Issue solved- Gas gun fun.

[Precision Underground]

I have an affection for precision gas guns so I was pretty happy when the 6.5 Mega Maten we put together shot dime size groups on the first two outings. After that it went south. It went from pretty much all good groups to mediocre/random groups mixed with bad groups for 100 rounds or so while I chased my tail.

I had changed the buffer spring out right before it went bad so I was sure that was it.....Put the old one back in and still bad. I looked over everything and messed around with the loads trying to figure it out. I had cleaned it already but decided to clean the crap out of it and stick the scope in it. Well this doesn’t look right...

Gas port is drilled in the center of a groove and has a huge chunk of copper on the front side of it. This is after some scrubbing with a wet patch, it was much worse before. I let a wet patch sit on it overnight and it finally wiped out. At this point I am hoping this was the issue-

Loaded 5 in a mag with fingers crossed.....

Figured I probably pulled the one out of the group because I hate shooting from benches. But this was much better than what it was doing before. Load 5 more....

And we’re back! Still a little pull in there on my part probably- but for a large frame from a bench I’ll take it! So PSA, if your gas gun starts to act stupid check for a wad of copper at the port. This was a new one for me. I think I had scoped it the first time I cleaned it but must not have looked closely at the port. I’m thinking if I keep the copper cleaned off the area for a bit it will smooth out and stop grabbing hopefully? Anyone ever have this happen?

 

[LANCER]

I'm gonna borescope mine cause it started shooting 2 inches with a known good load. Didn't think it would be fouled like that since it's only been 500 rounds since last cleaning. Maybe I have the same port issues you're having. Thanks for the heads-up.

 

[bigjake83]

Who makes the Barrel and did you JB it?

 

[Precision Underground]

I'm gonna borescope mine cause it started shooting 2 inches with a known good load. Didn't think it would be fouled like that since it's only been 500 rounds since last cleaning. Maybe I have the same port issues you're having. Thanks for the heads-up.

Yea take a look and see. I’d say 500 is plenty to need cleaning for accuracy. Some barrels maybe not but some barrels will need it by then for sure. Ours has been hammering since keeping the port clean. It seems to be grabbing less each time I look and clean it.

Top group is a different gun. That is 5 shots.

 

[Precision Underground]

The Valkyrie is hammering too. Both of these guns are begging to be shot at a match.

 

[2aBaC̶a̶]

That's interesting. Now I'm curious to know where all mine fall.

I wonder do they plan where the hole sits in the rifling.

 

[Precision Underground]

That's interesting. Now I'm curious to know where all mine fall.

I wonder do they plan where the hole sits in the rifling.

Best I can tell most companies just let them fall where they fall. I think a few will put it between a land and groove with the thought that it will be the least offensive to the bullet. I think it doesn't matter as long as you don't get buildup on it. Mine appears to be smoothing out so hopefully no more cleaning every 100 rounds in the future!

 

[Gatorshark]

If I wanted a precision barrel that shot creed that well in my Maten, fowling aside, where would I find such?

I'm running a criterion and it's not quite that good.

 

[Precision Underground]

If I wanted a precision barrel that shot creed that well in my Maten, fowling aside, where would I find such?

I'm running a criterion and it's not quite that good.

Funny story. When putting this together I came across the Ballistic Advantage premium barrels on closeout for like $160 and I think the site even had 10% or so off of that. They had the length, profile, and fluting that I wanted so I figured at that price why not give it a shot...... I think the total was in the $140s. It's a freaking laser. Not to say all of them would be but this one definitely is. I've had a few criterion bolt gun barrels that are stupid accurate too.

 

[The DFC]

Interesting. I look for that stuff ever since i got my endoscope.

 

[Gatorshark]

BA does put out some good barrels. I have one on a 5.56. If the word ever gets out that they are under priced, they wont be any more.

My Criterion doesnt do quite that good yet but I just cant shoot a gas gun with precision for nothing. Action shooting is a different story. Thanks for the share.

 

[RedDogN8]

Could you post the after pictures of the gas port after cleaning? Just like to see the difference.

 

[Precision Underground]

Could you post the after pictures of the gas port after cleaning? Just like to see the difference.

I didn’t take any but I will next time I clean it. Where you see the copper there on the groove im sure was squared off when it was new. The first time I cleaned it all off it was kind of rough looking like maybe the corner popped off but it’s starting to get tapered smooth which is what I was hoping for.

 

[Sieg]

This is where a bore scope pays solid dividends.

 

[Precision Underground]

This is where a bore scope pays solid dividends.

For sure. I had to stick a wet patch down to the area and let it sit overnight. No way I would have known to do that if I couldn’t see it.

 

[2aBaC̶a̶]

Imagine what kind of tool it would take to debur or ream the hole inside the barrel.

 

[Precision Underground]

Imagine what kind of tool it would take to debur or ream the hole inside the barrel.

Don’t think I didn’t consider it lol.

 

[2aBaC̶a̶]

Don’t think I didn’t consider it lol.

I've been thinking about it off and on all day since I saw it.

 

[Gatorshark]

There no telling how often something similar effects accuracy. Then again many "shooters" would not think twice about the flyers.