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Discussion Starter · #1 · (Edited)
Sig Sauer 516 Review with Problems and Issues with Shooting:

FTF, Cycling and Locking Open, Fixed, Solved with Buffer Spring



I have two Sig Sauer 516 rifles. Both had the similar problems that are posted all over the web about not firing correctly with not feeding in the new rounds (FTF), so not cycling correctly, and after the last round is shot, failing to lock the bolt open.

There have been many excellent posts about suggestions of how these issues were fixed. Some worked and others didn’t…, and many were still confused, often sending their upper or entire rifle back to Sig Sauer 1-2 times. I have analyzed many posts and my two Sig 516 rifles and others…, and did testing and experiments to find the exact cause of the issue and how to fix it. I did not want to have to send in my rifles to Sig. I wanted to completely understand and know my rifles. I did a thorough initial cleaning and re-lubing…, so I KNEW it was not the cleaning and I was NOT going to clean the rifles again.



Sig Sauer 516 Review with Problems and Issues with Shooting:

The Issue: Straight to the point: Buffer Spring Weight too Tight (for .223 ammo, usually not 5.56)

Some of the buffer springs are too tight from the factory and not all the springs have the same tension/weight, so that is why some fixes worked and why some rifles shoot the .223 ammo perfectly, while other rifles do not operate correctly when shooting .223 ammo and do not cycle correctly or lock open.

Read the above sentence slowly, it shows why there is a great variance on why some rifles work perfect and why others do not…., I will write it again…, “not all the buffer springs have the same tension/weight.”

These buffer spring variances can greatly affect how the rifle acts when firing .223 ammo due to its low pressure. So when .223 ammo is shot, there is not enough pressure to push the bolt back far enough to load the new round and there is not enough pressure to lock the chamber open after the last round. Some of the springs are too tight from the factory for some .223 brands.

Generally, the Sig Sauer 516 shoots fine with 5.56 rounds due to the higher pressure from the 5.56 ammo, which the spring variances do not affect.



Sig Sauer 516 Review with Problems and Issues with Shooting:

How to Fix Sig Sauer 516 FTF and Chamber locking when shooting .223 ammo: (a few ways):

1. Sometimes just a good cleaning and lube makes everything glide easier
- Clean the black packing grease off the bolt, inside and out, re-grease or oil
- Remove gas seals from bolt (they are not needed and confirmed through Sig that they are not needed and simply come from the factory like that). Removing the gas seals might make things slide easier. I left mine in and just wanted to focus on the springs.

2. Shooting 5.56 ammo for a while until the buffer spring is broken in and looser, then switch to .223 if you want due to the cheaper cost of .223 ammo.

3. Shoot .223 ammo on the Extreme Gas setting. Using Extreme gives another 1 to maybe 2 lbs of blow back pressure (when using .223 ammo) and will help loosen up the spring. Switch back to Normal Gas pressure after spring is looser. This works on some of the tighter springs, but not all, because using the Extreme Gas setting when using .223 ammo only mildly affects the added pressure. Do not be worried about using Extreme setting when using .223 ammo, from my testing, the extra blow back pressure is only around 1 lb (more or less) of extra pressure, which is not much. Now using 5.56 ammo might give you 2 to 3+ lbs of more blow back pressure and that is why in the Sig manual, it is stated not to use it for a prolonged time. The Extreme setting is there to use for when you are in battle and get the rifle wet or dusty or muddy or bloody (which all can cause friction on the bolt and components sliding back), and you need to override that added friction from the dirt, blood, mud, etc.

4. Shooting heavier .223 ammo (above 55 gr.) might work until the spring is broken in and is looser. Sometimes however, on the super tight springs, this still does NOT work. Use 5.56 ammo instead which has more pressure.

5. Leaving the chamber locked open for a day to a few weeks breaks the spring in and makes it looser, it actually loosens it up by a few pounds over time enabling to shoot .223 ammo.

6. Instant Sig Saur 516 Fix: Cut the buffer spring: Cut 1/2” to 1.5” (more or less) off the BOTTOM of the spring, NOT the top. Works instantly. It relieves about 1 lb to 2+ lbs of pressure (defends how much you need to cut) to allow shooting .223 ammo with correct feeding of new rounds and locking the chamber open. There have been several posts on doing this where local gunsmiths and local gun shop workers have done this, simply cutting off around half an inch to1.5 inches off the bottom of the buffer spring. All have proven successful. Super tight springs might need 1.5 inches cut off.

