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300grn 338, seating depth?

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Unread 07-06-2009, 09:39 AM
Silver Member
Join Date: Oct 2008
Posts: 106
300grn 338, seating depth?

What are you guys finding for seating depth on the sierras 300grn 338 bullets that shoot the best are they in or out of the lands and all that good stuff?
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Unread 07-06-2009, 11:40 AM
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Join Date: Jun 2004
Location: Texas
Posts: 1,075
Re: 300grn 338, seating depth?

I've only shot them in a .338 x .378 Wby, but the longest load I've tried is 4.00" OAL. That still leaves me with .115" of freebore in my factory dimension chamber. I don't intend to get any closer to the rifling than that. I have seen 1/2 moa groups in several custom Wby Boomers with factory magazine length ammo, so the 1/4"+ freebore that they're shooting through doesn't seem to hurt accuracy. The 300gr Smkhp's are too long to seat to mag length in my opinion and need to be single loaded. If you decide to shoot the 300 gr bullets in loads that exceed magazine length and in chambers that have a lot of freebore, you'll have a lot of room to experiment with oal. I wouldn't get closer than .100" off the rifling, but you should still be able to find a sweet spot.

Stay safe, Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member

A big fast bullet will beat a little fast bullet every time
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Unread 07-07-2009, 06:53 PM
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Join Date: Jul 2009
Location: Greenbrier, Arkansas
Posts: 78
Re: 300grn 338, seating depth?

Barnes says 0.050 back from contact with lands.
Michael M. Moore
NRA # 166336949
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Unread 07-07-2009, 07:59 PM
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Join Date: Jan 2004
Location: Blackfoot, Idaho
Posts: 8,876
Re: 300grn 338, seating depth?

I rig up a dummy case that "just" holds the 300 SMK. I then let the chamber seat the bullet.

That usually results in the best of everything, velocity and accuracy.

The action is a 700 REM single shot and loaded that way. A loaded round can be barely extracted. Cartridge is 338 RUM chamber is factory.
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Unread 07-08-2009, 06:13 AM
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Join Date: Jul 2006
Location: Harrisburg, PA
Posts: 2,764
Re: 300grn 338, seating depth?


All of my .338-.408's like the 300 SMK between .005" and .015" off the lands.
I've had them on, and just "in" with no appreciable gain in accuracy.
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