Wide variance in load data?

[Dave0317]

I’m used to seeing various loads for round like .308 vary by 1-3 grains of a given powder for similar bullets of the same weight, maybe using different brands of brass, primers, etc.

Lately though, while researching 45-70 loads with a Sierra 300 grain, I’ve found some load data that seems downright contradictory.

Hogdons data has a minor conflict of velocity with a trapdoor load Showing 1826 FPS with 57 grains of powder, and out of a lever action, the same bullet, powder, case, barrel length, etc, shows a velocity of 1800 FPS with 58.5 grains of the same powder.

The Sierra manual/app suggests that 52 grains of this powder should produce 1800fps with the same bullet.

The Sierra manual also seems to suggest in one section that 48.4 grains is a safe load, and in the lever action loads section, suggests that anything under 59.7 grains is a low pressure load that should be approached with caution.

All this data relates to the Sierra 300 grain JHP pro hunter, and IMR 4895. Why the wide spread of safe vs unsafe powder weights and seemingly contradictory data?

 

[SDHNTR]

You need to see what rifle the load is being used in. It could be a load for a 140 yr old Springfield or Shiloh Sharps or it could be a new modern Marlin lever gun. Big difference!

 

[homebru.trout]

I have noticed over the years that the Sierra manual occasionally deviates wildly from other sources. While I totally understand the standard disclaimers, I'm one of those annoying people that has to know the how and why of two individuals getting two completely different answers to the same math problem.

One Sierra Max load for 260 rem was 5 grains of 4064 over other published loads. 5 grains of 4064 is A LOT as you approach max and if you use that as the basis of an OCW ladder, you actually wind up over everyone else's max on the sighter loads before the first group.

In the other direction, one 30-30 load of interest was 3 grains under multiple other reputable sources for BL-C(2) which is a fairly stable ball powder not known for spiking. Hodgdon max is like 25K CUP or something like that.

I love Sierra bullets and the price point they hit, but their published data always makes me a little nervous so I consult multiple other sources before diving in on load development.