Moon Clip Cylinder Problem

RetentionDNA · Oct 25, 2021

I just purchased a BNIB 627 in .357 magnum.. I shot it yesterday without moon clips & 1-2 bullets (per cylinder) didn’t fire... The primers were struck but not deep enough to shoot.. This problem repeated for maybe 70 rounds until I inserted the moon clip.. The moon clip I suppose filled the gap between the bullet & hammer.. I contacted my aunt who owns a 640 & she has the same problem.. There’s a review on concealedcarry.com addressing this.. I’m baffled as to how S&W doesn’t mention this; people use these to protect their families.. To sum this up; I dislike moon clips & if I can’t find a solution to this or get a cylinder not cut for moon clips I’m selling this gun & never shooting it again.

RetentionDNA · Oct 25, 2021

If my review comes off as harsh or critical I mean no malice. I respect S&W team & their products.. If anyone has advice or information leave a comment

Protocall_Design · Oct 25, 2021

You probably need a longer firing pin. Many of the factory ones are marginal or too short. The minimum length you want to see is .495". A length of .500 or more is better.

Lou_the_welder · Oct 25, 2021

I would first check the strain screw, to be fully tightened. They loosen through use sometimes.
Next I would ask if the 627 was purchased new. The 627 has to fire rounds reliably without moonclips . If it doesn't, it needs to be sent back to the factory . Under warranty. (Why would you have to pay for the fix)

That 627 should fire rounds reliably with or without moonclips. The moonclips are not necessary for its function.

But, in my opinion, the moonclips do make the revolver alot more fun. But that's just me.

H Richard · Oct 25, 2021

I know of no "factory" 627 or 640 that takes moon clips. Custom milled cylinders yes, but they then need to be used with the moon clips. Are these custom guns?
Tightening the strain screw would also be my 1st move if I had a failure to fire, and if these are custom guns, has anyone done "Trigger Jobs" and installed lightened springs or cut springs?

Nightowl · Oct 25, 2021

H Richard said:
I know of no "factory" 627 or 640 that takes moon clips. Custom milled cylinders yes, but they then need to be used with the moon clips. Are these custom guns?
Tightening the strain screw would also be my 1st move if I had a failure to fire, and if these are custom guns, has anyone done "Trigger Jobs" and installed lightened springs or cut springs?

The 627 pc and the 627-5 8 shots are all cut for moon clips from the factory.

Georgia1911 · Oct 25, 2021

And the 640 Pro is also factory cut for moon clips. While we are on the topic, I will add that S&W moon clips do not play well with all cartridges.TK Custom offers them in various thicknesses to work with specific brass.

xtrtsqrt11 · Oct 27, 2021

I'd contact Smith even if it is used. They have taken care of me with an out of warranty situation before... At no expense to me...

Doug44 · Oct 27, 2021

I hate to you Richard but my 627 came cut for moonclips. Will shoot either way.

series guy · Oct 27, 2021

Since you need to remove the grips to check the strain screw also check to see if it has a power rib main spring from the factory. I have seen factory guns with this issue due to too short of a strain screw. Combining the round butt frame profile with the power rib spring can be a problem as the round butt strain screws are shorter. If you have looked at any other S&Ws you will notice that the main spring on these problem guns don't have near the arch that the old flat main springs had. Using a set screw in place of the factory strain screw solves this problem.

L-2 · Oct 27, 2021

Echoing some of the responses already made I've made some of the changes/mods to some of my personal S&W revolvers, as needed:

-firing pin, I was told by Apex its firing pin is slightly longer (don't remember actual length difference).
Revolver Firing Pin

-mainspring replacement with stock weight/power.
Wolff Shooter's Spring Pack TYPE-1 Standard Power Mainspring S&W K L

-a strain-screw can loosen, particularly if its a new S&W which probably doesn't have any thread locking compound applied (I don't think S&W puts thread locker on its new guns' strain screws).
Modern Sporting Rifle Vibra-TITE 213 VC-3 Threadmate Threadlocker,5mL Tube, Red 745619000286 | eBay

Also, I'm usually shooting factory ammo, not somebody's favorite personal loadings. Don't use "reloads" for any of this testing no matter how well they've been working in one's other guns until now.

