SIG516 7" Piston Upper. Photos and Vids Inside!

[Tokarev]

http://www.youtube.com/watch?v=rNRZ9v1cpPQ&feature=related

http://www.youtube.com/watch?v=3ZultOoAnJU&list=UUrr_y4vtTSQU00EC5hIuHXw&index=3&feature=plcp

[Tokarev]

http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/utf-8BSU1HLTIwMTExMjIwLTAwMDE3LmpwZw.jpg

[Tokarev]

http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/utf-8BSU1HLTIwMTExMjIwLTAwMDE4LmpwZw.jpg

[Jer]

What are the specifics on the rounds being fired? What is the twist of the barrel? Is the suppressor a 30cal? 5.56 + 7" barrel + suppressor = eventual baffle strike.

[Tokarev]

I've now had a pretty good chance to play with SIG's new 7" upper and wanted to share my thoughts. I really haven't bothered to try the upper for accuracy since I assume most people will be using this upper as a noise-maker or pistol upper. But I suppose I should shoot it for groups at 50 and 100 yards just to satisfy my own curiosity. If I have time, I'll mount my Leupold FireDot next week and give it a try.

Anyway, the upper is more than just a standard 516 upper chopped to seven inches. The gas block, upper and bolt/bolt carrier assembly remain the same but the gas parts are different. As you can see, the gas parts look alike when assembled with the exception of the overall length:
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000429.jpg

Note that the gas valve on the 7" model is, indeed, different. Gone are the small gas rings on the full-length system. These have been replaced with three grooves on the short system:
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000430.jpg
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000431.jpg

The piston assemblies are different as well. Note that the short piston lacks the small vent holes at the muzzle end of the cup:
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000432.jpg
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000433.jpg

The gas valve on the 7" model only has three settings. They are full-powered, suppressed and off. The upper will not run in the suppressed setting without a can in place:
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000434.jpg

Note the crazy short overall length of the 7" upper:
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000439.jpg

Even though the barrel and gas system is substantially reduced, the handguard lengths are similar. Note that the 7" model's rail telescopes over the gas block on the shorty. I like this and would like to see SIG extend the rail on the 16" model to cover the gas block. This would cover the bayonet lug but I don't think too many people would mind:
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000437.jpg

The short upper weighs roughly a pound less than its longer brother. Weights are about 4.75 pounds for the 16" and 3.75 pounds for the shorty. The reduced weight and changed center of gravity really makes for a handy little blaster.

I've been pleased with what I've seen from the SIG piston guns, for the most part. I've had good reliability from both lengths. The 7" upper runs fine in semi- and full-auto as does the 16" model. I don't care for the way SIG chose to secure the gas valves. These parts thread into the gas blocks and are held from rotation by a small detent. What I don't like is that the detent is very small and hard to depress without a cartridge or a punch and the gas valves themselves are hard to turn when fouled with carbon. I'd like to see SIG re-design the valves slightly and/or shorten the retaining detent a little so the shooter doesn't have to keep the detent continually depressed while unscrewing the valve.

The 7" upper is fun to shoot but the handgaurd's length is limiting even though it does extend around the gas block. The gas block is still exposed up top and I've found it very easy to burn a finger or thumb while shooting if not careful. A VFG is probably a requirement on such a short platform.

As soon as I can get some long range accuracy and some chrono data, I'll post an update.

Thanks for reading. Happy New Year!

[Tokarev]

What are the specifics on the rounds being fired? What is the twist of the barrel? Is the suppressor a 30cal? 5.56 + 7" barrel + suppressor = eventual baffle strike.


The barrel is hammer forged and chrome lined with a 1x7 twist.

The suppressor used in a Gemtech HALO. It wasn't used much due to concerns over baffle strikes.

[Darkop]

The barrel is hammer forged and chrome lined with a 1x7 twist.

The suppressor used in a Gemtech HALO. It wasn't used much due to concerns over baffle strikes.

Tokarev, I really like how that looks and runs!

I just got paperwork back on a lower that I am going to run my 7" Noveske Diplomat barrel on. I only have about 500 rds through it now. I had to change the bolt gas rings once already. I'm wondering if a piston gun might be a better option in this length. I will have to see if this is going to be a problem in the future. I am running a KX3 Pig with 9" rail.

I need to shoot some groups W different grain bullets to see how stabilization is before I run my HALO on it. I would be interested in bullet stabilization in your 7" gun.

I'm going to run My 7" on my M16 lower on Monday to see how it functions.

Does anyone have information on gas ring life on Super short SBR's?

Until that day,
Darkop

[Tokarev]

Another slow motion video of the upper in use:


http://www.youtube.com/watch?v=Ik0VJAtseHs&feature=related

[dpaqu]

What are the specifics on the rounds being fired? What is the twist of the barrel? Is the suppressor a 30cal? 5.56 + 7" barrel + suppressor = eventual baffle strike.

Is this due to lack of stabilization?

[Jer]

Is this due to lack of stabilization?

Correct. This is why I chose 300 Blackout for my new 9" suppressed upper because the 200gr projectiles stabilize sooner.

[Tokarev]

Is this due to lack of stabilization?

That's my understanding.

I've only used the upper with 62gr and 55gr FMJ so far but I'm curious about heavier bullets. I've got some 77gr BTHP ammo and will try this on paper as soon as I can.

[Polymerhead]

So, I'm curious - why does the RPM speed up? Is this a common thing with full auto guns? You can really hear the difference from the start of the mag to the end - it's like a lawnmower engine spooling up.

http://youtu.be/rNRZ9v1cpPQ

[Tokarev]

Okay, guys. I did a little chrono and accuracy testing this morning. I fired a couple groups from the prone at 50 and 100 yards and ran a few rounds over my Shooting Chrony.

First, the chrono data. All rounds were fired fifteen feet from the front screen.

55gr FMJ reload using AA#2460 powder. This powder is probably a little slow for the 223, especially from such a short barrel. We fired 60 rounds of this ammo in total and had three or four short strokes with it.
HI--2289
LO--2069
AV--2171

62gr Federal factory SP ammo.
HI--2138
LO--2026
AV--2099

77gr BTHP ammo from Silver State Armory. Cases headstamped "SSA 556"
HI--2131
LO--2096
AV--2115

The SSA ammo was very consistent and I was surprised that it chronoed in the same ballpark as the lighter stuff. Just to check the data, we fired a few rounds using a BCM 11.5" upper. Here's that data:

55gr
HI--2603
LO--2487
AV--2561

62gr
HI--2479
LO--2410
AV--2436

77gr
HI--2441
LO--2415
AV--2425

[Tokarev]

Here is five rounds of Silver State 77gr fired prone from 50 yards.
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000445.jpg

Same ammo at 100 yards. Again from the prone.
http://img.photobucket.com/albums/v221/tokarev/SIG516%20Patrol/P1000446.jpg