Tuesday, January 02, 2018

Basic Riflery, the MPBR, and more

Great article over at Ammo Land, concerning stuff I taught 40 years ago.  This stuff hasn't changed much, because physics hasn't changed much.  The article is based on the M4 carbine and standard NATO ammo, which is familiar to almost every shooter, but the math holds regardless of the caliber or the rifle.

The author defines Maximum Point Blank Range (MPBR) as that distance at which the bullet flight varies no more that 6 centimeters from the line of sight.  Six centimeters is approximately 2.6 inches, and is the height that the sights of an AR 15 is set above the bore line.   That's a useful measurement standard because it is readily available if you're holding an AR rifle.  But, in my day, we defined it differently.

I was taught (and I taught) that Maximum Point Blank Rage is that distance where the marksman can hit a man-sized torso target (from belt to head) by holding the sights on a center-mass point.  With a standard NATO 7.62mm ball ammo, that distance is somewhere about 300 meters, assuming still air at sea level.  Understanding the math, and the physics is fine, it's a wonderful thing, but physics and match make certain assumptions and those assumptions may not hold true in the field.

For example, I've never seen still air at sea level.  I assume that it exists, but every time I walk down to the beach, there's a breeze blowing.  Still, it's an assumption that exists, so it must happen somewhere.  So, after we understand the math and physics, it's important that we practice with our rifle.  Take it out and shoot it at every opportunity.  Practice from field positions.  Get away from the bench.  The marksman that shoots 100 rounds a year will be more familiar with his rifle than the marksman that shoots 10 rounds per year.

It's easy to sit at a computer and explore the variables.  It's something else again to get out in the field and see how those variables affect your rifle, your ammo, and your target.  Get some training, practice with your rifle, and when it comes time to make the shot you'll have both the confidence and ability to hit the target.


Old NFO said...

Yep, much like that infamous 'standard' day! Never seen one of them yet!

Retired Spook said...

Jeff Cooper, and his Scout Rifle followers (of which I am one, sort of) always contended that a practical rifle was not intended to be shot from a bench, but from a variety of positions in the field. It makes sense, since, as one of my Minions pointed out to a cranky range officer, "We don't have any shooting benches where we hunt."

Doesn't matter what kind of groups you get off the bench, what matters is the kind of groups you get in the field!