I am confused on this subject. Can an informed person comment on the relationship (or lack there of) between pressure and bolt thrust? I have read magazine articles and internet forum threads that mention certain actions that can or can't handle high pressure, or can or can't handle heavy bolt thrust from dangerous game cartridges. This has always puzzled me because I thought that modern barrels would contain most of the pressure without expanding too much. I would imagine heavy bolt thrust would be more of an issue in, say, pre-1920 mausers, than high pressure, when modern barrels are used. Can bolt faces be bushed, firing pins and pin holes be narrowed to improve pressure handling? Does re-carburizing help with bolt thrust and/or pressure? Informed opinions highly appreciated.

Try the Lilja site.

http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm

Pressure is the number of pounds per square inch inside the cartridge case.

Bolt thrust is the pressure times the number of square inches of cross section of the ID of said case.

For a 30-06 the case ID is about .40...give or take. (same for all '06 cases)...and Pi R square equals 3.14159 X .2 X .2 = .1256 square inches and times about 60,000 PSI equals 7500 pounds of thrust the bolt and receiver must hold.

Larger magnum case.....more thrust

greater pressure......more thrust

larger case and greater pressure (RUM cases) nuch higher bolt thrust.

Most modern bolt actions today are capable of holding several times the thrust created by the firing of the cartridge.

quote:

With your formula, and with all other variables being equal, wouldn't a larger inside case diameter lower thrust?

No...unless this allowed the pressure to be lowered.....and at times this is the case. Magnums however utilize more powder to keep the pressure up and thrust is therefore increased because of greater number of square inches to push against.

So, with this formula a 416 Rigby would only have a little more bolt thrust than a 30-06. I used CUP of 43,000 rather than PSI for the Rigby calculation, as I don't have any PSI data on hand for the Rigby. The Rigby has a roughly .5" ID. How, then, does bolt thrust relate to recoil?

quote:

does bolt thrust relate to recoil?

For the most part it Dont at all.....

Recoil is mostly a factor of the total of bullet weight and powder expelled from the muzzle, it's velocity, and the weight of the gun.

Example:
Bolt thrust on a 30-06 is likely less than on a 220 Swift.....but significantly more recoil.

Your shoulder will not feel what the bolt feels....only the result of the bullet exiting the barrel...how big and how fast!

Thanks for all the great info. Whenever I want to know something firearms related, I can always get them answered here.

Matt

quote:

So, with this formula a 416 Rigby would only have a little more bolt thrust than a 30-06. I used CUP of 43,000 rather than PSI for the Rigby calculation, as I don't have any PSI data on hand for the Rigby.

The Rigby is loaded to about 47,000 PSI if that helps.....bolt thrust about 9,000 pounds.....

the 30-06 about 7,500 pounds.

The Rigby while a far larger case has minimally more bolt thrust.

Do not confuse CUP for PSI...they're not related at all!