You could do as Les suggests but if you do there are a few things you need to make shure of.
the most inportant thing is that You need an accurate set of scales.
you need to find the tare (or empty ) weight of the bottle. which is usualy stamped on it. you also need to find the maximum weight of gas that it can hold. also should be stamped on it. Stand the bttle on the scales and fill with liquid from the other cyclinder untill the scales show the tare weight plus the maximium gas weight. then stop and disconect.
You realy dont want to just connect the botles to gether, open them and lert then equalise, as if there is too much gas in the refilled botle a vcery small external temp change can cause the bottle to explode!
You also cannot tell how much gas is in rthe bottles by looking at the preasure.
Its somthing i would leave allone personaly and get it refilled properly.
nb. also the valve on an argon shiled bottle is a gas only valve so you in theroy need to invert the large bottle to transfder the gas as a liquid.
Edd