I traded into a S&W AR-10 a few day ago. My first one.  
It has a Mag-pul rear stock on it.
The stock is too long for me even at minimum setting.
I’d like to change it out to a carbine type stock so length can be adjusted better for me.
Gun presently has a rifle length buffer tube.
Does the AR10 use the same tube as an AR15? Can I just swap it out? I have a carbine tube for an AR15 that I can use.
Yes I know I will need a new buffer and spring. Just trying to save a few $.

There are two different lengths of receiver extensions for collapsible stock .308 ARs. One type is longer than the 5.56 version, and uses a 5.56 sized buffer, with a .308 specific spring (this is what your S&W has from the factory). The other style uses a standard 5.56 style receiver extension, a shorter .308 buffer, and a .308 specific spring.   So, yes, you can swap your factory  receiver extension with a standard 5.56 style one, and use a short .308 buffer with your factory. 308 spring.

Install a standard carbine buffer tube, a special short buffer meant for this combo, and a standard length carbine spring.  
oops, forgot about the shorter spring, I had to cut about 2" free lingth off my Tubb's flat wire 308 spring to get it to work.
That was in 2009, so memory slipped a little

You are better off with one of Slash;s heavy buffers, and possibly a heavier spring.
Then you can use any standard collapsible stock you like.

I highly suggest a Magpul stock so you can add one of these: Cushy but pad.

I used a Pachmayr to mine many years ago, but a lot more work than just 2 screws, and cost more
Just went to a Magpul ACS when these come out.

Simple way would be to just buy a buffer tube kit

You should get together with this guy: M&P 10 buffer/spring
Take your buffer and spring out. Measure the inside depth of your receiver extension and the length of your buffer. Check to see if they used a ~2" spacer in the bottom of the RE.