AR10 accuracy question

[cal308]

Hello Everyone

I have a relatively new SIG716 that is causing me a lot of troubles in terms of accuracy at longer ranges. At 100m it is doing 5 shot groups well below 1MOA using Hornady 168gr BTHP Match ammo. At 300m the groups open up to around 10cm which is a little over 1MOA and still acceptable in my opinion. But after 500m the accuracy completely falls appart and at 600m the rifle is pretty much unuseable. The groups are in the 50cm range at 600m which made it impossible for me to reliably hit a 30×30cm steel plate at 600m.

I had the same issue now on all range trips so far. The wind conditions were not an issue generally since other shooters on the range had no issue hitting their usual target groups. Also the shooter is not to blame since multiple shooters including very experienced ones tried the 716 at the 600m target and everyone was unable to reliably hit the steel gong target, the hit rate was only 2/10 at best which is very dissapointing for a 308 even with a 16.5" barrel.

I also tried different ammo types with different bullet weights but nothing improved the poorer accuracy at longer ranges.

It is very strange to me that the rifle is a solid performer at 100m, but completely falls appart beyond 500m. Loose scope mount can be ruled out since that would also show up at 100m.

Thank you in advance!

 

[Malum Prohibitum]

What optic?

 

[brianf]

“Really” good ARs are 1.5-2 mos at 600

M110 SASS was a 1.35 or something requirement

Then add in shooting ability and a 2/3 moa group at 600 is right in line with reality

A nra high power 600 target is a 12” 10 ring ..2 moa. And those guys can shoot ARs.

Side note, never say never with mechanical items like mounts and scopes. Always check everything

 

[sinister]

... a relatively new SIG716G2 Patrol ... At 100m it is doing 5 shot groups well below 1MOA using Hornady 168gr BTHP Match ammo. At 300m the groups open up to around 10cm which is a little over 1MOA and still acceptable in my opinion. But after 500m the accuracy completely falls appart and at 600m the rifle is pretty much unuseable. The groups are in the 50cm range at 600m which made it impossible for me to reliably hit a 30×30cm steel plate at 600m.

... wind conditions were not an issue generally since other shooters on the range had no issue hitting their usual target groups. Also the shooter is not to blame since multiple shooters including very experienced ones tried the 716 at the 600m target and everyone was unable to reliably hit the steel gong target, the hit rate was only 2/10 at best which is very dissapointing for a 308 even with a 16.5" barrel.
... the poorer accuracy at longer ranges.

It is very strange to me that the rifle is a solid performer at 100m, but completely falls appart beyond 500m. Loose scope mount can be ruled out since that would also show up at 100m.

... pretty much useless for my application, where I want to go up to 800m which should still be doable with a 16.5" 308. If I had to guess the cause I would say low frequency barrel oscillations that only become an issue at longer time of flights.

What exactly are your requirements for this rifle and what is your shooting experience level at the ranges you wish to hit and score?

Are you trying for benchrest precision -- because you're not going to get that with a thinner 16.5-inch barrel, piston operating system, and GI trigger.

A GI E- and F-type target is approximately 20 inches wide, or 2.5 MOA wide at 800 yards. Do you have wind-reading experience to dope or hold-off for winds? Did any of the other shooters?

A capable shooter should be able to make an 800M shot any day of the week with a proper rifle, optic, and ammunition. A sub- 2MOA rifle should be able to hit that 30cm wide and high target at 600M.

 

[st1650]

Accuracy isn’t linear…. Especially in a gas gun … more so in a piston driven gasser.

But yeah also try a different scope/mount … could be parallax

 

[Rancid Coolaid]

You chose the wrong tool for the job.

I have that same gun, love it, but I accept that it isn't a precision bench gun.

Sell the Sig, get a bolt gun, rock on. And there is much truth to "1 MOA at 100 yards does not mean 1 MOA at 600 yards." A shit shooter can hide lots of terrible marksmanship at 100 yards. I'm not calling you a shit shooter, but your proof statements contain more than a few logic fallacies - so I also cannot rule it out.

 

[TonyTheTiger]

Just spitballing here, but have you been able to recover any fired bullets?
I once had a gun doing something similar, the accuracy at range fell off a cliff for no apparent reason, while the closer groups were unchanged. Found some bullets in the dirt and noticed that they had significant scoring on them on one of the land indentations in the bullet. Ran a patch through the barrel and you could feel a big nasty burr at the gas port. My theory was that the damage the bullets received from the port burr showed up more and more as the bullet and the rpms slowed downrange. Eventually shot that barrel out and it's replacement had similar baseline accuracy and much more linear groups at longer ranges.

 

[BCP]

I had a rifle that was grouping shitty at 100 but past 200 it was really consistent and it was scope parallax.

 

[cal308]

Thank you a lot for trying to help me!

What exactly are your requirements for this rifle and what is your shooting experience level at the ranges you wish to hit and score?

Are you trying for benchrest precision -- because you're not going to get that with a thinner 16.5-inch barrel, piston operating system, and GI trigger.

A GI E- and F-type target is approximately 20 inches wide, or 2.5 MOA wide at 800 yards. Do you have wind-reading experience to dope or hold-off for winds? Did any of the other shooters?

A capable shooter should be able to make an 800M shot any day of the week with a proper rifle, optic, and ammunition. A sub- 2MOA rifle should be able to hit that 30cm wide and high target at 600M.

My requirements are simply to hit a man sized target somewhere at 800m reliably, I am full aware that I will never get benchrest precision from an AR10. If I am missing a man sized target plate at 600m with my AR10 most of the time something is definetly wrong, that is just asking for basic military accuracy in a rifle, no real long range benchrest capabilities. Wind was definetly not an issue that day since nobody else had troubles hitting their targets at the exact same range, it was almost wind free. With a 308 bolt gun from another shooter I could hit my 30cmX30cm steel plate target at 600m 10/10 times with no issues at all.

