A question on throat erosion...(long)

I've been using my .300WSM as a primary hunting rifle for a number of years and it has seen a number of rounds- rough guess is 1k or so. In doing load development for the E-Tip, I measured the distance to the lands for the first time in well over a decade and came up with a OAL to lands of 2.927". The factory OAL is 2.80" with a max magazine length of 2.875"

Looking at CBTO with the E-Tip- the CBTO to lands is 2.371" and CBTO when loading to book length is 2.188" giving me a jump of 0.183". I know E-Tips like some jump... but wow.

I went and measured similar with my long favorite 180AB loads and got a CBTO to lands of 2.366". CBTO at book OAL 2.80" (same as factory ammo) of 2.184" for a jump of 0.182".

It seems odd that I could load to absolute max magazine length of 2.875" and still be more than 0.100" from lands with either load. That seems like a lot, but I've not measured a bunch of throats to date.

All that to say, are those numbers seeming routine? I know in the ye olde days the CW was to seat bullets out to 0.020" (or even touching!) the lands. I get that there might be some design consideration to keep people from jamming a bullet in the lands, but I can't even get closer than 100 thousandths. Or has the interim shooting just eroded the throat to the point that the lands are just further that much further away?

I've heard of people setting back a barrel, but I always associated it with rifles shot a whole lot more than I've shot this one.

Hard to say. I was able to get to the rifling with my M70’s in 300 WSM without too much trouble. But they were 3.0” magazines. I’d hazard a guess that you may have some throat erosion but it’s most likely always been longer than your magazine box.

I wouldn’t worry too much. If it’s still shooting and you’re seating Bullets straight it’ll likely shoot fine.

I would agree with SJB358.

Your numbers don't seem horribly out of line. I have a Sauer 100 in 6.5 Creedmoor which comes with a short magazine but uses a long action. When using the factory magazine I get significantly over .1 jump. With a 30-06 magazine, I can get it down to about 0.03".

SAAMI chamber for 300wsm. Any manufacturer is more than likely using this and I cannot imagine they would intentionally increase the throat length.


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Thanks for posting that! Going by my measurements, it looks like I've lost about 55 thousandths of throat. Yeah, with a 2.875 mag length, I'd never hit lands with any spitzer bullet I'm aware of.

That clears it up!

I can't get to the lands with quite a few rifles due to magazine length.
308 (Bergara, Sauer, Tikka, ...), 6,5 Creedmoor (Savage), 7x64, ...
Worst of all was a military Mauser in 6,5 X 55.
Bullets would be almost out of the case to get to the lands. But with 140 gr Accubonds it still shot sub Moa.


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