Well I'm no Leedy expert. But what I can say is that when I got my Slingerland C.O.B shell, there was bending in the shell. I needed to hammer it back to shape in spots. From my knowledge the Slingerland shells were thin, and if you weren't careful would bend in. So I'm gonna say if It happened with mine as well as other Slingerlands, and he claims only Leedy had this issue, I think this answers it.

Also got this from http://www.coopersvintagedrums.com/newslinghistory.htm

" Slingerland’s new 1956 Leedy drums were basically Slingerland drums fitted with Leedy lugs, strainers, and badges. This Leedy drum line was discontinued around 1966. "

I've had both shells, they are the very same shell only hardware differences that's all seriously,.Now if we're talking about real Leedy brass shells yes they are thicker, Than the Slingerland era shells.

Leedy versus Slingerland It all depends on the era your friend is talking about. The Leedy shells as per say were made in a thinner gauge over Slingerland , but they had very good support in the interior of the drum that prevented them from bending. Now Slingerland shell were made of a thicker brass shell but there support were very thin and has tendency to bend. In 1950 when Leedy they joined with Ludwig to form the Leedy & Ludwig there were many changes that many people did not notice. For instance inner support plates they were shortened by 1/4 of inch and this caused model made mid 52 thru 1954 to bend when tuning. This happen to many of the model made during that era. As Slingerland took over Leedy They also made numerous changes that cause drums to bend when tuning also few Model that Leedy had were never owned by Leedy and Slingerland made Replica models to have a similar product. One of the examples that Leedy never owned was the timbales the had manufacturing rights only. The Patient belong to Charles Tappan and Henry Adler. Same with few other model Leedy had on there under there control

The OP said it was a Shelly Manne model, so that would mean the Slingerland era.

I have an early 60's Shelly cob. It's a slingerland with a different badge, lugs and throw off.