Note: Things to understand when cutting the spring
1. I would only shoot .223 ammo if you cut the spring. First cut half an inch to see if that works. If not, cut more. If you decide to start shooting straight 5.56 ammo (which has a higher pressure), then replace the cut spring with a new carbine spring. A cut spring (over time) will be too loose for 5.56 ammo and “over time” could damage the piston rod components, that is why Sig Sauer will NOT cut the buffer springs because the gun is made to be efficient for 5.56 ammo.
2. Over time, with keeping the chamber open and firing rounds, the buffer spring loses strength by a few pounds of compression strength.
3. Carbine springs are only $4 to $10 to replace, so when you want the gun back to original specs or want to shoot 5.56 only, or super heavy .223 loads, simply replace the cut spring with a new carbine spring.

The Sig Sauer 516 rifles were designed to shoot thousands and thousands of the 5.56 bullets and were tested FIRST with 5.56 bullets which have a greater pressure than .223 bullets and so 99% to 100% of the time the rifle will shoot fine with 5.56 bullets regardless if the buffer spring is too tight because the high pressure of the 5.56 will override the springs tighter weight.

Now…, after the Sig Sauer company tests with rifles with 5.56 bullets, they then test with the .223, which…, at the company, work fine with the rifle…, why…, because the springs by that point are broken in and are looser so the .223 bullets shoot and feed fine and locks the chamber open on the last round. That is why Sig Sauer claims no issues with the gun. Also…, there are variances of the springs…, so many of the springs are perfect to shoot .223 ammo with right out of the box, while other springs are 1-3 lbs heavier in compression weight and will not shoot .223 ammo correctly.

All it takes is 1-3 lbs of too much buffer spring weight to cause the bullet feeding issues (FTF) and chamber locking issues when using .223 ammo. Sometimes the buffer spring might be only half a pound off from working correctly, so that is why a good cleaning can sometimes do the trick. That is also why some people send in their rifle to Sig and Sig cleans it and polishes and shoots it and suddenly it works, because only half pound of difference was needed to fix the issue, but other times, Sig gets the gun returned with a super tight buffer spring, does all of that, and then fires 5.56 ammo through it and there are no issues. Sig sends it back, the owner fires .223 through it and there are issues. Again…, all due to a tight buffer spring and .223 ammo having a lesser pressure compared to 5.56 ammo. There can be 5,000 psi to 25,000 psi. difference between .223 ammo and 5.56 ammo. That is why people using 5.56 ammo experience no issues with the gun.

When using .223 bullets on new springs, because .223 ammo has less pressure, some rifles will feed the new bullets fine and lock the chamber open fine (because those particular rifles happen to have looser buffer springs) while other rifles will NOT shoot the .223 ammo correctly because those springs differ with a greater tightness from the factory and the low pressure of the .223 bullet cannot override the tighter springs. The rifles with the tighter buffer springs then fail to feed new rounds (FTF) and the chamber does not lock open after the last round because the bolt is not pressed back far enough for either action to occur correctly.

I did tests on several Sig Sauer 516 buffer springs with testing the weight of the springs with being pressed back at 2” and then at 3”. Each new factory spring tested differently!!! Some were 1-3 lbs tighter at both the 2” mark and 3” compression mark that I tested them at. So there could be up to a 3lbs. difference between spring tightness.

See Below for Spring Weight differences per lbs. at 2” and 3” compression between different factory buffer springs from Sig Sauer for the Sig Sauer 516:


Note: The Sig Sauer 516 shot 5.56 ammo fine with all springs. The .223 ammo shot fine with only the looser springs. There was up to a 3 lbs difference between the various springs tested.

1. 2” compression: 6lbs and 9lbs on the various springs tested (up to a 3 lb difference)
2. 3” compression: 8lbs and 11lbs (up to a 3 lb difference)
- Again, 5.56 ammo shot fine on all springs. .223 ammo only shot fine on the looser springs.

I hope this info helps out all the people that were frustrated thinking there awesome new Sig Sauer 516 rifles were broken with failing to feed (FTF) rounds from the magazine after being shot and failing to lock the chamber open. All the trouble comes from a simple part…, a too tight of a buffer spring that makes the gun very temperamental with shooting .223 ammo. Simply break that spring in, or cut it, and all will work fine.

Overall, the Sig Sauer 516 is an awesome gun. I love it and would recommend it. Sig Sauer company just needs to fine tune some quality control and testing.
 

