Greetings all. My first post here so please excuse my ignorance, I'm brand new to the AR platform.

I just picked up my S&W AR15 Sport a few weeks ago and am trying to learn as much as possible about it.

I live in a restricted state so I have the compliant gun: no threaded barrel, no bayonet lug, no high cap mags, no adjustable stock.

With that being said, what I want to do is change out the non adjustable stock for a traditional rifle stock. No sense having a pseudo adjustable, and besides I like the traditional look. I know about the A1 vs A2 stocks, A2 being 5/8" longer. My question is do I need a Mill Spec or Commercial buffer tube? I ask this because I'm finding conflicting info on the net. My main concern are the threads on the lower matching properly with the threads on the buffer tube. I'm finding the Mill Spec threads are 1.185" dia, while the Commercial threads are 1.170" dia.
So what are on the Sports lower? I want to make sure I get the right one and have a nice tight fit.
Like I said, I'm new to this, so if I'm in error kindly set me straight. Thanks for your insight.

Mil Spec is what you need

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Live free or die.

First off, Welcome to the forum. The Sport normally has a milspec buffer tube for the adjustable version. In your situation, it is irrelevant. The lower receiver will accept either milspec or commercial tubes as the threads are the same, but the tubes themselves are different diameters, the commercial tube being larger. If you're going to install a fixed stock, you need only insure the buffer tube you get matches the stock you're using. If your stock is marked as milspec, use a milspec tube, and vise versa. Also, since you're essentially installing a rifle length tube and stock, you'll need to install a rifle length buffer spring and buffer.

Good Luck and good shooting.

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SFC, US Army, Retired

Not sure that you need to replace the tube. Why not replace just the stock? As to whether or not your rifle has a mil spec or commercial tube, I'm told the easiest way is to remove the stock and check to see if the end of your buffer tube is flat, or has a slant. A flat end would indicate it is mil spec.

A rifle tube is a rifle tube. There is no commercial or mil spec in fixed stocks. Use the appropriate rifle spring and buffer as well. If using an A2 stock the A2 spacer is needed as well.

Check out the Magpul fixed stock. It mounts to your existing buffer tube.

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-John

That is a quick way to check, but there are some commercial tubes that are flat as well. The only way to know for sure, if unknown from factory, is to measure.

As stated by a couple of others, if he is changing to a rifle stock, there is a different receiver extension that is required for a rifle stock.

Once you know the diameter of the tube check out the Magpul Fixed Carbine Stock. It is shorter than the rifle stock and rock solid, I put the .050 butt pad on mine to extend the pull just a tad. This stock will use existing buffer components.

Thanks for all your reply's. Looks like Mill Spec's the way to go. Thanks for the suggestion for the MagPul Fixed Carbine Stock, I like the classic look of the A1/A2 so I'll probably go with that. I'm sure I'll be back with more questions. Thanks again and shoot safe.