Anonymous Ballistics: Selecting a CQBR (Close Quarters Battle Riffle)

I set out this last year with the goal of purchasing my first AR. I knew I wanted a close quarter’s rifle and not a sniping platform but I didn’t know a lot about what made one AR better than another. I wasn’t about to drop over $1000 dollars on a rifle without being able to make an educated guess at the very least. So I began to scour websites and forums trying to sift out what made a reliable AR-15. The best advice I could give any of you would be to read this forum post by Jwise:

So you want to buy an AR-15, huh?

Go ahead and take a few minutes to read through it...

Done? Okay.

Yeah, it’s a long one but full of very useful information. Most importantly it helped me to identify what I needed and what I wanted in a battle rifle.

Needs:

16 in barrel length: Shortest legal length in my state. Essential for close quarters/ urban combat.
5.56 NATO chamber: I want it compatible with military ammunition. In case of a disaster that may be the most readily available type.
Chrome lined chamber and bore: the barrel is the heart of the weapon and this will deter corrosion
1/9 twist: The minimum rifling twist you need to be able to accurately fire heavier grain bullets.
No Mismatched feed ramps: Only really problematic if the upper has M4 feed ramps but still don't want to press my luck.

Wants:

1/7 twist: More accurate than 1/9 twist when firing heavier grain bullets.
M4 Feed ramps: Would be nice even if they only prevent 1 jaming in 1000 shots.
Optics ready: Got a buddy who works for L3. He's going to get me a deal on an Eotech red dot sight.

There was one last thing I needed to consider and that was the action. Do I want a direct impingement gas operating system or a piston driven operating system? A quick google search will return a bunch of forum posts saying how the piston driven systems are superior to the direct systems. On a Direct impingement gas system the gasses from the cartridge are routed back to the bolt, blowing it back and loading the next round as it closes. On a piston driven system the bolt is pushed back by the metal piston leaving the bolt cleaner since the gasses aren't blowing carbon all over the bolt. Most folks will quickly tell you that the piston driven system is superior for this reason and it’s true that it’s statistically less likely to jam as a result.

But…

What happens when they do jam? Both systems WILL jam given enough use. Most operators running a gas system reported that upon jamming they were able to squirt some oil on the bolt while in the field and were able to resume firing the weapon. On the other hand the piston driven system was only able to be returned to operation after the piston was replaced which requires the rifle to be field striped. So the question is not so much which system is better but weather you want to pack oil or a couple spare pistons in your gear/range bag.

So I figured I had enough information now to make my selection. I knew I didn't want to go with a kit. Being my first AR I didn’t want any mismatched components. I knew Colt makes the rifle by which all others are judged but I didn’t want to be spending more than $1000 on a rifle. I checked out some Smith & Wesson, Bushmaster and DPMS rifles. They were all nice but made me compromise on a need from my list. Then I found this beauty on sale:

This is the Sig M400 SRP (sight ready platform). MSRP is $995.00

It has a chrome lined 16 inch barrel, the shortest legal length in my state. It’s chambered in 5.56 NATO caliber so it’s compatible with mil-spec ammunition and .223 caliber ammunition. The 1/7 barrel twist (one rotation of the bullet for every 7 inches of travel) allows it to fire heavier AP rounds at distance without losing accuracy. There is no fixed front sight to obstruct the view through a red dot sight (I plan to add one next year) and it come with M4 feed ramps just for good measure.

First thing I did was replace the foreword grip with a UTG quad rail and mount the Magpul flip up sights.

Barrel markings: Hard to see but these show the 1/7 barrel twist and the 5.56 NATO cambering on the opposite side.

Feedramps: Not the deepest M4 feed ramps I have seen but still nice.

Front sight base: This was one of the major selling points for me. I didn't want a large front sight obstructing the view through a red dot sight. I would have mounted the backup sight on the gas block but the sight is made of polymer and there's a chance it could melt if the block heated up too much.