.257 Roberts, 120g Grand Slam and Partition

[Coyote Hunter]

Thought I would post the results of some tests I got about a week ago (was out of town all last week or would have posted sooner).

The goal was to find good loads with the Speer 120g Grand Slam or Nosler 120g Partition.  Good, as in "good enough" to go down to Raton, NM, and the NRA Whittington Center and plink at the metallic silhouettes out to 500 meters and the White Buffalo at 1,000 meters.  (My 7mm Mag and .22-250 are verboten on the steel range, but I have used my Marlin .375 and .45-70 there before, with excellent results out to 500 meters - never did hit the White Buff that I know of.)  

My .257 hunting loads (+P) use a 115g Barnes Triple Shock @ 2958fps and are more than accurate enough, but at $1 each they are a little more pricey than my wallet will afford for casual shooting.  I picked up the Grand Slams for under $12/box and didn't pay much more for the Partitions.  I was hoping to get an accurate load in the 2850-2900fps range using +P data.

The results were disappointing.  After shooting just 2 or 3 powder charges I stopped, as I was uncomfortable with the pressure and had already exceeded the velocity limit I had determined was maximum.  This afternoon I tore apart all the unfired loads.  My next step will be to start at 46.0g and work DOWN in .5g increments.  The goal is accuracy above all else, so if I end up at 2700fps that's OK, but I'd be happier in the 2750-2800fps range.  If I can't get the accuracy I'm looking for I'll switch powders (to H4350 or Varget) and try again.

Here are the results.  Temperature was about 68 degrees and I was shooting in a protected 100 yard range (cut into a hill to minimize wind deflection).

Code: [Select]

Speer 120g Grand Slam
Winchester brass @ 2.223"
CCI 250 primer
COL 2.821"
H4891-SC powder
Target @ 100 yards, 4x scope

45.5g = 2831fps,  14fps ES,  9.9fps STD, 0.65" group, 2 shots
46.0g = 2864fps,  22fps ES, 12.4fps STD, 3.95" group, 3 shots
46.5g = 2899fps,  23fps ES, 10.1fps STD, 2.80" group, 4 shots (3 of 4 in 1.25")




Nosler 120g Partition
Winchester brass @ 2.223"
CCI 250 primer
COL 2.896"
H4891-SC powder
Target @ 100 yards, 4x scope

45.5g = 2834fps,  4fps ES,  2.0fps STD, 3.52" group, 3 shots (2 of 3 in 0.60")
46.0g = 2904fps,  5fps ES,  2.5fps STD, 2.41" group, 3 shots

[Lawdog]

Coyote Hunter,

In my Roberts I never got good accuracy using bullet over 115 grains.  Best accuracy is always using 100 grain bullest.  My Roberts will group 100 grain bullets under MOA all day but move up to 115 grain bullets and I am lucky to keep the groups under 2".  I'll be watching to see if you work up an accurate load using heavier bullets.  Small groups(I hope) and tight lines to you.  Lawdog
 

[Carl l.]

Coyote Hunter,

I agree with Lawdog on the 120 gr bullets. I have used the .257 for 45 years now and when I was young I tried every thing. The 100 gr. shoot real good but mine shoots 87 gr better. They have a lot of new powders and bullets out now and I haven't tried them. I hope you get the .257 to shoot them ok.  Happy loading Carl L.