I have a few stocks and my mil spec buffer tube shakes inside my mft battle stock.  Is it suppose to rattle a little when extended all the way out?

are you saying that the buffer tube is actually twisting and shaking? like if you take off the MFT stock and twist it the stock will move? or are you saying that the stock kind of wobbles when put on the buffer tube? If so that's fairly normal for most stocks. the MFG minimalist has less wobble than say a MOE, but it might have some. depends on the dimensions of the buffer tube

wait...what?


the stock is moving around the buffer tube?...that's fine, it can be annoying but its perfectly fine

the tube is twisting, that's an issue, you need to snug that castle nut down and grab yourself a punch and stake that castle nut, takes 30 seconds and your squared away

If the buffer tube is moving, then yes you have a problem and need to stop shooting it until you get it corrected, if the stock is sloppy, then no that is not a problem, might be annoying, but it is not a safety situation.

I put a few layers of tape under mine to help with the rattling.  put it more towards the rear of the buffer tube

A MIL-SPEC stock on a MIL-SPEC receiver extension should have enough clearance to slide easily, but not to "rattle."  Do you have the correct type of stock for your receiver extension?

If you're using a Mission First minimalist stock and it "rattles around" on a mil spec tube I can reasonably assume you have a commercial spec stock, as the mission first stock is VERY tight on the ones I own. As far as other stocks rattling, I have a pile of PSA and other M4 stocks that have 1/8" gap and rattle something fierce! I started replacing my M4 stocks last year when I was bear hunting and the stock was so noisy I was afraid it'd scare away game.
Stocks that don't rattle:
Mission first minimalist
DD
Rogers Super Stoc
Hogue over mold

Just make sure it's a mil spec stock on a mil spec tube.