How long before an 80's vintage Model 64 (pre-lock, pre MIM, firing pin on hammer) looses it's timing?

Shooting standard pressure 130 or 158 grain .38 special loads with the occasional +P defense loads for testing, how many rounds before a tight and excellent condition gun needs to get sent back to the factory to be re-timed on average?

Anyone know this answer?

Given proper TLC, never. I have an old 4 screw K38 from about 1958 that I use for PPC and my night stand revolver. Granted, I don't load it with +P, but it sees a fair share of stoked 160gr SWC loads. It is as tight and in time just like my 14-4 K38 Masterpiece that I use for bullseye matches. If you don't mistreat it, your children will still be shooting it.

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Judge control not gun control!

I agree same frame is used for the 357 models. Take a long time to wear it out. just getting broke in at 10,000 rounds

First, what you are asking about is "carry-up", not "timing"! Carry-up is subject to wear of the hand and ratchet but timing is not. Timing is the relationship of the charge hole bores to the barrel bore and is pretty well fixed for the life of the revolver regardless.

For all practical purposes even carry-up is not significantly affected by rounds fired, and BTW dry-firing counts just as much as live firing!! I, and many members, own S&W revolvers well over 100 years old that still function perfectly as to carry-up, and which likely have fired thousands of rounds in their lives to-date! Age and rounds fired have little effect on either timing or carry-up as long as the gun is not abused. Failure to keep the mechanism properly cleaned and lubricated does constitute abuse of the gun, which seems to be rarely appreciated.

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Gunsmithing since 1961

So then, what DOES knock a S&W out of time or disturb the carry up? Because I've handled some than are certainly out of time in the sense that I understand it, shave lead when fired, and/or have significant endshake.

What causes this?

I own and shoot (a lot) many S&W Revolvers and the only two I ever had to fix carry-up / timing issues on were two of the guns I inherited from my Dad. He was a Fed from 1950 - 1977 and was also on the Bureau's pistol team. I could not tell you how many tens of thousands of rounds he put through them, but I know it's a huge amount. One was his Combat Masterpiece (his main competition gun) and the other was his 2" back up Baby Chief's Special. The Combat Masterpiece was out of time but still functioned if the trigger was pulled normally in DA - not so well when pulled slower. A new larger Hand solved that problem 1,2,3.

The Baby CS was an absolute disaster! It would only fire about 2 rounds out of 5 (firing pin would miss the Primers) and I wound up replacing all the Springs, Hammer, Trigger, Hand, Ejector Rod, Rebound Slide, Cylinder Stop, Screws, etc. He used this gun for back up however he practiced extensively with it and also used it for BUG "side matches". The Frame, Barrel, Cylinder and Grips are still original but thankfully I had ALL the period correct parts (not so easy to get these days for a Baby CS) to rebuild the rest of the gun without having to buy anything! 'Till this day I can not believe these were HIS guns as he was very anal. I guess that is what happens when you get older and sick - guns become not so important I suppose. Anyway, both guns function 100% now and I still shoot them. The hardest part was filing the new Ratchets on the Baby Chief's Spl. - not an easy job but it did come out great after hours of fiddle futzing.

Other than those two guns, none of my other Smiths ever had carry -up / timing issues. However, usually replacing the Hand with an oversized one solves it with no further ado. Not a hard job, but just make sure you know what you're doing before you start.

If you have no carry-up / timing problems now you can expect many years of service out of it unless you are an extreme high round count shooter. There is no "expected" round count for the timing to go out at.

PS: the Baby Chief's Spl. (I/J Frame - early 1950's) is a lot more fragile and slightly smaller gun than today's M36/60's are.

Theoretically, as long as you shoot rounds that stay within the standard pressure limit of that revolver's given caliber, it should last a very long time before problems arise from carry-up or other.

Where problems occur is when folks shoot overpressure loads, abuse the action, carelessly handle it, or shoot extremely high round counts. The first three are the normal causes of issues, but certain folks do get the high round counts and instruments made of steel will eventually wear out of spec. Overpressure loads are the major cause of revolver issues in my eyes and it doesn't take many.

Also factor in manufacturing variables like production lot quality differences and overall build quality too. Those can cause issues to arise, especially when coupled with the factors mentioned above.

So if anyone doesn't want to put wear on a gun, they should shoot standard pressure loads for it and never abuse the action or the gun itself. You would be amazed at how clean and like new one can keep a gun by only shooting standard target loads and gently cleaning it after.

You will probably "run out of time" before the revolver does.