the T4 instructions say to only use steel bb's.
on the lead balls it says not to use in bb guns.
anyone know why?

I have a guess.......Could it be because the lead ball is softer than the steel BB and could result in a deformation in the projectile prior to departure from the barrel, resulting in a plug?

you could be right Todd.
i just shot both lead and steel thru er and they both seem to pass well, slow but well.

I don't know either. You could measure the dia of the steel bb and compare it to the lead one. If the steel bb is smaller than the lead one then I would have to go with Todd's theory on possibly plugging the barrel. Is the barrel rifled or smooth?

it's the Crosman pellet/bb barrel with the light rifling.

i get way better accuracy with daisy steel bbs than with the cheap copper ones, they are alot more consistent and dont deform. lead BBs may shoot ok if you hand load one at a time but if theres any kind of self loader it may deform the lead, kill accuracy and possibly cause a jam. I know the way BBs loaded in my 15xt wouldve smashed the crap out of a lead ball

BB's made of steel are used in many BB guns because they rely on a magnetic tip in the breech/loading area to hold the BB in place. Most BB's measure .173 or so and are not a tight fit in the .177 barrels. The all lead Beeman perfect rounds I have measure around .173 also. The lead BB's are heavier and do penetrate better. I have used them in my Crosman 357 revolver, with good results. They fit well in the clips .Not as accurate as the pellets though.The lead BB's will roll right out the barrels of most .177 guns.