The Great Shield .45 Machine Mark Mystery Solved: Official Answer from S&W

Over the past few months, there has been a lot of speculation on Forum threads about the machine marks/cuts on the bottom of the slide of the Shield .45 (see attached photo). Some, (including yours truly) believed that they were there to help seat the top round to the back of the magazine to prevent failures to feed, but some thought that they had no purpose, and that they were simply a reflection of a manufacturing shortcut. One LGS salesman told a buyer that they were there to "slow down the slide". Other Forum members have asked S&W customer service reps about the marks, but those customer service reps didn't know why they were there. Finally, tiring of all this, I sent an email to customer service. I hoped someone would be able to look up an answer before they responded. And it came to pass. Here is what I take to be the final word on this issue from good old Nate of S&W customer service:

"Those are there only on the .45 Shield to assist with feeding the .45ACP rounds.

Smith&Wesson values its customers and we are happy to have served you today. Please do not hesitate to contact us should you require further assistance.

Regards, Nate"

So there it is. Now we can go back to spending more time on rebates.

It would be nice if they had included an explanation of how that feature actually assists with feeding...and why it is necessary only on the Shield 45.

I'd rather continue talking about this than rebates...since I bought my Shield 45 before the rebates were announced.

Not to long ago, someone on one of these threads said that those "ridges" bothered him and he polished that area smooth! I wonder how his Shield 45 functions???

...and they assist with feeding the .45ACP rounds by slowing down the velocity of the slide while at the same time seating the top round to ensure optimum function. Makes sense to me

Colonel said:

Not to long ago, someone on one of these threads said that those "ridges" bothered him and he polished that area smooth! I wonder how his Shield 45 functions???

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This is a classic example of ruining a perfectly good pistol. Too bad someone cannot find that post and send that guy a PM with S&W's response.

The bad part will be that the next buyer will not know better and will but the ruined pistol from the "kitchen table gunsmith."

This guy provided the definitive answer:

"Because of the tight fit of the .45 cartridges in the Shield's magazine well, they have a tendency to hang up below the feed ramp and thus create a failure to feed if they are not fully seated all of the way back in the magazine. The purpose of the scalloped ridges is to grab the top cartridge and pull it back to its rearmost position to prevent it from hanging up. "



(Thank you, SWSIG!)

So if every slide is not machined/marked exactly the same, it could create feeding variations from pistol to pistol right? For example, pistol A is cut with a new tool and has nice crisp "machine marks" which grab the case nicely and seat in the magazine, while pistol B is cut with an old tool and doesn't grab the case as well.

GKC said:

This guy provided the definitive answer:

"Because of the tight fit of the .45 cartridges in the Shield's magazine well, they have a tendency to hang up below the feed ramp and thus create a failure to feed if they are not fully seated all of the way back in the magazine. The purpose of the scalloped ridges is to grab the top cartridge and pull it back to its rearmost position to prevent it from hanging up. "



(

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That does not engender confidence in reliability
of the overall design, lol!

Think of it as also helping prevent the potential for "live round ejection" during cycling with the really light .45 pistol, which could happen if the top round was displaced (jarred by recoil) forward enough for it to "jump" out from under the magazine lips.

The heavier mass of the .45ACP rounds, and the heavier recoil of the cartridge in a lightweight .45 pistol (like the light weight Shield 45), might potentially result in forward displacement of the top round in the magazine during recoil/cycling. The machining on the bottom of the slide's pickup rail helps prevent forward displacement of the top round. Neat trick, too.

FWIW, the little 3rd gen CS45 used a different method to help mitigate forward displacement of the top round in the magazine during recoil in the itty bitty pistol. The magazines for that model incorporated a second set of indentations to help hold the top round stationary during recoil and cycling. Unfortunately, this also made it harder to load, and especially manually unload, magazines for the little pistol, and it made the magazines for the CS45 model-specific.

