Old Cane! There is no reason why not, but you won't see it regularily. I've seen lots of "non-IHMSA" guns on the line over the years. Two examples are one of our members using a 2" Colt .38 for Field Pistol (She hit 7x40 & thought it was a hoot!) and another using an AMT longslide .45 ACP (He shot a 28x40.) also in Field Pistol. I occasionally drag out my old High Standard Double Nine & give it a go in Small Bore just for fun 'cause it was the first handgun my dad bought me. Come to a match, bring what you got, & shoot what you brung! Hope to see you at the range sometime somewhere.
Steve