lube and velocity.

[mto7464]

It seems when I try to push my velocity in my K31, using linotype with 50/50 beesway/alox, I start to lose my groups. It seems to be starting around 2050-2100. Could this be a lube issue? The other day at 1950 fps I was getting sub 2" groups then yeaterday with a step up 3-5" groups.

boolit is lyman 165 SIL.

[Larry Gibson]

mto7464

Not a lube issue at all. I've conducted recent tests to 2500 fps with two different .30 cal cast bullets (Linotype alloy was used) in 3 different .308 Winchester rifles with 5 different lubes. Alox/beeswax 50/50 worked as well as the highly touted "new" lubes. I recently shot a 2" group that had 9 of the shots in 1.5". This was with a 14" twist Palma barrel using 311466 over 34 gr of 4895. Velocity was 2519 fps and the RPM was 129,600. At 2635 fps (135,600 RPM) the first 6 shots went into 1.88". At 2827 fps (145,500 RPM) the first 5 shots went into 2.75". Thus you can see accuracy at high velocity is quite possible and consistent if one keeps the RPM within the threshold. Even at high velocity it is obvious that the increased RPM is beginning to cause a corresponding decrease in accuracy. That bullet at 2 moa accuracy at 2650-2750 fps would be a 300 yard deer killer on any day. BTW; Lube for the above bullet was Javelina and there was no leading.

I plan on testing LBT and 2700+ lubes with the 311466 over 36, 38 and 40 gr of 4895 again (previous test was with 311291). The velocity level should run from 2600+ fps to 2800+ fps. The bullets are already cast and are the same batch as with the above mentioned loads used with Javelina lube. The Javelina appears to be pooping out above the 2519 fps load. I will see if the other two lubes perform some sort of magic.

Your problem is RPM and it is a classic case of it. You have come up against the RPM threshold with that load in your rifle. The RPM threshold is most often between 125,000 and 140,000 RPM. It is where the centrifugal force of the RPM overcomes the rotational stability of the bullet while in flight and inaccuracy begins to occur.

What is the load you are using with the Lyman 165 SIL?

You can do some things to push the threshold and obtain accuracy at a higher velocity. However with that bullet and the twist of the K31 accuracy at 1950 fps is going to be about as good as it gets. At 1950 fps you are already pushing over 140,000 RPM.

Larry Gibson