Rebarreling and Home-Shop Machining

Revised July 20, 2005, added photo 9 Final Small Base Die photo.

Sizing .300 WSM Cases Continued

            All of my .300 WSM cases have been fired at least three times now. The Norma brass in this caliber is a little harder than the .308 or 30/06 brass that I have used. This has a couple of effects. One is there is more spring back to the neck than usual after a sizing. The .335 inch neck full length die was no longer giving me sufficient bullet to case grip after a few firings. Evidence of this is visible when you disassemble the cartridge in a kinetic bullet puller. The bullets were coming out with one tap. The lack of grip might lead to higher spread in velocities.

            Recently a Lee Collet Die has become available in .300 WSM, so this is how I prepare the cases now after 3 firings. Full/ length size with a full length die that has been renecked to .335 inch. I bump the shoulder back using a set of Redding Competition Shell holders, and an RCBS Rockchucker Press to be .0005 inch shorter than chamber length. I then use a Lee Collet Die to shrink the necks a little further. I use a small base body die described just below if a case still rubs the chamber when I do a trial insertion in the rifle of the empty case (cocking piece removed). I sized 36 cases fired three times this way. 5 cases had runout less than .0001 inch, 13 cases less than.0005, 12 cases < .001, 5< .0015, 1<.002. Using the renecked full length die followed by the collet die was about a factor of 2 improvement over using a Redding Full Length Die with .334 inch floating bushing. I got a lot more of the true cases with the collet die. Sizing the case this way also reduces the formation of a donut inside the neck close to the shoulder. The lee collet die does not reduce the neck in the area that the donut forms.

            Note that increased neck tension has also increased my peak pressure. I have reduced my 180 grain bullet load about 1.7 grains to 71.3 grains of HS4831SC in the long leade long action .300 WSM Project rifle. The temperatures in Houston are also really hot right now. One session was 105F in the shade.

Making a Small Base Body Die

            After firing a case several to many times depending on caliber and pressure, the bottom portion of the brass case will expand some and no longer chamber and extract easily after a full length sizing. This condition comes sooner when using hot loads. I have just a few .300 WSM cases in this condition.

            Redding makes a small base body die in a few of the calibers used in competition like the 6ppc, .223 Rem, and .308. It is not available for .300 WSM. I had a spare Lee full length die that I wanted to convert to a small base body die. The purpose is to size the lower part of the body without touching the shoulder.

            I first used a cut off wheel in the 4.5 inch grinder at the vise. The die has a tiny hole in the middle of the shoulder to expel excess sizing lubricant. I used this as a guide and cut at the hole. I cut off the top of the die leaving about .030 inch of shoulder. (The die can be used without a lockring. With this short .300 Winchester short magnum die, leave more of the die to grind out if you desire to use a lockring.) I touched up the die on the bench grinder leaving about .020 inch of shoulder. I set the die up in the four-jaw chuck and indicated it true. I then used my home-built Dewalt tool post grinder to remove the shoulder entirely. I then cleaned up the die end with a larger 1 inch stone. Grind about .1 - .4 inch off the bottom of the die so that the stubborn case can be inserted a little farther than normal into the die. Use a homemade flap wheel to polish and expand the upper part of the die so the diameter of the case is not reduced too much. Finish sizing with a standard full length die to bump the shoulder back. I tested the die now and it works well. It reduces the part of the case just above the web. The top of the case body is only .0007 inch smaller than normal. A test target is shown in photo 7 and 8.

            Avoid contact with the shellholder as the die is not hardened through and through. I ground a shellholder shorter to use with this die so that It would not leave an untouched part of the case near the extraction groove.

Test Results (New)

            I sized some Norma brass that was fired in the .300 WSM long leaded long action project rifle 3 times with the procedure described just below. I selected 3 of the best rounds and shot this group at 100 yards in the high prone position with a Harris S 25C Bipod in the lowest position. The rifle has some wiggle from this position so I was pleased with the group. See photo 7 for details.

            I shot a second group with a slightly reduced load of 71.0 gr of HS4831 SC from the bench to get some velocities. This load which used brass fired 4 times averaged 3081 feet/second with a low spread of 10 feet per second. This is a good hot weather load for my .300 WSM. See photo 8 for more details.

Long Range Trajectories for the 180 grain Nosler Accubond (New)

Range, Drop,                        Windage

200 yards, -.75 MOA, Windage at 10 mph 1.3 MOA

400 yards, -5.0.9 MOA, Windage at 10 mph 2.7 MOA

600 yards, -10.75 MOA, Windage at 10 mph 4.4 MOA

After2 shots at 600 and then a cooling period use -10 MOA. You can never really get the rifle back cool without excessive waiting. This is with a100 yard zero and an approximate muzzle velocity of 3100 feet/second.

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