Magtech 200-Grain Subsonic .300 BLK: What FMJ Does and Doesn't Do

Heavy, slow and jacketed all the way through. That description is the whole product, and it tells you both what to use it for and what to leave it out of.

What the label tells you

The Magtech .300 Blackout 200-grain subsonic is a full metal jacket round. That single phrase, with the 200-grain weight and the word subsonic, covers most of what you need to know. The weight is heavy for the cartridge. The jacket runs the full length of the bullet. The design goal is a slow, steady projectile for quiet range work.

The retailer listing we link sells it in a 150-round quantity, and some other retailers list the same Magtech product under a "First Defense" line name. That name is a marketing label. The bullet is still a full metal jacket, and nothing about the line name changes how it behaves.

Why .300 BLK gets paired with subsonic loads

.300 Blackout was designed so that one AR-pattern rifle could shoot a heavy, subsonic bullet and a lighter, supersonic one. The heavy bullet is what you load for quiet shooting. Without a suppressor, a subsonic .300 BLK is still a loud rifle shot, because the muzzle blast is the main source of noise. With a suppressor, removing the supersonic crack leaves the muzzle blast tamed and the bullet crack absent, which is the combination people have in mind when they talk about "quiet" rifles.

For the wider map of which calibers have subsonic options, see subsonic ammo by caliber. BuyMoreAmmo's best .300 Blackout ammo piece covers the subsonic-versus-supersonic decision at more length.

Expansion honesty: it is FMJ

This is the part that belongs in plain words. A full metal jacket bullet is built to hold its shape. It is not designed to expand the way a hollow point or a soft point does, and a slow bullet at subsonic speed has even less energy to deform. That has consequences:

• For range use, FMJ is a perfectly conventional choice. It is straightforward, it holds together through targets, and it is a common construction for subsonic range ammunition.
• For hunting, it is a poor fit. Many jurisdictions restrict or prohibit full metal jacket bullets on big game, and a non-expanding bullet is not designed for the job in any case. If you plan to hunt, read your state's regulations and pick a bullet intended for that purpose.
• For defense, do not rely on it. Self-defense decisions involve legal, practical and safety issues that go well beyond an ammunition listing, and nothing on this page should be read as a recommendation of this load for that use.

Cycling: the variable you have to test

Subsonic .300 BLK produces less gas pressure than a standard load. In a gas-operated rifle, that can mean the bolt does not travel far enough to lock back on an empty magazine or to eject the spent case reliably. A suppressor adds back pressure and often helps. Gas-system adjustments exist on some rifles. We have not tested this ammunition in any rifle, so we will not claim it runs in yours.

A sensible approach:

1. Buy a single box before a full case.
2. Fire it in your rifle with the suppressor attached, since that is the setup you will use.
3. Watch for failures to eject, failures to lock back, and stovepipes.
4. If you see problems, check cleanliness and the can maker's guidance before you blame the ammunition.
5. Keep notes on temperature, because the same load can behave differently in cold weather.

Accuracy

You will see strong claims about subsonic .300 BLK accuracy online. We do not have measured data for this load to offer you, and published group sizes depend heavily on the rifle, optic and shooter. Treat accuracy as another thing to check yourself, and treat the 200-grain weight as a hint about the intended use rather than a promise.

Safety: same cartridge family, different rifles

.300 BLK cartridges fit magazines made for 5.56, which is a convenience that doubles as a hazard. A .300 BLK round fired from a 5.56 chamber is dangerous. Mark your .300 magazines clearly, keep ammunition boxed and labelled, and never mix them casually. BuyMoreAmmo's wrong ammo piece explains the failure modes.

Where this load fits

Pair it with a short host like the CMMG Dissent compact or a rifle-length option like the CMMG Resolute. For quantity buying habits generally, BulkAmmoFinder has a bulk .300 Blackout buyer's guide.

Alternatives worth knowing about

If you need a bullet that expands, look for a .300 BLK load designed for expansion rather than adapting a range load. If you want a different quiet-shooting trade-off, a suppressed .22 LR or subsonic 9mm are other routes; our pistol versus rifle .300 BLK post compares formats within the caliber.

Hearing and legality

A suppressor is not a substitute for hearing protection. See A Suppressor Is Not Hearing Protection. And suppressor ownership is a federal and state matter that changed in 2026; our buying walkthrough lays out the questions in order.

Bottom line

Magtech's 200-grain subsonic is a plain, honest range load: heavy, slow, jacketed. Use it for what FMJ does well, test it in your own rifle, and keep it out of jobs that need an expanding bullet.

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.