[No Time Toulouse]

I always thought that horizontal drop outs were for track type single speed set ups. What ever the case, I find vertical drop outs much easier to deal with.

No, actually track bikes use Track Ends (a.k.a. Fork End), not dropouts. Look it up. https://en.wikipedia.org/wiki/Fork_end

 

[Fredrico]

I've heard/read that Campagnolo horizontal dropouts are a carryover from their early Cambia Corsa derailleur geared dropouts, which allowed the axle to roll forward and back to slacken the chain and allow shifting under movement.

A Campagnolo masterpiece: the Cambio Corsa – B.G. legendary Bikes (bglegendarybikes.com)

And it worked! Assume that's a free wheel.

The dropouts look just like their later ones, minus the adjusting screws. Investment cast, man. Rock hard. Clamp that wheel in there with Campy skewers, and that thing won't come out!

 

[Mike Overly]

I picked this up the other day. It's a beauty. Not a show bike but it's going to be a great every day club rider. It's an early to mid 90's Corsa Extra TSX with Dua Ace 10 speed. View attachment 483753

Beautiful bike! I think we've all experienced the rear QR foible -- as others have already stated, QRs from Shimano or Campy (of any era, so long as the length is correct) fix this issue. Enjoy!