Big Redhead,
I had to get out my #13 Speer manual after your comment about the differences in 7x57 data between 760 and 414. Here is what I found listed in maximum loads:
110-grain: 760--54.0 grains/3250 fps
414--54.0/3141
115-grain: 760--53.0/3095
414--53.0/3053
120-grain: 760--47.0/2778
414--48.0/2851
130-grain: 760--50.0/2960
414--50.0/2952
145-grain: 760--50.0/2743
414--50.0/2748
160-grain: 760--46.0/2605
414--46.0/2582
175-grain: 760--44.0/2442
414--44.0/2403
Pleae note that in only one bullet weight is there a 1-grain difference in the maximum powder charge. The others are all exactly the same. And with the 120-grain bullet, if the powder charges were the same the muzzle velocity would be about the same.
There are some differences in muzzle velocity, though the only really significant one is with the lightest bullet weight. The others are so similar that they could be averages from different 10-shot strings done on the same day.
I also looked at a bunch of the other 760/414 data in the Speer manual. Very occasionally the maximum charges varied by 2-3 grains, but only in fairly large cases (60 grains or more) at the extremes of the powder's usefulness. This is also pretty normal. 760/414 is a powder best suited to medium-sized cases with medium to heavy weight bullets. When used with lighter bullets or in cases with large capacity to bore size, performance varies more.
These 2-3 grain differences in FEW instances could be due to the normal variations in a 10-shot string, or to using different lots of powder. Some of the data may have been shot months or even years before the other data. This is also quite common in loading manuals, and the company doesn't see any reason to re-shoot the load if the performance is still within the normal range.
I have seen many powders change enough between lots that charges had to be adjusted 2 grains in the same rifle in cartridge cases of 50-60 grains powder capacity. This is a 3-4% variation.
I didn't go through the entire manual to see how many times the data for 760/414 was essentially identical, but did look through all the rifle data from .25 to .30 caliber. About 80% of the time the maximum loads listed for any bullet weight/case combo are identical, and muzzle velocity as close as two 10-shot strings would be with any chronographing done on the same day.
You will notice the same level of agreement in 760/414 data in any current manual.
