Another Day the Paper-patch Way - Dan Theodore


Image of original .45-90 PP cartridge furnished by BPCR.net

A wonderful day by The Bay was had at the Cabot Gun Club in the hills east of San Leandro and north of Castro Valley. The rifle range is in the Lake Chabot Regional Park, a beautiful area with a commanding view of the San Francisco Bay. Conditions today were excellent: temp in the mid-sixties and little to no wind with bright sunshine. And, hardly anybody was at the range for a change.

 

Today more PP testing was done to refine the load shot at the American Creedmoor Cup as well as do some testing with the 45-cal BACO PP bullet. A 0.4410" diameter PP mold was the prize for being high PP shooter at The Cup. The bullet actually mics at 0.4424" when cast in 20-1, which was the only alloy tested today. The 16-twist, 45-90 with a replica of an original Sharps PP match chamber was used as the test platform. A number of different powder charges using Swiss Fg and 1.5 were tested.

The loads tested were:

 

Browning 45-90 PP Rifle

 

  • F150 Match Large Pistol primers with over-primer wad
  • Starline Nickel 45-90 brass
  • 90.0 Swiss Fg
  • 92.0, 94.0, 96.0 & 98.0 Swiss 1.5
  • 60 thou LDPE
  • BACO PP bullet cast in 20-1, 537 grains
  • Patched with 9# onionskin that mics at 2.3 thou, but after wet patching
    and drying on a hotplate adds only about 7 thou to the bullet shank's diameter
  • Bullet seated only 0.125" into the case

 

Unfortunately the Oehler chronograph was not put in the SUV before leaving for the range, drats and double-drats.

Only one load showed some promise, the 94.0 grain load of Swiss 1.5. All the others were more or less unacceptable: 2 to 3 MOA core groups with flyers. Testing was done off-the-bench at 100 yards. The 94.0-grain load produced a very small core group with 2 flyers. One was 1 MOA high and the other was 2 MOA high from the center of the core group (8 rounds) which was 1 MOA wide by 1/2 MOA high. It should be noted that the slower a bullet leaves the muzzle, the higher it prints on paper at 100 yards with BPCR's. I know that is counter-intuitive, but trust me on this one. That means that the flyers had a considerably slower velocity over their trajectory than the bullets that went into the core group. It should also be noted that if a bullet prints out of the core group by 1 MOA at 100 yards it DOES NOT do the same from the 1,000-yd line, that is print out of the group by 1 MOA. Since vertical dispersion, as a function of bullet speed over its trajectory, is a function of time-of-flight to the second power, or squared, there is a non-linear relationship to how far the bullet will be lower than the core group from the 1,000-yd line. As a matter of fact, computer simulations have shown that the vertical dispersion will be on the order of 10 times the affect or 10 MOA, not 1 MOA.

 

At this point in time, my hypothesis is still that the paper did not come off the bullets properly as they exited the muzzle thereby reducing, at a faster rate, the bullets' velocity on their trip to the target.  Mr. Wasserburger suffered a similar fate at The Cup: tight "core" groups followed by low shots.  Keep in mind that the rifle used today has a chamber specifically designed for PP shooting and has a choked barrel, but the same problem was observed.  The chamber design and choked barrel were still not enough to have consistent accuracy. I will further state that I still believed that the smaller diameter bullet was the cause of the flyers. The Paul Jones PP Money Bullet, which mics at 0.44645", was also shot with no flyers using the tweaked match load. Since it was quite calm, the smoky confetti showers were quite evident. The BACO confetti had large chunks of paper even though the patch used was short by "normal" standards. The Paul Jones bullet produced fine confetti with no large chunks. If I may reiterate, large chunks of confetti seem to indicate the possibility that the load will produce flyers. So far that seems to be the case.

 

A 10-twist, 38-70 was also tested with PP bullets. The chamber is of my standard grease-groove design with no freebore and 3 degrees per side leade angle. The bullet used was a Paul Jones # 1 Elliptical designed to be shot as a GG'less bullet with a 0.500" long, 0.3760" diameter shank. The bore-riding section is 0.3680" in diameter. A 0.3680" diameter Fred Cornell push-through bullet sizing die was used to reduce the shank diameter. The flashing, caused by swaging-down the shank, was removed from the base with an X-acto knife. While this is not optimum, a mold that casts the proper PP bullet is the way to go, it was a quick, cheap test. The results were excellent for a first SWAG at a load. Only one was tested. The barrel is a 10-twist Lilja chromoly with a choke lapped into it. The load components were:

 

Browning 38-70 Grease-groove Rifle

 

  • F150 Match Large Rifle primers with over-primer wad
  • Starline Nickel 45-90 brass formed to 38-70
  • Swiss 1.5; 72.0 grains
  • 30 thou HDPE over-powder wad
  • Paul Jones Elliptical # 1 cast in 16-1
  • Patched with 9# onionskin that mics at 2.3 thou, but after wet patching and drying on a hotplate adds only about 7 thou to the bullet shank's diameter
  • Bullet seated deep into the case, 0.336". The wad was at the neck-shoulder junction for those of you familiar with the 38-70 cartridge.

 

I was pleasantly surprised at the preliminary results. The 10-shot group went about 1.125 MOA of horizontal by 0.86 MOA of vertical. I must admit that the paper-patches had a bit too much overlap. It was not noticed when wet wrapping, but after the bullets were dried the overlap was noticeable. Too much overlap can't help accuracy. How much it degrades accuracy is not known, at this time, by this writer. Since the brass used was neck-turned for bullets that have shanks in the 0.3760" diameter range, the bullet-to-case-to-chamber-neck fit is not what I believe to be optimum so new brass is being made so that there is a tighter fit for the loaded rounds. Even though thicker than normal paper, for my current match loads, was used there was only fine confetti in the plume of smoke, nary a large chunk to be seen or found. Since the bullet shank is 1 thou over bore-diameter, the paper really got shredded/cut but good. More work to come once a "real" Paul Jones PP mold is in hand as sizing down the current bullet does not fit well with what has come to be my mantra for loading BPCR PP rounds: consistency, consistency, consistency. That much sizing can't produce a base that is perpendicular to the shank of the bullet like an as cast bullet from a PJ mold.

 

Cheers,

 

Dan Theodore - March 31, 2008