CMMG Banshee .300 BLK: 8-Inch vs 12.5-Inch Barrel, Suppressed

Four and a half inches of barrel changes more than the numbers on a spec sheet. With a suppressor attached, it changes how the whole gun carries.

Same family, different personalities

CMMG's Banshee is a compact AR-pattern platform, and the listings we link put it in .300 Blackout with a 30+1 magazine. The three versions here are the 8-inch Banshee, the 12.5-inch Banshee in a tungsten finish and the 12.5-inch Banshee in a coyote finish. The two 12.5-inch guns are the same barrel length in different colors, as far as the listings show, so the real decision is 8 inches versus 12.5.

What a few inches of barrel changes

Velocity with supersonic ammunition. A shorter barrel generally gives a cartridge less time to burn its powder, so muzzle velocity drops, and .300 BLK supersonic loads are designed to give up less than a typical 5.56 load does. Exactly how much depends on the load, so check the ammunition maker's published numbers rather than a generalization.

Velocity with subsonic ammunition. Subsonic loads are built to land well under the speed of sound from a range of barrel lengths. The difference between 8 and 12.5 inches is smaller here, and gas-system behavior matters more than raw velocity.

Overall length with a suppressor. Here is the practical point. A suppressor adds its own length to the barrel. An 8-inch barrel with a can attached is far more compact than a 16-inch rifle without one, and 12.5 inches with a can is somewhere in between. If you plan to carry the gun in a bag, a vehicle or a safe, measure the suppressor maker's published dimensions against the space you have.

Noise. A suppressor handles most of the muzzle blast on both barrel lengths. A shorter barrel delivers more unburned gas to the muzzle, which a can has to manage, so the can maker's guidance on host barrel length is worth reading. This is the sort of detail that you must check in the suppressor's documentation, and we do not claim measurements here.

Subsonic cycling by barrel length

This is the question most buyers want answered, and the honest answer is that we have not tested it. What we can describe is the general picture:

• Gas-operated AR-pattern guns balance the amount of gas they bleed from the barrel against the energy they need to cycle the bolt. Subsonic .300 BLK produces less gas pressure than a standard load, so the system has less to work with.
• A suppressor adds back pressure, which can make some guns cycle more vigorously or produce more gas at the shooter's end. The effect varies by gun and can.
• The gas port's position relative to the muzzle is different at 8 and 12.5 inches, which can change how a given load behaves.

So the practical routine is to buy a small amount of the ammunition you plan to use, test it in your gun with your suppressor, and see whether the bolt locks back on empty. The Magtech .300 Blackout 200-grain subsonic review discusses one specific load.

Side by side

The legal category question

A short barrel raises a legal question that is worth taking seriously. A firearm with a barrel under 16 inches built on an AR-pattern receiver can be a pistol or a short-barreled rifle depending on how it is configured and how it started. The 8-inch listing says pistol. The 12.5-inch listings do not state in the product names which category they fall into, so read the product page and the manufacturer's description.

Stabilizing-brace and stock rules have changed more than once in recent years, and agency guidance has been in dispute. Check current ATF information and your state's law before you swap any stock or brace. Do not attempt to turn a pistol into a short-barreled rifle without paperwork, and do not assume that a federal change in tax or process alters state law. We do not publish instructions for converting firearms.

On the suppressor itself, the federal process changed in 2026 while states vary. Our buying walkthrough lays out the order of questions, and the status page on the NFA ruling tracks the moving parts.

Pick the 8-inch if, pick the 12.5-inch if

Pick the 8-inch if you want the smallest practical suppressed .300 BLK, you will mostly shoot subsonic ammunition, and you are comfortable verifying how the pistol category works where you live.

Pick the 12.5-inch if you want a little more barrel for supersonic loads, a longer platform to hold, and a gun that is still compact. Choose between Tungsten and Coyote for finish.

Consider neither if you want a hunting rifle. In that case, look at the CMMG Resolute 16-inch, which is a rifle-length option and has its own review.

For a broader view of .300 BLK formats, see .300 Blackout pistol versus rifle for suppressed shooting, and BuyMoreAmmo's .300 Blackout versus 5.56 is useful if you are still choosing a caliber.

Hearing

A suppressed .300 BLK is quieter than an unsuppressed one, but it is not hearing-safe. Subsonic ammunition helps; the action noise remains. Keep hearing protection on, and read Quieter Does Not Mean Quiet for the reasoning.

Bottom line

The Banshee choice is mostly about carry size versus a little extra barrel. Pick based on how you will carry and store the gun, not on a single velocity number, and treat subsonic cycling as something you verify yourself.

Editorial note: This is an independent editorial overview built from manufacturer specifications and publicly available information. We have not performed hands-on testing of the products discussed, and nothing here is a performance guarantee. Verify specifications, compatibility and legality for your own situation.

Affiliate disclosure: Some links on this page are affiliate links to Ammunition Depot. We may earn a commission if you buy through them, at no extra cost to you. Our editorial choices are not influenced by commissions. Check current price, stock and specifications directly with the retailer.