Back toward the end of the 80's the FBI did some extended testing comparing some aluminum framed service-type guns to a proven steel gun in use by their HRT at the time (Browning HP).
It was observed that a couple of the popular alloy 9's of that time (including the 459) could develop frame cracks by 10,000 rounds.
Before someone freaks out about that, this was considered within perspective against the existing 5,000 round frame service life specified for some military pistols of that period. In the report, the president of one of the major gun companies (not S&W) was reported to have responded that if LE wanted a gun that would offer a much longer frame service life than a gun designed to just meet military specifications, the feds should make a request for such, and their engineers would design one.
As time passed, and the major gun companies wanted to win LE sales, we started seeing some improved aluminum framed guns. The S&W 3rd gen's were released about that time, and even they enjoyed continuing improvements throughout their production (culminating in the TSW's).
As other folks have mentioned, a few "secrets" to maximizing a useful service life with alloy frames aren't "secrets" at all.
*Keep them properly cleaned and lubricated. Run them dry, and you risk accelerating wear of the frame rails and damaging them.
*Periodically replace the recoil springs. S&W Armorers are told to replace recoil springs either every 5,000 rounds fired, or every 5 years, whichever occurs first. I like to replace mine a bit sooner than that, erring on the conservative end of preventive maintenance. (In the Chiefs Special pistols I replace them much sooner, as those are pretty short recoil springs, and those little guns develop some respectable slide velocities.)
*Use good quality factory ammunition of the proper caliber. (I prefer to use factory ammunition made by one of the major American companies who have acquired experience making duty ammunition for LE/Gov.)
Now, when all is said & done, steel is still
steel and aluminum is still
aluminum (although S&W did offer that rather nifty, and expensive, Scandium aluminum 4040PD for a short time).
I tried to wear out one of the issued 6906's I carried some years ago. I didn't keep an exact count of rounds fired, but tried to monitor boxes or cases of ammo fired on a monthly basis for preventive service needs.
I ended up replacing a lot of the common parts in the gun due to wear (starting with an extractor after I'd fired approx 12K rounds, but remember it was a previously issued gun before I started using it), and finally a slide (due to a tolerance issue in the extractor slot). I went through a lot of recoil & other springs, too.
I finally retired the gun after what I estimated was approx 45+K rounds fired (a mix of issued/approved standard pressure, +P & +P+ loads). The frame was starting to exhibit a lot of wear, but it remained within spec and normal functioning. I just decided that since it was my primary
duty weapon for my regular plainclothes assignment, it might be prudent to retire the aging 6906
before it reached the useful end of its service life.
I had someone bring me a personally-owned 3913TSW (original version) for an inspection/service one day. I discovered a short half inch crack in the leading edge of the frame dustcover. The owner had thought it was a scratch, and since the gun was running fine he'd ignored it. He was a firearms instructor, and said the gun had been fired between 12-15K rounds by the time he noticed the "scratch".
The gun was returned to the factory. They said it was a puzzling spot for a crack to develop. They said it wasn't in what they felt was a critical spot, but since it was a crack, the frame should be taken out of service. They asked if the owner had been replacing the recoil spring within the recommended period (he had, since I gave him new recoil springs periodically). They commented that it was just one of those weird things that could happen, and cheerfully replaced the gun with a new version of the 3913TSW (apologizing that they simply didn't have any more of the original 3913TSW frames available by that time).
The owner of that new 3913TSW has been using the replacement 3913TSW for a lot of years, and has exceeded the total rounds fired through his first one some time ago. Still doing fine. (I could wish he'd keep the gun cleaner, but he shoots it all the time on the range he has setup on his rural property. At least he says he's periodically replacing recoil springs with new ones I give him between inspections.
)
I've seen a couple of 5904's that experienced excessive frame rail wear due to being run insufficiently lubricated. That's one way to ruin a frame.
I remember the instructor during a Sig Pistol Armorer class continually repeating how critical it was to keep Sig P-series pistols properly lubricated. He said that if the guns were insufficiently lubricated, or were used "dry", they would be damaged and ruined. Not subtle about it. The answers to one of the written test questions about proper lubrication involved the presence of sufficient lubrication being able to be confirmed by sight & touch, BTW. And yes, he repeatedly mentioned that Sigs were considered to be "wet" guns ... but that they also shouldn't be excessively lubricated.
I certainly don't have the "answer" to how long any particular aluminum (or even steel) pistol frame may last.
I do, however, make every effort to maintain my alloy framed pistols in a manner recommended by the gun company who made it, and don't lose sleep about it.
There's another member who occasionally posts in this forum. He worked for the ISP, who enjoyed a long period of using S&W TDA pistols with alloy frames. His agency was also, if I remember right, involved in the development of the original 115gr +P+ loads by Winchester & Federal. He's sometimes related experiences of how well those older aluminum-framed TDA pistols lasted the folks at his former agency.
Now, also bear in mind S&W's ammunition warnings in their owner safety manuals.
Not all +P & +P+ ammunition may be the same. Buyer beware.
Also, +P+ means it exceeds +P standards, but it doesn't tell you by how much, since there isn't any defined upper range or limit for "+P+".
That's one of the main reasons I prefer to only use ammunition made by one of the big companies who have made large amounts of ammunition for LE/Gov customers, including the higher pressure loads like +P & +P+. It's in their interest to not provide duty ammunition that's likely to blow up good quality LE guns of modern design, right? Then again, sometimes signed waivers were asked of end users of higher pressure LE duty ammunition, too, and some of the ammunition was commonly restricted from the commercial market.
I've always asked questions during armorer classes about the viability of using different +P or +P+ loads in different makes/models of guns. Ditto asking different folks when calling back (as an armorer) to talk to other people at the companies (repair techs, engineers, LE sales, etc).
Sometimes I'd be told to use whatever was issued (with the presumption it was going to be something made by one of the big name ammo companies), and sometimes I'd be told to either limit the use of higher pressure ammo, or not use it. (I've been told that +P+ shouldn't be used in the Shield 9, for example, but some +P is okay.)
I went through a couple of folks trying to get a definitive answer about using +P loads in that older production run of 37-2's made for off-shore LE sales. (Some of which were apparently produced using what seemed to have been 442 barrels containing markings for +P loads.) I got a couple of "definitive" answers ... both approving and prohibiting the use of +P in my 37-2.
The "final" answer I was given came after someone in customer service actually called over to the head of production, asking about the older "non-Magnum" 37-2 frames and using +P ... and the answer was that the 37-2 was NOT intended to be used with +P loads. Well, since the barrel on the particular 37-2 I'd received didn't have the +P language, I decided to go with the "don't use +P" recommendation in
my gun.
Just my thoughts.
