I have the crappy buttstock that came on my m&p15. I'm running a Primary Arms red dot with MBUS set up to cowitness. I cant get a cheek weld with this setup so I'm looking at Magpul buttstocks and it is a little overwhelming. What do they make, 15 different ones with different acronyms that mean who knows what? Their site doesn't have a compare feature that I can find so I started writing down specs on each one trying to make some sense out of all the acronyms... ACS, ACSL,STR,SL, etc. Its almost as bad as choosing my gender on Facebook. Anyone know of a easy way to make sense of all of this or recommend something. This a multi purpose rifle, my only AR. I am 6 ft tall so I think a slightly longer stock may feel a little better. Thanks for reading.

For adjustable stocks that use carbine receiver extensions:

MOE is the basic model.

STR is a step above the MOE, with an extra locking lever to keep the stock from wiggling. CTR is basically a STR with storage tubes for batteries.

ACS has storage tubes for batteries and a storage compartment and the extra locking lever. ACS-L lacks the battery storage tubes.

MOE SL is the newer model. Locks up very tight with only one lever and has an integrated QD mount. MOE SL-K is a smaller version without the QD mount, and MOE SL-S is a version with storage tubes for batteries.

Other way around. MOE + locking lever = CTR, CTR + storage tubes = STR

I have a rifle with a CTR and one with the STR. STR has a better cheekweld and doesn't pull my beard hair out.

Thanks, that does clear it up somewhat. Here's the page I'm looking at: https://www.magpul.com/products/firearms-accessories/buttstocks
For an AR it lists:
CTR
uBR
mOESL
ACS
ACSL
MOE carbine
MOE rifle
MOE fixed
MOE sL-K
MOE SL-S
PSR gen 3
UBR gen 2
STR
Most of these are available in multiple colors and for mil spec or commercial
Clear as mud, right?

I found an article that clears up some of the acronym confusion.
http://www.thefirearmblog.com/blog/2012/05/23/magpul-str-stock-review/

You forgot the plain ol' MOE-SL.

I can't get a cheek weld with any stock without a riser. I have more of a chin weld but that doesn't stop me from popping clay pigeons at 100yds , standing , no bracing with a red dot. Just pic the one you like and if you need more height some magpuls have an available cheek riser.

The CTR is the only one I see a riser for. They have them in 1/4", 1/2", and 3/4".

Sounds like you need to mount your optic lower. This is also why lower 1/3 optics are so silly to me. Pepole not trying to clear an IR laser and not running fixed irons have zero need for lower 1/3 optic height. It's as silly as mounting optics on top of your carry handle. You should have a perfect cheek weld with ANY of those stocks... provided your optic height is around 1.40" to 1.44".

To tho OP... you don't need or want battery tubes. Its a waste of space IMO. The MOE is rattley but light and cheap. Cure that with the CTR by the lock or MOE SL with the spring. It is an aesthetic choice really. After owning 15 different stocks, I gravitate toward lightweight, with a short toe to clear armor, with rattle mitigating features, with a QD socket, and a clean simple design that fits my shoulder well (no 90 degree but angle like a SOPMOD). MOE-SL, BCM, and CTR are my go to stocks on a gunfighter type carbine.

I thought about a lower mount for the red dot but this is my only ar and my HD gun so I should keep the MBUS in case the RDS fails. Just yesterday I made some makeshift cheek pads, even made a thread in GD.
http://www.ar15.com/forums/t_1_5/1974442_Makeshift-cheek-pad.html

What?? Lower 1/3 offers the same picture as co witness plus higher. You can't see through the A2 tower, and you'll only see from the lower ears up anyway... so co witness is a waste. Lower 1/3 does everything a co witness does and more.