Sierra's 7 RUM load suggestions

[bblaine2k]

Sierra\'s 7 RUM load suggestions

Hello LR brethren,

Just thought I'd pass on some info that may be of interest to the LR shooters using the 7mm Remington Ultra Mag.

E-mailed Sierra's Rich Machholz and asked for load suggestions with the 168 Match King.

He suggested the following for the 168 MK.

Hodgdons 1000 up to 88.0 grains
Hodgdons 50 BMG up to 98.0 grains
Reloader 22 up to 80.0 grains
Reloader 25 up to 82.0 grains

He suggested starting them 3 grains short and work your way up.

He also suggested 175 SBT's because of their "higher" ballistic coefficient which I couldn't find data on instead of the MK.

I'm sticking with the MK because I already have them and have had good initial accuracy with them.

Just wanted to pass this along.

Good shooting!

 

[dwm]

Re: Sierra\'s 7 RUM load suggestions

So if all of these powders will work, isn't the best choice the slowest burning one?

1. Much lower pressures from slower burning powder, easier on all components
2. Longer barrel life because it doesn't get as hot all in one place.
3. Small errors in charge weight are less significant to the overal charge weight
4. Slower burning powder is better for heavy for the caliber bullets
5. Slower burning powder makes better use of the really long barrels

I do have a question though, is powder temperature stability related to charge weight?

Or

Is a large charge weight more or less sensitive to variations in temperature?

Doug

All this doesn't really matter if it won't consistently produce tiny little groups though, huh?

 

[dwm]

Re: Sierra\'s 7 RUM load suggestions

I guess my last question was more about temperature sensitivity being chemically based as opposed to based on mass like metal.

If it is a chemical reaction that changes with rizing amounts of powder, then more powder could indeed make it worse.

Just a thought,

Doug

 

[bblaine2k]

Re: Sierra\'s 7 RUM load suggestions

Doug,

Don't wanna get too technical here because I don't think it is overly useful out in the field. But, large masses are less affected by changes in temperature than smaller masses. In other words, it is possible that a heavy (high mass) load could be less affected by temperature than another. I think it was Nosler that recommended that the best groups typically occur somewhere around 80% case capacity. That volume is what probably affects burn rate more than the mass(weight) of the load.

Bottom line, as you pointed out, what difference does it make when you find a load that shoots itty bitty holes in the paper. Other things come into play like air-powder volume ratio, primer type, etc. etc. but I try to focus on the steak instead of the peas!

By practicing a lot (different days, different temperatures, different ranges, elevations, positions, ad finitum) I usually iron out any concerns.

Good luck!