You chose the wrong tool for the job.

I have that same gun, love it, but I accept that it isn't a precision bench gun.

Sell the Sig, get a bolt gun, rock on. And there is much truth to "1 MOA at 100 yards does not mean 1 MOA at 600 yards." A shit shooter can hide lots of terrible marksmanship at 100 yards. I'm not calling you a shit shooter, but your proof statements contain more than a few logic fallacies - so I also cannot rule it out.

I know its not meant to be a precision bench gun, but reliably hitting a man sized target plate at 600-800m distance is not asking for that, this is a basic military accuracy requirement for any 308. I am aware that MOA group size vs shooting distance is not linear at all, but if a rifle is shooting 0.75MOA groups at 100m but completely falling appart at 600m, it is still very strange. There was another shooter who was experienced with gas guns (he has a 6.5 creedmoor AR10 and shoots very accurately with it), but he also could not hit the target any more reliably using my SIG716 compared to me shooting it.

Just spitballing here, but have you been able to recover any fired bullets?
I once had a gun doing something similar, the accuracy at range fell off a cliff for no apparent reason, while the closer groups were unchanged. Found some bullets in the dirt and noticed that they had significant scoring on them on one of the land indentations in the bullet. Ran a patch through the barrel and you could feel a big nasty burr at the gas port. My theory was that the damage the bullets received from the port burr showed up more and more as the bullet and the rpms slowed downrange. Eventually shot that barrel out and it's replacement had similar baseline accuracy and much more linear groups at longer ranges.

Good idea, I already checked the gas port with a borescope camera but it looks smooth. I also chambered a round and ejected it without firing to see if the bullet jacket gets badly scratched or dented somewhere on the feedramps, but it comes out without any damage.

I have another theory that maybe the stock SIG716 muzzle break is to blame. The design looks strange with the steep angles on the chamber fins and it is very cheaply produced from cast aluminium with some powder coating. I will try the rifle without any muzzle break to see how the groups change. Poorly designed muzzle breaks can harm the accuracy of a rifle due to bending the barrel of the rifle when the bullet exits the muzzle, which leads to an uneven thrust force exerted on the bottom of the bullet due to the gasses exiting the muzzle. This is especially an issue in short barreled rifles, where there is a lot more remaining gas pressure on the muzzle.

 

[BCP]

I will try the rifle without any muzzle break

That's a good idea. You could always try it on a paper target to see if they're tumbling. I have had that happen too because the barrel was really coppered up they were flying straight at 100 but tumbling at 600.

 

[tekmann2377]

Another very important factor is ammo/bullet choice. What is your velocity and ES/SD for the ammo you are shooting? Excessive ES/SD will introduce considerable vertical dispersion which is not apparent at shorter ranges. It may also be that your rifle shoots better with either 155 gr or 175-178 gr bullets instead of 168.

Hitting a 2 MOA target with a reasonable hit percentage using a 16" large frame AR isn't impossible (a MWS is a good example), but everything needs to be fairly well dialed to do so.

 

[cal308]

Another very important factor is ammo/bullet choice. What is your velocity and ES/SD for the ammo you are shooting? Excessive ES/SD will introduce considerable vertical dispersion which is not apparent at shorter ranges. It may also be that your rifle shoots better with either 155 gr or 175-178 gr bullets instead of 168.

Hitting a 2 MOA target with a reasonable hit percentage using a 16" large frame AR isn't impossible (a MWS is a good example), but everything needs to be fairly well dialed to do so.

I once measured 5 rounds of the 168gr Hornady BTHP ammo using a Magnetospeed v3 and the result was actually pretty good with an ED of 7m/s (23fps) and SD of 2.8m/s (9fps). The average velocity is 764m/s which would bring me into transsonic range at around 900m at my range ambient conditions.

Trying even heavier bullets is definetly a good idea considering my rather fast barrel twist rate of 1:10 combined with the short 16.5" length. I should still have some 180gr GGG match ammo laying around that I can try. I already tried more lighter 147gr ammo, but didn't notice any improvments. Right now I only have fast access to a 300m range, but that should still be enough to judge if anything improves since the groups already started to open at that distance.

 

[bfoosh006]

I would also suggest making sure your parallax is set properly .

While looking at the sky, focus the reticle first.

Then bobble head, while looking through the scope, adjust the parallax until there is no visible shift of the cross hairs..

This a simple description.... watch some videos on line.

 

[cal308]

I finally got it figured out, it was indeed the muzzle brake which was screwed on too tight. I installed it again with Rocksett and torqued it down less than it came from the factory and now my group sizes pretty much halfed at 600m. I finally have no issues in hitting my 30×30cm steel plate at 600m with a 9/10 hit rate. I havent tried it out up to 800m yet but I think I could still get a decent hit rate on the plate.

I am still surprised the torque had such a big impact on this, but the barrel is already thin and the cross section reduces even more around the muzzle where the threads are cut, so I can imagine a tight muzzle break causing some changes in the bore diameter. Thank you again for your help!

 

[jLorenzo]

Another very important factor is ammo/bullet choice. What is your velocity and ES/SD for the ammo you are shooting? Excessive ES/SD will introduce considerable vertical dispersion which is not apparent at shorter ranges. It may also be that your rifle shoots better with either 155 gr or 175-178 gr bullets instead of 168.

Hitting a 2 MOA target with a reasonable hit percentage using a 16" large frame AR isn't impossible (a MWS is a good example), but everything needs to be fairly well dialed to do so.

You need to shoot 30 or preferably 50 rounds to get a statistically relevant ES/SD reading.