Am I figuring this right? .300 WSM freebore

I don’t know about the bore, but between 28 and 30 I’d say 28. In a hunting rifle I’d actually prefer 26 or 24. The point in a 300wsm (over 300 win. mag.) is shorter and lighter. The cartridge is remarkably efficient, so you don’t need a very long barrel.

also good luck finding powder.

Notwithstanding advice from a smith or competitive shooter familiar with the bullet used in WSM - Get the bullet dims, plan your seating depth target based on the neck length and boattail length, then see how much bearing surface you have left in front of the neck. Add desired jump and see how far you might be from either reamer.

https://www.wheeleraccuracy.com/
Give Alex a call, he is an authority on the subject and a good dude as well.

https://forum.accurateshooter.com/t...-1000yds-and-what-barrel-type-to-use.4078311/

additional reading for the op

On a side note... remember, freebore is sometimes used to help mitigate pressure spikes.

Look at the freebore on most Weatherby made rifles, chambered in the Weatherby cartridges.

https://faq.weatherby.com/free-bore-on-weatherby-magnum-calibers

And even the 5.56 NATO chamber uses a longer freebore.

So watch for pressure signs if you use a bullet seated closer to the lands.

I am not recommending anything. Just throwing out som visuall aids that may give some perspective to your questions.
I scaled an image of the 30 cal. Nosler 180 gr. AccuBond bullet from the photo on the Nosler website then entering the SAAMI 300 Win Short Magnum dimension values into the Cast Bullet Design~Ultimate software to make up these drawings.
Perhaps they can show a little more insight into the fit of the bullet in a SAAMI spec chamber.










Hope this Helps.

Respectfully
Tom Myers
25820 CoRd 26, Sebeka, MN 56477
[email protected]
https://www.tmtpages.com

This visual representation above Tom provided (wrong bullet for the OP, but you get the idea) is the mathematics I suggested above. Berger offers dimensions of their bullets in their manual, just plot out the lengths and see where your bearing surface to ogive transition ends up. You may not be able to do the math to account for the leade, and of course, a thousandths of throat diameter change throws everything off considerably, but you’ll at least get an idea of where you’ll end up.

The better option, as I mentioned in my first, is to contact an experienced rifle builder - like Alex Wheeler that @South Prairie Jim recommended - to gain access to their experience in cutting chambers to put leades in front of bullets which are placed in cases, all optimally for performance.

bfoosh006 said:

watch for pressure signs if you use a seat closer to the lands.

Click to expand...

Pressure - for a given charge weight - decreases as we seat longer, until we reach the lands.

Equally, entering here, the 5.56 increased freebore over the 223 isn’t as much a concession for pressure based on bullet jump, but rather to allow longer bullets be used without jamming, noting specifically that pressure is reduced when seating longer, UNTIL we touch the lands.

IALoder said:

I was planning on making up a couple dummy rounds, but th barrel maker I've been wanting to use said he only has a SAAMI reamer in .300 WSM, no throat reamer right now. The other one has a max 27" barrel, but has a throat reamer and can do whatever I want. With the WSM being for long range and the 7mm RM (24") going back to hunting duty, I'm leaning towards a 30" to wring out some more velocity.

Click to expand...

maybe you should switch your hunting and target rifle tasks. the 7MM would be better then the 30 for long range work.also shouldnt the gunsmith know what has to be done for your bullet of choice? I had a 1x8 twist 22-250 barrel put on a ruger target rifle and the guy asked me what bullet I wanted it throated for.