Assembled they look a lot like this…
Head scratching over powder selection…
Powder selections, after preliminary testing, worked out a little differently than anticipated. Alliant Re 25 and Hodgdon Retumbo worked well at the heavy end and IMR 7828 on the light end, at least for accuracy. IMR 7828 tapped out with light weight bullets, perhaps because of low load density and also because accuracy seemed to fall away with heavier bullet weights. 7828 SSC small granules seemed to exacerbate the problem.
Velocity achieved is considerably higher than Weatherby factory ammo velocity, but as a sanity check, within a minimal +/- nudge of Hodgdon and other mainstream reloading data. These are maximum loads, however, there were no mechanical signs of excessive pressure; flat primers, exceptional report, sticky extraction, case head expansion. With the 338-378 WM’s 30% greater case capacity than the 340 WM, and both operating at the same 63,817 PSI max pressure, I am not quite sure why Weatherby 340 and 338-378 magnum factory ammo have such a narrow separation in velocity. Perhaps performance at a level that there is no need to push futher?
Retumbo is a natural for this cartridge, as previously noted, with heavier weight bullets. I had Norma 217 on hand, which I believe would yield similar results, but I did not have the opportunity to thoroughly qualify it for inclusion within the table. Both powders have an optimal burn rate for case full charges and both release a good deal of energy for pressure persistence. A few of the other powders that were tried, but would not produce satisfactory results in terms of accuracy and/or velocity were: MagPro, H1000, H870, H4831SC, and Norma MRP. Combinations that did not work, produce accuracy consistent with the rifle’s potential were omitted.
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Warning: Bullet selections are specific, and loads are not valid with substitutions of different bullets of the same weight. Variations in bullet length will alter net case capacity, pressure and velocity. Primer selection is specific and primer types are not interchangeable. These are maximum loads in my firearms and may easily be excessive in others. All loads should be reduced by 2%, and developed following safe handloading practices as represented in established reloading manuals produced by component manufacturers. Presentation of these loads does not constitute a solicitation for their use, nor a recommendation.
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Firearm: Weatherby Mark V Accumark
Some exterior ballistic examples from the table –
| 215 Grain Sierra – 340 Yard Point Blank Range Max 3″ Ordinate | |||||||||||
| Yards | 0 | 50 | 100 | 150 | 200 | 250 | 300 | 350 | 400 | 450 | 500 |
| Velocity – fps | 3469 | 3358 | 3250 | 3146 | 3044 | 2945 | 2847 | 2751 | 2658 | 2566 | 2476 |
| Energy – ft.-lbs. | 5744 | 5383 | 5043 | 4724 | 4423 | 4139 | 3869 | 3613 | 3372 | 3143 | 2927 |
| Momentum – lbs-sec | 3.30 | 3.19 | 3.09 | 2.99 | 2.90 | 2.80 | 2.71 | 2.62 | 2.53 | 2.44 | 2.36 |
| Path – in. | -1.5 | 0.8 | 2.3 | 3.0 | 2.8 | 1.6 | -0.5 | -3.7 | -8.1 | -13.7 | -20.6 |
| 300 Grain Nosler – 305 Yard Point Blank Range Max 3″ Ordinate | |||||||||||
| Yards | 0 | 50 | 100 | 150 | 200 | 250 | 300 | 350 | 400 | 450 | 500 |
| Velocity – fps | 2978 | 2911 | 2846 | 2781 | 2717 | 2654 | 2592 | 2531 | 2471 | 2411 | 2352 |
| Energy – ft.-lbs. | 5907 | 5646 | 5394 | 5151 | 4917 | 4692 | 4475 | 4266 | 4065 | 3872 | 3686 |
| Momentum – lbs-sec | 3.95 | 3.86 | 3.78 | 3.69 | 3.61 | 3.52 | 3.44 | 3.36 | 3.28 | 3.20 | 3.12 |
| Path – in. | -1.5 | 1.0 | 2.5 | 3.0 | 2.3 | 0.5 | -2.6 | -7.0 | -12.8 | -19.9 | -28.6 |
Closing comments….
The rifle performed flawlessly and, in very real world terms, admirably. Accuracy was as good or better than Weatherby had inferred in the certification documents. Three shot groups were fired with ten minutes between groups, which was enough during our cold weather for the barrel to stay reasonably cool. Brake on or off, the rifle had a terrific shooting personality. It is a very powerful, yet very manageable firearm. As has been the case with every other Mark V rifle I’ve shot, the action is slick with effortless ejection, feed and chambering. The Mark V looks and feels like a rifle that instills pride of ownership.
In regard to the RC designation and signed target… I love spending hours developing handloads that result in tiny groups. With the information provided with the Weatherby Mark V Accumark RC, I was able to begin handload development with a point of reference for the rifle’s potential. If I weren’t an inveterate handloader, the factory information provided I would know exactly what factory ammunition would provide optimal performance. There is a $300 difference in MSRP between the Accumark and Accumark RC. I’d think it would be would be worth this price, the equivalent of a few boxes of ammo, to begin with a factory expert’s insight.
Weatherby’s Mark V Accumark RC 338-378 WM Part 1
Weatherby’s Mark V Accumark RC 338-378 WM Part 2
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