A Simple Method to Improve Pit Safety For BPCR Longrange Matches



The current method used to determine whether a rifle and load combination is safe for shooting Long-Range (Creedmoor) matches is the NRA Power Factor. The NRA Power Factor is calculated as follows:

Muzzle Velocity in fps X Bullet Weight in grains
-------------------------------------------------------- = NRA Power Factor
                          1000

The above fraction must be over 500 to quality at the Longrange NRA National Championships at Raton. As you can see by looking at the equation the Power Factor does not estimate trajectory which is the reason for its use. The Power Factor only estimates a value similar to muzzle momentum and has nothing to do with 1,000-yard trajectory angle. It is trajectory angle that is of concern with regard to pit safely. Match directors are concerned about bullets dropping into the pits as a result of extreme rainbow-like trajectories, as well they should. The NRA Power Factor only calculates a value similar to muzzle momentum, which does not predict long-range bullet trajectory.

For example, a 650-grain 50-caliber bullet launched at 770 fps makes the power factor. A rifle loaded as such should never be allowed to shoot a Creedmoor match, as the risk of bullets dropping into the pits is too high. The trajectory angle at the pits from the 1,000-yard line would be about 9 degrees below horizontal for the 50-caliber bullet. On the other hand, a 350-grain, 38-caliber bullet launched at 1,350 fps will not make the power factor as its value is 472. But this 38-caliber rifle, with a 12-twist barrel, loaded with a 350-grain bullet, launched at 1,350 fps would shoot flatter than almost any rifle/load combination on the line at last year’s NRA Creedmoor Nationals and there for be safer for the pit crew. The trajectory angle for the 38-caliber bullet shot from the 1,000-yard line would be about 3.3 degrees below horizontal at the pits. A typical 45-70 load of 70 grains of BP launching a 500-grain Government bullet to about 1,200 fps has a Power Factor of 600 and a 1,000 yard trajectory angle of about 4.1 degrees below horizontal. As you can see the 38-caliber load will not make the Power Factor but it shoots flatter and has a smaller trajectory angle at the 1,000-yard line and is therefore safer but would not be allowed to be used at the NRA Longrange Nationals. The Power Factor does not predict trajectory angle from the 1,000-yard line which is what must be known to keep the pits safe. Low muzzle velocity 45-calibers with inappropriate bullets for longrange matches are currently the greatest danger to pit safety.

Another issue that has been raised concerning pit safety is the mistaken belief that smaller caliber bullets will deflect off the target frames into the butts. Considerable use of 35 and 38 caliber bullets in Longrange matches has shown that the bullets go right through the frames just like larger caliber bullets so that is a non-issue. A benefit to using the smaller caliber bullets is when they do hit the uprights or frames there is less damage so the frames and uprights last longer. High Power Long-Range rifle marksmen shoot 70 to 80 grain 223 bullets at 1,000 yards. Those bullets are only going about 1,200 fps when they hit the 1,000-yard line. If any bullets are going to be easily deflected into the butts by the target frames or uprights, the 223 bullets will as their momentum is only about 0.43 lb-s for the 80-grain bullets while the above mentioned 38-caliber bullet retains about 1.36 lb-s, over three times the 1,000 yard momentum. It is evident that this is not a valid reason for restricting calibers to above 40-caliber as some ranges do.

A more appropriate method to implement so that the target-pullers in the pits are safe is to set a minimum muzzle velocity for all rifles, minimum bullet weights by caliber and finally minimum barrel twist requirements by caliber. All of the above are very easy to calculate and a chart can be produced that will allow match directors to quickly and easily determine whether a rifle and load combination is safe for Creedmoor events.

During last year’s Creedmoor Nationals at Raton, there were numerous times when shots fired produced tumbling bullets at the pits. These are the MOST dangerous bullets concerning the pit crew safety. A tumbling bullet CAN and WILL, due to the dynamic properties of a tumbling bullet, fly into the pits upon contact with the target frames or uprights. Also, a tumbling bullet will have an extremely steep trajectory, due to its greatly diminished ballistics coefficient, that can allow the bullets to more easily deflect into the pits. Shooters whose bullets are tumbling MUST be pulled off the line after the first tumbling bullet. That should be an important aspect of the Pit Safety Officer as well as those pulling targets. Even better, with the rifle and load qualification procedure proposed above, such a competitor would not be allowed on the line in the first place as correct barrel twist for the caliber and bullet weight/length shot will preclude this from happening. It is very easy to know when a bullet is tumbling by the sound produced as the bullet passes over the pits as well as the shape of the hole through the target. Please keep in mind that the shooters, whose rifle/load combination produced very dangerous tumbling bullets at the pits last year were shooting rifle/load combinations that had passed the NRA Power Factor.

Safety is always the most important focus at any match. We can ill afford an accident in the pits caused by an inappropriate rifle and load combination. Caliber does not predict pit safety. The simple procedure outlined above can easily be implemented to make long-range BPCR matches safer for the shooters pulling targets in the pits. All that is required is the currently measured muzzle velocity and a simple chart that will insure that inappropriate rifles/loads will not be allowed on the firing line.

The proposed chart is as follows

 

         Minimum Muzzle Velocity for All Calibers = 1,225 fps

Caliber

Minimum Twist

Minimum Bullet Weight

38

13

340

40

16

400

44

18

460

45

20

500

50

26

625

 

This simple rifle/load screening method, which is actually quicker and simpler then the current method, will make the pits safer for the pit crew. Only the muzzle velocity needs to be measured. The competitor will also tell the testing official his or her bullet weight and barrel twist. If the competitor does not know their barrel twist it can easily be measured with no more than a cleaning rod and yardstick.

The trajectory angles for all of the above calibers and bullet weights with 1,225 fps muzzle velocities will produce the same trajectory angle, about 3,8 degrees below the horizontal at the pits from the 1,000-yard line.

All the best,

Dan Theodore
2-23-05