Smith & Wesson M&P 15-22

General Information

The Smith & Wesson M&P 15-22 is an AR-style rifle chambered in .22 Long Rifle.

The 15-22 forum on smith-wessonforum.com is probably the best source of information.

The 15-22 forum on RimfireCentral.com is also a good source of information.

    This thread (542600) has tons of great information about what mods you can make to the 15-22.

Parts & mods for the 15-22:

Parts diagrams & Exploded Parts Views:

    Smith & Wesson does not officially publish an exploded parts diagram for the M&P 15-22.

    Patent info from the Firearms blog: http://www.thefirearmblog.com/blog/2010/07/08/sw-applies-for-patent-on-mp15-22/

    Some parts information: http://smith-wessonforum.com/smith-wesson-m-p-15-22/327703-parts-diagram-yes-again.html

Disassembly instructions (with pictures): http://www.gunsumerreports.com/review_smith_wesson_M&P15-22_p4.php
    

Parts & mods notes from forums:

• Tacticool22 has both information and parts for the 15-22.
• Great info about what you can change, from user photoracer:
  On the 15-22 you can use any .154 pin AR trigger group. With the correct tools you can remove the quad rail and mount any AR handguard you want. Can't use AR charging handles but there are a few available in alloy aftermarket. Any AR stock that will slip over a standard mil-spec carbine buffer tube (commercial will also work but will rattle a little). Any hand grip, any comp, suppressor, or flash hider that fits on a 1/2-28 AR sized threaded barrel (as long as you have a 15-22 with the threaded barrel).
  No aftermarket barrels
• For commercial stocks, according to user Nolan...
  (you can stop the rattle by putting a 6" strip of black electrical on the top of the buffer tube before you slide on the stock)
• Fixed stock (I'm in NJ, so no adjustable stocks for me... someone around here thinks they cause crime):     Magpul MOE Fixed Carbine Stock (mil-spec)
• Voltr hand guard, Magpul MOE butt stock and grip. Spikes battle trigger, KNS anit- rotaion pins, EOTech XPS 2.2 and a barrel shroud
• Safariland SS lockable stock, Geissele Super 3-gun trigger, KNS locking trigger pins, Ergo handgrip, AP Custom carbon fiber handguard, Magpul BAD, Allchin 15-22 compensator, and a Truglo dual red/green red dot sight
• Taccom small diameter carbon handguard, and Tacticool22 barrel nut adapter
• Jard 1 & 1/2 lb adjustable trigger, the KNS MP15-22 anti-rotation pins, a Magpul grip, an NDZ Oversized Charging Handle, and an NDZ Speed Bolt Release. I originally used a Magpul BAD lever, but I had to bend the BAD lever quite a bit to get it to clear the polymer receiver, so I switched to the NDZ SBR which fit better
• You can build a blazingly fast and light 15-22 trigger by using a Geissele Super 3-Gun trigger and a set of JP "yellow" reduced power springs. no issues but eventually went back to the Geissele springs at 2.5# 
• what tools should I have to remove the quad rail and and replace it with a different one?
      I used a barrel vise and barrel nut tool from Tacticool22.
• I replaced the S&W barrel nut with a Tacticool22 barrel nut which has standard AR15 barrel threads to fit any standard AR15 barrel nut.
• The handguard is a Taccom Carbon fiber ULW.   It uses a standard AR15 barrel nut and attaches to it with a single 8-32 screw.
• waiting for a couple of extra 15-22 barrel nut adapters because if you use regular AR-15 handguards you will usually find that getting the Tacticool22 adapters out of a given AR-15 barrel nut is a losing proposition so keep a couple extra on hand.

Last Shot Bolt Hold-Open Issues

If the bolt OCCASIONALLY does not hold open after the last shot, user RedNeck_Jim says:
This is a not-uncommon problem. It comes from a combination of two things: a too-strong spring in the bolt latch and a too-weak spring in the 25-round magazine. The solution has been known for several years, now.
Drift out the pin holding the bolt latch paddle and cut 1.5 or 2 turns off the bolt latch spring, then reassemble. Problem solved forever.  Use a 3/32" punch.  Do not need to drive the bolt catch pin all the way out.
It also helps to put a single drop of CLP or other cleaner/lubricant on the bolt latch pivot point.
If you search, you will see many discussions regarding this. I did this on my first 15-22 & have never had that problem again.

Here is one of the past discussions but there are plenty more:Last shot hold open

User tacticool22 adds: Also be sure to not hold the mag. Or even touch it or rest it on the bench. That could lead to bolt hold open issues.