Not all of my S&W revolvers with factory moon-clip cylinders had a light-strike problem.

A 640 won't have a strain-screw so no need to look for one.

Let us know how it goes and I hope you don't get rid of the subject revolver without finding out if any of these low cost, easy-to-install potential fixes are first tried. Do get the right size/type of screw-drivers for any of this work, however.

colt_saa · Oct 27, 2021

RetentionDNA said:
I just purchased a BNIB 627 in .357 magnum.. I shot it yesterday without moon clips & 1-2 bullets (per cylinder) didn’t fire... The primers were struck but not deep enough to shoot.. This problem repeated for maybe 70 rounds until I inserted the moon clip.. The moon clip I suppose filled the gap between the bullet & hammer.. I contacted my aunt who owns a 640 & she has the same problem.. There’s a review on concealedcarry.com addressing this.. I’m baffled as to how S&W doesn’t mention this; people use these to protect their families.. To sum this up; I dislike moon clips & if I can’t find a solution to this or get a cylinder not cut for moon clips I’m selling this gun & never shooting it again.

Welcome to the Forum.

As others have said, the first thing to check is the strain screw. If this was a used firearm, it may be suffering from someone messing with the springs and screw while trying to get a lighter trigger pull.

I have many 27/327/627 revolvers that are enabled for moon clips, they have been fed 10s of thousands of rounds of ammunition since I purchased the first done back in 1996

Did your 627 have this issue with all the brands of Factory ammunition that you tried in it? And if this problem is with hand loads, what primers are you using?

I have not experienced light primer strikes with any of my revolvers. I shoot a mix of factory ammunition and hand loads

Let Smith & Wesson solve your problem for you if nothing suggested works

I know of no "factory" 627 or 640 that takes moon clips.

All 627s, with two exceptions (SKU 101024 & 163357), are moon clip enabled when they leave the Factory

As to the 640s, as already mentioned, the 640 Pro is moon clip enabled. I can not recall another

JDinAZ · Oct 30, 2021

RetentionDNA said:
I just purchased a BNIB 627 in .357 magnum.. I shot it yesterday without moon clips & 1-2 bullets (per cylinder) didn’t fire... The primers were struck but not deep enough to shoot.. This problem repeated for maybe 70 rounds until I inserted the moon clip.. The moon clip I suppose filled the gap between the bullet & hammer.. I contacted my aunt who owns a 640 & she has the same problem.. There’s a review on concealedcarry.com addressing this.. I’m baffled as to how S&W doesn’t mention this; people use these to protect their families.. To sum this up; I dislike moon clips & if I can’t find a solution to this or get a cylinder not cut for moon clips I’m selling this gun & never shooting it again.

I would just about bet that if you put a new extractor/ratchet in and ensure the new one is properly timed to that gun it would take care of the issue. The lack of case rim support from the machining is most likely the culprit.

Yes a 38/357 cartridge should fire without a moonclip, but if the machining is too wide (larger of an OD in the recess) or if the chamfer at the charging hole is too heavy it can create a condition where the semi supported case rim does not get enough support from the cylinder to fire reliably.

bananaman · Oct 30, 2021

I am not sure if they have a moon clip for your application. Rimz Poly Moon Clips. They are great, because you need NO TOOLS! I use them with my 625 JM. Bob

colt_saa · Oct 30, 2021

I am not sure if they have a moon clip for your application. Rimz Poly Moon Clips. They are great, because you need NO TOOLS! I use them with my 625 JM.

The plastic moon clips will not work in revolvers that chamber and fire what is traditionally rimmed revolver ammunition

The plastic moon clips can not be made thin enough to fit between the rear of the cylinder and the recoil shield.

This is not an issue for revolvers that are chambered for traditional rimless auto loading cartridges as they have a very large space between the rear of the cylinder and the recoil shield to accommodate the extractor groove

Because the plastic clips do load and unload with less force, the cartridges are likely to pop out of the moon clip if it is dropped. I have also seen ammunition pop out of the plastic moon clips when a batch of them are carried loose in a shooting bag.

Moon Clip Cylinder Problem

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H Richard

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