I think you can, surprisingly, sink the rear sight. Below is from the Bullseye reference url
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EIC Service Pistol Mods - from
http://www.bullseyepistol.com/dcm.htm
Trigger pull must be at least 4 lbs.
Grips, right and left, must be "mirror image" no thumb rest.
Pachmayr style wrap around grips are legal as long as they do not have finger grooves. [ed. I believe there is also a total width restriction]
ADDITIONAL RESTRICTIONS:
LEGAL ITEMS
Extended Triggers
Adjustable Triggers
Vented Triggers
Trigger Shoes
Bright Finish
Colt "Gold Cup" (no illegal items)
Front Strap Stippled
Gold Cup Dimple
Lowered Ejection Port
Rear Sight "Melted" into Slide
- - -
ILLEGAL ITEMS
Allen head or torx head grip screws
Ambidextrous Safety
Beavertail Grip Safety
Combat style hammer
Covered Mainspring Housing
Extended Magazine Release
Extended Magazine Well Funnel
Extended Slide Stop
Extended Thumb Safety
Magazine Base Pads
Ribs
The reason most hardball guns don't have a sunken rear sight is for the longer sight radius the high mount allows. You can't have the comfort and higher grip of a beavertail if you want to shoot service pistol but it would be ok for conventional BE. Other than that, BE allows a 3.5# trigger pull while service is 4#s...the rest of the variations among the disciplines (pin, plate, BE, service) would be in bullet wieghts, powder loads and recoil springs.
/Bryan