A couple of more things to point out.
One, the instructions and the web site are quite clear that JP Rifles won't warranty any sight that has elevation or windages screws that have been damaged by trying to over adjust them. If you feel any increase in the resistance on the elevation screw, STOP THERE and install the angled shim that is provided. This sight does NOT have a positive stop on the elevation or windage screws so you do have to be careful to NOT overdo it.
Second, make sure to take that shim plate and hex keys to the range with you because you may need them. My 610 required no shim to zero the sight, with my 617 I needed to angle the sight down with the shim to get it zeroed. With my 620 with no shim, it will zero for a 130 grain 38 spl. but it's at the limit of the range of adjustment. However, since the 130 grain 38 is the lowest shooting round I'll use in the 620 I've left it as is, this leaves me the full range of elevation adjustment to correct for higher shooting loads. Point is, you won't know if you need to use that shim until you've actually done some shooting with this sight. BTW, with mine the molded in dowels on the shim were a real bugger to get on the sight, it is a VERY tight snap fit, so make sure you install it correctly the first time. BTW, I had to cut a very slight lead in chamfer on the front pins to help it snap in place, so you may want to take an exacto knife and some high power readers to the range with you.
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