Jump-to-the-lands question

RVNvet · Sep 20, 2009

After doing some careful measurements, I find that my 7.7 Japanese 125 grain bullet reload (see below thread 'Houston do I have a problem?') will jump-to-the-lands .32 of an inch. I also checked and determined that the 180 grain Norma bullet jumps .22 of an inch. Is this excessive, or dangerous? Will I loose any gas before the bullets reach the lands?
Thanks,
Max

(7.7 Arisaka sniper conversion)

HappyRoman · Sep 20, 2009

When Weatherby came out with the high (really High) pressure rounds, the space your talking about was the throat or "FREEBORE" space. this allowed for Higher Pressure from a cartridge as it has a small space to expand just before it pushes the bullet forward.
In order times, when the variety of bullet lengths/weights was not as today the Ogive was not always long enough to fit the bullet time and to the Ogive to the Lans and grooves..
I beleive you should be just fine,, If it is shooting well, and Your having no pressure signs or issues, I think you have a winner. Nice looking piece. that's my .02c/worth sr

rodell · Sep 21, 2009

Not a problem if it shoots. As HappyRoman points out, Weatherby calibers have a relatively long freebore.

Given where you are with the rounds, I doubt you could touch the lands with any known bullet. You might want to check with a borescope and make sure the throat has not eroded, but is really that far out there.

As far as gas loss, it isn't likely. Check the neck of the case after firing. Since you're using fireformed brass, I doubt it very much.

Bob

Oohrah · Sep 23, 2009

You are more apt to have acurracy problem with the short body light bullets being accurate due to rifling twist than free bore. Yeah both can have an effect, or maybe not. Back a few years when I first started loading with an old Lyman 310 tool for an 03A3 DCM rifle, I used a 100grain Hornady Short Jacket plinkers. They should not shot well at all with that 1 in 10 barrel. Not target accuracy, but 1.5 to under 2" at 100 yards. Flat tore up Jack Rabbits up to 150 yards, with still nasty beyond. These were loaded with 4559 powder to under 2000fps. Same rifle with 180gr. Sierras and a casefull
of 4831, would shoot sub minute of angle all day. With those light bullets, I can't picture a danger, but they may not prove to be an accurate load. Your case necks may prove to be a little smoked up. By all means follow your loading manuel for that bullet weight, and what ever powder you use