[Grumpy]

Seems pretty simple to me. Look at the rear of the ejection port. The block is angled so that ejecting brass hits it and heads somewhat forward and down and also imparts a "flip" to the brass which would cause the case mouth to strike the receiver. You can also see on the bottom of the ejction port itself, there is similar wear, probably caused by the same thing. Ejecting brass does all sorts of weird things depending on what it hits and the slight variations in ejection speed

 

[LCSO264]

my first thought was it was from the forks of a colapsable stock... but in looking closer at it, I think that is too far forward... so, I'm going to go with what Grumpy said... think of it as a beauty mark.....

 

[hkshooterusp]

Seems pretty simple to me. Look at the rear of the ejection port. The block is angled so that ejecting brass hits it and heads somewhat forward and down and also imparts a "flip" to the brass which would cause the case mouth to strike the receiver. You can also see on the bottom of the ejction port itself, there is similar wear, probably caused by the same thing. Ejecting brass does all sorts of weird things depending on what it hits and the slight variations in ejection speed

The angle of the buffer has nothing to do with it. I've had three different 91 types and they all do it. I'd like to see a low motion video of the ejection as it would be interesting. One thing is for sure, you don't want a finger in the way. I use a wood handguard on my SAR8 and tend to grip the gun in front of the magwell. Sometimes my fingers will wrap around the receiver and end up near the ejection port but I'm reminded to move them when one of the empties hits a finger. Hurts like hell. And that's on the bottom of the port, not the top or rear.

 

[seasmoke]

Slow motion vids

CETME ejection 420 frames per second - YouTube

CETME ejection @1000 frames per second - YouTube

HK G3A4 firing in slow motion - YouTube

 

[hkshooterusp]

Thanks for those links.
It doesn't look like the cases are hitting below the port in those vids. The 1000fps version is the better one to observe. It would be nice to have a high quality up close version but regardless, that rifle doesn't seem to be hitting below the port. Certainly shows why there's no paint left behind it though.

 

[The_Great_308]

Toku58, I had a PTR with the port buffer and carry handle on to the ejection port side like yours is and had a simmilar thing happen. Every once in a while a shell case would bounce off of the back of the folded carry handle and wedge in the ejection port as the bolt was comming forward. I removed the carry handle and turned it around the other way so that when folded it lays on the other side of the reciever (non-ejection side) and the problem never happened again.

 

[brn2xl]

Since the shell is ejected to the next county, how does this marks get on the receiver?

Sure looks to be from ejected casings hitting the receiver. If brass is "ejected to the next county", you may want to switch to a #9 locking piece. It will reduce the force with which the brass is ejected... and possibly lessen the marking of your receiver. It will also reduce recoil, as it will delay the unlocking of the rollers just a bit.

I have an HK11 built from a 91. It was throwing the brass a mile, and recoil was higher than I wanted (especially when in full auto). I switched to the #9 locking piece, and found it to be the answer.

 

[toku58]

Seems pretty simple to me. Look at the rear of the ejection port. The block is angled so that ejecting brass hits it and heads somewhat forward and down and also imparts a "flip" to the brass which would cause the case mouth to strike the receiver. You can also see on the bottom of the ejction port itself, there is similar wear, probably caused by the same thing. Ejecting brass does all sorts of weird things depending on what it hits and the slight variations in ejection speed

THis isn't my rifle. It's just a picture I found. My rifle didn't have the port buffer on it, but it still has these types of marks.

Toku58, I had a PTR with the port buffer and carry handle on to the ejection port side like yours is and had a simmilar thing happen. Every once in a while a shell case would bounce off of the back of the folded carry handle and wedge in the ejection port as the bolt was comming forward. I removed the carry handle and turned it around the other way so that when folded it lays on the other side of the reciever (non-ejection side) and the problem never happened again.

Sorry this isn't my rifle. I don't have the carry handle.
But I've seen this mark on most if not all the HK .308 that I've looked at. Mine included. But on my rifle you need to look very closely, when you tilt the rifle at a certain angle, and you can see these marks. It appears that the paint is gone but the parkerizing is still there.

I'm thinking that it has to be the casing somehow? But the casing shoots out of the receiver so quickly, I can't see how it could do it?

Even the Youtube videos don't seem to be making contact.

The rifle in the picture I posted is a PTR91.

