Well, I've been seeing this for quite awhile, and though I'm not a mod or anything, I'm posting this in hopes it would help everyone and anyone with pump questions.
Q: Is it normal for the backblock to move when you're shooting?
A: Yes, look at this video by Heretoleave:
http://www.youtube.com/watch?v=_0rN-...eature=related
See how the backblock moves a little? (with a normal hammer/valve setup instead of mq, it may go back further.
What is the difference between Mini and Regular?
Regular:

Mini:

The body of course! Look how there's a Vert. ASA attached to the regular body, however there's that square piece missing on the mini.
What's the difference between 2k+ and pre2k?
2k+:

Pre2k:

The place where you put in the pump kit, or screw for front block is different in size. Pre2k is SMALLER (roughly 1/4") and 2k+ is Larger (roughly 1/2").
So to compensate with each body, "What kind of pump kit should I get?"
As said in here -
Pump Kits, and You- There are many different pump kits to choose from, just which one would fit yours?
For
MINI cockers, you can only choose "mini pump kits". Companies may vary from , CCM, Sanchez Machines, or any private/custom mini pump kits. They look like this:
CCM:

WWA:

Sanchez:
Regular pumps just use any other pump kits that you can literally buy anywhere. All regular kits are shown in "Pump Kits, and you" link above.
Hope that covers some of the questions out there

If there's anything I need to add, you can post here or pm me. Oh, and mods, if this is breaking the rules feel free to delete.
-valk