Starting loads for the Gew 88 using IMR 4064?

[Silverplate]

Hi everyone,

I plan to work up a plinking load for my turked Gew 88/05 using Hornady 150 grain SP and IMR 4064. I've slugged the bore and have a .311" bore with .325" grooves.

All my reloading manuals use a 98 action for testing the 8x57JS, with the heavier loads approaching 49,000+ CUP. I believe the Gew 88 action is rated for a max of 40,000 CUP? I would like to keep my loads under 37,000 CUP to be on the safe side.

I have two copies of the online Hodgdon reloading data (2008 and 2013) and noticed that there is a large difference in charge weight when using IMR 4064 and a 150 grain bullet. It is interesting to note the differences between listed powder weight and pressure.

Hodgdon 2008 - no start load given/ max 36 grains, max pressure 37,000 CUP, velocity 2305 FPS.

Hodgdon 2013 - start 42 grains/ max 49.5 grains, 34,800 CUP/ 46,200 CUP, 2486/ 2839 FPS.

There is a difference of six grains between the 2008 max and the 2013 starting point. I don't know if a reduction of 10 percent from 36 grains would be going too low for the initial starting point.

What would be the safest starting point for these older actions?

Thanks.

Silverplate

 

[polaris]

I would go with 36grs, sounds right to me.

 

[Goldenlakepete]

My Lyman 47th edition doesn't give pressure readings for IMR-4064 with 150 gr bullets, however, with a 220 gr bullet and starting load of 35.2 grs of IMR-4064 the manual says that load produces only 29,300 CUP. The MAX load of 40 grs of IMR-4064 still only produces 35,800 CUP.

 

[Andy]

I'd go with the recent data, and work in the 40-44 gr range. If you start too far below the suggested minimum load you could get inconsistent ignition.

 

[Silverplate]

Thanks guys.

I'll try reducing the current data to 40 grains and see what I get for velocity. If it's in the 2300 to 2400 FPS range I'll take it as an indication of approaching the max pressure rating for this action. I'll work up or down depending on what I see.

Silverplate.