Diagnose the problem with the S&M pistol


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4v50 Gary
August 31, 2007, 09:02 AM
Please view this newsclip and then join me in diagnosing this problem with the CHP's S&W pistol.
Click here to view. (www.ktvu.com/video/14017246/index.html?taf=fran)

Consistent failure to feed the last round? I'm trying to figure out why. It's not the feed lips since it fed all the rounds before it. It's not the ammo as the ammo is cycling the weapon. It can't be the shooter since there's eleven failures. I'm wondering if it's the engineering behind the magazine spring. They (S&W) should graph the pressure on the spring as it cycles to see if there's any difference between all the previous rounds and the last one. It could be too stiff and when it's too stiff, it can be sluggish.

Resistence on the feed rib (of the slide) is exerted by the cartridge that is pressed up by the follower (via the magazine spring). If the resistence is too strong, it can make the gun sluggish. Sluggish extraction can result in slower return of the slide to battery and hence the malfunction (failure to feed).

The Germans would be good at this as they've the scales to graph everything on a gun. I'm sure S&W does too. (which means it could be a failure on the part of their spring supplier).

Please, no discussion about Calif. State Senator Romero questioning the methods the CHP buys its weapons. Let's talk about the gun, not the politics.

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Jim Watson
August 31, 2007, 09:26 AM
As you say, if insufficient magazine spring, a stronger one might put enough drag on feeding the TOP round to hurt. That is reportedly the reason Tripp started then stopped making 9mm and .38 magazines of the design that does well with .40 and .45; it was too difficult to balance out the spring load to suit all guns.

If the magazine follower profile and the body taper from double column to center feed did not match up, the last round might not be lifted all the way into the lips.

The follower lacks the "1911 pimple" to keep the last round from getting displaced by the next to last one feeding forward over it.

ABBOBERG
August 31, 2007, 01:00 PM
Could it also be that the follower just did not reach? Maybe the magazine spring just got too weak at this point and did not deliver the round to the lips before the slide returned.

Just to make sure I am understanding this right, could failure to feed also mean that the round went into the chamber but got ahead of the extractor?
I had this problem with my Sigma SW40VE.

fastbolt
September 1, 2007, 01:31 AM
Dunno what's involved with this current situation ...

However, I remember when S&W was replacing some 4006/3 magazine springs in LE guns a few years ago.

As I recall, listening to an armorer instructor during a recert class, it was discovered that a bulk shipment of magazine springs S&W received from one of their vendors had a problem which slipped through. When S&W examined some of the springs after receiving some complaints of feeding issues in some LE guns, they reportedly discovered that their vendor had made some small change or another in the specifications of the provided springs, and this change affected the performance of the springs.

Last-round feeding failures would make me at least consider the spring tension, as well as the shape and angle of the top coil. I once had a magazine spring in another make/style of magazine which was giving me some last-round tension issues during bench-testing, and the only obvious difference I could see between the involved spring and all others was a canted top coil, which seemed to lessen the tension on one side of the follower. When the spring was almost completely uncompressed it may have been affecting the lift being exerted on the follower.

Again, I don't know what's involved here ... haven't asked anyone, either ... but it made me think of this ...

A less-easily-visibly-seen tolerance change ... coil dimensions, angle of coil winding, tempering, etc. can be tricky to isolate and identify ... if that even turns out to be a factor.

Dunno, but I'll wait to hear whatever may be discovered in the future.

Magazine body tolerances can similarly potentially be examined in feeding issue situations, too, you know ...

hankdatank1362
September 1, 2007, 06:43 PM
Gary, you really need to turn the "M" right-side up in the title... or else this thread takes on an entirely new meaning!

revitup
September 2, 2007, 09:42 AM
"S&M" pistol? Is that the one with the black leather grips?

deadin
September 2, 2007, 10:07 AM
Diagnose the problem with the S&M pistol

"It's probably caused by the whip getting tangled in the chains":D


Sorry about being a little OT, but this opportunity was too good to pass up...

Coronach
September 2, 2007, 04:55 PM
So, does it fail to strip the round from the magazine (slide locks back on a non-empty mag), or does the round just fail to feed, preventing the gun from going into battery?

What is most intersting is that this is a Gen3 autopistol. They're new manufacture guns, but they are using an existing, proven design, which was seemingly immune to this problem before. In many ways, this makes problem diagnosis easier. All S&W (or S&M ;) ) has to do is ask "what did we just change?"

Mike

PS Or, more problematically, "what did one of our subcontractors just change that they may or may not have told us about?"

Owen
September 2, 2007, 05:04 PM
almost guaranteed its a magazine issue. If it was a feed ramp or extractor issue, it would be constant thoughout the magazine.

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