Okay thanks for the update! If the facilities are being improved then the money talks. If Century works during the week great-once it is ready. Still it is very hard to shoot a rifle in the southeast of England. We need more ranges, underground, purpose built or otherwise.
errrrmm, where do the army train ? There is a fair few military ranges in the south-east. Try approaching some of the local clubs who use them to see if they will allow you to shoot as a guest, then zero then.
But, you have taken your stock off, and ? If its a free floating barrel, then the return to zero, assuming it is a good wood/metal fit, should be pretty darned close, I take my stock off all the time, a quick shot to confirm its ok, and carry on.
If your land is small, then I'm guessing most, if not all of your shots are under 150yds, so even at worst case, it's 1moa out, it's still only an inch and a half at 150, still well within a 'kill zone'.
I'd be tempted just to put a small, A4 sized target up where your average distance is from your highseat, and confirm from there, in real world conditions, rather than spend time and money going to bisley and shooting prone at 100yds.
If you get the target 100yds from your highseat, you should only need one shot to confirm, or two if adjustment is needed, assuming your scopes click values are actually what they should be and your rifle can throw an accurate cold bore shot.
Regards
Pete