Danish oil is adulterated linseed oil that sometimes contains harmful additives and would be one of the last finishes I would apply to a decent gunstock. As for using 3 in 1 you would be mixing a mineral oil with a natural one and not to be recommended. If as you say you do not spend much time with your gun then a wipe-over with raw linseed is as good as it gets, it will have soaked in within a couple of days leaving no sticky residue as the boiled version can do. As someone who was apprenticed to the trade 60 years ago and was taught all about the different finishes, I am sometimes horrified at advice given and consider a little knowledge potentially dangerous. If you stick to natural oils and polishes rather than other propriety products then you will not go far wrong.