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Discussion Starter · #1 · (Edited)
I owned a 8” Gen 2 MPX and wanted to have a 4” to go with it. Over time I have been gathering parts. I bought a new upper receiver from Sig a while back. I got the newer version which is the gen 3 upper. When I tried to run my Gen 2 BCG I found it would bind on the new ejector of the Gen 3 upper.

So waiting for ever I Sig finally had the BCG in stock so I ordered it. I recieved the Gen 3 BCG. This BCG runs smooth as silk in the Gen 3 upper.

So to anyone trying to build up a new Upper receiver for their MPX it’s going to work and run best with the latest gen parts. Trying to mix Gen 2 with Gen 3 parts in the upper will cause problems in my experence.

FWIW, I have not tried the G3 BCG in the G2 receiver.

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Thank you for this info. I have a gen 2 MPX and would be interested in compatibility between gen 2 receiver and gen 3 BCG.
 

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Did you buy and used the black recoil pad from the Gen 3 for use with your gen 3 upper receiver/BCG on the gen 2 lower? I asked this because the gen 3 BCG rear opening is specifically cut to the contour of the gen 3 (black) recoil pad which is a bit different compared to the gen 2 (orange) recoil pad. They work but you can see the difference between the shape of the pads.

I tested the compatibility of these between my gen 2 and gen 3 MPXs by swapping uppers and recoil pads without any problems at all.
 

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Discussion Starter · #5 ·
Did you buy and used the black recoil pad from the Gen 3 for use with your gen 3 upper receiver/BCG on the gen 2 lower? I asked this because the gen 3 BCG rear opening is specifically cut to the contour of the gen 3 (black) recoil pad which is a bit different compared to the gen 2 (orange) recoil pad. They work but you can see the difference between the shape of the pads.

I tested the compatibility of these between my gen 2 and gen 3 MPXs by swapping uppers and recoil pads without any problems at all.
I had a spare Gen2 rear spring retainer and just used that so the Gen 3 retainer was not an issue. I’m using the standard recoil pad for the Gen 2.
 

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I had a spare Gen2 rear spring retainer and just used that so the Gen 3 retainer was not an issue. I’m using the standard recoil pad for the Gen 2.
That’s great. Thanks. At least it reinforced my testing.

I am using the Taccom recoil pad on my gen 2 When I swapped the uppers between the lowers.

Heres a pic of the recoil pads. Black gen 3 on top and Taccom recoil pad with spring on the gen 2 (lower pic).
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Discussion Starter · #7 ·
That’s great. Thanks. At least it reinforced my testing.

I am using the Taccom recoil pad on my gen 2 When I was swapped the uppers between the lowers.

Heres a pic of the recoil pads. Black gen 3 on top and Taccom recoil pad with spring on the gen 2 (lower pic).
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It does make you wonder what the purpose of the notch and the tab on the spring retainer are. Seems completely unnecessary in my mind.
 

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When the MPX was announced, I was one of the "TAKE MY MONEY PLEASE" people. Right up to the release when they fumbled with the Gen1 and Gen2 versions. I am wondering if the bottom upper is actually a Gen 4 (or higher) since upper looks really different below the red dot from what I've seen. But seeing all these Gens in guns, and hearing there are issues with parts being swapped between them, how can I feel comfortable relying on a platform that this time next year might be on the next gen and spare parts or even the factory upgrades have gone the way of the dodo, assuming they existed in the first place. I wish Sig would stop using us as their unpaid beta testers and make sure these guns that are designed for .mil/.gov agencies are bombproof before releasing.
 

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Lots of my questions answered. Thanks.
 
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When the MPX was announced, I was one of the "TAKE MY MONEY PLEASE" people. Right up to the release when they fumbled with the Gen1 and Gen2 versions. I am wondering if the bottom upper is actually a Gen 4 (or higher) since upper looks really different below the red dot from what I've seen. But seeing all these Gens in guns, and hearing there are issues with parts being swapped between them, how can I feel comfortable relying on a platform that this time next year might be on the next gen and spare parts or even the factory upgrades have gone the way of the dodo, assuming they existed in the first place. I wish Sig would stop using us as their unpaid beta testers and make sure these guns that are designed for .mil/.gov agencies are bombproof before releasing.
Unfortunately, that’s Sig’s business model. It’s cheaper for them to have us as beta testers while making money in doing so.

With that said, I still like my gen 2 (8” sbr) and my gen 3 16” competition model. Both had been very reliable especially my 8” with almost 20k on it. I use them both in competition so reliability is very important. Cleaning them every 1000 rounds makes a huge difference in making sure both of them work well.
 

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Discussion Starter · #14 · (Edited)
When the MPX was announced, I was one of the "TAKE MY MONEY PLEASE" people. Right up to the release when they fumbled with the Gen1 and Gen2 versions. I am wondering if the bottom upper is actually a Gen 4 (or higher) since upper looks really different below the red dot from what I've seen. But seeing all these Gens in guns, and hearing there are issues with parts being swapped between them, how can I feel comfortable relying on a platform that this time next year might be on the next gen and spare parts or even the factory upgrades have gone the way of the dodo, assuming they existed in the first place. I wish Sig would stop using us as their unpaid beta testers and make sure these guns that are designed for .mil/.gov agencies are bombproof before releasing.
I hear ya, I wasn’t all to pleased finding out I needed to get a second BCG for the upper I bought. Sig has a very tarnished image with allot of it’s past fans. I was a true fanboi at one time, then I bought a lemon 938.. Also my US built 9mm Sigs aren't nearly as accurate as my older german 40sw sigs. With the MPX, I was looking forward to a 40sw and a 45acp version… Yea that will never happen now.
They are full of broken promises and creating obsolete guns that are only a year or two old.
 

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Based on these photos, my MPX PCC is a combination of gen 2 and 3 parts. The upper receiver is a gen 2, while my BCG is a gen 3. Then looking at my MPX 8 inch that I recently bought, it does not come with MPX trigger, yet has the gen 3 upper receiver with MLOK HG, and gen 2 BCG. Wondering about reputation now that it seems they just mix up parts.
 

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Based on these photos, my MPX PCC is a combination of gen 2 and 3 parts. The upper receiver is a gen 2, while my BCG is a gen 3. Then looking at my MPX 8 inch that I recently bought, it does not come with MPX trigger, yet has the gen 3 upper receiver with MLOK HG, and gen 2 BCG. Wondering about reputation now that it seems they just mix up parts.
That sucks. Rest assured though that even though they’re mixed and match sets, they’ll still work. However, it’s not great to find out you bought expecting them to be in a certain configuration yet find out that they’re not.

Have you tried emailing Sig CS about it? By the way, welcome to Sigtalk.
 

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Discussion Starter · #17 ·
Based on these photos, my MPX PCC is a combination of gen 2 and 3 parts. The upper receiver is a gen 2, while my BCG is a gen 3. Then looking at my MPX 8 inch that I recently bought, it does not come with MPX trigger, yet has the gen 3 upper receiver with MLOK HG, and gen 2 BCG. Wondering about reputation now that it seems they just mix up parts.
Do they function? If Yes, then they are fine.. Gen3 is commonly refered to as a conglomeration of changes Sig has made since the Gen two design came out. Sig does NOT recognize a Gen 3, why? I’m guessing because all the assemblies should function well together no matter if it’s a 2 or 3.

Just because my Gen 2 BCG was binding in my Gen 3 upper, doesn’t mean yours will.. In this case if it’s working it’s not broken.
 
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