Brass is 7mm RUM brass necked up to 375 in two passes, heat treated between sizings, used the first time without fireforming.

• Frontier Range Master 245 grain monolithic.

• Peregrine Glidemaster 300 grain monolithic.

• Norma 204

• IMR 7977

• IMR 4955

• VIhtavuori N560

• VIhtavuori N565

• VIhtavuori N570

• Fiocchi Large Rifle

• Federal 215 Match

• CCI 250

There is no manufacturer load data for the bullet I am using.

There is enough data from manufacturers to indicate which powders are safe for the lighter and heavier bullet weights.

Based on existing load data, Norma 204 was chosen, the max load in the Norma book says 92.8 grains for a 300 grain bullet. I tested to 93. I tested over the max listed load for a few reasons :

• my bullets are seated much further out

• my bullets have less bearing surface

• the 4966 and 7977 loads are documented in the book, the minimum charges of which can serve as a reference for expansion measurement

From the Hodgdon data, H1000 can be used for 300 grainers to 105 grains charge weight. I chose IMR 7977 because it is what I had on hand, and it is suggested by Hodgdon as a replacement for H1000.

You may find that the case cannot accomodate the weight of powder in the loading guide. I intended to load to 105 grains, but I could only get 100 grains in the case. With 100 grains, the powder level was to the case neck, although seating was not a problem. 105 grains would overflow the case. The solution to packing more powder in a case comes from blackpowder cartridge reloaders in the form of a long powder drop.

The IMR 4955 was chosen as an in-between powder, as the equivalent of H4831, which the book says load to 97 grains using 300 grain bullets.

The 300 grain bullets in the load data are not the 300 grain bullets I am using, but I have advantages using the 300 grain Peregrine Glidemaster

• the bullet shank is shorter than a lead core bullet

• the shank diameter is around 1 thou smaller

• the engraving pressure of the monolithic is less than the lead core bullet

• the freebore permits this particular bullet to be seated out further, the base of the bullet is clear of the main powder column.

The big difference betwen the load data and what I have is barrel length. Mine is 30 inches, the load data is for a 26 inch barrel. I can reasonably expect to at least equal the book velocity, and perhaps even a slight gain with slower powders.

The rifle is single shot, so I do not have a magazine length to conform to, my AOL is limited by available freebore. With the 300 grain bullet, the max OAL is 4.160 inches. With the 245 grainers. the bullet is not yet in the case neck at freebore max.

For the 300 grainers, I went with a AOL of minus 30 thousands to start, the intention is to optimise group size with increased seating depth after that.