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Discussion Starter · #3 ·
You are welcome..., glad you liked it. Spread the word to all the frustrated 516 owners. I know I was frustrated. And thanks to all the people that also posted thoughts and ideas which helped me test things out.
 

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Discussion Starter · #5 ·
Hello mrbossman,

Not sure about Sig sending you another spring. You can buy a spring on Amazon for $10 or less. The stock spring seems and looks exactly like any carbine sized spring and I did test my other non sig carbine springs and they were the same. Why did you want another from Sig? To have an extra or were you hoping the new one might work better?

Did you try any of the options I mentioned to soften the spring you have? If you want to tinker with a spring other than the stock then just buy any carbine spring and use that one to cut and try.
 

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Discussion Starter · #8 ·
What method are you using to test spring pressure? Is the 516 buffer spring flat wound like the 716 spring or is it a more traditional buffer spring?

I sure hope you're correct in that all of the machining/parts are correct and it's simply a matter of wearing a spring in. That would be the best thing for owners of the rifle. This doesn't say much about Sig to me though, I understand that they probably source these springs from a supplier, but you have to wonder about a company that would allow their product to take such a beating from a word-of-mouth standpoint because of a part that probably costs them $1.

You would also think they would do some QC testing of the parts they're getting from their supplier and finding the variance as you have. You'd also have to wonder why in the world their testing wouldn't be more thorough, this would allow them to discover their issue and make a change so that their customers don't end up frustrated and they as a company don't have to pay shipping on so many rifles to get them back for repairs.

For my part, I really like the overall design of my rifle (716) and I want it to be reliable and fun (I bought a piston gun for it's reported long term reliability over DI), it's been a frustrating ownership experience thus far. I think my rifle is finally where it should be, but it took me almost a year of shooting, cleaning, sending the rifle in, reading, testing, etc. to get it there, it simply shouldn't be like that. It will be interesting to see where the 516 and 716 end up in a year or two, hopefully they'll come out long term with a good reputation, they seem like well made rifles for what amounts to very competitive pricing if they work right.

Hello MJ91GT,



I have not seen the Sig 716 buffer spring up close so I do not know. The 516 buffer spring seems like the normal carbine spring and looks and seems exactly like my other DI carbine springs. If I mixed them up, I would not be able to separate them.

As far as being correct with what I wrote about, I feel that I am correct for this particular situation. There could be of course other issues that are similar, but for me and my two 516 rifles (and many others), the buffer springs seemed to be the issue with the .223 ammo. The rifles shot fine with 5.56 ammo, but I do not want to shoot with 5.56 ammo due to the higher cost.



Testing your Spring Weight:



I simply took my postage scale, I happen to have a 150lbs scale that weights to the tenth; so for example, I can see the scale showing me 7.25lbs. See below for how I test. I am sure there are other ways…, but this is how I did it. And like many of you, my life is super busy with a wife and kids and work…, so my testing’s are not 100%, but pretty close.



Testing the Spring Weight:

Supplies needed: Scale and tooth brush (or anything similar in structure). Take a ruler and mark the tooth brush from the end at 1”, 2” and 3”. You will use the tooth brush to press down the buffer to compress the spring within the lower. In order to cycle correctly and lock the chamber back, the bolt has to go back around 3+”.



1. Place scale on level hard surface.

2. Remove the lower from the upper

3. Leave the buffer and spring in the lower.

4. Place the butt of the stock exactly in the center of the scale

5. Zero-out the scale with the lower on the scale.

6. Have someone balance the lower from moving side to side but make sure they do NOT press down in any fashion.

7. Take the end of the toothbrush and press the buffer down to where the 2” mark comes level to the top of the lower, simulating that the buffer was pressed in two full inches. Write down the pounds displayed on the scale (should be around 6 to 9 lbs.). Then do the same at the 3” mark of the tooth brush.

8. I tested each mark 3 times to make sure it gave me constant results every time (it can vary each time by around .10 of a lbs, due to your hand not being perfect with pressing down, so I then took the average of the three press downs for every mark measured.

9. I then tested every spring I had and my DI carbine rifles too just for the heck of it.

10. I then slowly started cutting the spring and re-measured the cut springs and wrote down the measurements.

11. I had the “cut springs” measure around 6lbs. at 2” pressed down and around 8lbs at 3” pressed down. That worked for me with shooting .223 ammo. I left my gas rings in the bolt. I did not remove them. I do however know other guys that did remove them, claiming it eased the sliding motion. And it was verified through Sig that the gas rings in the bolt are not needed for the piston drive carbine. They are only needed for DI carbines.

