"First gun purchase" "270 or 308". I do not know what experience you have with firearms. But if it is your first purchase and no experience shooting buy a "lowly" 22lr a cheap scope and a bulk box of shells. You can do all of this for less than $500 and probably have money left over for a box of beer amd some smokes! Start shooting at 25yd then 50 then 75 then 100. Learn trigger control, breathing, hold, etc. A 270 or 308 is not something i would think a person should buy as a first firearm. Again i do not know your personal experience just my 2 cents.