Being that you're measuring from base to bullet tip you are leaving a possible .050" variance in your rounds.. So as long as you are not too long with your brass you won't see a difference accuracy wise.

Thank you for the info.. Thats great news. Now If I could just get my hands on some dang Varget down here in Dallas, TX I would be set.. It's like gold around here. Only 1-2 places carry it and they can't order enough.

 

[Patch700]

If you were to start measuring your loaded rounds with an appropriate comparator that measures off the bullets ogive and were able to hold tolerences to .001" then you may consider keeping your brass length to withn the same parameters.. Differing lengths in brass can have an effect in areas such as bullet grip etc that may show up on paper... Those differences would be lost in the noise so to speak if you were measuring OAL from base to tip of bullet is what i should say.

 

[dcali]

Brass trimming is mostly a safety issue - if you let it get too long, it can jam into the throat, which is bad...

And yeah, get a bullet comparator - you'll get much more consistent measurements. It's a cheap tool that is almost a requirement once you get more into reloading. I like the Hornady tool, but there are others that work just as well.

 

[Ned Ludd]

The amount of brass gripping the bullet is critical for consistency. Trim your cases as consistently as you possibly can, regardless of the measurement method you use to determine seating depth of a loaded round.

The next issue is the measurement process itself. Precision is all about consistency/reproducibility. Using COAL as a method for estimating seating depth is not optimal because of the significant variance in bullet OAL, even those from within a single lot. If you're measuring COAL, that means you already have some kind of calipers. Get yourself a bullet comparator and the appropriate insert and measure cartridge base-to-ogive (CBTO). It's a better way of doing it and the cost isn't much at all:

http://www.sinclairintl.com/reloadi...insert-style-bullet-comparator-prod34014.aspx

http://www.sinclairintl.com/reloadi...r-set-22-6mm-25-270-7mm-30-cal-prod35659.aspx

 

[waldo1979]

Hey guys,

This might be a dumb question but I haven't been able to find a good answer. I'm a long time gun enthusiasts but fairly new to making hand loads..

My question is how important is it to trim all your cases to the same length if you're seating your bullets based off the OAL measurements?

I'm trimming. 308.. I have case variences of 2.35 to 2.65. I'm playing around with different setting depths of .020 -.005. So far .005 is the most accurate with 178 grain AMAX & H4895. Lapua brass, Shooting a Savage 10 FCP, Shilen Match Barrel 26" 1/10 twist.

when you size your brass with a neck/full length sizing die the expander ball it tends to cause the brass to grow. Trimming is just to make sure it will still fit in the chamber. The SAAMI spec for trim length is 2.015" most books say trim to 2.005" but actual chambers have way more slack. Check out this PT&G FTR reamer for example... the neck is 2.025":
http://s1308.photobucket.com/user/golf0312/media/image-1_zpsceb5a4f7.jpg.html

A good strategy would be to trim every other reload. I've been told that irregular lengths can result in some carbon being pushed off into the bore. Not sure how true that is.

The A-Max is a Secant profile and likes to be jammed into the rifling (hence the short 0.005" jump shooting good).

For COAL measurements i prefer this gauge over the stony point gauge:
http://www.sinclairintl.com/reloadi...lair-bullet-seating-depth-tool-prod35491.aspx

It lets you measure using your sized brass and produces more repeatable results than the Hornady/Stoney Point gauge.

 

[Steve Ladino]

Important to have same length brass ? Absolutely !