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 rifles and others…, and did testing and experiments to find the exact cause of the issue and how to fix it.
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.
Read the above sentence slowly, it shows why there is a great variance on why some rifles work perfect and 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.
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 1-2 lbs of blow back pressure 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.
4. Shooting heavier .223 ammo (above 55 gr.) works 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.
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 ½” 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 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 to one inch 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 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. Sometime 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 issue 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.