Poor barbell press output

[CBRMitch]

Okay, I wasn't blessed with naturally large shoulders, and never really did anything arm specific until I started strength training 2 years ago. So I feel my shoulders lag a little bit behind where my other levels are in the other big, main compound exercises like barbell bench press, squats, etc.

Particularly, I can't seem to find a good form for standing barbell press. At 55lbs I stall on my 2nd rep on my fifth set of five; at 50lbs I can complete 5x5 but I feel my form suffers (pressure on my lower back, exercise clearly has two stages instead of one clean push). Are my hands too close together? Far apart? Right now I'm just trying to build core strength and stability. I am thinking of switching to seated but still unsupported presses. What other exercises help built stability in the shoulders?

Thanks guys n gals.

[skarotum]

Honestly, I think it does sound like a core problem to me. Maybe you should do more "supported" shoulder routine until your core is up to snuff so you don't cause injury?
But again, that is just a guess from what you described so it may not even be the case.