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Breach pressure in a BSA sporting rifle


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59 shares, 51 points

 

Q:My uncle gave me a BSA sporting rifle in .30-06 calibre. While thisrifle appears to be very strong and rugged, I noticed that the barrelis stamped “18 tons per square inch.” If this markingrefers to British long tons of 2240 lbs that translates into apressure of only a little over 40,000 psi, or a lot less than the55,000 psi and more for which Amercian rifles of this calibre arerated. Is this rifle safe for use with American factory ammo and myhandloads?

CyrilWaters

 

A:Have no doubts about the strength of your BSA. The difference betweenthe mean service pressure of 18 tons per square inch and the 50,000to 60,000 psi more standard for the .30-06 in America is due to adifference in pressure measurement. In the U.S.A powder pressures areobtained by the “radial” method, in which a gas pistonthrough the side of the chamber compresses a copper crusher, fromwhich the peak pressure is calculated. The British, on the otherhand, use a “base” method whereby a suitable copper crusheris contained in a special breechblock. The cartridge case is oiled sothat it may move back bodily and compress the crusher. The greatermass of the base piston effects slightly the amount it compresses thecrusher. The pressures shown by base crushers are about 90-percent ofthose obtained by radial copper crushers. Soin fact, the 18 tonsmarked on your rifle would be about 20 tons or 45,000 psi by Americanmeasuring methods. By the same token British ammomakers rarely everloaded cartridges above 19 tons (47,500 psi) since they reckoned thatmost of their big game ammo would be used in the tropics whereprolonged exposure to high temperatures will raise firing pressuresconsiderably. In any event you need feel no concern about using anymodern factory ammo in that BSA of yours. The Mauser-type BSA has oneof the strongest, safest actions ever made.


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