What is a frozen scope?

[Blairguy]

Would you please explain what has to be done to mechanically freeze a scope.
Also when and why it is worth it.
Thanks, Mike

[rpollock]

Mike,

First some background. One of the weak links in the quest to shoot small groups is the sighting system. The sights need to be able to hold perfect point of aim, otherwise you end up chasing a shifting point of aim, unbeknownst to the shooter. Various theories abound about this topic whereby most agree the aiming system can't hold perfect aim in typical rifle scopes, and can account for anywhere from .025" shift (good) at 100 yds, or over .100" shift (very bad). The frozen scopes came along to try and eliminate this shifting point of aim. This is interesting because it really forces you to go back to externally adjustable scope mounts to change point of aim, pretty much the same as Benchrest had back in the 1950's and1960's!

The various frozen scopes you run across today are typically accomplished by filling the erector housing with a resin (epoxy) to try and lock up the movement in this assembly, then you need a pair of externally adjustable mounts to aim it. It works but like a lot of things there are a couple of drawbacks, such as it can be tricky to adjust point of aim in the middle of a match or between relays if you have to. Also switching between 100 and 200 yard zeros can cause problems if you are in hurry and make a mistake. Some folks don't switch between 100 and 200 yard zeros to avoid this problem.

Like a lot of things in BR we have come full circle on sighting systems and still don't have an ideal solution, so people keep looking.

Just FYI most scope manufacturers consider anything less than .100" movement at 100 yds to be excellent and that includes BR scope manufacturers. Think of that next time you are struggling to shoot in the 1's.

[Blairguy]

Rick,
Thanks for the excellent explanation.
Are there any tricks for determining how much unwanted movement we are actually getting from an adjustable scope?

Mike

[DanO]

Another point to coincided is weight, most external adjustable mounts add weight.

[rpollock]

Mike,

You can use a hood scope checker if you can find one, which is tough since Charlie does not make them anymore. With a hood scope checker you mount two scopes on the same rifle to check for any differences in aiming points as you shoot the rifle a bit. These sort of work, but it can still be tough to figure which of the two scopes is shifting. I built a testing fixture to mount 3 scopes and simulate the firing loads on a scope. The result of that experiment was to discover all scopes move a bit. It can be difficult to spot since they might be fine for a number of shots then shift. How would you know? You can also mount them on a rail and check them that way since the rail usually doesn't shift point of aim. Even that is subject interpretation due to changing sight picture on account of mirage, and the gentle recoil of a rail doesn't load the scope that much. Sorry, but I don't have an answer your question. Scopes are the weak link!

[Blairguy]

Rick, Dan,

Thanks for the replies. Much appreciate your help.

Best of the season to everyone, Mike