I cut ¾ of an inch off one of my springs and just over an inch off the other.



NOTE: Now keep in mind that every gun might vary a pound either direction as far as what is best for your rifle with shooting .223 ammo because not all rifles are 100% the same within the entire motion of the rifle, different oils, lubes, greases, tightness, leaving gas rings in the bolt or removing them, might all be slightly different for every rifle. So some might have to have their springs at 5lbs at the 2” press down mark and at 7lbs at the 3” mark if their rifle is tight.



Or if someone’s rifle is really slick and easy sliding, then maybe 7 lbs. might work at a 2” press down and 9lbs might work at a 3”. But at least I think you get the point.



12. One of my springs I only had to cut about 3/4 of an inch. The other spring I had to cut just over an inch because it was a much more stiffer spring.



My Story and what I did:

I have 4 rifles. Two are AR 15 DI mid length gas systems and the other two are my beloved Sig 516 Piston Systems.



(Shooting with .223) On Extreme Gas Setting:

When I took both to the range, Sig 516 #1 shot with sporadic cycling (FTF) and Sig 516 #2 did not cycle at all, so every round shot had a FTF occur. And both rifles would fail to lock the bolt open on the last round.

After testing the springs on the scale…, low and behold…, it turned out that Sig rifle #1 had the softer of the two springs (as I suspected), hence the sporadic FTF, so sometimes it would cycle and sometimes it would not, and Sig 516 #2 had a spring that was 1-2 lbs stiffer on every measurement and had a FTF with every shot fired. So that is why I only had to cut about 3/4 an inch off Sig rifle #1 and I had to cut a complete 1+” off Sig Rifle # 2.



After Cutting the Buffer Springs: On Normal gas setting

Both Sig 516 rifles worked completely fine with .223 ammo after my first cut of both buffer springs. They cycled perfectly NO FTF and locked the chamber open. I used the Normal gas setting.



Preparing other Springs:

Ultimately I want non-cut springs in my gun so I can shoot .223 and 5.56 anytime I want, as many times as I want, without the worry of damaging the piston with using 5.56 ammo (this worry might not even be an issue, but who knows). So when I returned from the range I removed my cut springs from the lower and inserted new carbine springs that I purchased and I re-connect the upper and lower together and stored the rifles with the bolts locked open to loosen up the new carbine buffer springs. I did tests on the new springs and after just 1 full day of the buffer springs being compressed with the chamber locked open, the springs lost 1lbs of strength. So over time I will have more springs ready to go.



(Shooting with 5.56) On Normal Gas Setting:

I had no issues with shooting 5.56 except the issue of the bullets costing more. I do not want to shoot 5.56 on the range. I wanted to shoot my cheaper .223 at the range.



My Thoughts and Review about Sig Sauer and the 516:

I like Sig Sauer. And when I say like…., I mean love. I also love my 516 rifles. I think Sig Sauer developed awesome, dependable, battle ready 516 rifles that have been proven with 5.56 ammo. I say this because battle ready rifles will shoot 5.56 ammo and there are no issues with this rifle shooting 5.56 ammo. I also think Sig Sauer tested .223 and all proved successful because either the springs were loosened up by the time they tested the .223 ammo or they had a good batch of springs to begin with that did not need any loosening up.

I feel the problem of quality control lies with whoever makes the springs and if Sig Sauer trusted the spring manufacturer (which they should have been able to), then ultimately it is not Sig Sauer’s fault. If the company who makes the springs had better standards then the springs might not vary so much.

However, I do feel that once Sig Sauer was alerted to the issue, then I hope they invested some time to figure this out like I did and many others. Since I do not know that answer, I will not comment on it.

Thank you,

JZhouse
 

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Discussion Starter · #9 ·
Hello all Sig Sauer 516 owners..., if anyone has any other valuable info on how they fixed their FTF or chamber locking issues, please feel free to post. I know with many it will be the buffer spring but I have also heard certain magazines mess up the cycling, if so, which ones should we stay away from? Also, has anyone only removed the gas rings on the bolt to see if that helped? It is confirmed by Sig that they are not needed. The rings with lube do produce friction. So if removed I imagine there would be less friction to help with easier cycling.

Thanks,
JZhouse
 

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ftf sig 516...

Thank you for the info. Helps a lot knowing its not the gun its self. But at same time it is. I know now that i can still buy cheaper ammo and shoot.
Thanks again. And as for you Sig, fix the issue!!!
 

