Gold ended at $1723.50/oz on 2/3/12.
1 troy ounce = 31.1 grams
That makes the price/gram, based on Friday's ending price, $55.41, making the price for 5 grams $277.05 (just a little bit more than what you believe the gun to be worth).
Gold has trended down the last couple of days from a high of $1762, so you will need to keep an eye on gold prices so that you do not lose money. You are also assuming that whomever buys your gold will actually pay you the going price for it; it is more likely that the price you receive will be greatly discounted.
The price is also determined by the karat weight of the gold, which ranges from 10k to 24k, so there are several variables that will have a HUGE effect on the value of the gold you receive; you need to be sure to ascertain the karat weight of the gold you will receive. As an example, based on the current price of $55.41/gram for 24 karat gold, 14 karat gold is worth $32.32, making the value of your 5 grams of gold $161.60 - significantly less than you believe the gun to be worth.
Looking at prices listed online, it appears that this gun sells brand new starting at around $250 to a high of around $320; I wasn't able to find any prices for a used model.
Anyone else have any thoughts?
PS -- to find the value of a given karat weight of gold, divide the karat weight by 24; this will give you a decimal value. Multiply the current price/gram by that decimal value, and you will have your price/gram for a given karat weight:
10KT = 10/24 = .4167
14KT = 14/24 = .5833
18KT = 18/24 = .750