Originally Posted by drgonzo
It's not that hard to do yourself with a drill, but anyone with a drill press should be able to do it
Yep, and if the guide is already drilled out and all you're doing is enlarging it a little bit, you don't even really need a drill press.
Just take your time and use each bit sequentially to avoid going out of alignment.
I did this on my WWA ultra mini kit as well as enlarging the valvechamber of my Superbolt.
I ended up being able to drop the working pressure by at least 50psi, but I think most of it was the passage in the body more than the guide rod.