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Before I fired my 516, I called CS with a query and the CS guy I talked to volunteered info about breaking it in with 5.56 ammo first. About 3-500 rds. Of course this was done after it was cleaned and oiled. My query was about a manufacturing date (only a month earlier). I don't understand manufacturers who say you can shoot their firearms right out of the box, for who knows how long the firearm has been sitting on a dealer's shelf???
Good shooting all...
 

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2016 SIG516 Same Problems

Beginning shots all fired with piston in normal position and only one round in the mag.

RESULTS: (1) WW 55g FMJ .223, Fail to LB (FTLB), accuracy very good. Re-fire in adverse mode and LB. (2) PMC 55g FMJ NATO, FTLB, in normal mode, accuracy was very good. Refire in adverse mode and LB. (3) Black Hills 52g. Match HP .223, LB in normal mode and extremely accurate. (4) WW 55g. BST Frag Poly Tip, LB in normal mode and extremely accurate. (5) Fed 55g. FMJ-BT, FTLB in normal mode, extremely accurate. Re-fire in adverse mode and LB.

SIG 10 shot magazine used WITHOUT any problems LB with any ammo Other mags were Magpul Gen3 and Lancer.
 

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First Shots

Yes, these were first shots thru a cleaned gun. No problem running rounds through mags when loaded with 10 or so rounds. Total rounds thru gun- 45. Tried different ammo and mags to narrow down the problem. Sat with a custom gun builder tonight and he gets calls all the time re this problem. His fix is to just barely open up the gas port. He's had 100% success so far. I'm going to follow the wait and see/fatigue the spring ideas mentioned above. Tomorrow will be with Gov't metal mags. Ordered a different set of polishes buffer springs and buffer to see if that has any effect on it. Really appreciate the write up you guys have done.
 

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I had a few FTE/FTF issues (6-9) within the first 120 rounds through mine, and after it that, I had no more issues with feeding through over 1,000 rounds, other than discovering that Independence 5.56 will foul the gun within a couple of mags being shot through it, to the point that it won't cycle consistently, and that Wolf .223 will eject, but not cycle strongly enough to pick up the next round. I will say both of those observations were only on normal setting. Btw, mine's a Gen 2 from March 2013.

I would run about 100 rounds through it, on normal or adverse, as needed, before looking at any modifications or sending it back, and would also recommend letting Sig deal with it if it continues, as they will warrant it, but if you have the port opened up, that may well void your warranty.
 

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Independence 5.56 will foul my Gen 2 within a couple mags so bad that it becomes a straight-pull bolt action. Even on adverse setting. I haven't had issues with Wolf, if I run it on adverse. On normal, same story as above.

My fix: I went back to DGI. Never have had a problem with any DGI. Yet. I still shoot the SIG, but it isn't my go-to.
 

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I purchased a new 516 on 6/17/16 from a national USA "firearms super center". The gun was cleaned by the gunsmith, yet has continued FTF issues when gas valve is set to normal setting. When set to adverse condition, it does feed .223 normally. However, after several hundred rounds, the gun still has 20% failure to lock open at empty mag using both 5.56 and .223 target ammo, no junk. This is my first AR and in researching the issue, I learned the gun sold to me June 2016 was manufactured June 2013 and delivered to gun store warehouse July 2013. Needless to say, I was not happy about buying such an old "new" gun, which is now on its way back to Sig. A replacement with current model would be great, but I will settle for a new gas valve, buffer spring, anything else they find wrong.

I have great confidence in Sig Sauer, and the local dealer has done their best to make it right. I think they are embarrassed about the gun's age but not much they can do after the sale. I am 60, and I usually research gun decisions more carefully, but I rushed into the purchase after Orlando. Everyone should ask and verify what year model gun they are buying, especially when buying from the box stores.

I have had guns all my life and never had a strong desire for an AR. The format is so lied about by the gun control freaks and so misunderstood by the general public. However, when the government recently pushed more gun control rhetoric and appeared ready to rush judgement again on the AR, I decided my future grandkids and their kids deserve the opportunity to own the AR either out of desire or future need.

This is older thread, but timely for my "new" purchase. Thanks to all for posting, you never know who benefits.
 

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My 516 was made in March 2013, and is a mid-generation 2, so yours should be the same if made in June 13. Mine had a few FTE/FTF during the first 90 rds and then settled down and no issues except with independence 5.56. Newer 516s don't seem to be much different mechanically than 2013 production other than losing the bayonet lug and different forend options. You'll enjoy your 516 once you've got it back from Sig.
 
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