Including Taurak 250 and Mica
By John Rhodes
The Browning Model 71, .348 was produced with a throat made specifically for jacketed ammo. This makes it next to impossible to get any kind of accuracy with cast bullets. The best solution is to re-ream the rifle's leade. This wouldn't be that difficult if we were dealing with say, a .308 or .30-06, but just try to find a .348 reamer. The cost to have one made could fund NASA, so I wanted a second and less expensive option.
In issue #152-9 (August 2001) of The Fouling Shot, I described the Browning .348 as having a narrow short leade in which the lands are steeply tapered and are still evident at the beginning of the bore. This is specifically shaped for jacketed ammo. When a cast bullet is chambered, the leade including the raised lands at the bore entrance starts to peel a layer of lead off the bullet. Upon firing, the bullet enters the throat where it continues to be peeled like a banana. The high temperature and pressure atomizes the peeled lead and blasts it back onto the cartridge neck and shoulder, hence the expression, "ring around the collar and lead necks."
The bullet being used is Rapine's #350235 which actually weighs 245 grains with a gas check attached. It is also a flat nose bullet cast of wheel weights and sized 0.350" which is 0.0008" larger than the groove diameter. Since I prefer case-filling charges of slow powder, I was using Lyman's Cast Bullet Handbook, 3rd Edition's recommended charges of 35 to 46 grains of 1MR 3031, though I started with 40 grains. A charge of 45 grains of this powder sends the bullet downrange at an estimated velocity of 2,000 f.p.s. Lee Alox lube was also used. Nothing seemed to help accuracy so CBA member Mustafa Curtess made the following suggestions:
o Quench the bullets as they drop from the mould
o Change to a powder with a faster burning rate
o Lower the velocity by lowering the powder charge
o Lube the bullets with Taurak T250 and include a light coating of mica
I was skeptical of the T250 and mica but Mustafa realized this and provided me with a sample. I wasn't enthusiastic about a faster powder or lowering the velocity either. I hope to someday use this bullet and rifle for hunting so diminishing it to a plinker was not my idea of a solution to the original problem, cast bullet accuracy.
To start, I tried the T250 and mica with some of the bullets I had on hand (wheel weight, not quenched) and loaded them with 40.5 to 46 grains of IMR 3031. Just as Mustafa had explained, the combination of T250 and mica seemed to fill the gap between the cartridge mouth and the throat, preventing the atomized lead from getting deposited on the case neck. After subsequent shooting, the blasted lead was progressively deposited farther back on the case. None of this had any effect on the deplorable accuracy. In fact; a few of the bullets appeared to have made keyholes in the target. This wasn't the success I was hoping for but the fact that it reduced the case neck leading offered hope.
Returning to Mustafa's suggestions, I made a new batch of bullets, including quenching them as they dropped from the mould. I also changed to Reloader 7 (Re7), though Mustafa had suggested IMR 4198 or IMR 4895. Re7 isn't listed for the .348 but Hodgdon's, Powder Data Manual, 35th Edition, page 62 lists it as having a burn rate as follows:
Burn rate Powder
30-31 IMR 4198-H 4198
34 IMR 3031
Since they are so close, I felt I could use Re7 and be able to fill the case with more powder than if IMR 4198 was used. Besides that, a double 36 grain charge (72 grains) fills the case to the mouth so a double charge is easily spotted.
It was time to put Mustafa's suggestions to the test. Using quenched wheel weight bullets lubed with Taurak T250 and coated with mica, I returned to the range. Making a long story short, 36 grains of Re7 printed a 3 shot 1 3/8" group at 50 yards. There was a very small amount of lead deposited on several cases but most were devoid of lead deposits. Charges of 38 and 40 grains of Re7 opened up the groups several inches but recoil was starting to get to me. I later discovered that my case necks were kissing the end of the chamber and pressures were going up.
One week later I wanted to verify the above shooting. To do this, I like to repeat the test shots a second time. After annealing and trimming the cartridges, I was ready for a second trip to the range. To my chagrin, the 36 grain charge of Re7 produced a 3-1/8" group at 50 yards. I felt much better after a 3 shot group of 1-3/8" at 100 yards was attained. None of the cartridges had lead deposited on their necks either.
While discussing my use of Taurak T250 with NECO (the manufacturer) and the situation with the Browning, I was informed that their computer program gave my load (36 grains of Re7) a velocity of 2,073 fps and a pressure of 39,597 p.s.i. NECO sells T250 in the lube sizer sticks for $3.75 or you can get block of it for $5 a pound. For more information, write to NECO, 536C Stone Road, Venicia, CA 94510 or call 1-800-451-3550.
The change to quenched bullets provided a stronger bullet that could better endure the trip through the rifle's cast bullet destroying throat. The lower charge of Re7 reduced the bullet's velocity to an estimated 2,000 f.p.s. per NECO's computer. The use of the quenched bullet should have been taking place all along rather than the unquenched bullet which invited performance failure, no matter what the rifle's throat was like. What ever the drop in velocity really was, it shouldn't eliminate the load from being used for hunting. The Taurak T250 and mica appeared to fill the gap between the cartridge mouth and bore entrance, eliminating "ring around the collar and lead necks". I can't explain what happens in the chamber when Taurak T250 and mica are used but for me, it's "success at last". Though I've found a load that's accurate and eliminated the lead necks, in reality, it only masks the real problem. The real solution, reaming the rifle's throat, still remains.