Hi, I just bought a M&p 15 sport 2 that is not threaded. I’m looking for an adapter to add a muzzle brake. Does anyone know the diameter size of the barrel?
Thanks

Bro there is no such thing.

You will need to have the barrel threaded to attach a brake.

I'm not sure they make a adaptor so you can use a threaded brake but there are several companies that make clamp on muzzle brakes. Here are a couple.

Clamp-on Muzzle Brakes – Kahntrol Solutions

Clamp-On Brakes - Witt Machine

There ARE adapters for a variety of guns. I forget where I got this one for this Remington Nylon 66 many years ago, but I found it on the internet.

John

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I would suggest buying a set of dial calipers and measure your barrel. They aren't that expensive and have multiple uses. Then you will be able to order the correct clamp on style for your barrel. I would offer to measure mine but 1) it's threaded, so might not measure correctly behind the threads for what you need and 2) I don't have an M&P15, so the barrel might not even be a match to begin with.

Learn something new every day. I would absolutely not trust a clamp on brake. Thing comes loose and some real damage can happen.

Just get the thing threaded. Your options will be almost limitless

What the gent above said. If you get an actual brake and it's efficient, the forces trying to pull the item off the barrel are substantial. If there's any misalignment between brake and barrel before it departs, you may get a bullet strike in the brake, resulting in damage to the brake. Possibly more.

I've seen what happens when clamp on/set screw retained front sight bases moved forward while firing. I wouldn't want to be on the firing line with you and a clamp on brake. .

Get the barrel threaded. Doing it right the first time is much cheaper than fixing the probable results and then doing it right. Just for informational purposes, without a brake, the recoil of a .223 carbine/rifle is about half that of a .38/9 mm handgun.

I've used a clamp on brake on my .308Win rifle. It never moved. Of course it needs to be installed properly...

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Just change the barrel for a threaded barrel. BCA had them for $60 a few months ago...