[The_Cube]

Ok so I have a HK MR556a1 serial number ending with 1971. I recently took it down to the range after thorougly stripping it down and lubing with CLP and using M Pro-7 bore gel on the bore. Anyways, I shot 150 rounds of PMC X-TAC 55gr and I noticed that the rifle is extracting at the 2:00 position, and it's dinging my brass about a centimeter up from the rim. Also the neck of the brass is getting mashed so the hole where the bullet is looks like part is flattened. I'm using all stock new HK parts with 16.5 inch factory barrel.

That's not what I'm really worried about. I noticed that the brass has been hitting the bottom of the brass deflector (sharp edge of the brass deflector) and has chipped off the finish. It's making a small crescent of silver at the bottom of the brass deflector where it meets the receiver. I'm wondering if this is normal. Should I be worried about it? Will my entire deflector be chipped away after a few thousand rounds? Does it matter that my rifle is a bit overgassed?

Brass deflector marks - Page 2 - AR15.COM The brass deflector pics on this page are pretty representative of what is happening on my rifle.

 

[mikecleonard]

I'm not sure about the brass getting mashed up...but everything else you described sounds normal for any AR15 I've ever used.

Also, the Hk's tend to run at a bit faster cyclic rate.

 

[The_Cube]

Is the cyclic rate going to mess with the service life of the gun? Is the brass deflector wear going to level out, or will my upper eventually be ruined by chipping brass?

 

[mikecleonard]

I'm unsure of your frame of reference. Are you asking whether the service life of your MR556 will differ from other MR556's/416's, or differ from other AR15's?

Do you not think the cyclic rate of your rifle is within spec for the 416/MR556 platform? Hk designed it to run at a fast cyclic rate for specific reasons. As is, the fast rate allows 416 pattern rifles to work with a wide range of ammo, and allows the rifle to function even when it's really dirty. On the flip-side, faster cyclic rates also mean more recoil, and greater stress on materials. It's kinda par for the course with regard to piston operated AR15's. That being said, the Hk's are known for having a greater service life than a Colt for example...even though a Colt will run at a lower cyclic rate. The cyclic rate of your rifle won't mess with it's service life anymore than wearing your jeans will mess with their service life. If you're concerned that it's operating too fast, you could always try the Vltor A5 buffer system to slow it down...I've heard really good things about that recoil system...but then again, you might void your warranty doing so.

The anodizing on your brass deflector is what has worn off from shooting. This happens on all AR15's as anodizing is not strong enough to resist wear against hundreds or thousands of brass casing smashing against it. It's nothing to be alarmed about, as the aluminum underneath will hold up just fine.

Is this your first AR15?

 

[bermise]

It must be his first because every AR I ever shot has small knicks on the brass deflector. Totally normal, remember it's a tool.

 

[Grumpy]

Excessive bolt speed can increase wear in the gun. Ejecting to 2 o'clock and damaging the brass is indicative of excessive bolt speed, but excessive bolt speed can be mimicked by other factors.

Have you added a Crane "O" ring or Defender "D" ring to your extractor?

How many rounds do you have through the gun so far? If you have more then 5K, i'd suggest inspecting your action spring and the buffer pad on the end of the buffer. If this rubber buffer is starting to flatten, mushroom, or develop cracks, then your bolt speed is excessive and will cause undue wear on the gun.

Main culprits that either cause or mimic excessive bolt speed are the action spring (weakened from simple use or in a newer gun, perhaps one that wasn't manufactured properly and somehow made it past CQ), a worn and weakened ejector spring, an overly agressive extractor (usually due to the addition of an "O" or "D" ring when unecessary).

In the 416 type system, i'd also keep an eye on the op-rod spring, and the cleanliness of the gas block vent hole.

When you clean and lupe your rifle, do you lube the piston and inside of the gas block? Some lubes do not do well when exposed to carbon and high heats and instead of simply burning off, they can cause excessive buildup of carbon in the vent, thusly keeping more gas in the gas block and speeding up the cycle rate.

To be honest, while it has been recommended that the gas rings be kept lubed, due to the direct contact with the burning gasses being ported off the barrel, any lube in that area will be burnt off in such short order that it's functionally useless to lube it. I prefer to keep mine dry as I kept the gas rings in my regular AR's dry. I'll keep all other moving metal to metal contact areas well lubed, but i've never seen anything positive from lubing gas rings that are in direct contact with gas siphoned off of a gun barrel.

If you have doubts, go ahead and lube the piston and rings, then go shoot a couple of mags then remove the piston and play 'Where's Waldo' with the lube that you put on a few minutes before. Hint: It won't be there.

Lastly, when you used this bore gel, did you make sure that you also cleaned any remnants from the gas block as well when you were done? The bore gel might also have similar properties to some lubricants that hol onto carbon from the burning propellant and then bake in place creating an excessive amount of fouling that can severely effect the function of your rifle.

 

[The_Cube]

This is in fact my first AR. I've been using breakfree CLP on all the components, and running the rifle wet. I've put it on the piston and after 150 rounds the CLP is still on the piston. The rifle is new and only has 150 rounds through it.

 

[Grumpy]

If it's brand new and acting like this, then that's the way the gun is. As long as it works, shoot it. Not much to be done other then to look into heavier buffers or cut have the barrel cut back to 14.5 and perm attach an appropriate flash hider. (that's what I did, but not because of function issues, rather more as a weight reduction and length reduction thing).

Not sure how your's is doing it, but no piston i've ever shot kept lube worth a **** after a few magazines.

 

[The_Cube]

As for the piston. I can get most of the carbon off the piston, but no matter how much I soak it in solvent there's always some near the top that I can't get off. Is this normal?

 

[The_Cube]

Grumpy, what's your rifle's ejection pattern? Will HK void my warranty if I use Hornady 55 gr training ammo (steel cased, lacquer)? Will the steel stuff wear my extractor more than brass?

 

[forFREEDOM]

My 416 upper used to extract that way when it was new. I too have nicks on my ARs' deflector. It now ejects anywhere from 3 - 4 oclock. And I haven't seen any new nicks in the last 1000 rnds. I have about 4000 through her.

 

[Grumpy]

As for the piston. I can get most of the carbon off the piston, but no matter how much I soak it in solvent there's always some near the top that I can't get off. Is this normal?

Yes, this is normal. Don't worry about it. You can actually cause more damage to a gun trying to get it spotless clean then you do by shooting it. White glove treatment is for bootcamp.

Grumpy, what's your rifle's ejection pattern? Will HK void my warranty if I use Hornady 55 gr training ammo (steel cased, lacquer)? Will the steel stuff wear my extractor more than brass?

My ejection pattern was stright to 3 o'clock when I first test fired. After the barrel re-profile, it shifted back to about 4 o'clock. If it settles down more as forFEEDOMs did, it'll probably shift even a bit further back.

I personally am not worried about it shifting to a slower bolt speed with a little less gas in the system as I will br running suppressed much of the time which increases the gas in the system and speeds the bolt up. I would rather have it run slightly undergassed (but still fully operational) without the suppressor so that when I do run it with the can, it doesn't overgass it to unnacceptable levels.