Copied from my post on SigTalk

I purchased a SIG516 Gen2 last year, and right out of the box (yes I completely stripped, cleaned, and lubed it beforehand) it had short-stroking malfunctions, the same reported by some other owners.

To start... the rifle would function perfectly, on the normal gas setting, no malfunctions at all... ONLY with Federal "green tip" XM855 62gr 5.56. With this ammo, I had NO issues at all, however...

With ANY other ammo (all .223 and even 55gr 5.56) the rifle would short stroke and have failures to feed, and failures to lock back on empty magazine. The fail-to-feed would often result in a full on jam, due to me half-assedly pulling back the charging handle to check if it had failed or not.

If I set the gas valve to the "adverse" setting, it would at least reliably feed 55gr 5.56, but still fail to lock back on empty, and still fail in both ways with .223 ammo of any brand.

Now, I read quite a bit about this, mostly here and on AR15.com, and I tried many of the suggested fixes for these issues.

I tried the "leaving bolt locked back for days" trick, and stored my rifle with the bolt locked back, in fact, ALL the time for the first few months that I had it. This had no effect, so I actually purchased TWO new buffer springs, and tried them both out, after reading that perhaps the stock spring from factory could simply be too stiff/too long and never "break in" no matter how much I shot it.

I also forgot to mention that I certainly tried "breaking in" the rifle, and now have at least 500 rounds through it.

After both new springs failed to resolve my issues, I sent in for an RMA, and (very reluctantly) shipped my rifle to Sig for repairs. They sent it back a few weeks later, with their report stating that they "polished the feed ramp", fired one full 30 round magazine of 5.56 "NATO" rounds through it, with no malfunctions. I had SPECIFICALLY told them that it was .223 and 55gr ammo that was causing malfunctions, but all they would respond with is that the 516 was meant to fire "NATO" rounds.

This, to me, is unacceptable when other SIG516 owners, (not to mention countless other AR-15 owners, including MUCH cheaper, supposedly lower quality rifles) are firing any and all .223/5.56 ammo through their rifles with NO issues. Obviously, if their rifles are doing it, then there is a problem with mine. Sig did not seem to agree, or care about this at all. When I asked to actually speak with the gunsmiths who would be working on and testing my rifle, so that I could explain to THEM directly how my rifle was behaving, I was told this is not allowed. That's to be expected, but still didn't make me happy.

So now I still have a broken rifle, and I obviously I really want to get it working like any other SIG516, or high quality rifle (spent the MSRP $1600 for mine), so that it can fire any and all .223/5.56 ammo, with the exception of steel case, because it seems almost EVERYONE agrees that steel is junk and even GOOD rifles malfunction with it often.

So, my last ditch theory is that the problems are coming from the gas block/piston system. I believe that either:

a. the holes on the gas block and barrel are misaligned, and therefore not letting enough pressure into the gas valve

or

b. one of the holes, either on the gas block, or on the barrel, is poorly machined, or blocked in some way, and again resulting in not enough gas pressure entering the valve

I believe SIG knows this and doesn't want to put the time into removing my gas block and actually fixing my rifle with machine work, so they simply send it back after running a dremel buffer over the feed ramp and chamber.

What would you guys recommend? Should I send it back to Sig... AGAIN, and risk them "polishing" my feed ramp and sending it back with no improvement, or should I take this into my own hands and disassemble my rifle and fix it myself?

Had to split this into 3 posts and reply to myself because AR15.com won't let me post more than 2000 characters for being a new account.

If you run a few hundred rounds of the good ammo through it I bet it will "smooth out" and start running well with the weaker ammo.

Like I said, that's already been done. I've run at least 300 rounds of 62gr XM855 through it, and it still fails on anything other than the green tip 5.56.

Basically my question is, is it a completely stupid idea to try and take my own gas block off myself?

For $1600 you probably could have found a PWS Mod 1, which is twice the rifle the Sig is. I love my Sig pistols but would never buy one of their rifles.

I have 2 Sig 516 and never had any cycling problems. Shoots cheap steel Tulammo.

Send it back and ask them to test it with the ammo you're having issues with.

Do you know what weight your buffer is?
Have you tried a lighter buffer?

When building my AR with an Adams Arms piston, I was having the same issue. I had an H2 buffer in it, along with vltor A5 receiver extension.
Initially I was using an H2 (5.3oz) buffer. Then I picked up an H1 (4.56oz) buffer, and haven't had a problem since.

To simply test it out, you can take your buffer out, punch out the pin that holds the plastic cap on, then remove one weight from inside the buffer. Put it all back together then try it again.

I bought three recoil springs from different manufacturers and had few from different stock makers and nearly everyone was different and they were all meant for a carbine collapsing stock. Springs are cheap I'd buy a selection and try them out. You want a spring with more wraps; a longer spring is actually weaker. Thinner wire is of course weaker too. And if that doesn't work you can try cutting a coil off that makes for a stronger spring but less preload which will get the bolt moving faster.

Keep sending it back to them until they get it right.  It is their product, and their responsibility to stand behind it to make it work, not yours.

If you cycle it by hand, do you notice any drag?  I had a tight lower on a build that would function if I pulled the rear pin so it was loose.  Short stroke is either binding or not enough gas.  Every once in a while a dog gets out the door, they sold my new to me PWS without an op rod.  Your rifle should function on anything you put in it, period.

I"m not sure if you have access to one, but try the LWRC bolt carrier in place of the SIG modified bolt carrier. The 516 was originally designed with the original heavier carrier (the revised carrier is a little less than 2 oz lighter). Please snap macro pics of your piston operating rod of the gas holes, feed ramps, and interior upper so we can compare. Also, wipe down your components with alcohol and throw some Fireclean on it as it will help with any drag/friction issues. I have a GEN 1 that has been running flawlessly. The lower powered 223 ammo does not gaurantee 100% bho.

recoil spring and a lighter buffer...bet it works then.

Make Sig fix this.

I had the exact same issues as you described and honestly its sorry to hear that these issues are still occurring with their product.  I asked them polish my feed ramps and they determined to put in a "larger gas piston system".  I put larger gas piston system in quotes because I don't have the invoice handy to reference the actual line item .  However when the rifle was returned to me there was a completely different gas piston selector dial at the front of the gas piston block, feed ramps clearly polished.  After this fix the rifle has run flawlessly through at least 1500 rounds shooting AE 55 gr.

The rifle has redeemed itself in my eyes, but I'm not 100% on how I feel about Sig's QA.  I just ordered 500rds of Silver Bear which is a stepping stone for me in terms of trust in this rifle as it choked very bad on Tula, pre-warranty repair.  In my opinion a rifle purchased the for reliability of a piston system should eat steel case 5.56.

Anyway, I know it sucks to be without your rifle for 2 weeks (again), but...  Make Sig fix this.

To me, the rifle sounds like it was designed to use the original, heavier gen 1 carrier and all of the issues have come from the forced redesign of the carrier.

My gen 1 is the ever ready bunny. It just keeps running and running.

I cleaned it once.

Once.

I have a new Gen 2 I just picked up and it has ran flawlessly right out of the box.

I have had very good luck with my sons 516 gen2 , eats everything , every time.

Other than being a little front heavy , I can't complain about anything.