I have noticed some of the older models have what appears to be spot welds along the rails while the newer ones appear to have these missing. Anyone know if there is integrity issues without the welds or was it originally over engineering by the Swiss? I love my 556 I got just checking to see if anyone knows if SIG Sauer reloved them for cost cutting or did somthing else that didnt require the welds. I have noticed on the original 550/551 receivers Ive found pictures for the Rails appear to be in 4 separate pieces two for the left rail one for the right and the rear trunnion the 556 appears to be a solid piece welded across the bottom.

I have 2 older Classics with the spot welds. There have been posters here which had issues with the rail coming loose on the non welded guns, but it seems to be very, very rare. They must have found some other technique to secure the rail without the visible spot weld.

I might attempt to get a hold of SIG and see if they will bring some insight.. probably not but still want to know if they did something that produces the same effect.

Definantely a decontenting/cost saving move on Sig USA's part. It appears they are relying solely on a bead of weld running along the bottom of the receiver now. The Swiss guns had the roset welds for a reason. Mine is an older piece and does have them. It has coiled roll pins at the gas block also v the current standard pins(another little change they slipped in).

surprisingly mine has the coiled pins (looks like a C). Hopefully there is a bit more to it but it does appear your correct. I do hope it holds up the way it is but time will tell and it does appear to be some quality welding work.

i wrote up a big thread on mine quite some time back. it was a gun that i [regrettably] SBR'd, only to find the issue after the fact...

in my case, the rail on the ejection port side of the gun had, for one reason or another, drifted down and away from the receiver being that there was no weld to hold it where it should have been held. the result was the bolt head impacting the surface of the front trunion that should have been contiguous to the rail, peening the bolt and the trunion. i can only surmise what the long-term ramifications of this would have been. i also noted that the receiver itself lost quite a bit of structure with the rail no longer being welded; being that it's only sheet metal you could squeeze the receiver by hand around the ejection port area and bend the receiver wall in a good bit.

my gin seems to have been a "transition gun" of sorts, as all the guns i was seeing in shops at the time i discovered the issue were completely welded. bear in mind that when i discovered the issue was about 6 or 8 months AFTER i bought the gun. (i ran some rounds through the rifle after i bought it, filed my forms, bought and made tools, got my barrel shortened, and found the issue when i was putting the gun back together.)

in the end, sig wasn't going to touch the gun since i had monkeyed with it quite a bit at that point (i don't blame them. the seal was most-definitely broken at this point). and i didn't feel the gun was worth anything more than a "wall hanger" in the condition it was in. since i wasn't satisfied having that much time, money, and effort tied up in a "wall hanger", i ended up milling the receiver and welding the rail.

it turned out well enough that i feel any competent gunsmith can do this, probably substantially better than i did.

the other issue i ran into, which turned out to be a bigger cluster-fuck than the receiver itself, was the rubber dust-covers... i melted one while welding the receiver. i could have easily avioded this had i been paying a bit more attention, but i destroyed one. while sig offers a service to replace these as a warranty issue, they will not do it otherwise. this left me to order some new dust covers and rivets, and devise a new methodology, and design and make a special tool for installing them. it took several iterations to get the tool working correctly, and getting the rivets right took about 1/3 of the total time of the project (think: several months). had i paid a little attention i could have avoided this altogether, but, hindsight and all.

anyhow, in the end i refinished the gun and piece it all back. had i known there was this issue with the receiver, i probably would have never purchased the gun to begin with,. considering it was going to be SBR'd and all. i'm at a weird place with that gun since i'm not satisfied with the current state (i wanted to do a full 551 conversion, using a 551 parts kit, welding the holes in the top of the receiver and adding the correct swiss sight, as well as the swiss lower), but i also don't want to invest anymore loot into that receiver. i've put several thousand rounds through that gun since the rebuild and it runs 100%, but... i don't know.

anyhow, i'm getting off-track here. here is a picture of the completed gun:

After all that, and it still looks great!

you should see it in person.

it looks, and runs, perfect. now.

i've just come to believe that SIG has done a really substandard job on what should be an unbelieveable firearm.

Damn. I have heard some stories about the rails without the welds drifting but a lot with no issues. I started looking for SIG 551/552 pictures etc and noticed that it goes back and forth with the pictures i see too with the welds. A lot have them and quite a few don't. Is it really a work around to be cheaper or is it another way to do it (the spot welds used to make sure the damn thing is on there in case the others didn't take properly etc.). Hopefully i don't run into this problem and have to rebuild it, but then again I'm sure with what home gunsmith work I have done it should be doable. Nice rifle though to bad it took that much work.

i wouldn't worry about it unless you are having alignment issues.

as far as why they decided to skip the welding... i don't know. i thought mine was a "flier" when i noticed as nobody else had seen one like that, and seemingly newer guns at the local shops all had the welds. it was only later i found out that sig had recently changed their process.

after i got mine back in one piece and ran the hell out of it, i decided that if i got another, i'd poach a used one that had the correct welds. that may be what i do when i finally suck it up and buy a 551 kit.

The way it looks if it hasn't fallen apart after 650 rounds it probably isn't going to. or at least i hope so. The welds look well done so I hope it doesn't decide to crap out on me. I love these rifles though just wish SIG wasn't being cheap with things. Got my Swiss folder and likely going to  turn the pos one into a target.

I just checked mine and I don't believe mine was welded.  Mine is an early release JS003xxx and I have 4 torx screws that seem to hold the rail on.  Is that something Sig started to save money?

We are talking about the Bolt guide rails and not the Top accessory rail. Don't think SIG welded any of the top rails.

another bad decision IMHO, especially considering the reports of threaded inserts pulling out coupled with the fact that ALL sighting provisions are attached via the rail.

Quite true, But I have found a friend in JB weld.