Caliber selection for an SPR in a Designated Marksman role.

[Part 2 in my Designated Marksman series]

Bottom line up front: For the majority of people, your SPR should be in 5.56mm.

Does it have the best external ballistics? No.

Does it have the best terminal ballistics? No.

Is it the best caliber for most DMs? Yes. 

Lets talk about why that is. 

Flexibility:

First and foremost, the DM is a rifleman. You need to be able to do with your rifle what everyone else is doing. Patrolling, clearing buildings, rapid fire engagements at close range, shooting under nods and thermals. Can you do this with a larger caliber as well? You sure can. Is it as well suited for that role? No.

External Ballistics:

(Bullets flight through the air, I will only be discussing 77gr projectiles)

The ballistics of 77gr 5.56mm aren't amazing compared to most true precision rounds like 6ARC, 6.5, 308 etc. But I will argue they are good enough for the ranges of most environments.

In my 16in Criterion barrel, shooting 77gr OTM at 2734fps, and my level of skill, which I would consider intermediate at best, I can reliably achieve first round impacts at 700yds. 800-1000yds is doable, but not reliable for 1st round impacts for me at my skill level. Shooting 5.56 will force you to get good at wind calls, as wind pushes the lighter round around a decent bit. 

My point is that it gets the job done. This is not a sniper rifle, and should not be expected to do sniper rifle things. 

Terminal Ballistics: 

People get wrapped around the axle on this, and I’m going to lay out my reasons why I am hardly concerned with it. 

In a scenario where I am shooting a person at 700yds with my 5.56 SPR, I am not concerned with making an ethical shot. Putting a hole in someone is going to ruin their day, and take most people out of the fight. You can also shoot a person more than once given the semi auto and low recoil nature of the gun. If they survive to return to their group, they will drain them of resources as they die of infection or blood loss. That’s a win. 

Weight/Capacity:

Weight and capacity is a real consideration. “Lift more bro” is not always the answer. As a DM in the GWOT, carrying a .308 EBR, I could only carry 7 magazines of 20 rounds each. 140 rounds total. That was fine in that scenario because I was at minimum accompanied by 1 other dude with a SAW, 2 other guys with M4’s, and a radio with air support one call away at all times. We do not have that luxury as a Civilian in a DM role. 

A very sad Havoc, carrying half the ammo and more weight than everyone except the 240 guy

Ammo Commonality/Cost and parts:

If you are with a team, it is very important that you are able to share ammo. You should also know your dope for rounds other than your preferred load. Personally I have 3 different dope reference cards that can be swapped out on this Coletac Cheatsheet. One for 77gr, one for 62gr green tip, and one for 55gr FMJ. 

Cost of ammo is a consideration too. The most important factor of this skillset is training and trigger time. You need to be able to afford a large amount of ammo to train with, and paying .55 to $1 per round is much more feasible than $3-$4 per round. 

Other than your barrel and scope, most of your other parts are just normal AR parts. Bolts, BCG’s, extractors, gas rings etc are all plentiful and cheap.

Exceptions:

As everyone loves to say “everything is METT TC dependent”. Well the first T in METT TC is Terrain. 

If you live in wide open terrain where 1000yd engagement distances are likely and plentiful, the pendulum swings the other way and I would say to fulfill your role as a DM you need a bigger bullet, and the negative trade offs are worth it.