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Are the 516 and 716 FTF Issues Due to the Buffer Spring?

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Sig Sauer 716 Problems and Issues with Shooting:

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



Hello,

I do not have a 716, but I do have two 516's. The 516's had the same FTF not cycling issue and the bolt not locking open. All of it was due to too tight of buffer springs. I did several tests and the buffer springs, spring weight varied by several pound between various springs. That is why some guns have no issues shooting out of the box while others have issues until they are broken in or shot with hotter loads.

I don’t have the time to re-write my 516 article for a 716 or the time to test a 716, so just replace your thoughts with the 716 as you are reading the 516 article. Everything sounds very similar with the issues between the same guns and how using hotter loads work. So…., the below article might help.

Bottom Line: (after cleaning and lubing)
Cut the buffer spring or break it in…, and the gun should be able to shoot any type of ammo and not just hot ammo.

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. 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 of course did a thorough initial cleaning and re-lubing.
The Issue: Straight to the point: Buffer Spring Weight too Tight (with HOT ammo it worked fine)

716 Insert:
(When reading the below article…, just replace the 516 with the 716 and imagine the lighter loads versus the hotter loads… the 716 seems to be having the same issues as the 516’s. The 716 shoots great with hot ammo or .308, but not always with the lighter loads….. read on….)

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 lighter ammo perfectly, while other rifles do not operate correctly when shooting light ammo and do not cycle correctly or lock open, but do with hot ammo. In fact, some springs are up to 3lbs heavier than others causing these issues.

These buffer spring variances can greatly affect how the rifle acts when firing light ammo due to its lower pressure. So when light 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 light ammo.

Generally, the Sig Sauer 516 shoots fine with 5.56 hot rounds due to the higher pressure from the 5.56 hot ammo, which the spring variances do not affect. Same goes for the 716 with shooting hot ammo.


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

716 Insert: (this might be the same for the 716’s with light ammo and hot ammo…)

1. Sometimes just a good cleaning and lube makes everything glide easier
- Clean the black packing grease off, inside and out and 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 hot ammo for a while until the buffer spring is broken in and looser, then switch to .223 light ammo if you want due to the cheaper cost of the lighter ammo.
3. Shoot .223 light 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 dirty or bloody.
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 lighter 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 light 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.

716 Insert: (I am not sure how much the spring should be cut, so start off with only half an inch to 1.5 inches.)
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.

716 Insert:
( I am not sure what type of round Sig Sauer tests with the 716, HOWEVER…, I am guessing they test with a hot military round just like they do with the 516 rifle…. Read below regarding the 516 rifle….)

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.

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 light 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.

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 light and hot ammo. That is why people using hot 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: 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 or 716 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 seems to come from a simple part…, a too tight of a buffer spring.
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Discussion Starter · #2 ·
Continued from last post…. (read post before this post) See above first…



Sig Sauer 716 Problems and Issues with Shooting:

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

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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Very interesting stuff JZ, but...wow.

I own a Smith M&P15 and an Armalite AR10 and have had ZERO problems with feed and function. I use both of them for varmint work and in thousands of rounds, much of it with handloads {all handloads in the AR10} and no problems at all.

All this detailing of problems with SIG rifles here and on other sites has me dead set against ever touching one.
 

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Discussion Starter · #4 ·
Very interesting stuff JZ, but...wow.

I own a Smith M&P15 and an Armalite AR10 and have had ZERO problems with feed and function. I use both of them for varmint work and in thousands of rounds, much of it with handloads {all handloads in the AR10} and no problems at all.

All this detailing of problems with SIG rifles here and on other sites has me dead set against ever touching one.
Well, I do agree someone messed up on the quality control of the buffer springs, but once the springs are worn in or slightly cut, so far, besides that, the Sig 516 has been bullet proof. And many 516's came with perfect buffer springs and had no issues at all. But Sig should have caught this earlier. Anyway, enough said.
 

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ftf

Just got a used 516(gen??) patrol rifle. Have not shot it yet. Came with 223 fed ammo. Noticed in the forum a lot of threads regarding FTF. Some suggested cutting the recoil spring. There were also mention of gas rings alignment. I think piston-driven BCG don't need gas rings. Has anyone tried removing the gas rings in their piston-driven ARs? Maybe it will work for the 516 patrol rifle.
 

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Discussion Starter · #6 · (Edited)
Just got a used 516(gen??) patrol rifle. Have not shot it yet. Came with 223 fed ammo. Noticed in the forum a lot of threads regarding FTF. Some suggested cutting the recoil spring. There were also mention of gas rings alignment. I think piston-driven BCG don't need gas rings. Has anyone tried removing the gas rings in their piston-driven ARs? Maybe it will work for the 516 patrol rifle.
Hello,

I am not sure if you read this entire thread but I did mention that the bolt gas rings can be removed and can ease up the friction. I just removed mine on both my 516's and most people that have piston driven ARs do remove the 3 rings. I also confirmed with Sig and the bolt gas rings are not needed. I also wrote about the buffer spring and all the things you can do to make it work better. Just read this entire posts above. Hope your 516 shoots well. So far ours work great, but I did cut some off the buffer spring to help it out.
 

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Just adding my experience.

I have a 516 produced in July 2013 and have the usual host of issues. I am basically only having FTF and not FTE issues. I think the bolt is cycling back with enough force and far enough to eject the shell, but not quite enough to load the next round. I have about 120 rounds through the gun. I exclusively shot 55gr Federal XM193 (indoor range) and have to shoot it on the #2 gas setting in order for it to cycle properly. I have some 62gr .223 that will go in next and some 77gr that I have to try, but just a little disappointed. Like most of you, I'm fully convinced this is a buffer spring issue and have noticed that the action has loosened up with each firing and successive cleaning. I hope the next trip to the range has different results. As suggested here, I will try to "train" the spring by storing with the bolt open. Am I wrong for wondering if there's a lighter spring on the market? Most springs seem to be pretty standard.

And unless you couldn't tell. I'm new to the platform, but happy I hopped on board!!
 

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I would try some of the other ammo and try working it on normal setting to see what kind of results you are getting, but if it doesn't clear up shortly, I would recommend sending it back to Sig for repair. Mine acted up a bit at first, but settled down and hasn't had any further issues after about the first 120 rds. Some have said the heavier ammo and/or the higher pressure 556 ammo may cycle better than 55gr 223, but since you are already running 556, that would not seem to be the difference in your case. I've run mostly 55gr in mine, both 223 and 556, and other than the 556 being louder, I can't tell a difference in the way it shoots.

Regardless, if it doesn't work itself out during break-in, I wouldn't hesitate to send in back to Sig and let them stand behind their product.
 
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