Measure the slide width with a caliper. If it's a tad less than 1 inch it's a thin slide, if it's over an inch it's a thick one. With good ammo these pistols are phenomenally accurate in spite of the tiny sights and if you reload, you'll like the neat pile of the empties they produce. I just love the simplicity and quality of the early all steel Berettas like '34/35 and '51 models. You can safely carry them with the hammer down on live round and safety off. P.38 Walther even being a double action has nothing on 1951 Beretta. I highly recommend getting one while they are still relatively inexpensive.... I polished the feed ramp on mine and shot hundreds of Hornady XTP hollow points through it with zero problems. You did the right thing by tearing yours apart, they do come filthy. Make sure that you get the firing pin out and clean the channel really well.