What is "your" reasonable jump space to the lands?


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Skulptor
February 2, 2013, 05:44 PM
Just curious as to what your personal opinion is about the set back length from max. oal to the realistic usable oal? (after in depth "plunk test")
I have seen a couple different opinions as to the lengths people prefer and was wondering if there was a reason for the different opinions. ie. possibly lead vs. cast, RN vs. TC, 9mm vs. .45, etc....
I am doing a 9mm but this may help .45 shooters as well.
Thanx.

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JLDickmon
February 2, 2013, 06:14 PM
as long as will chamber reliably.

I make up five dummy rounds when I set something up, and dry cycle them through the action..
I work up the load from there..

GLOOB
February 2, 2013, 07:33 PM
If I run into mag related feeding problems, I find the max OAL that appears to feed properly, then I reduce that by 10-15 mics. When talking chambering issues, this number is going to be a little more concrete. It either fits or it doesn't. So you can cut it closer, but you have to consider the amount of variation you get from your seating die and mix of brass. This is more a game of loading up 10 dummies of a mix of all your headstamps, and shortening them til all 10 pass. Then going shorter by another 5 mics or so for insurance. Just my perspective.

Skulptor
February 3, 2013, 01:28 PM
Sound like reasonable math.
But I'm still kinda interested in what works for a set back for others.I don't have any mag issues. I will try your method.
Thanx!!!!

fguffey
February 3, 2013, 02:01 PM
A very boring subject, in the real world, starts with “I want my bullet .002” off the lands, or touching or rat up there”, I am the fan of the running start, I want bullet jump, I do not want my bullet to even think about hesitating, I want my bullet past the rifling/lands before it realizes the bump (of passing the lands/rifling).

My rifle is going to shoot good when the bullet is off the lands or it is not going to get shot. I can not get interested in those conversations that go something like “Oh, my rifle just doesn’t like this or that, to get it to shoot I have to etc., etc..” Like Randy Newman, “I don’t (gotta) have to do nothing... .” I do know the distance the bullet travels before it hits the rifling, I do make transfers to move the chamber dimensions from the chamber to the seater dies.

I want my bullets up to speed before it hits the rifling, no hesitation, the bullet hits the rifling before it knows it is there, again, I am the fan of the running start.

F. Guffey

noylj
February 3, 2013, 02:45 PM
Semi-autos:
Lead bullets: I adjust COL so the case head is just flush with the breech (minimal head space). I have never seen any pressure signs from having the lead bullet in contact with the lede/rifling in any handgun.
Jacketed bullets: I back off 0.005" from the max COL that will chamber freely.
From there, I can reduce the COL if needed to ensure reliable feeding and chambering.

For a revolver, I always have at least 0.1" of the bearing surface of the bullet in the cylinder's throats.

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