Ballistics for Service Rifle

The AR-15 is the Service Rifle that is breaking records set by Garand and M1A rifles. It is doing this with bullets that have less advantageous ballistic coefficients than the larger 30 caliber bullets. This often sets up a conundrum for people looking to get into the sport, should they go with the cheap AR-15 with suboptimal but cheaper bullets, or go with the more expensive M1A with better but more expensive bullets? What equipment do they choose if they want to win?

Look at the 80gr Amax bullet, with a nominal G1 BC of .453, and it is considered a great bullet for the 600 yard line. However, it still at a disadvantage over the old 168gr HPBT with a .462 G1 BC. Now these G1 BCs are really only applicable close to muzzle velocity, as they decrease with distance as velocity decreases with distance, BUT if you compare the G7 BCs you’ll see the same thing: the 30 caliber match bullets have a ballistic advantage over the 22 caliber match bullets.

This is really confusing until you remember a few things:
1, Service rifle is only between AR-15, M1A, and Garands (NRA now allows the AR-10, but not the CMP).
2, Service rifle competition is limited to 600 yards maximum.

With those two considerations in mind it is easier to make the argument that the AR-15 is an easier platform to shoot than the M1A or Garand, and that the ballistic advantage of a higher BC bullet is minimal at 600 yards and under. Even with very high BC bullets like the 175 SMK, 178 Amax, or other newer bullets, the advantage over the .223 Rem is minimal.

175 SMK at 2,650 fps muzzle has 15.9 minutes of drop to 600, and 5.1 minutes of windage adjustment for a 10mph crosswind. An 80gr Amax at the same muzzle velocity, distance and conditions has 16.2 minutes of drop and 5.4 minutes of windage. The advantage of the 30 caliber round is 0.3 minutes of drop, and 0.3 minutes of windage, which translates to 1.8 inches either way. The 10 ring is over 12 inches at that distance, if the 22 and 30 cal shooters made the exact same wind call and shot, it’s likely that they would have the same scores, so shooter skill becomes the primary factor for shot success.

The further beyond 600 yards you go, the more impressive the 30 caliber advantage becomes, but for Service Rifle the 30 cal advantage is minimal from a ballistics standpoint. The other advantage that 30 cal rifles have, is that they make 30 cal holes in the target, and with the “outside scoring” methods a 30 cal bullet has a slight advantage in breaking the scoring ring for the exact same impact point over a 22 caliber bullet.

But all this talk of ballistics ignores why the AR-15 is such a good platform for Service Rifle, and that is modular rifle design, low recoil, and ergonomics. It is simply a much easier platform to build into an accurate platform (there is absolutely no bedding to worry about, unlike the M1A or Garand), and it is much easier to size to shooter (A1 or A2 buttstocks were allowed, now this year adjustable buttstocks are authorized as well as cheek pieces). Simply put, the ballistic advantage of the bigger 30 cal rifles isn’t enough to overcome the “shootability” advantage of the AR-15.

Interestingly the AR-10 is not yet CMP Service Rifle legal, so we won’t see the AR-15 and the AR-10 go head to head in EIC (excellence in competition) matches any time soon. But, we have seen the AR-10 replace the M1A for the US Army Marksmanship Unit long range (1000 yards) NRA High Power matches. And again the AR platform is beating out the older M1A in the hands of skilled shooters (despite only having a 20 inch barrel).

To sum it up, get out and shoot. Even if you don’t have a Service Rifle as long as you can safely compete you can compete under the “match rifle” category. You may not win, but don’t let not winning stop you from participating. Any match where you walk away a better, more experienced marksman is a great match.

This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s