With the exception or the Burris swivel inserts, the best rings/bases made cannot compensate for a receiver that's out of spec from the mounts.
The same with alignment bars. They can help eliminate ring twist when mounting but can't correct a thing if one ring is canted away from the other. That's where lapping comes in.
Exactly. Some receivers are very bad. I've had very good luck in that regard. I'd also have to add that most guys shooting "long range" are using rails and good heavy rings. Generally those don't have to be lapped. Like Tyrone said, if you use good rings. This is the longrange forum, so again I'm pretty sure most guys are going to be running a good steel m1913 20 moa+ pic rail for this application. Back to the OP's question:
I have never had experience using lapped rings and I'm wondering if this is done to prevent ring marks on the scope? How much accuracy improvement would you expect from lapped rings on 5 shot 400 yard groups, if any help at all?
Thanks
If the receiver is crap, where you should be lapping those rings, you will sometimes have issues with the scope not tracking properly. I've seen non lapped rings cause issues, on poor receivers, and thin tubed scopes (not going to mention Leup names). It stresses the scope tube enough to affect tracking. With a scope that does not properly track, it can indeed cause "accuracy" issues at any distance.
