I took my H&R Model 999 to the range at Indy Arms Company, with the just-installed new rear sight the Data Viking had located on eBay, and shot a scary ghost face in the target at 21 feet:
This is about a hundred rounds of .22, and "dialing in" the sights consisted of me working out if they were set for point of aim atop the front sight or covered by it. I set the rear sight at home by lining it up with the barrel. I don't know about long guns, but if your pistol sights aren't lined up with the point of impact when centered on the barrel or slide, it may be time to reevaluate your shooting technique; the manufacturers do go to great lengths to align the bore with the gun.
Here's what I brung:
L-R, Sistema Colt, H&R 999, Astra "Constable" (thank you, MK!) and an Iver Johnson TP-22. (On the latter two, "No, Mr. Bond, I expect you to use a .22 clone.") Alas, the little Iver Johnson wasn't happy, but the rest of them ran fine. My .45 ACP shooting is not so good, with six or seven rounds out of fifty in the 9-ring at 21 feet. They're all supposed to go in the center! The gun does hammer-bite a little and that's not helping -- I don't want to put a modern beavertail on this nice old gun, so it is what it is.
6 months ago