Understanding Pressure Signs.

[Potashminer]

Good information about the "long throating" thing. I was told on CGN that STIGA did similar to be able to make 30-06 chambered rifles from the M94/M96 Swede receivers - take the peak load off the bolt and receiver - but, as per your post, may not actually see a reduction in velocity at the muzzle. Cool.

I think that I follow the idea - muzzle velocity not really a function of peak pressure, so much as the "volume under the pressure curve". So I think the extra free-bore drops that peak level, but allows similar or perhaps slightly more "volume" on the graph...

I had previously read similar about the Weatherby - in that case, it was a "custom made" barrel without that Weatherby free-bore - would lock up the bolt tight with factory Weatherby ammo. Had nothing to do with accuracy - was from a time when "speed" was everything - who cared where it was actually going, so long as it went there faster than the other guy's!!!

 

[dan belisle]

Good information about the "long throating" thing. I was told on CGN that STIGA did similar to be able to make 30-06 chambered rifles from the M94/M96 Swede receivers - take the peak load off the bolt and receiver - but, as per your post, may not actually see a reduction in velocity at the muzzle. Cool.

I think that I follow the idea - muzzle velocity not really a function of peak pressure, so much as the "volume under the pressure curve". So I think the extra free-bore drops that peak level, but allows similar or perhaps slightly more "volume" on the graph...

I had previously read similar about the Weatherby - in that case, it was a "custom made" barrel without that Weatherby free-bore - would lock up the bolt tight with factory Weatherby ammo. Had nothing to do with accuracy - was from a time when "speed" was everything - who cared where it was actually going, so long as it went there faster than the other guy's!!!

On a Weatherby note, you need to pay attention to the generation of Weatherby it is. Older ones had a LOT more free bore than newer ones do. Almost double in some cases. Measure first, then calculate what you can do with what's there. - dan

 

[Andy]

The thing that additional freebore gives is more effective case capacity, which is the case capacity under the bullet once it engages with the rifling.

That provides two options; lower pressure at a given MV; or more commonly, more powder at a given pressure for a higher MV.