Ruger M77 Adjustable Trigger Help

My Ruger m77 (the oldie with the tang safety) is great in every respect, but I was in a tinkering mood and tried to see if I could adjust the trigger pull weight. There is almost NO overtravel, No creep, and it breaks clean at 4.5 lbs every time. I was hoping there was a way to bring that 4.5 down to a 3-3.5 pull. I don't think I need to mess with the overtravel or creep.

After some research online, I found what I thought was the correct pull weight screw (part D-43, according to the Ruger expanded view), but the darn thing was so small, I couldn't even tell what head it had on it! It looks like a rediculously small Allen Wrench, but I didn't have one that fit it (the smallest I had was a 1/16). I found how to tweek a model 70, Rem. 700, and a Ruger m77 mark 2, but NOT my m77!

What size/head type is the screw?

Can it be adjusted at all?

Any info you can provide would be great. Thanks HighRoad!

I agree that it's already a very nice rifle with a trigger that will easily drop game, but I want something that breaks a little lighter, and I'd like to know HOW to achieve this.

I know I said it broke at 4.5 lbs, but after further investigation (and a better test scale), it's more like 5 lbs.

Again, I'm wanting to adjust the pull weight. What is the easiest way to do this, and what tools do I need to accomplish the task.