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.