The bolt block pin sticks out on one side of the hand about midway up the hand. It prevents the bolt from moving forward when the hand is in position at the moment of firing. Perhaps your gunsmith could show you the difference between hands with and without a bolt block pin, and could show you (using a revolver with the side plate removed) how this difference could have an influence on function.
There was a change in the Hand, with the newer hand for the Magnum J-frame guns listed as "229510000 $16.00 HAND J .357".
The last time I called to order a couple of spare parts, including some J-frame hands, I was specifically asked whether the parts were going to be used in .38 or .357 Magnum models. The gentleman reminded me that some of the parts, such as the hand, were different for the .357 J-frames.
I'm certainly not inclined to take offense at the opinion of anyone else.
Your gunsmith can probably better explain in person why the center pin must remain within a certain tolerance range in order to provide for proper function.
The center pin, however, being a fitted part for each revolver, must remain within a certain specification in order to function as intended. If being fitted at one end of the recommended spec range results in a lessening of the condition you're seeing, and the gun still otherwise functions as designed, then it sounds as though you will achieve your desire.
I wouldn't necessarily be in a rush to consider this condition a 'problem', though, not without receiving the input of the folks who have designed and manufactured the gun. the first response I received was that it didn't appear to indicate a 'problem'. I haven't since then felt it necessary to try and follow up by asking further 'up the line', so to speak. Maybe later, if only out of curiosity sometime.
There are any number of conditions which someone may be surprised to observe with their firearms, but which are often just a condition occurring as a consequence of normal functioning in any given design/model made using the materials involved in a particular model.
For example, there are still folks who believe that the 'ring' around the cylinder, caused by contact between the ball of the cylinder stop and the cylinder, can be (and should be) prevented and 'fixed'. This marking, called a 'stop track' by S&W, is indicative of how their revolver design operates and is a cosmetic consequence, as it were, not an indication that something is 'wrong'. It's to be expected in a properly built S&W revolver. The degree of its occurrence may vary a bit from any one revolver to another, being influenced by how the various parts and components fit in place and work together in any particular gun.
As far as communicating by email with the company? I have the emails of some of the folks, and sometimes it's not inconvenient to wait for responses, but direct personal conversations can more easily resolve so many more issues without the delay involved of back & forth exchanges.
I've had email exchanges about issues take several days to complete, and then I've had phone conversations with the CS reps, repair techs and even engineers clear up and resolve issues in less than 5 minutes. Of course, it depends on whether the schedules and daily activities of the persons involved allowed a phone connection.
A brief and concise response delivered via email can often be delivered and clarified, if need be, much more easily in person. Think about receiving an email response that merely stated, "Within normal spec. Not a problem." Then think about how a short 1-2 minute explanation might better clarify why it wasn't a problem, and how it might better set someone's mind at ease.
On the other hand, if the company was taking the time to provide an in-depth and detailed explanation for each and every person who called them to ask questions, it might be hard to find the time to go about their other business activities.
