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Old November 5, 2018, 05:26 PM   #1
FoghornLeghorn
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"Short stroking" Sig 716?

I went to the range today to prep/sight in my Sig 716 AR 10 for a pig hunt. I had problems as follows.

Insert full mag.
Chamber a round.
Fire the round.

The bolt ejected the spent cartridge but did not strip the next round off the mag. The bolt rode up halfway on the next round and stopped, while the next round was still in the mag.

The mag is a magpul 20 rounder. Bad spring? Bad magazine?

The bolt was sufficiently oiled.
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Old November 5, 2018, 05:49 PM   #2
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Probably need to move this to the semi-auto subform--sounds like you might have a gas problem (not enough to eject and strip next cartridge). I would try simply sticking a single cartridge into the chamber, drop the bolt on it and insert an empty mag and fire--does the bolt consequently eject the case and lock back open?
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Old November 6, 2018, 10:57 PM   #3
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You have one of two possible problems. #1 the bolt isn't coming back far enough to feed the next round, or
#2 it is coming back far enough and the next round is not in the proper position to be fed.

First step, change the magazine. If the spring is weak, and isn't getting that top round up fast enough the bolt over-rides the rim. Test different mags, see if all do it, or just one. If its just one, that's your problem, a bad mag (spring, most likely but other causes are possible, a bad follower allowing the rounds to tip in the mag, for example).

If you are getting bolt override on all your mags, the problem is the rifle, and why the bolt isn't doing its full job right.

Quote:
I would try simply sticking a single cartridge into the chamber, drop the bolt on it and insert an empty mag and fire--does the bolt consequently eject the case and lock back open?
DO have the rifle pointed safely down range if you do this. Dropping the bolt on a chambered round isn't supposed to fire it, but "isn't supposed to" is NOT the same as "can't" or "won't". Slamfires have happened.

Since there is no reported issue with chambering and firing that first round, I don't see why you would need to chamber a round then drop the bolt on it. Simply using a mag with one round in it, will do the same thing. Chamber and fire the round, if the bolt locks open on the now empty mag, its not short-stroking.
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Old November 7, 2018, 01:50 AM   #4
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Quote:
DO have the rifle pointed safely down range if you do this. Dropping the bolt on a chambered round isn't supposed to fire it, but "isn't supposed to" is NOT the same as "can't" or "won't". Slamfires have happened.
Absolutely right--I should have pointed that out. I would add that I always assume a slam fire or AD is a possibility--magazine or not--and always point the weapon in a safe direction whenever/however I charge it with a live cartridge.
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Old November 7, 2018, 12:01 PM   #5
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Thanks guys. I'm headed to the range just for this issue. And also to decide if my Wilson barreled Ruger #1 is worth keeping. I just might be listing a couple of rifles on Gunbroker and making the trek to the Wannamacher gun show this weekend.

Concerning the Sig 716, I posed the same question on Sigtalk. One guy said,
Quote:
My P716 has been back to sig three times for that issue, it now does okay until it gets a little dirty then you have to clean it, cranking up the gas helps for a bit.
The 716 is six years old and functioned fine the very few times it's been fired. However, it's out of warranty and I'm not about to ship it to Sig for repair on my dime. I'll simply sell it along with the necessary caveats.
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Old November 7, 2018, 04:54 PM   #6
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I just got back from the range with the 716. I took several brands of ammo. JIC.

Monarch would fire the first round fine but would not feed another round off the mag. The bolt hung midway up the cartridge.

Barnes Vor-TX would fire the first round fine, plus it fed the subsequent rounds just fine. The bolt did not lock back when the mag was empty however.

Winchester Power Max 150 grain would fire the first round fine, it stripped subsequent rounds off the mag and also fired fine. Plus, the bolt locked back when the mag was empty.

Is it safe to say the gun simply prefers certain ammo and there's nothing wrong with the gun?
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Old November 8, 2018, 08:48 AM   #7
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It sounds to me like, for whatever reason, your carrier is not receiving enough inertia to complete its rearward motion. I encountered similar problems when working at Kalashnikov USA (that's a whole other story).

That generally leaves two issues: either a gas problem (not enough gas) or a mechanical problem (late unlocking or too much resistance against the carrier).

If you want to try to fix it yourself, you need to look at the contact points and see where friction could be happening. Does the piston move and return freely or is there friction there? Does the bolt head rotate easily in the BCG by hand, or does it have any drag or grit? If you press the buffer assembly by hand, do you notice that it moves smoothly, or does it hang up at any point? How does the operation of the rifle feel when cycled by hand?

A quick search shows that this has also been brought up on other forums. Feed ramp angle and surface finish has been brought up as a potential factor in these rifles in feeding issues. It could also be that your feed lips are too tight or the magazine is over sprung - you could try removing 5 rounds from the mag when loaded with PMC and see if that makes a difference in function. However, the failure to lock to the rear on an empty mag with the Barnes points to there being an issue with your BCG not moving far enough to the rear.

On another forum, one user reports that they sent their rifle back to Sig. They received it back with notes from the warranty department stating "polished chamber, adjusted gas mechanism, fired 2 magazines of federal 150gr without issues.". A rough chamber could definitely contribute to extraction delays and lost inertia. Who knows what adjusted gas mechanism means? Could mean just changing the settings. Could mean swapping out their gas plunger or dial (I don't know what the part is on the 716, I've never seen one) until they found one that fits better. Could mean the gas port was misaligned with the gas hole on the barrel and that was corrected. Might help if you could get more info on the other rifles that had these issues.

Sometimes the right lube in the right place will get the rifle running well enough to shoot it past the "break-in" point where everything starts working. I personally like Modern Spartan Systems products for leaving an incredibly smooth, low friction finish. I AM affiliated with them but only after trying their products on my own gun and liking it. On malfunctioning AKs, we did the same thing with LSA.

Other possible things it could be (just spit-balling):
Over-sprung buffer
Tight headspace or rough finish on barrel extension
Hammer spring putting too much upward pressure on bolt carrier
Gas hole undersized, not straight, or has burrs
Piston over-sized or out of round

Hope that gets you started in the right direction. For a rifle of that price and use, I really wouldn't be happy with it being so picky that it won't cycle common ammo.
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Old November 8, 2018, 10:33 AM   #8
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I recently had a feed malfunction on one of my AR builds that had formerly been working without any issues. Very similar, there were intermittent cartridges jamming and failures to lock back while firing. What I eventually figure out was the magazine--a high-quality steel one, BTW--had expanded just enough on the the sides to allow the stacked cartridges to have problems being stripped--and sometimes resulted in more than one cartridge being released by the feed lips. To test that theory I put tape on the sides of the magazine to take up slack in the mag well and push the sides in--all the problems disappeared and the rifle functioned flawlessly with all levels of power reloads. Just another consideration, not saying that's the issue based on what you have.
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Old November 8, 2018, 01:40 PM   #9
T. O'Heir
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Short stroking can have several causes. Including the ammo, gas system being dirty, etc, etc.
Go here. https://www.thetruthaboutguns.com/20...hort-stroking/
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Old November 8, 2018, 03:25 PM   #10
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Is the OP of this thread the same Foghorn Leghorn as the article that T. O'Heir linked to?

What irony that would be, being linked to one's own article for information.
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