barrel ulcer!

[jvw2008]

I have a Rock River ATH that shot lights out for the first 300 rounds but accuracy is now rapidly deteriorating with my pet load (approximate 52,000 psi load based on QL calculation). Same scope and rings (triple checked tight). Group dispersion is random - not all vertical or horizontal, but scattered. 100 yard groups have gone from average 0.300 MOA to 1 and 1/2 inches. Same powder lot, same bullet lot and same average muzzle velocity (2860 fps). My bore scope indicates the lands are very clean and the rifling is excellent. The barrel gas port however is a different story. At that site the barrel metal has a cavitation which is deepest at the port hole and extends throughout the groove half way into an adjacent rifling (rest of rifling is very good). The surface of the ulcerative-like change is pitted, but the surrounding metal is very clean. I haven't had the opportunity to scope enough gas AR barrels to know if this is an expected change or if it is indicative of a defective gas system or barrel metal. Through routine cleanings I know the gas system is clean and the rifle cycles normally. Anyone seen this before? What are your thoughts?

Thanx for any help,

Jerry

[MarkCO]

I have seen a lot like that, but they had a lot more than 300 rounds on them. The gas port is one of the first places erosion starts and is more pronounced with slow powders. On a new barrel, it can be due to poor chrome lining, heat treatment or a dull bit with the gas port was drilled.

If it is a new barrel, you need to have the manufacturer get you a new one!

[jvw2008]

Chatted with RRA yesterday. The tech wasn't willing to state that this change was the cause of decreased accuracy. I don't blame him - hasn't seen the rifle and doesn't know if the problem is the rifle or the driver. I thought about sending it back for a replacement barrel but I'm dickering with the idea of doing a rebuild with a 22 to 24 inch heavy match barrel. Unfortunately I'm not familiar enough with our Colorado gunsmiths to know who would be a good choice for the job. Any suggestions?

[Great-Kazoo]

Chatted with RRA yesterday. The tech wasn't willing to state that this change was the cause of decreased accuracy. I don't blame him - hasn't seen the rifle and doesn't know if the problem is the rifle or the driver. I thought about sending it back for a replacement barrel but I'm dickering with the idea of doing a rebuild with a 22 to 24 inch heavy match barrel. Unfortunately I'm not familiar enough with our Colorado gunsmiths to know who would be a good choice for the job. Any suggestions?

It's a 10-20 minute job with the right tools. I or someone else in this area might be able to assist.

[beast556]

Buy the barrel you want and take Jim up on his offer. Changing out an ar barrel is a simple task with the right tools. Jim has helped me out many times in the past and knows what he is talking about.

[Great-Kazoo]

Buy the barrel you want and take Jim up on his offer. Changing out an ar barrel is a simple task with the right tools. Jim has helped me out many times in the past and knows what he is talking about.

When i'm sober[er] ;)

I'll just watch and make suggestions.. WHAT DA FUK YOU DOING ??????