Does a peep with a smaller aperature {hole} exist that installs in the factory {non ranch} rear sight? Or... a aftermarket rear sight that works with factory front sight? Looking for a little more precision for a 185 series GB.
Ram-Line made a molded peep sight replacement with a short "sun shade" way back in the 80's. I believe it is still around for pocket change. Will not rust
For the steel blade or molded types, It is no great feat to dab on some JB-Weld and drill whatever size aperture you desire.
Note: IMHO, accuracy will not be markedly improved with just a smaller peep. Try improvements in both sights (optics are much better), trigger work, crowning and most important of all, HIGH-QUALITY AMMO.
Accuracy Systems in Odessa TX - http://accuracyriflesystems3.homestead.com/ - will be your ultimate solution, they are simply the best and most-experienced at turning the Mini-14 into a target-grade rifle.
Your problem is going to be the withe of the front sight... front sights are designed for your maximum distance to target and on the mini's this is about a hundred yards.