US869 in 30-338/.300 Lapua + 240MK

[jmden]

Tiff

Just ran the numbers in QL.

Using the standard case volume of 102gr, Sierra 240gr MK seated to a cartridge OAL of 3.7", and 97gr of US869, using 3625psi initiation pressure, the supplied case weighting factor of .55, and a guessed 26" barrel, resulted with 2832fps and a max chamber pressure of 64981 psi. The listed max pressure for the 30-338 Lapua is 63817 psi, so you might want to back off a little more. 94gr shows 57.7Kpsi, and that might be a better place to start! This was done with the Temp setting on 70 deg, but adjusting it down to avg 55 deg, the pressure falls to 63Kpsi, which is right under max listed pressure.

If you want to run the numbers yourself, send me a pm and I'll give you the QL info for US869.

Yes, one crucial piece of info about my load is that it is a cold weather load created for November elk hunting. 104g may not work well at 60F degrees. I keep these in the cooler at about 35F if its not about 40F or below. Sorry I forgot to mention that specifically. When I said 97 or 99 grains, I was thinking in about 40F temps or below.

However... If that is the necked down 338 Lap case, which the OP says it is, that case, as I understand it, and many attest to, is a much stronger cae than the RUM case, although the SAAMI loads don't reflect that. I get a case capacity of 114g H2O for the Lap case which puts it at pretty much exactly the same capacity as the RUM case. With it's extra strength, it should hold a RUM load, at appropriate temps, just fine.

 

[Tiff]

Tiff

Just ran the numbers in QL.

Using the standard case volume of 102gr, Sierra 240gr MK seated to a cartridge OAL of 3.7", and 97gr of US869, using 3625psi initiation pressure, the supplied case weighting factor of .55, and a guessed 26" barrel, resulted with 2832fps and a max chamber pressure of 64981 psi. The listed max pressure for the 30-338 Lapua is 63817 psi, so you might want to back off a little more. 94gr shows 57.7Kpsi, and that might be a better place to start! This was done with the Temp setting on 70 deg, but adjusting it down to avg 55 deg, the pressure falls to 63Kpsi, which is right under max listed pressure.

If you want to run the numbers yourself, send me a pm and I'll give you the QL info for US869.

Thankyou very much for that. I will start at 86gr since my COAL for the 240MK for a 10thou jump is little less at 3.500". Interesting that a newer version of Quickload lists the new lower max pressure of 63,817psi, for my rifle was proofed at 75,000psi for the old max operating pressure of 68,167psi! Personally I'd like to keep it a bit lower than that...

Thanks again for all your help

 

[Jon A]

Let us know how it goes, Tiff. I'm not optimistic the 240 will stay supersonic to 2000 yds but it'll be interesting to hear your results.