I just received a Bushmaster XM15-E2S with a telescoping butt stock.  

The stock wiggles a bit from side-to-side.  Is this normal?    

As my last black rifle was an A2 in the Army, I'm not familiar with the telescoping stocks and wanted to verify this issue before I started tinkering away.

This is for M4 or other stocks with the nylon type plastic ( not the alum. stocks) that are loose on the buffer tube .  
Take the stock off the tube and put it in a vise with a rag around it to keep from marring it up . Squeese it  in the vise but don't go crazy , while it is in the vise take a hair dryer and blow through the stock heating it up , do both ends , this only takes about  1min all together , then ck it for fit on the tube , repeat if nessesary to get desired fit .
You then have a stock that fits nice and tight no rattling !       IceMan_1    

I've done this to Bushy's , RRA's , & J&T , they should all be the same !

Teflon plumber's tape. A few times around the threading on the stock since it's pretty thin stuff.

Quoted: This is for M4 or other stocks with the nylon type plastic ( not the alum. stocks) that are loose on the buffer tube .   Take the stock off the tube and put it in a vise with a rag around it to keep from marring it up . Squeese it  in the vise but don't go crazy , while it is in the vise take a hair dryer and blow through the stock heating it up , do both ends , this only takes about  1min all together , then ck it for fit on the tube , repeat if nessesary to get desired fit . You then have a stock that fits nice and tight no rattling !       IceMan_1     I've done this to Bushy's , RRA's , & J&T , they should all be the same !

+1

Out of all the so called "fixes" this is the only true fix that works and is permanent... The others are only band aids, and band aids need to be changed or replaced every so often...

all i can say is the hair dryer method worked for me. need to spend some time testing the fit. just like anything else PATIENCE shall pay off. this thing rocks and is quiet..

My butt wiggles, and it's stock....

....oh...wait...you meant on the rifle......sorry