Very much depends on where you are and what you did to get arrested, I've been 'arrested' four times but always let go, three of those times involved guns, sort of.
The first was during high school in a very rural county, we were playing a game called fugitive which is like advanced hide and seek with the seekers having cars and the game being over an entire town. I was the seeker and I got pulled over and handcuffed for being an accomplice/getaway driver in a B&E. Apparently my stupid friends decided to hide in someones basement as I drove by. The guy then called the cops (obviously), gave a description of my truck and my friends, and we all got nabbed. I had a varmint rifle and a .22 pistol with me, and I was only 17. Long story short the cops were pissed but after about an hour they cooled off, laughed about how dumb we were and told us to go the hell home. No mention of me being underage and having guns.
The second was in college. Mid sized town, lots of drunken stupidity, way more serious police. My friends from the previous story came down for a weekend and one night we decide to buy airsoft pistols, go to the big kids park that closes at dark, and have a big gunfight. Cops get called about people running around with guns on a playground and as we leave we get met by four officers with guns out, yelling at us to drop our weapons and get on the ground. We did, they searched us, found no actual guns, gave us a major lecture about how we could have been killed, and warning tickets for trespassing on city property.
Third time was in another small town with a bad drug problem after a room mate of mine bought a '64 International pickup and we had just hauled it home using my truck. We went out for a test drive in his new truck, it backfired about three times and died in a residential neighborhood. Out of gas. So we push it off to the side and walk back to our house to get my truck and some gas. We come back to his truck with a lit up cop car behind it and a cop in the truck searching it, so we get out and his partner pulls his gun and tells us the usual 'get on the ground'. We ask what the hell is going on and he tells us somebody called in a report that an old truck pulled up and two men got out with assault rifles and shot off a bunch of rounds before running away. We say no, it backfired and died so we went to get another vehicle and some gas, they still search us and both vehicles. They find, again, my varmint rifle and .22 pistol but since neither one fit the description of assault rifle and there were no casings anywhere they let us go.
TL;DR - Rural cops don't care, city cops and cops in bad neighborhoods tend to freak out.