Sprite Frames

I finally got back into Doom editing. It's like a black hole, you can't escape it. But anyway, onto my question.

I'm using Legacy for this project I'm working on. My only exe editor is of course, DeHacked. This is what I'm trying to do:

Get Doom to play more frames for a 'thing' than originally intended.

I want to make the rocket explosion sequence about 11 frames long, at a duration of about 1 or 2. The ORIGINAL sprite names are MISLB0 through MISLD0. I added frames all the way up to MISLO0. (MISLOzero)
The 11 or so frames are in the wad, though it only plays the 3 original frames. Some help would be really, REALLY appreciated. Oh yeah, put it in laymans terms too, if possible. :)

OMG TUTORIAL:

What frames are you willing to give up in order to make the explosion longer?

I would go with the TFOG and IFOG series, they are way too long as is.

Or you can use the Pain Elemental Respawn Frames and not waste anything.

There's a couple more unused frames which Enjay pointed me towards here.