Bushmaster M17s Modifications Barrel Shortening, Disassembly & Piston Cleaning

The stock OAL is 30" and the stock barrel length is 21.5". Depending on the state you live in and their regulations will depend on the length you can legally shorten the barrel. According to ATF regulations the OAL can be no shorter than 26" and the barrel length no shorter than 16" without registering as an SBR on form 1 and paying the $200 tax stamp. The standard shortening that I will perform is 3". That will take the OAL to 27" and the barrel length to 18.5". This will take you to safe dimensions and no room for interpretations on the measured dimensions. This will also allow the Barrel sleeve to still be utilized but shortened. I can also shorten it so the barrel sleeve does not have to be used, and you will be at an OAL of 26.375" I can shorten it to any length you want as long as I am not in possession of your lower which is the registered portion of the firearm.

Standard length Barrel
3.0" shortened barrel
3.6" Shortened barrel

Standard length Barrel
3.0" shortened barrel
3.6" Shortened barrel

 
Dirty Piston

Cleaned Piston

M17s Barrel removal

  • 1. Remove the barrel nuts and or flash suppressor from the end of the barrel. You will need a ¾” spanner wrench to do this. If these have never been removed they are very stubborn to remove as they are put on at the factory with red loctite. You will need to apply heat with a heat gun to get them loose so they will be easier to remove. Once they are off you can also remove the lock washer and barrel sleeve.
  • 2. Remove the lower by pushing out all three pins that hold it on to the upper receiver.
  • 3. Remove the socket head cap screw that is holding the barrel on to the receiver. This is also attached with red loctite and may need some heat to break it loose. 
  • 4. Pull back the charging handle all the way and push the barrel into the upper receiver so it can be removed. If it does not push out of the locator spot easily, thread the cap screw all the way back into barrel without the washer and give it a light smack with a mallet. When you smack it with the mallet make sure the charging handle is pulled all the way back.
  • 5. Once the barrel is loose it will pull out the front of the tube along with the end cap. You will need to pull and twist back and forth so it will come out the front.