CMMG Dissent .300 BLK Compact: A Short Suppressed .300 for the Bag

Short barrels and subsonic .300 Blackout were made for each other on paper. The details are where you decide whether this one works for you.

The package on paper

The CMMG Dissent .300 BLK compact in our listing is a .300 Blackout with a 10.5-inch barrel and a 30+1 magazine, in the semi-auto pistol format that retailers use for this model. CMMG calls the series the Dissent MK4, and other retailers' listings of the same family mention M-LOK handguards, a linear compensator and, on some versions, a left-side charging handle.

Those details add up to a compact, modern-looking gun that is clearly meant to carry a suppressor. It is also a firearm where you should read the exact listing rather than rely on a model family description, because options differ from version to version.

Why short .300 BLK and a suppressor go together

The cartridge was designed to give an AR-pattern gun a heavy bullet that stays subsonic and a supersonic load that does not give up much from a short barrel. With a suppressor, the logic is simple: the shorter the host, the more compact the whole setup is. A 10.5-inch barrel plus a suppressor can come out comparable in length to a much longer unsuppressed barrel, which is why short .300 BLK guns are popular for people who want something they can carry in a pack or a car.

Our post on .300 Blackout pistol versus rifle for suppressed shooting walks through that comparison. This review is about one specific compact.

Questions to answer before you buy

What is on the muzzle? Listings across this family mention a linear compensator. That is a muzzle device, and it may or may not be the thing your suppressor attaches to. Whether the gun is threaded, what pitch it uses, and what muzzle device it ships with are questions to settle in the listing and with the maker. Do not assume that a 'suppressor-ready' look means a mount-ready barrel. If you need help sorting out thread names, our thread pitch cheat sheet covers the common ones.

What is the configuration? Pistol, rifle and short-barreled rifle are different legal categories, and they can turn on details like stock, brace and overall configuration. ATF's position on that area has been in flux, so check current guidance and your state's rules before you change anything on a short-barreled gun. We do not publish instructions for converting firearms.

Where is it legal? Several states restrict short-barreled firearms, magazines of this size or suppressors themselves. A sound plan starts with your state's law.

What will you actually carry it in? The appeal of a compact is portability. A suppressor adds length, and a loaded 30-round magazine adds more. Measure your bag or case against the combined length, using the suppressor maker's published dimensions.

Subsonic ammo and cycling

The Magtech .300 Blackout 200-grain subsonic is the ammunition we pair with this host. It is a full metal jacket round, which is a common choice for range work because it is straightforward and widely available. A few points apply to any short-barreled .300 BLK:

• Short barrels and subsonic loads can be a cycling challenge. The gas system has to work with less pressure than a standard load produces, and a suppressor changes the back pressure. Owners often find that a suppressor helps rather than hurts, and some guns need gas-system adjustment. What your gun does, we cannot tell you, since we have not tested it.
• Test before you buy in bulk. Start with a box and observe whether the bolt locks back on empty and whether rounds eject consistently.
• Do not mix up magazines or ammunition. .300 BLK cartridges fit magazines made for 5.56 but must never be chambered in a 5.56 rifle, so mark your magazines and keep ammunition clearly labelled. BuyMoreAmmo has a plain account of what goes wrong in wrong ammo swaps, and its best .300 Blackout ammo piece compares subsonic and supersonic options.

Our separate look at that ammunition is in the Magtech 200-grain subsonic review.

Noise: what to expect and what not to

A suppressed subsonic .300 BLK is quiet compared with an unsuppressed rifle, but it still produces noise from the action and from the bullet striking a target. The loudest component can be the mechanical noise of the bolt carrier group. Keep hearing protection on. See A Suppressor Is Not Hearing Protection for why.

Who should and should not look at it

If your priority is a longer barrel, compare with the premium .300 BLK hosts roundup or the CMMG Banshee 8-inch versus 12.5-inch comparison, and the CMMG Resolute 16-inch review for the rifle-length option.

The suppressor side

You still need a lawful, rated suppressor, and the federal process changed in 2026 while state law varies widely. Start with the buying walkthrough. We do not publish steps for manufacturing, modifying or assembling suppressors, so this article ends where the can maker's own instructions begin.

Bottom line

The Dissent compact is a sensible small package for suppressed .300 BLK, as long as you read the listing closely, understand the legal category of a short-barreled gun and test your subsonic ammunition for cycling.

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.