Rebarreling and Home-Shop Machining

            The saga of the long leade .300 WSM long action Remington 700 rifle continues. First I should report that the I have been using a 70.5 grain maximum load of H4831 SC with a 200 grain Nosler Accubond in new unturned cases. My last session at the long range was in preparation for a couple of pig hunts. I shot 3 pair of shots. 1 pair at 200 yards. Two pair at 400 yards. The groups (pairs of shots) averaged in the .3's (Minutes of Angle, MOA). If I take three shots at 100 yards, which I seldom do at the long range, the groups average about .75 MOA. The third shot in a rapid series is also 50 feet per second faster. Things are probably pretty toasty in the bore after that second shot.

            The lead has moved forward in the rifle some and I have neglected to chase it by increasing the overall length about every 50 rounds or so. The headspace has stayed absolutely rock solid. It has not moved 1 ten thousandth of an inch from its original value. I have no indication of locking lug setback from overly high pressures.

            Although I am quite satisfied, I decided to tinker with a 180 grain Nosler Accubond bullet just to see what the rifle would do. I have heard good accuracy reports with a 180 grain bullet. I researched quite a bit of load data to decide what powder to use for a 180 grain load.

Here are some pertinent facts

            The 70.5 grains of H4831 SC that I used with a long leade and 200 grain bullets goes 1/4 of the way up the neck. When you seat the long 200 grain bullet you can hear the powder crunching as it compresses the powder. A 180grain bullet should require more of this powder, but, being shorter will compress the powder less.

            76.0 grains of H4831 SC goes up to the top of the neck.

            I experimented with vibrating the powder previously in the 30/06 as suggested on Speer Bullets Web site under Reloading Data, 30/06, Trophy Bonded Bearclaw. I was able to reduce the powder volume by half the neck by setting the case on the top of the vibratory case cleaner. I did not like having the case cleaner which contains solvent residue and lead dust in the house, however.

            A faster powder, H4350, would reduce the volume required but may also inhibit maximum load performance. A slightly denser powder like Accurate Arms Mag Pro powder might be ideal, but I had H4831 SC and H4350 in stock and I like the Hodgedon’s powders advertised velocity stability with temperature change.

Compressing H 4831 SC by case Vibration

            Photo 1 shows a dog shear which vibrates nicely to compress the powder charge before I seated the bullets in this experiment. I touched the plastic part of the shear against the side of the case with this metal funnel in place. Worked great. I was able to reduce the amount of powder volume by 2/3 of the neck and thus was able to load H 4831 SC up to and including 76.0 grains which proved to be slightly above the maximum load. There was some powder crunching on seating only with highest loads.

Safety in Case Vibration

            When I do any tinkering with a primed case, I envision the consequences of the primer firing. Instead of holding the case over my leg where a primer will shoot off the case and penetrate ½ inch of meat, I place the case head over the bench top. I wear safety glasses. If a primer goes off in an empty case the jet of hot gases coming out of the mouth will torch a nasty deep cut into a finger (Think small cutting torch), I have a personal report given to me on this. He used a punch and hammer to tap out a live primer. ( Use your reloding press and go slow instead). Powder in the case (without a bullet) will probably mitigate this hot jet but may send a jet of flaming little bits out the top. Have an extinguisher handy. I had no incidents and believe this procedure with the dog shear to compress the powder charge to be as safe as reloading in general is.

Case Sizing to an Exact Headspace

            I had some trouble sizing this hard fat .300 WSM case to an exact headspace. I know that my .308 rifle prefers this. On this .300 WSM rifle, I size the case as big as possible (for pressure reasons) but small enough so that the bolt with the firing pin removed will close easily on the case. There is some case expansion, with the loads that I use, in the long direction of the case. A full length sizing is required. The Lee Loadmaster press which had worked fine with my .308 and 30/06 had a little too much spring. Slight differences in hardness of the brass caused the cases to fall into two lots. Those just right and those too short by .003 inch or so. (These cases were purchased at the same time but come in boxes of only 20, so you are not sure to get the same lot). I bought an RCBS Rockchucker Supreme press shown in photo 2 to try resolve this issue. I made some shims with a case sized hole in it to place between a home ground .336 necked Lee .300 WSM full length die and the shell holder. I used a .016 inch shim stack with the press camming over the top with light pressure on the handle. Don’t over do this pressure on the handle as the force is multiplied greatly when the press is camming over. This gave me better control of the case length than unscrewing the die as all spring is eliminated. Redding has a set of competition shell holders that go up to .010, but these were too short for me. In another instance they were all too long on a .308 case. We sanded a shell holder. My chamber is go gauge + .001 inch so I don’ know why I need such a large stack. I need a .014 inch stack with a Redding type S full length die in .300 WSM. Photo 1 shows one of these .010 shims next to the shell holder on the white paper. I ground the hole out with a stone on the Dremmel. You put the case in the shell holder slide the shim stack over the top of the case and then size the lubed case. If they come out long, reduce the shim stack. Use a gage to measure the case length from shoulder to base. If the Redding competition shell holders will work for you then replace the shims with these eventually.

Incremental Load Results 180 Grain Accubond .300 WSM long leade long action Remington 700 Rifle

            Photo 3 shows 10 shots with increasing amounts of H 4831 SC Starting with 70.5 grains increasing by .5 grains up to 76.0 grains. I did not prepare a load at 74.0 grains and 75.5 grains. The powder was vibrated down with the dog shear as explained above. Load compression started at about 71.5 grains. The best cluster was shot 5, 6 and 7 at 72.5, 73.0 and 73.5 grains.

            Photo 4 shows a table of velocities obtained for all the shots. Load compression started at about 71.5 grains. The maximum load was 74.5 grains which went 3181 feet per second from the 26.5 inch barrel. The load at 75.0 grains had a slightly sticky extraction. The load at 76.0 grains failed to extract. Two light taps with the cleaning rod removed the stuck case.

Velocity Spread

            I prepared 3 additional rounds at 71.5 grains to determine the velocity spread with the vibration load compaction technique. The three shots went 3064, 3072, 3072 feet per second. I was getting very consistent velocities. Photo 5 shows a graph of the velocities in the chart from photo 4. There is one diamond for each shot.

|  Add to del.icio.us |  digg this