Rebarreling and Home-Shop Machining

            Photo 1 shows the new rifle consisting of a custom long leade .300 WSM chamber (whose print can be found below) on a 26.5 inch Hart barrel and a long action Remington 700 receiver. The goal here was to duplicate or improve on the .300 Win Mag with a non belted case. I put 11 rounds through the new rifle starting at 66.0 grains of Hodgdon’s H 4831 SC and then increased the charge by .5 grains for each round until I reached 71.0 grains. The purpose of these rounds was threefold. I could use the incremental load method to find a sweet spot for further study. I could determine the maximum load for this long leade chamber with the 200 grain Nosler Accubond. I could straighten some cases for future accuracy work.

Maximum Velocity

            Photo 2 shows a graph of the velocities obtained with a Pact Model I chronograph. I reached what I considered the Maximum load at about 70.5 grains which went 2960 feet per second. The case at 71.0 grains showed a slight shiny protrusion on the case head into the ejector plunger hole. All the cases extracted easily. At about 69.0 grains the load starts to become compressed as indicated by the need to adjust the seating die downward to obtain the same overall length. See the same data in tabular form in photo 3.

            The long leade allowed me to use 4 more grains of powder than the published maximum for the standard length .300 WSM from Hodgdon’s website which was 66.5 grains compressed of H 4831 at 2678 feet per second for a 200 grain bullet (24 inch barrel).

            My maximum load compares favorably with a compressed load of 72.0 grains of H4831 for the .300 Winchester Belted Magnum which reached 2825 with a 200 grain bullet (but from a 24 inch barrel) in data that is available on Hodgdon’s Website.

Accuracy

See photo 4. Shot 9 10 and 11 went into a fairly tight cluster which shows a potential for accuracy in this range. This corresponds to 70, 70.5 and 71.0 grains of H4831 SC. I am using 6 thousandths bullet jump which this bullet preferred in two other rifles. More to come.

Norma Brass in .300 WSM

            Norma Brass is available in .300 WSM. I measured the runout of 20 cases. 10 were less than 1.5 thousandths, and 10 between 1.5 and 3 thousandths. This is pretty good for new cases. I shot the 10 worst cases in this set to straighten them in this experiment. My chamber’s neck diameter is .340 inch. The loaded case neck diameter with the Nosler bullets was .339 inch. I measured the neck wall variation and it was 5 ten thousandths or less. I decided to use unturned brass as it was pretty uniform to start with. This would reduce the expansion after firing and help keep the brass straight.

            I note that a set of Norma Brass in 30/06 which I purchased previously was not near this straight and true.

Precision Grinding a Neck Size Bushing

            Since I decided not to neck turn the Norma brass, I needed a neck bushing slightly larger than I had on hand. See photo 5. I took a spare .3350 inch bushing and opened it up to .3370 inch which should work well on the neck whose final loaded size is .339 inch.

            I used my Homemade Dewalt Tool Post Grinder with the 1/8 inch collet and a Dremmel stone that is used to sharpen Chainsaw Blades. The grinder worked well and provided a very nice surface finish at 120 revolution per minute lathe speed .5 inch per minute feed rate. The Dewalt cutout (zip) tool turns at 30,000 revolutions per minute, same as a Dremmels top speed.

            The Neck bushing which measures .5000 on the OD just happened to be a light press fit in my .5 inch endmill holder which is through bored and is a Morse #3 taper. It is in a home modified Morse #4 to Morse # 3 adaptor which was made from a tanged drill adapter.

Magazine

            Photo 6 and 7 show some modifications to the magazine so that it would hold and feed three rounds. The rifle is originally a 300 Winchester Belted Magnum which I converted for use with the .300 Winchester Short Magnum. I cut some windows in both sides of the Magazine box. This does two things. It keeps a round in the magazine from sliding forward from friction of the round being chambered and it moves the rounds in the mag farther to the side to keep them captured. I also moved the breakover point in the receiver feed lips farther back to better suit the short fat case. I widened the back of the feed lips to just clear a round so a round can be loaded straight down rather than down and then back. I still push the rounds back after putting in the mag. I got 3 rounds to feed from the magazine. There is not quite enough room to chamber a fourth round with three in the Mag, so the gun is a 3 round gun.

If I were doing this magazine modification to another gun, I would not move the breakover point back until I had tested feeding with the modified mag box and widened feed lips first.

Bipods

Photo 8 shows a high prone position using my hunting pack and a tall bipod.  I returned the Caldwell bipod due to the difficulty and long time consumed in setting the height.  The spindly little part fo the leg also bent just from the weight of this heavy rifle.  Get the Harris Bipod.

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