Hello, I am currently adding new furniture to my S&W M&P 15 Sport II CA compliant rifle. So, I live in NJ and just moved here (big mistake) and didn't quite know the laws here so purchased the CA compliant version of the rifle. I have run into numerous obstacles with this thing because of the different compliance policies this version must comply with.

My question is this. I am adding a Mil Spec Magpul fixed stock with a Bravo Company Mil Spec buffer tube. The castle nut on the rifle is on there damn good. Will the Mil Spec buffer tube fit the lower receiver of this version of S&W's CA compliance AR15? Is S&W's AR15's lower receivers all the same? And do their lower receivers accept both mil spec and commercial buffer tubes? I just want to make sure before stepping into another unforeseen obstacle.

SFAIK, all AR receivers and all buffer tubes have the same thread specs. I do hope all the parts you're talking about are for the carbine length buffer tube/receiver extension.

Yes they are all carbine. Here are the products I used.

buttstock (MOE(R) Fixed Carbine Stock – Mil-Spec)

buffer tube (Stock Hardware Mounting Kit (Mil-Spec))

What do you think? Should it be ok to fit into the lower receiver?

Yes, indeed.

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S&W AR receivers will accept mil-spec and commercial tubes. So long as the buttstock is "mil-spec to mil-spec" and likewise for commercial you should be OK.

So are all S&W AR15's lower receivers identical despite the state compliance version it may be?

So are all S&W AR15's lower receivers identical despite the state compliance version it may be?

Yes, the threads are ALL the same. The diameter of the tube after the threads, and of course the exact grade and spec of material and finish, are what's different between mil-spec and commercial tubes.

So are all lower receivers on the S&W M&P15 Sport II, regardless of the version of the rifle for state compliance reasons, the same? All the threads will be the same as on my CA compliant version of it?

So are all lower receivers on the S&W M&P15 Sport II, regardless of the version of the rifle for state compliance reasons, the same? All the threads will be the same as on my CA compliant version of it?

Basically yes, all uppers and lowers are the same. It's what's bolted to the upper/lower that changes. Some lower priced models have simple basic stocks and handguards, others have higher priced and better quality stocks, handguards and barrels.

BUT a basic model, or even compliant model, can be stripped down and rebuilt

Do you think that this CA compliant version lower receiver will have to be stripped down in any sort if all I am doing is adding the mil spec buffer tube along with the mil spec butt stock?

No, just the standard work of removing and replacing the tube. Look up some vids on youtube, there are several small parts that make it somewhat tricky if your not prepared.

It's actually quite easy as long as you are patient and don't let the tiny spring and pin fly across the room and disappear.

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Interesting. Do you have any YT links on this? Was just thinking about this today as I plan to remove the stock sport 2 (CA locked compliant) rear stock off and replacing it was something a bit more adjustable (I feel like the stock config is too short for my arms).