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Old March 25, 2000, 04:39 PM   #13
Walt Welch
Senior Member
Join Date: November 3, 1998
Location: Alamo, CA
Posts: 424
OAL affects two things: whether the round will fit in the magazine, and whether the round will function through the gun.

Pressure is not affected by OAL. It is affected by bullet seating depth. Two bullets of differing lengths, loaded to the same OAL will yield different, perhaps drastically different, pressures.

I would suggest that you follow recommended OAL for a given brand of bullet as given in the reloading manuals, most of which are available on line. Failing this, pull some factory rounds, and find out what the bullet seating depth is, by measuring the case, the bullet, and the OAL. You may well just find that the bullet is the same length. In which, the same OAL is acceptable. If not, simple calculation will yield seating depth.

OAL minus case length yields the amount of the bullet protruding from the case. Subtracting this protrusion from the bullet length gives you seating depth.

I once had a nasty scare when Remington increased the OAL of their 115 gr. JHP's by 0.035". Had I used the same OAL, since the ogives were the same, I would have markedly increased the pressures, almost certainly into a dangerous zone, as I had created a condition identical to bullet setback.

Hope this helps, Walt
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