It would've been nice if S&W engineers had figured out the pick-up rail machining solution back when the CS45 was in production. If they had, then maybe the longer 7 & 8rd 3rd gen .45 magazines might've been useful as spare mags for the CS45, and the original 4513TSW and CS45 might've been able to share the same mags.

Hey I am an idiot as long as it shoots well and functions as it should I don't look that close or care LOL but that's me

The "top round ejection" is an interesting theory...

I did have a Ruger P-97 that did that at least once out of every magazine, every time out, with all kinds of ammo. Never did get it sorted out. Ruger finally replaced the gun with another one--which I promptly put on consignment, unloved and unfired.

Alternatively, I had an old LW Colt Commander .45 that never did that under any circumstances; nor has a new LW Ruger Commander .45. Ditto with a Kahr CW45. It malfunctioned in every other possible way, but not that.

My .45 Shield has only about 250 rounds through it but behaves very well. It's light, and the recoil is seemingly less than that P-97. At the end of the day my conclusion was a simple one--the gun was possessed by demons.

Bat Guano said:

The "top round ejection" is an interesting theory...

I did have a Ruger P-97 that did that at least once out of every magazine, every time out, with all kinds of ammo. Never did get it sorted out. Ruger finally replaced the gun with another one--which I promptly put on consignment, unloved and unfired.

Alternatively, I had an old LW Colt Commander .45 that never did that under any circumstances; nor has a new LW Ruger Commander .45. Ditto with a Kahr CW45. It malfunctioned in every other possible way, but not that.

My .45 Shield has only about 250 rounds through it but behaves very well. It's light, and the recoil is seemingly less than that P-97. At the end of the day my conclusion was a simple one--the gun was possessed by demons.

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Ruger told me that they'd eventually changed the magazines for their P90's & P97's to incorporate a couple of machined indentations on the lips (on each side) of their magazines in order to help prevent top round displacement when hotter loads were used.

The tech mentioned that some of the hotter +P loads could especially produce enough extra recoil force that it might cause the top round to "jump" forward. It was the mass and weight of the heavy bullets wanting to remain stationary as the frame/gun (and magazine) actually jumped rearward, under recoil, which caused it to happen. If it did happen, then the top round might either be too far forward to feed up the ramp, or, it might be jarred loose from under the feed lips (live round ejection).

Coincidentally, this revision to the mag lips also seemed to have occurred when they reduced the spring length and tension to allow an 8th round to be loaded into the magazine, and the follower changed to allow it. They sent me some of the new style mags to try in my KP90DC. I decided to keep the old style spring & follower, and only load 7 rounds, but thought the added dimple in the mag lips might be handy (as I was still shooting a lot of +P .45ACP at that time).

I had a Commander that started exhibiting live-round ejection, but I realized it was only with a aprticulr mag, and solved that problem by getting rid of the mag.

Another time to aware of the potential for top round displacement is when the top round is the last round, and the mag spring is at its least tension during feeding (during recoil of the next-to-last round being fired).

This is why some .45 mags of various designs may have either a raised dot/dimple on the top of the follower, or some sort of a "nub", to help keep pressure on the last round and help prevent it from being displaced forward (when the mag spring is exerting its least amount of force). Sometimes one of the early signs of a weakening mag spring is the last round not being held in the correct position during recoil/cycling so proper "feeding timing" can occur when the slide is trying to pick it up and feed it from the mag. If it moves too far forward it can't be presented at the right angle to negotiate the ramp/throat, or have the case base be captured against the breech face ... and if it is jarred from under the feed lips, then live-round ejection occurs (or the live round "sits" in the ejection port, depending on the "timing" of events).

In any event, keeping the top round - all top rounds, as the mag stack shrinks - properly positioned for normal feeding "timing" is important, and the supplemental indentations of the CS45 mags, and the machined steps of the Shield 45's pickup rail, are methods that have been incorporated by the S&W engineers ... or so I've been told, during armorer classes and conversations with folks at the factory. Might be so.