I want to build a short carbine w/ the following parts, what do you guys think?  (FYI, I am pretty new at this stuff, so please take it easy on the flames.  Thanks).

Bushmaster LEO Lower.
DPMS 7.5" A3 Kitty Kat Upper.
Vltor Collapsible Stock.
Surefire M951SU.
TangoDown VG-BK BattleGrip.
Eotech 512.

First things first.  
In that you state you are pretty new to this stuff (which is completely fine -- everyone starts sometime), I just want to make sure that you are aware that the barrel assembly you have chosen is only legal on an AR carbine or rifle (as oppossed to an AR pistol) IF the AR is approved by the ATF as a Short Barreled Rifle ("SBR") FIRST.

Merely assembling a short upper (defined as an overall barrel length under 16", which can include permanently attached flash suppressors, brakes or muzzle attachments) on a rifle lower (defined as one with a buttstock of any kind, designed to be fired from the shoulder, or ever having had a buttstock, etc) will yeild the following:
1. yes, it will fit, but
2. it is not legal unless the lower receiver is registered as a National Firearms Act ("NFA") "Firearm." (because the overall permamnent barrel length is under 16" AND overall rifle length would be under 26"), and
3. not following the necessary registration for an SBR under the NFA with the ATF BEFORE assembly of the upper and lower combination, above, is a major felony (10 years, if convicted)

The SBR registration process takes between 1 and 9 months for approval in addition to a $200 tax stamp fee.  There is an entire SBR FAQ on this process under M16 - Full Auto board.

Therefore, it is my recommendation that, since you are new to this stuff, you should choose a different upper -- one that provides a minimum 16" barrel (which on an AR carbine or rifle lower would give you also the 26" minimum necessary overall length)

For more information: The SBR FAQ should be a good place to start.  The NFA definitions are found in the US law here: 26 USC 5845 Definitions

If you intended to state, "I want to build a [legal SBR] carbine w/ the following parts,..." and I'm telling you stuff you already know, I appologize.
Most here would rather not see someone get in legal trouble for assembling parts that do fit but are not legal just because no one told them, especially when otherwise-legal parts are so easily attainable.

Cheers, Otto

Edited to Add:  The choices look good to me, but change to another (longer) barrel; DPMS upper are fine (I have at least 3), bu the 7.5 barrel has less than steller ballistics and a humungus muzzle balst & fireball (I have such a set-up on an AR pistol).

Thanks for the heads up.

http://ar15.com/forums/topic.html?b=3&f=118&t=200876

MUAHAHAHAHAHAHAHAHAHAHAHAHA!!!!

MUST regester as an SBR w/ ATF(or whatever)!!

if the caliber is going to be 5.56/.223, velocity, knockdown energy, and accuracy past 100yrds will SUCK!
h/w muzzle blast and fireballs will be quite nice

Quoted: I think Id rather have a 10/22

Quoted: AFAIK, SBRs are illegal in WA.

Yes, I have realized that.  However, a pistol registered lower, pistol buffer, and a 7.5 inch upper is considered legal pistol.  

Vertical grip on a pistol makes it an AOW, I think.  That's $200 to ATF also.  

Something simmilar (not mine) to what you're wanting:


-skuld

Quoted: I want to build a short carbine w/ the following parts, what do you guys think?  (FYI, I am pretty new at this stuff, so please take it easy on the flames.  Thanks). Bushmaster LEO Lower. DPMS 7.5" A3 Kitty Kat Upper. Vltor Collapsible Stock. Surefire M951SU. TangoDown VG-BK BattleGrip. Eotech 512.

You said you wanted a short carbine, not a pistol. So if you want a carbine that short you need to SBR it (if your state allows this) and if you want a pistol with a vertical foregrip you need to AOW it (again, if your state allows this). Sorry, but there aren't any other ways around it. HTH

Quoted: Quoted: I want to build a short carbine w/ the following parts, what do you guys think?  (FYI, I am pretty new at this stuff, so please take it easy on the flames.  Thanks). Bushmaster LEO Lower. DPMS 7.5" A3 Kitty Kat Upper. Vltor Collapsible Stock. Surefire M951SU. TangoDown VG-BK BattleGrip. Eotech 512. You said you wanted a short carbine, not a pistol. So if you want a carbine that short you need to SBR it (if your state allows this) and if you want a pistol with a vertical foregrip you need to AOW it (again, if your state allows this). Sorry, but there aren't any other ways around it. HTH

Yes, that was the original plan.  But, since WA doesn't allow SBRs, I have to stick w/ a pistol.