That's a century L1A1 sporter. It's got some inch pattern parts for sure, but it may actually be a mixture of inch and metric parts. Century is known for their half breed !!!!!!!s. Evidently some of them function well and are accurate, others not so much. If you're getting 1" groups at 100 yds, sounds to me like you may have lucked out and gotten a good one. She's ugly, and the century "butt"hole stock is one of the ugliest types ever designed, with such an awkward grip angle too, but it's nothing you can't fix if you have half a mind to.
That'd be a SWEET gun with a DSA X-series buttstock
DSA Online Order Center
or one of those tapco SAW buttstocks if it'll accept a metric stock.