Woody
Here is what it is: read on -
Wednesday, September 04, 2019, 10:08

The endurance package was developed to address shortcomings in the design that became apparent when the M29 was used extensively for Silhouette matches. You must remember that the S&W M29 came out in 1955 and withstood the test of time all the way until the mid 80's when the Silhouette Match shooters started sending a lot of "healthy" loads down range through them.

Stuff started happening as a result of that steady and frequent diet of "full house" (and then some) loads... the internal hammer, trigger and bolt stop pins started to shear from the frame, the cylinder locking bolt would drop and allow the cylinder to unlock from the heavy recoil, where it would rotate backwards to a previously fired chamber.

With the 29-3, S&W started to address those issues and continued making improvements with the release of the 29-3E (Endurance), 29-4, and 29-5.

Among the endurance upgrades were a deeper cut bolt notch on the cylinder, new style cylinder bolt, and a radius(flare) was put at the bottom of the internal pins so the were bigger/thicker where they attached to the frame, instead of being the same skinny size throughout its length.