SIG Sauer M400 Pro Review: The Best Entry Level AR? By:



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.

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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.