Houston, do I have a problem? (Newbie question)

RVNvet · Sep 16, 2009

In over fifty years of shooting, the cartridge on the left is the first round I have ever loaded. It's a 'dummy' round, with no primer or powder. I adjusted my dies carefully, and think I have them set correctly.

Both rounds are 7.7 Japanese (7.7x58). I'm trying to do up a good long-distance round for 'sniper' competitions at my gun club (200-300-600 yards, and possibly 800-1,000 at another range). I figured a smaller bullet would give me a flatter trajectory. (My Type 99 Arisaka has been fitted with a rangefinder scope, and had a 'spoon' bolt handle fabricated.)

My reload is with a Sierra 303 caliber (.311) 125 grain bullet, in once-fired brass...fired by my own rifle.
The other bullet is a standard Norma 180 grain bullet round.

As you can see, my reload is much shorter than the Norma round. It mics at 2.91 inches, compared to the Norma's 3.03 inches. Since this puts the round at-battery quite a bit short of the lands and grooves, is that going to be a problem? If so, what would be the solution? And am I correct in thinking I'll get more accuracy (and a flatter trajectory) using the smaller bullet with the same powder load as I would use with a larger bullet? And while I'm asking questions, would a .312 bullet be even better, or possibly a boat-tail? And, since I'm using a much lighter bullet, would I be safe starting with the 'maximum' load listed in the reloading charts? (My Arisaka is early issue, not 'last-ditch.')

Thanks,
Max

Huntbear · Sep 17, 2009

Heavier bullet weights are better down range than lighter bullets, as a general rule. They retain more energy, "buck" the wind better, etc.... Only way to tell is shoot em against each other and compare.

Jamie6.5 · Sep 17, 2009

Lots to consider here. First concerning bullet weight, with lighter slugs you gain velocity but almost always lose ballistic coefficient (BC). Like HB said above, if you want to know if it's a gain you're gonna have to shoot them both, in the same conditions (wind range, temp etc.) to tell.
Second thing is the "jump to the lands." Most MilSurps have long throats or freebore. This makes for a long "jump" after the bullet leaves the case but before it engages the rifling. This gives lots of opportunity for the bullet to engage the rifling out of alignment, inducing a yaw effect and causing groups to open up.
If you are going to compete with this rifle you should find where a particular bullet engages the rifling with a cartridge length/comparator setup. When you change bullets you need to start over with this as different bullets engage at different points based on their ogive/bearing surface relationship.
Don't dismay if you can't reach the lands with a bullet in the case though. Some rifle/bullet combos seem to like to jump. Others don't.
I would start with what you have, using a variety of powders, and start shooting them and watch for pressure signs. When you have reached the velocity and pressure you are comfortable with, and have consistent accuracy, then start loading the bullets out farther in the case (closer to the lands) and look for an accuracy gain. NEVER start at the max load!! If your bullet isn't listed in your books, call the manufacturer for a recommendation or have someone run a quickload recipe for you.
Remember that most cartridges need at least 2/3rds ([.311"/3]*2=.207") of a bullet diameter in the neck to develop consistent pressures leaving the case. Don't get it too far out there!

This is a pretty intensive process that can get expensive and time consuming. But if you are really interested in results, its a lot of fun and rewarding too.

Google up "ladder testing" and OCW and/or OBT testing also. These are different methods used to find what your rifle/load performs best with.

Good luck and have fun!