Can a shortened P226 .40 S&W barrel work in a P229 .357 Sig frame? Looking to reduce the herd a bit and found a great deal on a new P226 .40 tube

At least two issues:

Diameter of 357/40 P226 barrel is about 0.531"; diameter of 357/40 P229 barrel is ~0.551" .
The locking inserts of P226 and P229 pistols are different; a P226 barrel is not compatible with the P229’s.

So much for being cheap.