Anyone here who could help me with a LP300 I have just acquired second-hand?

The cylinder was at 200 bar when I borrowed it - lovely gun, so agreed to buy.

I ran it down to around 100 bar and it unscrewed easily. I pressurised it up to 230-ish bar and tried to screw it back on - very hard!

Let it down to 100 - screwed on fine, and then raised to 150 bar - tighter but fine.

Before I persevere up to 200+ again, can anyone advise me as to any issue here? I have cleaned threads carefully etc. and applied a small smear of silicone grease.

By the look of the valve design (in the cylinder) it would seem that it will get harder the higher the pressure in the cyl, but I'd value advice from those who know the gun well.

Thanks