M&P15 Sport Bayonet Modification

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CastingFool

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I recently purchased a Sport and am very happy with it. I have a question about fitting a bayonet to it.

I know that a standard M7 bayonet isn't going to fit properly because of the barrel length on the weapon. I was wondering if you could take another front sight assembly and remove all but the ring with the lug on it and attach it to the barrel far enough forward to properly accommodate the M7.

Stupid idea, or workable?
 
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I had to read that twice. I don't see why you couldn't chop down a 2nd A2 front sight post and mount it farther down the barrel so you can mount a bayonet. If it's what you want to do, go for it. I'd advise surfing Brownells or Midway USA for a 2-piece clamp on bayonet lug. I'm not sure if such a thing exists, but it wouldn't hurt to look.

Congrats on your new 15-Sport and welcome aboard!

It's your 15-Sport. Whatever reason you have for wanting to mount a bayonet to it is yours. If you want to do it, go for it. It's not my cup of tea, but it's not my rifle either. :)
 
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Seems silly to mount the M7 when only 3-4 inches will extend beyond the suppressor. I just want the option to mount a usable bayonet.
 
Does anyone know the barrel diameter off the top of their head? (Not sure where my micrometer is.)

Of course I could just look through the manual... (Idiot)

0.750?
 
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gm272gs said:
Okay. Now I've read everything.

Nothing new will surprise me when I read another M&P 15 Sport thread.
Click to expand...

LOL ... I hear ya.

It's tax refund season. The M&P 15-Sport is one of the most affordable AR-15's from an established manufacturer that has a reputation for quality. Tis' the season for new and very enthusiastic M&P 15-Sport owners, and questions.

New people, ask all the questions you want. Better to ask, get a few good replies (some of them may feel short and a bit gruff), than not.
 
Actually, a company manufacturted an extended pommel (M7) that fit 16-inch barrels correctly. Unfortunately, the name escapes me.
 
I picked up a used Colt front sight assembly on eBay. It's already drilled and has pins. As another installment in my bayonet saga...

What do any of you think about using one or both of the rings to secure the mount? IMO, one would look less obtrusive, but would both (connected by the bar just above them) be stronger and less prone to twist?

I know that this sounds like a ridiculous idea, but I really like the idea of having a working bayonet.
 
IMO:

2 Points Of Contact > 1 Point of Contact

Also who cares whether or not I think it's ridiculous or someone else thinks it's ridiculous? If it's what you want to install on your rifle, go for it. That's the fun of owning an AR-15. Make sure to post pics of your handiwork.
 
Interesting exercise. I've kind of thought of the same question myself

As an option, would converting the gas system to a mid length put the lug in the correct location to lock the bayonet? It would be a lot more work and you'd have to plug the existing gas vent.
 
If you are really going to do this, then to make it look decent, here is what I would do.

Since you purchased another FSB, I would shave down my existing FSB and replace my hand guards with a set of Magpul mid length hand guards. You will probably have to get a new hand guard end cap, because I would just dremel the old one off, and not remove the original FSB. Put the new FSB on in front of the hand guards.

Makes it look like a mid length set up and the bayonet will work.
 
After thinking about this, and discovering that mounting the bayonet lug would require drilling the pin holes, I've decided to go with set screws.

I was not an armorer while in the service, and did not realize that the pins needed a groove in the barrel to work. I believe that I can drill the dimples in the barrel for the set screws with a drill press. Or, barring that, have a gunsmith do it for me.

I was wondering, though, where should the ring on the bayonet that goes around the flash suppressor, go on the suppressor? Front edge? Back edge? In the middle?

I'll do some searching for some pics, but your opinions are much valued.
 
Here's a M7 mounted on a preban Colt. Keep in mind this is a 20" barrel. Also, the pins in the front sight are tapered...Don't know if you're aware of that.
 

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Yes, that's pretty much the configuration that I found during my search. Thank you. I learned that those pins were tapered, which explained the number of undrilled front sights on the market. I think that set screws will be the way to go
 
Was able to work on this project today. A bit daunting, playing gunsmith. The cost of the Sport, for me, was a chunk of change, so I was a bit worried that I'd cause inadvertent damage to my weapon.

Drilled and tapped one of the rear pin holes in the spare front sight to see how it would go. Grabbed the 8-32 drill & tap, so it took me a minute to figure out why the 10-32 set screw wasn't threading into the hole... dummy...

Redrilled and tapped for 10-32 and the set screw worked just fine. Drilled and tapped the front holes, used my Dremel to cut off the lug ring, and tried it on the weapon. Success! At least from my point of view.

I now need to drill the dimples in the barrel, use a grinder to round off the lug ring where it was cut away from the rest of the front sight, and color the cut portion of the ring to match the rest of it.

Here are some pics.

sight01.jpg

sight02.jpg

sight03.jpg
 
I've got spares, should I replace the steel crush washer, or reuse the original one?
 
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