How to get a scope to focus at 10 metres.

[Portzy]

What you are attempting to do is re-paralaxing, not all scopes are suitable for this so it would depend on the make/model. Fabricating a tool to fit into the slots that you see on the lens carrier is one way and if the lens carrier is stiff then a small amount of warmth or heat may ease the situation but you must be prepared to accept that the scope could become trashed if the tool slips or you otherwise force the situation.

Ideally, scopes with a decorative trim ring at the end are the easiest. Remove this with a couple of Mini Boa's, if it comes clean off the lens carrier then just wind the carrier out about 1/4 of a turn then check focus/parallax for your desired range and re-adjust as/if required. When all is good re fit the trim ring without upsetting the carrier, this bit can be tricky!

If the trim ring brings with it the carrier then only turn the whole assembly 1/4 turn and check as above. Once you have focus/parallax you have to lock the trim ring and carrier with tape of the black insulation variety.

Hope that makes sense.

Edit: The nitrogen, if that is what the scope was constructed using, is not under any pressure as such. It is used to purge the internals of air which itself contains moisture, the nitrogen is "dry". Moving the carrier should not allow the nitrogen out in the pressurised gas sense, removing the carrier totally and complete with lens will, simply moving the carrier forwards should not.