Next weekend I will be going hog hunting but as I was looking at the regulations for hunting hog on lake lavon I noticed that they only allow now and shotgun (no size larger than #2) would a shot size #2 take down a boar? I don't have a bow so that's why i am curious.

No buckshot. Slugs are allowed.

"Rifles, airguns, handguns, slugs, <#2 shot, and muzzleloaders are prohibited. All applies to all hunting area unless specially noted above."

The above quote was taken directly from here: https://lavonlakehunting.tamu.edu/policy

It appears that you cannot use slugs.. So, it looks like 00, or 000 buck shot is okay to use there. You might want to read through the information at the link I provided and see if you can make better sense of it than I can.

https://lavonlakehunting.tamu.edu/policy
Specifically noted here.
You cannot use buckshot of any kind.
Authorized Weapons

Hunting the legal game noted below is permitted in designated hunting areas only. In areas 6-13 feral hogs may be hunted with Smooth Bore Shotguns (slug only), in all other areasFeral hogs: bow and crossbow only. Anyone hunting with a shotgun may not use, or possess any shot larger than #2. The use of non-toxic USFWS approved shot is required for all hunting.

Hunt there quite a bit and have run into GW several times. No issues with ammo (slugs).

It's slugs only and north of 380. You can go by the station at the dam and verify. You'll need a permit. GW's have been out in force when I've been out there.

Make sure you look at a map and know what areas you are hunting in. As Zoedog posted, areas 6-13 you can use smooth bore slugs, everywhere else is archery only. It doesn't matter if you shoot a hog with 4 shot, that is illegal.

I did get checked one night by the GW in the archery only area and he told me that we could use slugs. I didn't argue, but called the COE office the next day and asked them. They said they would let him know he was wrong.