When I was 11 years old with a 55 cent/week allowance I bought a 1963 Shooter's Bible for $3.
A pre 64 Win M70 30-06 cost $139.
An unmodified one today is worth $800
The ratio is $800/$139 = 5.75
That was 1963, this is 2015
2015-1963 = 52 years
The 52nd root of 5.75 = 1.0342
That means a pre 64 M70 has been making 3.4% compounded annually for the last 52 years.
Almost all gun have made ~3% over the last 10 years, the last 50 years or the last 100 years. So have guitars. It is background inflation.
When i was a little kid, I read an article in Scientific American that compared the time rate of change in metallurgy for dated US minted coins to ancient Roman minted coins. It found the inflation rate to be the same.
I am aware that some guns are better, like Colt revolvers at 5% and some guns are worse, like Mossberg 16 ga bolt action shotguns.
Burying Gold in the ground since it settled out in exponentially damped sinusoidal ringing around $400/ oz in 1983 after deregulation in 1971 has been 2.9%.
But the bible suggests that burying Gold is the least productive investment, not as good as to get the Gold invested and working.
Over the last 20 years I have made in excess of 20% compounded annually by investing in something that grows; Microsoft, Apple, Google, Amazon, etc.
What does it all mean? Buying a gun is not an investment. It's value only grows at the rate that money shrinks. A real investment is something that works and grows.
I buy guns all the time, not as an investment, but as an indulgence to my hobby.