Scope Zero query

[VALE BOY]

I have a Richter 4-16x50 IR with side wheel range adjustment and recently it's proving to be inconsistent in it's shot placement. It's atop a HW98 .177 which until recently was a real tack driver
(and great at long range too hitting the bucket over 60 times out of about 70 shots at the Boinger Bash)

The problem is that after a couple of shots impacting approximately on the point of aim, at 20 yards it then shoots low about 6inches then the next shot maybe in the vicinity of the first 2 then it shoots high an inch or so then the next one can be about 4 inches low. The discrepancy is all on the vertical (elevation) plane as there is little or no differential in the horizontal (windage) plane. The scope and stock screws are all tight and I've tried 3 different pellets JSBs Weihrauch and Air Arms which all were on target previously.
All were shot from a bench rest where previously I could obtain 5p groups at 30 yards.

Can it be due to some internal fault with the reticle and if so are these scopes fixable and if so who can carry it out??

There is no obvious surface damage to the scope or rifle but it may have fallen over in the bag at some point and focuses fine and the clarity is good.

Hoping that some of you may have some suggestions to a solution.
Atb
Graeme

[Geezer]

Were you changing magnification or parralax?

If not, and assuming you have eliminated stock screws, mount screws, etc, and any other mechanical fault (have you tried the same rifle with a different scope?) then it is very likely that, to use a technical term, your scope is buggered. It is probably uneconomical to repair, unless still under a warranty or guarantee.

[jon_h]

Not something silly power wise? If it's only a change up and down I'd be checking power as well. I had something similar and it was a nick in the breach seal.

[Geezer]

How's the breech lock-up? I had an FWB once with a worn breech, which shot "groups" in a vertical line.

If you have 2 guns and 2 scopes, try swapping them to see if the problem persists.

[thisisdonald]

Hi Graeme - check that the eyebell isnt loose or that you havent screwed the fast focus out too much.. like geezer says, get a different scope on there.. that gun deserves a much better scope than that richter anyway.. the one on your fenman was cracking!
BTW Ive not forgotton about you - I straightened that 90 barrel and put the TBT kit in your 57, it needs some more attention though - Ive also stuck a wee scope on the 90 for you, nothing special, just an old jap 4x40 that was in my box... The C1 will have to wait as my lathe is being temperamental just now... its asking me for a service I think!!!

[VALE BOY]

Thanks for your advice, lads...I'm going to swap scopes with another rifle and try them out and see what the outcome is... A process of elimination and trial and error. I'm sure the rifle isn't to blame as I'm pretty certain the power is consistent but I'll find out next time I'm at the range.
I was wondering if the reticle can appear to be intact -which it seems to be- but somehow move internally and result in inconsistent points of impact? And is the reticle assembly accessible via the turrets?