Barrel speeding up, carbon rings, chasing lands, 6 Creedmoor

[JRodMT]

About the time I think I‘ve got shooting/reloading figured out, I come across something else that make me scratch my head.

I occasionally shoot competitively and reload for multiple rifles. My rifles generally shoot 1/2 minute groups and I don’t normally spend much time doing load development to get there. On average I shoot 2-3000 rounds per year. All I’m saying is I’m not a complete newbie but I feel like one.

The rifle is a 6mm Creedmoor. I’m on my 2nd barrel and it’s throated for 115 DTACS. I‘ve been shooting H4831sc through 28” Proof Stainless barrel. My theory is that with H4831sc and a long barrel that I can squeeze more barrel life out. I’m jumping .020” and I clean after every match with nylon brushes etc. It shoots 1/2 minute at 3035fps with 42.8gr of powder. Anyways...

Recently my groups have grown to 1 moa and I’m getting an ES of 25-30. I’ve never had a problem getting my ESs down on anything else so I know my prep and loading skills aren’t lacking. I‘ve got 1000rds on the barrel and it seems like it just keeps getting progressively faster, not slower. Tonight, I scrubbed and scrubbed the barrel with a brass brush this time thinking a possible carbon ring was to blame or hard carbon that just wasn’t cleaning out. I use Montana Extreme Copper Remover until patches come out clean. I remeasured the throat over and over by pulling the firing pin and seating the bullet until the bolt drops. I’ve also used the Stoney point gauge and getting similar measurements. It’s showing only .010” of throat wear which just doesn’t seem right.

I can’t explain the rise in velocities as I’ve pulled 2gr of powder (from the same 8lb jug) out of my load in 1000rds to try and sustain 3035 FPS. It’s just unlike anything I’ve ever experience. I’m almost slightly embarrassed to ask for advice as it seems like such a novice predicament.

What are your thoughts?

 

[spife7980]

How many firings on the brass? Annealed? Could be necks are getting harder.

 

[JRodMT]

3 firings on ADG brass. I anneal every other loading. I run Redding Type S bushing dies with .002” neck tension. No variations on seating depth which tells me the consistency is good.

 

[Timo Turl]

Check neck thickness vs new brass. I have a tight neck chamber, found brass necks thickened considerably and that led to a sharp increase in velocity. Speeds went back to what they were once I neck turned back to new brass dimensions.

 

[mustang-cars]

I believe you have a carbon ring. I know you said you've been cleaning after every match but my experience with carbon rings is they are very stubborn and problematic to prevent and without the proper maintenance once you get a carbon ring nothing short of bore polish will get it out. Some guys say CLR will do it but I haven't tried that. I use Boretech Eliminator for my first stage of cleaning and then I use Boretech C4 carbon remover with a soaked VFG aggressive pellet sitting in the throat for 20 minutes then I short stroke the throat and check it with a borescope to make sure its not building up carbon in the throat. I do this every 300 rounds and always check with the scope afterword to verify. This is the only way I've found, for me, to eliminate carbon rings. This is with a 6.5CM. I had several carbon rings with the 6.5CM which most people told me was not likely but time and experience have said otherwise. It is exponentially worse with a 6CM.

Long story short I would find someone with a borescope or buy the cheap one off of Amazon to verify what is going on. That's the easiest and quickest way to eliminate the problem.

 

[918v]

Stop cleaning with nylon brushes.

Nylon brushes are for bitches.

Bronze brushes don’t hurt the bore.

 

[Tnek13]

Try Sip 2000 - Carbon Killer there are others but this seems to work best. A borescope also helps to let you see what is going on as carbon and copper layer inside the bore.

 

[JRodMT]

Thanks for the help guys. I’d have to agree about using bronze brushes. I bought into the barrel damaging rhetoric and the only difference I see in using nylon brushes is that it takes twice as long to do a shitty barrel cleaning job. I hate to admit that is probably the majority of my issue. I’ve got some carbon killer ordered and I‘m going to switch up my cleaning methods. I’m more amazed that I haven’t came across this issue with any other rifle that I shoot and load for until now.

I did find after a more thorough cleaning/soaking that my ESs are in a more acceptable range and my groups are back to a consistent 1.4” @ 300 which after 1000 rds and minimal throat erosion, tells me that my theory of DTACs paired with 4831sc in a 28” barrel may provide me with significantly more barrel life than seen with other combinations. A borescope would also be a solid investment.

I also have .003” neck clearance in my chamber so that isn’t the an issue either but worth noting.