I don't like Nashville bridges and replace them with ABR1 bridges on every Gibson guitar I get. My historic GT of course already had one. Gibson parts tolerances are all over the place as has been discussed many times. Here are two ways that Gibson F's up your ABR1 before it even gets to you. 1) Bent saddle screws. This happens when techs at Gibson use a hammer or similar instrument to notch a saddle by hitting a string going over the saddle. Too much force and the saddle screw will bend like below. This make the saddle screw hard to turn and makes the saddle go up and down depending on in what position the screw is left. 2) All saddles are not made the same. Some are by design taller or shorter than the others. The idea behind the abr1 bridge is that the saddles should match a 12" radius across the bridge. Looking sideways at the bridge you can see the holes for the ends of the screws are aligned in an arc. If the saddles are all the same size, they will follow this arch also. BUT. The saddles are not all the same size. Some have more/less saddle to ride above the bridge, thus throwing off your radius and your string to string action. In this image, the saddle on the left will sit higher than the saddle on the right if they are put in the same slot. Years ago I tried to match up the taller/smaller saddles so that I had similar heights across the bridge by buying separate saddle replacement sets from Gibson. Those were still bad on a whole but I could cherry-pick to make roughly even sets. Now I just buy new bridges from Kluson for less than ten dollars more than those Gibson saddle sets. The Kluson, and other aftermarket bridges, are more precise and way less of a headache to deal with. Now, a good tech will notch saddles correctly regardless of the starting radius. Some saddles may seem slotted deeper than others and this saddle height discrepancy is the likely cause. But straight out of the box? Straight off the wall at a guitar store? No good tech will have probably been working on your guitar before you buy it. A wonky set of bridge saddles may keep you from buying an otherwise great instrument.