Many AR-15s look like advertisements for Magpul. All of the furniture from the handguard to the stock and everything else in-between are polymer. That’s not a knock at all on Magpul, I have plenty of their stuff. 

Whoever at SIG who was responsible for designing the M400 Pro though would likely be appalled by all of it. This rifle is SIG’s idea of a “real” AR-15. Sturdy, accurate, and versatile are words that you could use to describe it, and I’m sure SIG would agree with that. Let’s take a closer look at all that is the M400 Pro. 



SIG M400 Pro
The SIG M400 Pro is well balanced and range ready out of the box. (Photo: Ryan Domke/

Picking it up out of its box, it almost gives you a false feeling that it’s heavier than it is, mostly due to the solid handguard. It’s not too heavy at 6.5 pounds, but it has a certain heft to it. I’m used to finding PMAGs in the box with rifles, and I didn’t realize that this one came with an aluminum magazine instead, which only added to the “real” AR feel. Overall, I was very excited to hit the range with this one. 


The 16-inch nitride barrel of the M400 Pro is almost completely housed within the free-floating M-LOK handguard. On top of the handguard and running the length of the rifle is a top rail to mount all of your optics. Personally, I much prefer it when they are full length as opposed to only over the receiver. 

SIG Sauer M400 Pro
The adjustable buttstock features integral QD points. (Photo: Ryan Domke/

Moving on to other main furniture, SIG included its own grip and adjustable stock in place of the typical A2-style grip and basic adjustable stock. Both of which I’d consider to be large upgrades. The grip has internal storage that is great for keeping batteries or extra rounds and has a nice medium grip texture. Integral QD points and an angled curve at the bottom of the stock make it versatile and comfortable. When you pair it all together, you get a very ergonomic rifle.  

Even the small details did not get overlooked, such as the safety selector, charging handle, and mag release, all of which are ambidextrous. Even the sights are a step above the standard polymer flip-ups you find on ARs many times at this price point. They are quick deployable metal flip-up sights that are easy to adjust and add to the aesthetics of the rifle.

SIG Sauer M400 Pro
It's all in the details. The included metal flip-up sights and ambidextrous charging handle are just a couple of things that make this AR well-suited to run right out of the box. (Photo: Ryan Domke/

While none of these parts individually are reason enough to consider the M400 Pro, packaging them all together into one great bundle is a plus. I’ve added some specs below to give you a better idea of what this gun offers: 

  • Caliber: 5.56/.223
  • Operating System: Direct Impingement
  • Capacity: 30+1 rounds
  • Length: 36.5 inches
  • Barrel Length: 16 inches
  • Barrel Twist: 1:7
  • Weight: 6.5 pounds



SIG Sauer M400 Pro
My first magazine went as expected, leaving two-to-three-inch groupings out to 65 feet. Photo: Ryan Domke/

Since my indoor range doesn’t allow rapid fire or incorporating movement or reload drills, the real fun started once I hit the outdoor range. I did put a couple magazines through at the indoor range though to get a feel for the handling and controls and all went as expected. I was able to put five-round “bursts” in 2 and 3-inch groupings out to 65 feet. Once I took it outside, I was ringing 60inch gongs at 50 yards consistently. Reloads were easy enough, but it would have been nice to have more of a flared magwell. 

Reliability wise, I had zero issues. This thing went through mag after mag of mixed grain FMJ rounds, green-tip rounds, and some steel-case 55-grain ammo, and it didn’t skip a beat. I only had half of a box left of 77-grain SIG Elite Match Grade ammo, but with the 1:7 twist it shot like a dream. I don’t think there was any ammo that would cause this gun to continuously jam up, unless it was some reload that went wrong. I give it all high marks for reliability in my book. 


I feel like this rifle could be priced higher than it is, and it would still sell just as many units, which is strange for me to say. The quality of the parts, ambidextrous controls and 1:7 twist make it feel and shoot like a much more expensive gun. If I was in the market for another AR-15, the M400 Pro would definitely be on my list to consider. 

See what other customers had to say about this rifle in the reviews below:

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