help figuring COL AND freebore for .300 Weatherby

lightjunkie said:
but now I don't know how to figure out the free bore
Click to expand...

Why do you want to know the freebore length? It won't affect the length of the cartridge to know or not know it. Maximum cartridge length will still be limited by how far out the bullet was when you found it touched the lands. You can use Veral Smith's method (same one described in the link; upsetting a pure lead slug into the chamber) to learn the number. You can use Cerrosafe to make a chamber cast and measure the free bore length on that. But the information will only tell you something about the chamber reamer dimensions. Unless you are trying to get a reamer made that duplicates those dimensions exactly, I'm not clear what you will do with the number?

Perhaps the term is unclear. Check in the SAAMI glossary. In the image below, I added marking of the freebore just below the neck. Note that a freebore is often a thousandth or two over groove diameter, so the rifling doesn't actually begin immediately after the cylindrical freebore, but rather there is a tapering down that has to get to it first that finishes the jump. However, when most people use "freebore" they don't strictly adhere to the cylindrical definition and instead have it start where my drawing does, but then go all the way to the beginning of the lands.

308%20Chamber%20and%20round%20COL%20and%20Off%20lands_zps1dutyuuy.gif
 
Hornady makes a OAL gauge . MidwayUSA has them. Check it out, will help you find your OAL to your ogive. Another tool that is very easy an accurate for your OAL and Headspace is the RCBS Precision Mic. With your 300 Weatherby I wouldn't look to jam my rounds. Has to be able to feed follow up shots. If feeding one round at a time start out with a .020 jump and work up .005 to see what your rifle shoots best. My Remington 700 had so much free bore the bullet would almost be at the end of the case neck before to hit the rifling. I went with the listed OAL and found a load that worked. Hope I helped.
 
actually both helped

I'll have to keep saving up one but actually the Hornady Curved COL gauge was nice I'll have to save up but I do have 9+ months before next year's tags and I'd rather hankve it right
 
You must log in or register to reply here.
Back
Top