So I sprung for one of these a few years back when they hit the market and, overall, love the rifle.  I'm one of these weirdos who doesn't care much that it takes a proprietary mag.  In fact, that was part of what made the decision for me as I wanted one as close to the Swiss-made 551 as I could get.  I've got many different types of rifles including AR's and AK's, so the AK-style release is somewhat natural to me anyway.

So there is a roll pin that fits the mag/thumb release to the bottom receiver.  It's the roll pin that the mag release obviously rotates on.  I didn't have any problem for the first few years but, lately, the roll pin seems to have been coming loose.  After a few mags it tends to have a lateral movement and unseat itself.  When it does, it leaves the release somewhat to the rear and doesn't allow the mag to seat itself.  I have to use a punch and something to lightly tap it in order for it to fit back into its proper position.  Upon close inspection, it seems the roll pin isn't quite long enough to fit flush with both sides of the receiver.  If that were the case, it likely wouldn't have that effect.  

Anyone else experience this problem?  If so, is there a part available from SIG that would rectify this i.e. a new roll pin.  I've removed mine and tried to widen it some with hand tools but the tightness of it seems to be less of an issue than the fact that it seems to be a millimeter or two too short.  I haven't contacted SIG yet but likely will soon.  Any weigh-in would be appreciated.

This was a pretty well known issue on the early 551-A1's and IIRC, Sig did a recall, but I can't find a citation for that so maybe I dreamed it.

I too recall the change from the problem you are having. You are not the first. But as the other member stated, I am not sure what sig did to change it but I do know they did. Good luck.

I believe they changed it to a rivet.  That's what mine has.

Andrew

As usual, you guys came through and thanks for that.  I contacted SIG Customer Service yesterday while I was at work and the rep was very accommodating but said that's the first he's heard of the problem.  He stated it would be no problem for them to send a part, if a modified one does exist, or they'd be happy to take the rifle back and fix it under warranty.  He suggested I look at the schematic on the back page of the manual but the schematic is so small the part numbers for the lower receiver are illegible.  

I'm going to contact them today and see if I can have one of them research the part number for me.  Seemed very pleasant to work with so far so I will update when I have more information.

Thanks again, hive!

I can say that the 551A1 lowers that were sold in the aftermarket a while back all had a mushroomed rivet installed in the mag release. The one that I bought from CTD earlier in the year was that way.

I checked mine, and it has the rivet instead of the roll pin.  I got mine soon after they came out.  The S/N is 32XX.  When did they make the switchover?

I too have the roll pin but haven't had any issues with it. Granted I have shot it all that much. Will def keep an eye on it tho.

Just to give an update (and not a particularly exciting one), I contacted them last Friday and was told to e-mail them pics of the the roll pin and receiver so the rep I spoke with shot me a blank e-mail in which I responded with a couple cell phone pics and the serial number yesterday.  I'm awaiting further response but haven't heard anything back yet. They were pretty quick to send a follow-up e-mail requesting the serial number yesterday morning but haven't heard back yet.  I'll give 'em a few days and post when I hear something.

So here's the latest update: I finally received an e-mail back yesterday from the rep I was speaking with.  I was told there was a modification using a rivet instead of a pin and they could fix this if I return the rifle for a nominal fee so I'm getting the process started.  I'm assuming it's going to be kosher to send only the lower.  Seems a lot easier.  Will advise when there are new developments but, so far, this has been a fairly pain-free process and they seem to want to make good on it.

So here I am at the end of it all. FedEx sent me a shipping notice at the end of last week to advise that my lower has been shipped 2-day air mail.  They don't deliver on Sundays so I worked from home yesterday and the package showed up.  Upon inspection, everything looked good.  There is now a rivet where the roll-pin used to be.  It's flat at one end and has been peened at the other end.  Overall, it looks plenty solid.  I put the rifle back together, quickly cycled a mag in and out of it and seemed to hold and move just fine.

This has been my first experience sending a firearm or part of a firearm back to a manufacturer for repair and I'd have to say it went very smoothly.  The folks at SIG seemed very friendly, very professional and very helpful.  I would expect the manufacturer would stand behind a product I paid so much for but we all know that's not necessarily to be expected from everybody so good on them.  Hope this story helps somebody out in the future because I still think this is a great rifle system.

I have the old role pin, can you post a picture of the new rivet so I can see what they did to change.

Are 551A1 lowers still available from sig?

I'll try and remember to post a before and after pic if I can find them later.