Thread: OAL = COL ?
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Old September 3, 2012, 10:54 AM   #25
tobnpr
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Join Date: August 1, 2010
Location: Tampa Bay
Posts: 2,837
Yep...
Be careful with OAL...

I recently made up a bunch of match handloads for my son's K-31, chambered in 7.5 x 55....

The Sierra manual specifies an OAL of 3.06"...

So, I loaded up 50 rounds of MatchKings at that length, since the modified case for the bullet comparator had not arrived yet....

He was telling me that he was having trouble closing the bolt...extraction was fine, just hard to close the bolt.

After about ten rounds, I took the rifle from him. Bolt closed fine with no round in the chamber. With no explanation, and not wanting to risk an out-of-battery firing, we put the rifle up.

When the modified case arrived, I put a bullet in it, and chucked it into the chamber. OAL to the lands was 2.845- a far cry from the 3.06 in the manual...

We were jamming the bullet into the rifling by about a quarter inch...not a good thing...The loads weren't hot, and that was likely a good thing.

Turns out that, after some research, Swiss rifles chambered in 7.5 x 55 had ALOT of variations in throat dimensions and length.

Sierra, IMO, should have made that clear in their manual- but they did not.

If you handload, there is no reason not to spend the few bucks on a bullet comparator to develop your loaded lengths. More precision, greater accuracy.
Length to the lands varies not just by bullet weight, but ogive shape.

I realize this may not be as big an issue with handguns, but it should be noted nonetheless.
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