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SHR970 · August 23, 2012, 05:14 PM

Your pressures are also effected by the chamber, throat, and barrel (land/ groove diameter). If your chamber is tight at the case neck it can raise pressures. If you have a short or long throat / freebore your pressures will vary considerably. If you have a tight or loose bore that will also effect your pressures.

Example: 300 Weatherby Magnum. Known for a long freebore in typical Weahterby style for Weatherby brand rifles. If you have a rifle that is made with a short freebore (Say on a Rem 700 action), a minimum SAAMI spec chamber, and a tight barrel you can hit pressure limits early on and not hit close to book velocities.

OTOH if you take a 7.62 Mosin who's chamber is barely go on the field gauge, has a barrel worn from years, corrosion, and cleaning, and a worn throat that has lots of extra free bore, you can possibly exceed book by a noticeable margin and still be within pressure limits.

We must keep in mind that pressure barrels and chambers tend to be on the tight side of SAAMI spec to begin with. They do this to take into account the worst possible scenario that should be allowed to leave the factory.

August 23, 2012, 05:14 PM	#36
SHR970 Senior Member Join Date: January 24, 2011 Posts: 1,427	Your pressures are also effected by the chamber, throat, and barrel (land/ groove diameter). If your chamber is tight at the case neck it can raise pressures. If you have a short or long throat / freebore your pressures will vary considerably. If you have a tight or loose bore that will also effect your pressures. Example: 300 Weatherby Magnum. Known for a long freebore in typical Weahterby style for Weatherby brand rifles. If you have a rifle that is made with a short freebore (Say on a Rem 700 action), a minimum SAAMI spec chamber, and a tight barrel you can hit pressure limits early on and not hit close to book velocities. OTOH if you take a 7.62 Mosin who's chamber is barely go on the field gauge, has a barrel worn from years, corrosion, and cleaning, and a worn throat that has lots of extra free bore, you can possibly exceed book by a noticeable margin and still be within pressure limits. We must keep in mind that pressure barrels and chambers tend to be on the tight side of SAAMI spec to begin with. They do this to take into account the worst possible scenario that should be allowed to leave the factory.