SureFire's Scout Light Pro range is the default weapon light on a serious carbine, and its model names look worse than they are. M340DFT-PRO, M640U-PRO, M640DF-PRO — there is a system, and once you can read it the choice gets simple.
Reading the name
Three things are encoded, in order.
M340 or M640 — the body size. M340 is the Mini Scout Light Pro. M640 is the full-size Scout Light Pro. The Mini is shorter and lighter and takes one battery; the full-size is longer and takes two. That is the single biggest decision and everything else is secondary.
U, DF or DFT — the head and power source. U is the standard high-output head. DF is Dual-Fuel, meaning it will run on either disposable 123A cells or a rechargeable lithium-ion cell. DFT is Dual-Fuel Turbo — dual-fuel capability with a Turbo head.
PRO — the generation. The Pro models use SureFire's updated mounting system, which matters because it changed how the light attaches.
Mini or full-size?
The Mini Scout Light Pro exists because the full-size one is longer than most people need. On a short carbine, a full-size Scout Light eats rail space that you probably want for your hand. The Mini gives up some runtime — one cell instead of two — and typically some output, and buys back length and weight.
Choose the M340 if the rifle is short, if you run a forward grip or a hand stop and rail real estate is tight, or if you are building something to carry a long way. Choose the M640 if you want maximum output and runtime and the rifle has the room.
There is no durability difference worth worrying about. Both are built the same way.
What Turbo actually changes
This is the suffix people misunderstand. A Turbo head uses a tighter reflector to concentrate the beam into a smaller, more intense hot spot. It throws further and lights up a distant target better. What it gives up is spill — the wide, dim light around the hot spot that lets you see what is beside you.
So Turbo is not simply "better". For open ground, longer distances and identifying something out at the edge of a field, Turbo is the right head. For indoors, confined spaces and anything where peripheral awareness matters more than reach, a standard head is genuinely the better tool.
Our guide to choosing a weapon light covers the lumens-versus-candela distinction behind this in more detail — lumens is total light, candela is how hard it is thrown, and Turbo trades one for the other.
Is Dual-Fuel worth it?
Dual-Fuel means the light accepts a rechargeable lithium-ion cell as well as standard 123A primaries. If you train often, rechargeable pays for itself quickly and you stop thinking about battery cost. If the light lives on a rifle that sits in a safe, primaries hold their charge for years and that is exactly what you want.
The useful part of Dual-Fuel is that you are not locked in. Run rechargeable for training, drop primaries in for anything that matters, and you have not bought two lights. We stock both in batteries.
Do not forget the mount and the switch
A Scout Light Pro is a body. Two other decisions finish the setup, and both are easy to overlook until the light arrives.
The mount. Scout Light Pro bodies attach via SureFire's low-profile mounts, and you need the right one for your handguard — M-LOK or Picatinny. Buying the light without checking which your rifle takes is the most common ordering mistake in this category.
The switch. The tailcap that ships with the light gives you a click and a momentary press at the rear. If you want a tape switch on the handguard instead, you need a remote switch assembly — an ST07 tape switch, or a dual-switch tailcap like the DS-SR07 if you want both a tape switch and a rear button. If you run a laser as well, the dual-switch assemblies let one pad control both.
All of these live in weapon light accessories, and it is worth ordering them at the same time as the light rather than discovering the gap afterwards.
The short answer
- Short carbine, weight matters: M340 Mini.
- Maximum output and runtime: M640 full-size.
- Open ground, long identification distances: a Turbo (DFT) head.
- Indoors and close work: a standard head, for the spill.
- You train a lot: Dual-Fuel, and buy the rechargeable cell.
Browse weapon lights, the full SureFire range, or everything together in weapon lights and flashlights. If you are deciding between a light and a laser, or whether you need both, see weapon light vs laser.