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Old May 3, 2013, 11:08 AM   #3
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 10,257
Quote:
Originally Posted by ops
Nobody pays attention to COAL on straight-walled pistol cartridges?
Not sure where you got that idea? If you read through threads on loading .45 Auto or any other pistol round on this forum you will find lots of folks pay close attention to cartridge overall length (COL or COAL if you hyphenate overall to over-all, as was done before 1950) in handgun loads.

Quote:
Originally Posted by ops
I have definitive proof that cartridge OAL on a 45ACP is paramount to group size-that is-paramount to top accuracy.
It can make a big difference with cast bullets. I've had the illustration below on this board for years. Seating cast bullets to headspace by bullet contact with the throat rather than the case mouth (third from left) has cut group size as much as 40% for me, and reduces leading.



With jacketed bullets, on the other hand, it does not seem to matter nearly as much. The 25 yard group below was shot with Hornady 200 grain JSWC's seated with the shoulder of the bearing surface at about 0.020" in front of the case mouth, as is typical of commercial loads. It was not near the throat.



Quote:
Originally Posted by ops
Why does no bullet manufacturer's ballistician or any old-timer that can shoot reputable back-woods bullseye groups that I have spoken with agree with or consider this seating depth factor?
Be careful here. Seating depth and COL are not the same thing. You control seating depth (how far the bullet goes into the case) by adjusting COL (Cartridge Overall Length), but unless your cases are exactly the same length, the same COL for all will not yield the same seating depth for all.

Seating Depth = Case Length + Bullet Length - COL

COL = Case Length + Bullet Length - Seating Depth
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