I'm looking to do some work with my newly rebored 9.3x62 with Power Pro 2000-MR, and I have been playing around with "The Rules" that John published in Appendix 1 of "Gack I" and thought I'd share it. I'll show the examples, and end up using about all the formulae.
Background. I have a 35 Whelen AI with a long throat in a commercial 98 Mauser. Speer has published some pretty game changing tested loads for the basic Whelen with their 250 HotCor and 2000-MR, specifically, a max of 66.2 gr for 2709 FPS. In my 35 WAI, the 250 HotCor and 250 partition are near perfect analogs, giving same velocities and groups with the same charges. In working up in my 35 WAI with the 250 Partition, I stopped at 65/2000-MR for 2645 FPS and sub MOA accuracy. This load in my 35 WAI produces only .0002" CHE on the first firing and then no further CHE on subsequent firings. Assuming Speer was pushing the SAMMI max of 62K PSI with their load, I figure I'm around 60K or less, the same target JB has used for his 9.3x62 loads. So I want to "derive" some 9.3x62 2000-MR loads for the 250 AB and the 286 Partition using The Rules.
My 9.3x62 has the same 23" barrel as my 35 WAI and also a long throat so both rifles are magazine limited, and I load to a 3.375" OAL in both for good feeding, and am around .200" off the lands in both.
My 35 WAI holds 65.7 grains of water underneath a 250 Partition seated to 3.375" in a once fired case.
My 9.3x63 holds 65.2 grains of water underneath a 250 Nosler AB seated to 3.375" in a once fired case.
SO, if they were both the same caliber, the 0.5 difference in case volume would cost the smaller case about 5 FPS
...65.7/65.2 = 1.00767. Divide the % difference by 4 to get the velocity gain/loss at the same pressure - .00767/4 = .0019. .0019 x 2645 FPS = 5.02 FPS (not even a standard dev of change but we'll play with it) so I'll take off the 5 FPS and call it 2640 FPS.
BUT, they are not the same caliber, the 9.3 has a greater cross-sectional area for the gas to push on. The cross-sectional areas are .1007 and .1052 respectively, so how much faster should the 9.3 go if loaded to the same pressure?
.1052/.1007 = 1.0447, or a 4.4% increase, but the 4:1 rule says we only get about 25% of the increase in actual velocity so 4.4% / 4 = 1.1% potential velocity gain (big whup, right?) so 2640 x 1.011 = about 2670 FPS.
But I need more powder to get that extra 1.1% in velocity, and the 4:1 rule says I need about 4.4% more powder, bumping the charge I'll probably need up to 67.8 grains of 2000-MR to get 2670 FPS with the 250 in my 9.3x62, and that ought to be at about the same pressure as my 65/2000-MR load for 2645 FPS in my 35 WAI.
But I want to shoot the 286 Partition with 2000-MR too. The 286 is actually .005" shorter than the 250 NAB so I will have about the same powder capacity when loading to the same 3.375" OAL. So using The Rules I add the 2 bullet weights and divide by 2: 250 + 286 = 536. 536/2 = 268. I divide that value by the new bullet weight of 286 grains. 268/286 = .93706 and use this conversion to calculate my potential velocity and powder charge.
67.8 gr x .93706 = 63.5 grains. Velocity ought to be: 2670 FPS x .93706 = 2502 FPS.
In summary, I ought to work up to ~67.8/2000-MR for ~2670 FPS with the 250 NAB, and ~63.5/2000-MR for ~2500 FPS with the 286 Partition.
How does that compare to the little bit of published data for 2000-MR? Speer's max for their 270 HotCor is 59.3 for 2439 FPS. Hornady's max for their 286 SP Interlock is 62.4 for 2400 FPS.
Now going back to Mule Deer's guidance for developing sub-60K PSI loads in the 9.3x62:
"All published 9,3x62 loading data is based on old, low-pressure standards. I have NEVER run into any sort of "pressure sign" by starting with published maximums and working up to around 2450-2500 fps with 286s and 2650-2700 fps with 250s, of whatever brand. That's with three different 9.3x62s that had 21-24 inch barrels."
Does that look about right, John?. That was kind of fun. Our local range is closed UFN due to the coronavirus but when I get a chance to shoot again over my chrono, I'll come back and update.
Thanks for "The Rules." I'm looking forward to Gack III.
Cheers,
Rex
I've actually had two range sessions with the 9.3x62 since posting the above. All the work with 2000-MR was on the first trip. Here is the short version:
- I missed the velocity predictions by about 50 FPS with both the 286 Partition and the 250 NAB.
- Pressures with both the "max" loads were about equal to the Lapua factory 286 Mega (based on CHE)
- Accuracy with the 250 NAB/2000-MR was not quite as good as that from 250 NAB/Varget that I got on the first trip to the range with this rifle.
The long version:
Attempting to use John's rules of thumb to replicate the success of 2000-MR in my 35 Whelen AI predicted ~67.8/2000-MR for ~2670 FPS with the 250 NAB, and ~63.5/2000-MR for ~2500 FPS with the 286 Partition.
I worked up to both of those as follows and the velocities, group size, and CHE are also included (I measure to 4 decimal places with my blade mic for CHE - where 5 decimal places are shown, it's from averaging 3 rounds' CHE) Cases were new unfired Lapua, primers were CCI 200, and all rounds were loaded to 3.375", which placed them over .200" off the lands in my long (standard) throat:
Bullet Charge Vel./SD Group (100yd) CHE 286 PT 61.5 2329/3 1.50" .00073
" 62.5 2396/6 3.13" .0010
" 63.5 2440/13 1.86" .0009
250 AB 66 2542/14 1.66" .00067
" 67 2594/13 1.94" .00067
" 67.8 2621/15 0.95" .0008
Of note - I also took CHE on Lapua Factory 285 Mega, and it was .00083" with 2254 FPS and SD 19.
- There were no traditional pressure signs.
- No idea what happened to the second round of the second 286 PT it landed about 2 inches at 1:00 from all the other 286 PT rounds in the three groups.
- It looks like it would take just about another grain to hit the target velocities, and I suspect the associated pressures would be fine based on CHE comparison to the factory stuff. I know CHE is not a stand-alone tool but I think it can be useful for comparisons when other factors are considered as well.
Hope this helps anyone wanting to use PP 2000-MR in the Nine-Three.
Cheers,
Rex
