new AR wear marks concern

anmckenn said:
Excessive wear, u think, i lube with m-pro 7 and like i said only 150 rounds. Think there is a manufacturer issue here? Its a german sig 516
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So it's a piston gun, not a D.I. (not being mean, however that is a major difference between D.I. and Piston):


The bolt lugs will wear much quicker on a Piston gun because the piston Op-rod is slamming into the carrier and punching it back, the kind of wear on your bolt head is completely common and it's pretty much just finish wearing off. Something like Frog Lube that isn't an "oil" that can run off, will help prevent any wear.

As for the wear in the cam pin area, that's another tell tale sign of a piston gun, and it's companion: Carrier Tilt.

Because the piston "punches" the bolt carrier backwards, it wants to make the carrier lift nose up and rear down. So the extra contact is likely the cam pin scraping it a little as the bolt cycles quickly. You will also eventually see wear marks on your buffer tube where the bolt carrier sits at rest. Some companies put "sacrificial metal pads" onto the bolt carrier so it has more metal to wear away at, but ALL AR15 piston guns will do this over time.



Basically, as a piston gun goes: you're completely normal. You have traded longevity of components and smoothness of cycling for less cleaning and more reliable cycling of the action.
 
Thanks a lot raptor, thanks for your time, good explanation. My Tavor looks nothing like this, it was really making me wonder about this bulletproof german reputation... And after that little rounds
 
Boltgun said:
I think that is a piston not gas tube...end is rounded, look at the other pic with the BCG...no gas key visible where it should be.

Boltgun
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You are correct - I was looking on an Iphone on the london undergound.

Piston guns also have no resistance to the unlocking (like the stoner system which has pressure inside the carrier) so they turn faster and more violently. The cam pin will eat through the side of that gun. I've seen a few that were destroyed inside 600 rounds.

I've seen test guns with 30,000 rounds have less cam pin wear than that.
 
anmckenn said:
Should a sig wear like that, i mean for the money, should i try to send it back.?
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I don't think it's going to effect anything, in the long term it will eventually stop wearing, as the amount of movement is sort of limited by the charging handle (which is purpose built to contain the movement of the BCG) I would personally just go with a good grease for the bolt lugs and the charging handle area, it will reduce friction and reduce a lot of wear on the components.

The reason purpose-built pistons guns (guns that were from the ground up built with a piston in mind) like your Tavor (or the ACR, G36/SL8) don't wear in the same way; is that they have very large thick guide rails that prevent the carrier from moving around or canting off-axis. Even guns like the SIG 516 or the HK416 are just glorified conversions. They physically do not have the bearing surfaces needed to prevent carrier tilt. SOME guns have the piston rod built into the carrier so it acts as a guide system and prevents a lot of the carrier tilt (the Adcor Defense BEAR is one I can think of) but the way the gun was built originally, was so that gas entered into the gas key and then carrier chamber and pushed the carrier group strait back, and the bolt head forwards - equalizing pressure on the cartridge case and allowing the bolt head to rotate out of battery under no stress (or much less stress) which is why the AR can "function" with as little as 2 bolt lugs in place (although this is still a bad idea) it goes to show how genius the design actually was.



Seriously though, try some frog lube. P&D I think, and Canadian Tactical Cowboy Supplies carry it and it's a great product. Makes clean-up much easier, and it won't burn off or drip away like standard oils will.
 
Dsiwy said:
Worst thing to happen to the AR platform..... Pistons :( "sorry am Anti AR piston"
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Yep, pistons have their place, but the AR was designed for D.I. and after I looked into it and after building my first AR (heavily debating between piston and D.I), I have no more interest in a piston AR. Piston guns should have large locking lugs and big flat carrier bearing surfaces, that eliminates ALL the issues that the piston AR's have.

If you properly lube an AR bolt, it takes no more than 2 minutes to completely clean, and with the advances of plating technology (NiB and NP3, even hard chrome) you can just hose it down with cleaner and the carbon wipes right off.
 
If the wear progresses it will cause stoppages.

The side of the reviewer prevents the bolt from turning before it is fully forward.

The force of stripping a round from the magazine will try to lock the bolt, but the left aide of the receiver prevents the cam pin from moving.

If you remove enough material the bolt will turn prematurely on loading and the lugs will strike the extension preventing closing and locking.

The damage on the bolt may be early evidence of this.

The cocking handle will have nothing to do with this.

The picture is not good enough to say for certain, but it looks close to where I would scrap the upper from a duty weapon.

I don't want to be harsh, but stoner tried the piston and relegated it to the stamped steel gun pile. The stoner gas system has worked for for fifty years, billions of rounds and benefits from modern heat treating and coatings.

The piston AR is a solution searching for a problem.
 
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F22_RaptoR said:
Seriously though, try some frog lube. P&D I think, and Canadian Tactical Cowboy Supplies carry it and it's a great product. Makes clean-up much easier, and it won't burn off or drip away like standard oils will.
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I second this. Give it a good cleaning, and apply Frog Lube. Have you by chance visited either of the main dedicated Sig forums?
 
C77 said:
If the wear progresses it will cause stoppages.

The side of the reviewer prevents the bolt from turning before it is fully forward.

The force of stripping a round from the magazine will try to lock the bolt, but the left aide of the receiver prevents the cam pin from moving.

If you remove enough material the bolt will turn prematurely on loading and the lugs will strike the extension preventing closing and locking.

The damage on the bolt may be early evidence of this.

The cocking handle will have nothing to do with this.

The picture is not good enough to say for certain, but it looks close to where I would scrap the upper from a duty weapon.

I don't want to be harsh, but stoner tried the piston and relegated it to the stamped steel gun pile. The stoner gas system has worked for for fifty years, billions of rounds and benefits from modern heat treating and coatings.

The piston AR is a solution searching for a problem.
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Yeah this is true I spose, the charging handle only touches the key not the cam pin at all.
 
Considering the charging handle comments, i have run an aftermarket handle since about 50 rounds, i have lubed up and installed the sig factory handle and am going to hit the range soon. I have noticed a little extra play in the aftermarket handle since first installed which could be interfering with the bolts return path therefore causing rounding of the lugs when seating back in. And wobbling of the bolt in motion causing cam pin to score sides. Thanks for the great ideas, i think im on the right path now. You think i should blue up that receiver mark and see if the factory handle keeps everything back into proper alignment?
 
anmckenn said:
Considering the charging handle comments, i have run an aftermarket handle since about 50 rounds, i have lubed up and installed the sig factory handle and am going to hit the range soon. I have noticed a little extra play in the aftermarket handle since first installed which could be interfering with the bolts return path therefore causing rounding of the lugs when seating back in. And wobbling of the bolt in motion causing cam pin to score sides. Thanks for the great ideas, i think im on the right path now. You think i should blue up that receiver mark and see if the factory handle keeps everything back into proper alignment?
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Unless you got Aluminum blackening solution, a standard gun blue won't work :p

But you could try a sharpie marker and that might give you an idea of if it's progressing with the different charging handle!

I've seen some aftermarket charging handles that were incredibly tight, and some very loose, so it could be a loose spec charging handle is interfering and allowing too much movement.
 
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