I ran out of my "premium products" awhile ago ( Tetra Gun,Breakfree )so I looked around the house and I had a can of 3-in-1 oil.I didn't realize it's put out by WD-40.Well I've been using it for awhile.
Has anyone else out there used it on their firearms?

I know 3-in-1 Oil used to be very common back in the 50’s and 60’s.  At that time, it got a reputation as being a poor quality oil suitable for door hinges and such, but not firearms.

It seemed to disappear for a while and, as you mentioned, is now being marketed by WD-40.   I don’t know if it has the same formulation as before.

Regardless, given the really fine modern gun oils available, I personally wouldn’t even consider using it on any firearm except in emergencies.

I used it back in the late 1970's-early 1980's.
It worked o.k.,but there was not much to compare back in those days as far as gun oils.At least for me anyway.
I still use 3in1 around the house and shop but thats about it.
The only real issue I had with it is it would contaminate a scope real fast if any got on it.
It will also swell orings rather fast.
The oil also tended to make a varnish over time and gum up badly with powder fouling.
I had a Remington 742 stop working due to the varnish/fouling that built up in the bolt.Fast too.
It just does not compare to any of the clp's on the market.
Get some Firepower FP-10 and use it.You will not believe how much difference there is in it and other gun lubes,not to mention 3in1.FP-10 rocks.
Raymond

 Every now and then I use it when I need an oily rag or something to clean adhesives or gunk off of a surface...but anything else would work just as well....I guess I just keep it around as a cheap alternative to use if I don't want to waste the good stuff.

Many oils have a percentage of parafin in them.
the amount of parafin can gum up or gel in colder temps. Many newer lubricants are
not oils( Mobile 1 is not an oil) and have various properties. Militec-1 adhears into the
metal( similar products stick and lubricate the valves in transmission valve bodies). Still,many of us have our favorites that the mainstream of users don't use.

Breake-Free and TW25B are synthetic and not petrolieum based as well.

No.

But when I went into the Border Patrol in 1980, my Dad decided to do me a "favor" by protecting all my guns from humidity/corrosion by drenching them in WD-40

When I discovered this, it was 1999.

I DID question him as to whether he had inadvertantly used SUPER GLUE as weapons lube.  He claimed "Alzheimer's moment," but I suspect practical joke (because I would do shit like that).

I love my Dad far more than any stupid gun, but they were some really nice weapons (including a real Government Springfield 1911 from WWI).  

The epilogue is that after soaking them in Butch's, they freed up and cleaned up perfectly.  No damage that I can see at all.

Would I USE 3 in 1 oil?  Hell, I'd use K-Y Jelly in an emergency (of course, . . . that would be a different KIND of emergency I suppose?).  But I'd clean it with something more appropriate when there was a lull in the action.

Just a thought though.  When I was still "on the job," it was my practice to buy my guns brand new.  In sets of two.  In the Smiths, have the magazine disconnect removed by the local P.D.'s armorer.  Install Trijcon's on both guns.  Get some range time on both of them and pick "#1 carry gun."  

Then clean and maintain both of them.  Put one away in an alternate "safe place." And keep other people's hands off of them (except to shoot them, etc.).  

I bought two because I never carried anything we issued and if my handgun broke, nobody was going to give me another one of what I shot, while the other one was in the shop.