Rebarreling and Home-Shop Machining

            My next project rifle will be a .308 with about a 20 inch barrel. I decided to make it with a tight neck that will require turning of the necks of the brass. Most factory ammo will not chamber. This type of chamber is commonly called a “turn neck” chamber. The brass neck is turned to leave only about .001 clearance on the diameter. The advantage here is that once fired brass will be very straight. Typically less than .001 inch on neck runout. Possibly as good as .0003 inch (3 ten thousandths inch) or better. I will be able to use the rifle in the woods and in Hunter’s Benchrest Competition. I will hunt around for a suitable action.

Range Rod & Reamer

            I purchased a floating pilot range rod for use on the rifle below. It had some side to side play in use, so it was not as good as a homemade brass range rod for aligning the barrel for chambering. I did not use it; instead, I used the brass range rod in photo 1. The reamer is an M42 Cobalt Steel Titanium Nitride Coated reamer from Dave Kiff at Pacific Tool and Gauge.

Final Notes on the .300 WSM Long Leade Long Action Project Rifle

            I am quite pleased with the final results of this project rifle. The rifle has over 400 rounds now. It is shooting good groups with 180 grain Nosler Accubonds. I will probably hunt with 70.0 grains of H4831 SC. This load averaged 3065 feet per second with good groups. I will use a slightly reduce load of 69.5 grains for practice. This will require less cooling of the rifle between groups. The 69.5 grain load produced excellent groups in hot conditions. The gun is very pleasant to shoot prone. The recoil pad is soft, so I don’t need a pad on my shoulder. The impact on the shoulder is less than my heavy barreled .308 which requires a pad in my shooting vest for extended shooting. The muzzle blast of the .300 WSM is quite normal due to the long barrel.

            I have a suspicion that I would have already thrown out .300 Win Mag Cases with 5 firings, with hot loads, because of the difficulty of dealing with the belt. There is a collet die available (not from Lee) to shrink the body above the belt. Yes, I am getting some web expansion with 5 firings on the .300 WSM cases. My small base die with a shortened shell holder shrinks this back to size. My primer pockets are not expanding.

Four Round Gun Now

            The magazine and feed lips mods that I described below allowed this long action to do a good job of feeding the .300 WSM round. With some additional polish of the magazine cutouts and slightly decreasing the radius of the corners of the cutouts (I ground out the corners a little with a small stone), the magazine will now hold 3 rounds and allow a fourth to be chambered. The gun is a four round gun now. Ejection and feeding are good with the mods that I made.

Velocities with the Long Leade

            The velocity of 3065 feet per second with 180 grain accubonds and cases fired 5 times is now on par with .300 WSM rifles with factory ammunition with no particular advantage to the long leade except that used long actions, with a magnum bolt face, are cheaper and more abundant. My loads are only slightly compressed with the long leade. I am still using vibration to settle the powder to avoid crunching the powder in the seating die. With new cases and 200 grain bullets the velocity at 2960 feet per second is quite a bit better than you can achieve with a standard leade .300 WSM rifle. I did not do an extensive attempt to tune this 200 grain load for accuracy, but it was making about 3/4 inch groups when I switched to 180 grain bullets.

I Reduced my Load for each Firing of the Brass

            I found that each firing cycle of the cases (which also may have coincided with a 5 degree increase in ambient temperature) required me to reduce my load. I did this in about .5 grain increments. My home-made small base die has about .4 inches removed from the bottom of a standard Lee Full length die. The shoulder is removed as well. This still sizes the brass bigger than a new Norma case. I have about .0005 inch clearance on the radius all around and in the headspace when the sized case is chambered in the rifle.

Chase the Leade

            About every fifty rounds you should make the rounds a little longer to compensate for wear of the leade with this Magnum caliber.

Barrel Temperature Compensation

            When shooting 600 yards the first two rounds will require about .75 Minutes of Angle (MOA) more elevation than subsequent rounds with the warmed up barrel. I still cool between pairs.

Current Hot Weather Load

            I am using 69.5 grains of H4831SC now under a 180 Nosler accubond at 103 F at the last range session with turned Norma cases fired four times with a CCI Magnum primer in the .300 WSM long leade long action project rifle.

            I fired two three shot groups with this load at 100 yards to test function. Unfortunately it was only 90 F on this day. I simulated hotter weather by firing the two groups close together in time. The second group thus had a hot barrel, higher velocity and grouped well. The cold barrel shot was very good as well. See photo 2.

            I repeated one group with this load on a subsequent day and got the good results in photo 3.

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