.308 Seating Depth/Load question

[jakeb]

Hey All - FIRST POST!

I've just started loading a practice load and have run into a sticky spot...

The load in question is a .308 Win load using REM brass, WIN LR primers and IMR 3031 powder pushing a Hornady 150gr FMJ w/cannelure.

The Hodgdon site has the following load data that I was going to start with...

40.2gr - COL 2.800" - VEL 2658 - Pressure 44,300 psi

The issue I'm coming against is that if I seat to 2.800" the cannelure is above the top of the brass (trimmed to 2.005"). Once I get this batch fired I will measure my chamber and trim my brass to that length.

To get a decent crimp on the cannelure I have seated the bullet to 2.699". I also have measured a factory Remington UMC 150gr round and it using a similar bullet has a COL of 2.697".

Am I in risk of overly high pressure starting at the lowest end of the published load at this seating depth?

Thanks,

Jake

 

[Walkalong]

You are fine. That is how they are meant to be loaded. Crimp into the cannelure and that is the correct O.A.L. for that bullet.

 

[jakeb]

Thanks Walkalong, I appreciate it!

 

[kludge]

Once I get this batch fired I will measure my chamber and trim my brass to that length.

Jake, what do you mean by this? FWIW, don't ever go past the "max" length. Standard chamber necks are cut a little bit long, like about 0.010" past the "max" case length to give clearance for the case mouth to expand and stretch to release the bullet. Without the added chamber length over max case length you can pinch the bullet, raising chamber pressure.

IOW, If you let your brass grow to the chamber length you will run into problems. Trim them when they get to "max" or beyond.

I've seen new brass stretch 0.010" to 0.015" on the first firing, since most factory ammo is sized well below what will normally feed and be reliable in many guns - people with small or dirty chambers don't like it when there ammo doesn't feed. Many full length sizing dies will do the same thing

If you have new brass you will likely have to trim after the first firing, but then after that (assuming a bolt gun) you can adjust your dies for minimal headspace (like 0.002" to 0.003") and your brass will last longer and you will trim less often. Much of the factory ammo can have 0.006" perhaps more.

BTW, good first post.

 

[jakeb]

Jake, what do you mean by this? FWIW, don't ever go past the "max" length. Standard chamber necks are cut a little bit long, like about 0.010" past the "max" case length to give clearance for the case mouth to expand and stretch to release the bullet. Without the added chamber length over max case length you can pinch the bullet, raising chamber pressure.

kludge,

I would be using a Sinclair Chamber Length Gage and then trimming the brass down to just under the measured value (0.005")...averaging 3-5 measurements to be sure. More than likely my chamber will end up being close to recommended Trim to Length.

Sinclair Chamber Length Gage



And BTW - Thanks for the praise on the first post!

 

[rcmodel]

You are wasting your time treating your brass as if you were shooting a benchrest match rifle, and then using FMJ bullets in it.

Just trim the dang things to 2.005" and stop obsessing about chamber length.
Once they get past 2.016", trim them again.

It will make absolutely no difference at all unless you use more accurate bullets then those FMJ. And even then it will make no difference if they are all the same length.

rc

 

[jakeb]

I just thought I would do that so that when I do start load development for some of my heavier bullets I would already have the brass trim length sorted out. Like I said earlier...practice load...once I go for my hunting load and my competition load I'll be ready with the proper trim lengths for new brass.

 

[Walkalong]

Don't cut it to close on case length. It won't help, even with good bullets, and can get you in trouble.

 

[USSR]

Good advice by rcmodel and Walkalong. Doing what you are proposing won't help you in any measurable way.

Don