Conflicting Reload Data by "Experts"

[Unclenick]

Because bullet lengths vary, even when they have the same weight, it isn't the COL, but the seating depth that determines how much space is under the bullet and whether or not the H110 space is getting too big (I did find one databook starting load that appeared to be at 89% fill from Hodgdon).

Incidentally, when Winchester came out with their branding of this powder (as Winchester 296) they had just one charge weight for each bullet weight and said not to use anything else. No load workup, just a fixed charge number. That was still true in their 2003 load data manual. For a 158 grain JHP, my copy of that data says THE load was 16.6 grains. For a lead bullet THE load was 14.5 grains.

Hodgdon thinks another 0.1 grains on the upper side is OK. That's not much disagreement and using a different bullet (they use an XTP, but don't say if it is the FP or HP version, the latter being slightly longer). However, when I look up the lengths of the 158 grain XTP bullets, it quickly becomes apparent the Winchester fixed charge and the Hodgdon maximum are 100% loading density, at least for some brass, and the pressure still is about 90% of SAAMI maximum. So, in your shoes and not knowing your case or your bullet, I would try an experiment:

First, calculate your seating depth (see below) using a case that is average length among your cases (after resizing) and prime that case. Crease a piece of paper and put some powder on it. Set your caliper to the calculated seating depth and put the depth probe down into a primed case with the back end of the beam perched on the case mouth. Gently pour the powder in until it is level with the tip of the depth probe. Dump the powder from the case onto your scale and weigh it. Use that charge weight number or the Hodgdon maximum, whichever is lower.

Seating Depth = Case Length + Bullet Length - COL.

Winchester warns a good hard crimp is required for this powder. These days I use a Redding Profile Crimp Die, but the Lee Collet Style crimp die is available in .357 Magnum and would also be a good choice for a hard crimp.

[Nathan]

Good point on the COAL. Not sure I’ve seen it impact pressures like you are saying, but I’m new to 300 BO.

The primers last ok a little light pressure wise, was my point.

The lands are a mile away!

Since accuracy is weak now, I think I will increase the charge and see if it gets better.

This is a bit off topic, but it amazes me with std chambers that data can vary sooooo much!

[mikld]

Reloading manuals are not hard and fast formula, they are reports of the results the lab techs found when they used the components and amounts listed. There are differences in manufacturing lots of components. There are differences in equipment used. These differences add up to the different reports (reloading manual data)...