 

[toku58]

Sure looks to be from ejected casings hitting the receiver. If brass is "ejected to the next county", you may want to switch to a #9 locking piece. It will reduce the force with which the brass is ejected... and possibly lessen the marking of your receiver. It will also reduce recoil, as it will delay the unlocking of the rollers just a bit.

I have an HK11 built from a 91. It was throwing the brass a mile, and recoil was higher than I wanted (especially when in full auto). I switched to the #9 locking piece, and found it to be the answer.

Does that increase your bolt gap? Would changing the rollers be the same effect?

 

[brn2xl]

Does that increase your bolt gap? Would changing the rollers be the same effect?

No change in head space. It's a 40 degree locking piece, while the 91 has a 45 degree... the 5 degree reduction in angle requires more energy to break the rollers free. That dissipation of energy reduces the speed at which the BCG travels rearward, reducing recoil and the energy imparted to the ejected brass.

 

[bluetwister]

If you watch the 3rd video, of the Greek G3, its pretty clear the ejected shell hits the bottom of the ejection port near the middle. It would be nice if the video was a bit slower for clarity.

 

[toku58]

If you watch the 3rd video, of the Greek G3, its pretty clear the ejected shell hits the bottom of the ejection port near the middle. It would be nice if the video was a bit slower for clarity.

Sorry! Hey Mark you're right! I only looked at the 2nd video. But in the 3rd video it does look like the shell is flipping and making contact with the receiver!

 

[blfuller]

The barrel in the 3rd video sure has some whip to it.

 

[hkshooterusp]

3rd video? Did he edit in another? I only saw two, on my way to watch the other.

 

[hkshooterusp]

He's right, it looks like the cases are ejecting differently than the cetme and hitting the bottom of the port. Both of my SAR8's and my old Hesse clone have done this.

I'd not recommend ****ing with the locking piece if the gun is running correctly. HK wanted the empties out of the way to make room for the new ones as quickly and efficiently as possible, caring nothing for cosmetics. Never forget, this is a battle rifle design, not a delicate flower that wants it's water an ounce at a time and only on mondays, wednesdays, and fridays. People forget that just because they over pay by 7-10 times what the gun is really worth and treat the guns like Rolexes don't mean that they fit some sort of magical and glorious image they have for them.

 

[toku58]

He's right, it looks like the cases are ejecting differently than the cetme and hitting the bottom of the port. Both of my SAR8's and my old Hesse clone have done this.

I'd not recommend ****ing with the locking piece if the gun is running correctly. HK wanted the empties out of the way to make room for the new ones as quickly and efficiently as possible, caring nothing for cosmetics. Never forget, this is a battle rifle design, not a delicate flower that wants it's water an ounce at a time and only on mondays, wednesdays, and fridays. People forget that just because they over pay by 7-10 times what the gun is really worth and treat the guns like Rolexes don't mean that they fit some sort of magical and glorious image they have for them.

What?!? Are you insane!! My HK is a Delicate Flower! Which needs to be handled with the utmost of care, and tenderness!!

LOL!!!

I'm planning to install a Protective skin over that area. I'll also modify the claw piece that pulls the shell out. The ejector claw tears at the base of the shells. I don't think it needs to hold the shell so tightly.

 

[tmbrwulf]

I have to agree with USP. If the gun is running right don't mess with it. Granted, You can do you what you want to your rifle. Yes the extractor pulls the rim of the case head and leaves a mark. It does not prohibit the case from being reloaded. Try a piece of gaff tape or heavy duty duct tape to cover the lower part of the receiver below the ejection port. A hand towel can be hung over the port and it will catch the catch the case before it strikes the back side of the ejection port. The battery and extraction process in a roller locked gun is a violent process. A tight extractor is needed to reliably do its job. I did like the joke about the delicate flower, it was funny. Have a good afternoon on the island Sir

 

[hkshooterusp]

toku58, I got a chuckle out of that one. LOL

Like tmbrwulf said, your gun, do what you want. But what you describe is happening by design and my advice is to leave well enough along.
About the ejection port, I've seen folk degrease that area really well and then tape over it with black electrical tape to protect the finish. Seems to work well. On my own guns I consider those marks badges of honor that mean my gun is tougher than your safe queen. LOL

 

[seasmoke]

Kudo's to 'Perro Del Diablo' for vid 1&2.