A while ago I picked up a NIB Sig P938 SAS. Sweet little gun.

I was shooting it at the range, probably at about 500 rounds (total), and notice the trigger getting progressively heavier and heavier, to the point that it became obvious there was a problem.

But, the cause of the problem wasn't obvious.

I took it home, gave it a good cleaning, and with dry firing found that the trigger was still very heavy.

I did a complete disassembly and discovered the problem is with the mainspring housing.

The mainspring housing on the SAS model (not sure about other models) is made of plastic. It has a "nub" (that's the technical term) that goes into a hole in the sear spring, and keeps the sear spring in its proper place. As you can see in the picture, this nub has started to wear down:



Luckily I happened to have an aluminum mainspring I had bought and just not got around to install yet:



This is what the nub should look like from the side:



And this is what it looks like installed in the gun:



Everything is back to working the way it should.

Warning: replacing this part requires a pretty complete disassembly of the gun.

I'm a little disappointed in Sig, but, that's the way things go sometimes I suppose. I had already purchased the aluminum MSH before the problem came up.

ETA: Just did a little googling and it looks like this is a fairly common problem.

Thanks for the informative post. I've just started looking into 938s and had heard mention of replacing msh with aluminum but hadn't really seen or read why, so I really appreciate the post. My understanding was that this problem was primarily in the earlier 938s and not so much the new stuff, but when I get one I think I'll just go ahead and get an aluminum msh. Do any of the models come from the factory with aluminum msh or are they all plastic? I've been kinda favoring the SAS, but there are a ton of 938 models...

I believe they all have the plastic MSH, but I am not 100% sure about that.

Does the 238 suffer from the same issue?  Mine takes a gorilla to squeeze...

It may be NIB but it looks like it is the design from a year or two ago. The gun may have been sitting on someone's shelf for some time.  It is/was a known problem with certain P938's. Mine is the same design but I have never had the problem. SIG redesigned that MSH and sear spring assembly. It you ship it to them, they could install the newly designed one. Problem fixed.

This has NOT been a problem with the P238.

The only difference between P938 models are the colors and grips. The internals are all the same. Before you order any parts, especially if you have a newer one, check that you do not already have the redesigned MSH and sear spring. You may be buying parts you don't need.

I posted this months ago but my 238 G10 MSH failed and locked up the trigger.  I bought a 938 and replaced the MSH immediately.

Good info. I am bouncing between a Sig 938 BRG, a ported 9 Shield Tritium, or a Kimber Micro 9 for my next purchase.

Is this a free fix for existing owners? This is why I have stayed away from guns without lifetime warranties, (Kimber).

I don't know, I replaced mine with an aluminum MSH from hogue.

It should be a warranty fix for the original owner. On another Forum some of the users who sent the 938 back for other minor issues had the MSH replaced automatically by the factory without even asking. It may be something they automatically check for. I can't say for sure.

They do not.  My Extreme came with a G10 housing.  I think some models may have an aluminum housing, but don't quote me on that.  

I do not think the Hugue G10 grips have anything to do with the MSH. You can change the grips to whatever you want for whatever look you want. It does not affect the internals. I bought a Blackwood and changed grips to Rosewood to match another gun I have. Did not touch the MSH at all.

If you have the older original MSH/Sear Spring design, the best thing to do is get it back to SIG and have the new design parts installed.  I think they may sell the parts that would allow you to change it yourself. Call and ask. You can search online for photos that show the difference between the two.

Technically no, but if your grips came G10 then so did the MSH and that's what broke on my 238.  My 938 was g10 but the grain was opposite from my 238, replaced it anyway.

I looked at the Hogue site and see the difference. Interesting enough, the MSH they sell only works on the new design spring, not the old. If you buy a new MSH from them, you need the new design sear spring also.

http://www.hogueinc.com/grips/sigsauer/p938/mainspring-housings

I read that too but my 238 was old and my 938 was different, worked on both so I don't know.

This is a known problem.  I had to replace my 938 MSH twice.
Sig has an updated version.

I havent noticed it in my 238, I have 2500+ documented round through mine that is 5 years old, my trigger pull is still good to go and breaks at (guessing) a touch above 5lbs.