311284 keyhole

[Will]

I loaded some 311284 for my 30-06 03 springfield with 40gr 4831. They work well for hunting close in brush but my son tried some at longer ranges and found they started to keyhole at about 300yds and were nearly side ways by 500yds. Is this just because they were running out of rpms by this distance? He was using an 03A3 with a 2 grove barrel.

Will

[trooperdan]

No, the spin of a boolit slows very little over the flight-time. it is the velocity that is dropping and making it go unstable.

[Will]

How many FPS at the muzzel to be stable at 500yds?

[Bass Ackward]

How many FPS at the muzzel to be stable at 500yds?


Will,

No set rule. It takes what it takes.

But 40 grains for me is only 1750 fps muzzle. My ballistic program say that 500 yards is 850 fps. Just so you know.

[Larry Gibson]

The bullets are probably beginning to go subsonic around 300 yards and are buffeted by the turbulence. This further causes instability.

Larry Gibson

[fishhawk]

now wait a second here dan i got to think this out...if a boolit makes one turn for every 10 inches of forward motion the slower the velocity the slower the RPM of the boolit at 1750 FPS that boolit should spin at 126000 RPM but drop it to 1000 FPS and you drop to 72000 RPM so if he has dropped to 1000 FPS at 500 yds the RPM will be slower. or am i just blowing in the wind?

[Blammer]

don't equat forward motion with rotation.

once the rotation is started it will pretty much stay the same even though the forward motion (commonly referred to as FPS) will fall and eventually stop.

think of a top like a childs toy top.

Set it spinning and then count to two.

Sure the rotation has slowed but probably not enough to notice in the two count.

Same thing with a bullet. The two count is WAY more longer time than a bullet will typically travel. Starting with Max velocity out of the barrel and ending in min velocity 100's of yards away. There just isn't anything to affect the rotation, unlike velocity and forward motion where AIR is the big resistor.

[Larry Gibson]

Blammer is correct.

Once the bullet's RPM is established by the barrel twist and muzzle velocity it slows down very little during the bullets flight conversley to the forward velocity of the bullet.

Larry Gibson

[Bass Ackward]

When you think of a bullet flying from a two groove it will make you cringe. The bullet is completely deformed, redesigned, remolded, and rebalanced from what you originally launched. If you could see the bullet coming at you it would look like a football flying side ways with two dumbbell weights jammed on the end of the football. :grin:

Speed that thing up. My Two does OK with a 311284 with 60 grains of H-870 torched by a Fed 215. You don't say how hard your shooting, but if you have 15 BHN and I size right at .308 which is a little undersize for my bore, it will hold 1 1/2". It's a little dirty, so you will be happier if you have some carnauba in your lube. That's 2100 outta my tube. That keeps you just at 1100 fps, (the barrier) @ 500 yards.

[44man]

Thats the reason it is so hard to find a good boolit for BPCR. Darn things just don't start out fast enough and some little thing in the boolit design will make them go haywire down range. :confused:

[Larry Gibson]

Bass and 44man are correct. It's hard to push a 311284 that fast with accuracy and be able to stay sonic (the barrier as Bass mentions) to 500 yards let alone 600 yards for NMC matches. I swtched to 311299/314299 which has a better BC. Out of my 4 groove match '03 it barely hold sonic at 600 ysrds (won't do it on a cold day (below 40). Best acuracy is in the 1800 fps range but that won't cut it at 5-600 yards. I push it to 2100 fps and it just holds sonic to 600 yards. However accuracy runs 2 - 2.5 moa for 22 shots (clean barrel) vs 1.5 moa for the slower load. Have to give up a little accuracy initially to get there.

Larry Gibson

[Will]

If I bump the load of 4831 up to near 50gr should I get around 21-2200 fps? Will that keep stability out to 500yds? Can you shoot a WW bullet that fast and still have any accuracy?

[Bass Ackward]

If I bump the load of 4831 up to near 50gr should I get around 21-2200 fps? Will that keep stability out to 500yds? Can you shoot a WW bullet that fast and still have any accuracy?


You may have to harden it if you want to stay with 4831. 46 or 47 grains should get you to 2100 fps. But in the end, you just have to try it.