I have a Bushmaster Varminter with the hand guard pictured. I want to mount a light to the side of it but I don't know what that mount is called. I'm aware of Picatinny and Weaver mounts but what are the slot type mounts called so I can get a light with the correct mount. Thanks.

M-LOK mount

1 minute ago, JohnnyB said:

M-LOK mount

Thanks.

I'm not sure those are M-lok. They look a bit big.

I think they are called cooling vents.

13 minutes ago, Mr.Stu said:

I'm not sure those are M-lok. They look a bit big.

I think they are called cooling vents.

Interesting. Could someone with known M-lock measure the width of the slot? thanks.

36 minutes ago, Tonester2 said:

Interesting. Could someone with known M-lock measure the width of the slot? thanks.

32mm long and 7mm wide or 1.25" by .25" as just measured by my micrometer.

12 minutes ago, JohnnyB said:

32mm long and 7mm wide or 1.25" by .25" as just measured by my micrometer.

Thanks for providing the measurements. This confirms that mine doesn't have M-Lock because the slits measure 1.87" long and 0.37" wide. Looks like an entire upper replacement for me.

Why do you need a whole new upper?

If you want to mount a light you have several options.

1. There are mounts that clamp onto the barrel. Probably not the best idea for you as it will effect the harmonics of the barrel and probably make your varminter less accurate.
2. Replace the gas block with one that has a picatinny rail on it and attach a pic mount to that. I would still not recommend that for the same reason as the clamp on mount.
3. Replace the handguard with one that has m-lok or picatinny rails built in.

One thing that puzzles me though. The Varminter is a rifle set up for long range accuracy. What flashlight would you mount that can illuminate that far out?

If you're thinking home defense maybe a 16" upper would be a good idea as it is way more maneuverable than a 24" would be. 

8 hours ago, Mr.Stu said:

Why do you need a whole new upper?

If you want to mount a light you have several options.

1. There are mounts that clamp onto the barrel. Probably not the best idea for you as it will effect the harmonics of the barrel and probably make your varminter less accurate.
2. Replace the gas block with one that has a picatinny rail on it and attach a pic mount to that. I would still not recommend that for the same reason as the clamp on mount.
3. Replace the handguard with one that has m-lok or picatinny rails built in.

One thing that puzzles me though. The Varminter is a rifle set up for long range accuracy. What flashlight would you mount that can illuminate that far out?

If you're thinking home defense maybe a 16" upper would be a good idea as it is way more maneuverable than a 24" would be. 

Good points but I got this mostly for home defense. I got it used at a decent price. As mentioned on my other post, I want to put fixed or iron sights on it but decided it was too much of a hassle to replace the stock gas block with one that has a front sight on it. Now with the fact that I can't mount anything to the hand guard and the stock one doesn't have the delta wring with a spring type retention ring, that makes removing the guard difficult. So I'm thinking the better way may be to replace the entire upper with a shorter barrel and keep the stock one for when I want to do long range shooting or just sell it.