QUICKLOAD help with 6-284?

[6ixxer]

I'm shooting a 6mm-284 that seems to love Hodgdon Retumbo. Chrony shows 5-shot spread of only 21 fps and groups are 0.51" at 200 yards. However, I'm not getting the velocity I expected. Can someone run on Quickload and help me out with what the simulation shows with expected muzzle velocity?

Rem 700
Douglas 28", 1 in 8"
Smith: Dave Carver @ IT&D
Lapua 6.5/284 case sized and trimed to 2.150"
COL = 3.030"
Berger 105 gr. VLDs G1=0.532, G7=0.272
Hodgdon Retumbo @ 53.5 gr
Fed 215M

Thanks in advance

 

[LouBoyd]

The Quickload database shows only a 6mmx284 Shehane cartridge but I suspect that may not the same as what you're shooting. That case has a capacity of 67 grains H20. With a Berger 105 VLD seated to 3.03" and the case trimmed to 2.15 the shank is only 0.167" in the case.

The problem is that with 53.5 grains Retumbo the load calculates to be a 91.2% case fill and gives only 36342 PSI. For a 28" barrel Quickload calculates the muzzle velocity at 2921 fps.

Something is odd. 36KPSI is low for a cartridge rated 59456 psi. Either the database cartridge is not the same case capacity as the cartridge you have or it's just a light load. It's not unusual for the database to be wrong on wildcat cartridges. The case volume depends on the chamber reamer and can vary for different brass manufacturers. If you could weigh a fired case (fired in that rifle and not resized) empty and then filled with water and subtract to get the case volume in grains H2O Quickload give a more reliable answer. Make sure you don't leave bubbles in the case or drops on the outside for the wet reading.

With any ballistic calculations including Quickload the answers are no better than the data given it. This is why Quickload needs to be used with a chronograph while working up loads. A chronograph reading would indicate if that was just a weak load or if the case capacity data is wrong.