Home Forums Reloading Big Game Rifles Charge Weight Discrepancy (Speer vs VV / 85grain Boat Tail)

Sat down at the bench this morning to work up a ladder for some recently acquired 6mm 85 grain Speer Boat Tails for a 243 and I've come across something in the VV and Speer books that concern me enough to pause and research. Stated openly from the outset; I'm comparing N540 weights to N560 weights here.

The Speer manual lists N560 as having a charge weight range of 46 - 50 grains of powder (the 50 grain charge listed as compressed).
The VV manual didn't test 540 for Speer's 85 grain bullet, but the N540 weight range (VV book) is 33.5 - 38.6 grains of powder for an equivalent weight Partition, with the Barnes bullet being slightly higher.

I realize the 560 is a slower powder, but the charge weight difference for the starting charge weight of N560 is over 33% heavier.


There is no other place in the VV manual for 243 Winchester where the charge weight differences between 540 and 560 are this wide for equal weight bullets (90 grain bullets for instance).


For the sake of checking, I loaded an empty 243 case with 50 grains of N560. It fills past the shoulder to the base of the neck easily, but it doesn't overflow and there is enough room to seat a bullet properly (by the eyeball). It would be a compressed load. If I could find another manual entry using the 5 series powder for this I'd be more settled with it, but none of the manuals I have on hand use the 5 series powders for 243.

Reducing the charge weight is the obvious answer I know, but I'm curious if anyone else has OTHER thoughts on this.

If you are loading Speer bullets, use their data. Especially if VV doesn't list the powder you want to use, nor do they list the exact bullet (Speer) that you are wanting to use. Don't use Nosler or any other data. This is not that hard to figure out.

I had to read your post a couple of times to understand what you’re saying. I think you’re trying to use linear logic to compare the two different powders. Kinda like using a burn rate chart to see if the powder you have on hand ranks close to a powder in the chart and thinking that the loads should be similar in weight. I don’t think linear logic applies here. Or, maybe I think I know what you’re thinking and I’m totally off base.

N560 is a slow burning powder in the Norma MRP - Re22 range.
In a 243 case you should be safe using a 90% density starting load and moving up towards your desired velocity.
I don't think you will be able to exceed maximum recommended velocities for that bullet weight except maybe with a heavily compressed load and a magnum primer.
Watch for speed increment progression as you increase your charges and you will be safe.

First - Thanks for making the effort to digest my post. My concern wasn't so much a lack of linear charge weight differences, but more of the fact that I couldn't find any other examples of the drastic charge weight change on other tested bullets in the same manual. Think of it as a question posed because I do NOT operate on a blind faith protocol when I read these manuals, and I only had one manual. Again, zero blind faith. I like my lips on my face. Sure, maybe this is all born from an over-abundance of caution, but I'll sing that position in any choir.


Thanks for chiming in. Your comments about the volume concern are helpful.