6CM Update for 6CM shooters

[joesr]

Disclaimer: I know that many people are tired of the “pimping” regarding the 6CM. This post is not intended for people not shooting the 6CM. I know that my customer read these posts regularly and possibly some people thinking about chambering for the 6CM may be interested.




I bore scoped my barrel today for this first time in about 700 rounds. The current barrel has about 3300 rounds and is showing wearing of the lans for about ½ inch, best as I can estimate) and some fire cracking for about 3”.

However, I looked this barrel over, from both ends, and I’ve come to the conclusion that, at some point in the near future, I’m going to set it back by 1” and I have to believe that the overall shots through the barrel with “winning accuracy” will be close to 6500 or 7000 rounds.

The barrel I’m talking about is a Kreiger in 1:7.5. 4 grove. Currently, it is still shooting great. However, if it is rechambered before it starts to go it should be good for many more rounds.

As soon as I have my next barrel ready to go I’m going to pull this barrel and have it rechambered. The current barrel shoot extreamly well, many groups under ¼ MOA and giving this barrel another season by rechambering is my goal.

I never intended to rechamber a 6CM. I thought that the barrel would ware out throughout the entire barrel before the throat area gave up. But with today’s inspection, I know the throat is going to go long before the rest of the barrel.

However, looking at the barrel, not much beyond the throat, I see no reason not to rechamber the barrel.

The current barrel is 28” and I’m not sure what the velocity difference will be at 27”, but I’m sure it will be less that 100 fps. Furthermore, this barrel shoot great and I’d hate to give it up.

It will be later this month when I get a new barrel ready and then probably July before this barrel is rechambered. So it will be a few months until I have the results of the accuracy for the rechambered barrel and it will probably be almost a year until I have the actual round count from the rechambered barrel.

But, assuming the rechambering is successful and the barrel can be used for another season. If that is the case, I will have shot the same 6mm barrel going into the 3rd season.

If the rechambering of my barrel is successful, then probably my customers should, when the time comes, send back their barrel to be rechambered rather than buying a new barrel.

Only time will tell.

However, I am now expecting my 6CM, with rechambering, to yield over 6000,probably 7000) rounds per barrel with the initial chambering yielding close to 4000 rounds.


Joe Hendricks

 

[Raptor]

Joe,
I am not a gunsmith so I don't know for sure on this. I had a 260 that was a 26" barrel.,Pac Nor 3 groove) When it was a 26" barrel I was never really happy with the accuracy. I originally had it built as a tactical rifle and it shot well enough for the type of shooting that I was doing under field conditions so I stayed with it.

At a match in Wyoming I got the barrel very hot on a man on man match and after returning home the rifle fouled heavly. I had it bore scoped and found that a small piece of the barrel had actually came out of the rifling!!

I sent it back to Pac Nor and Chris said that it was flaw in the metal an he would replace the barrel at no charge to me. He did and I got the old barrel back too.

After cleaning and bore scoping the barrel it was heat cracked for at least 7"s down the barrel.,When this all happened the barrel had close to 1600rds through it).

To make a long story short I got a wild hair and had 4"s cut off the chamber end and made a 22" barrel out of it and put it back on the action. The smith told me it was a junk barrel and he would not recommend doing this. He also said the barrel would "NOT" last very long in his opinion.

Well when I got it back it went from a .6 gun to a .3 gun!!! I shot it another 700rds or so and then put on a new Kreiger that I had won at a match. It was still shooting very well when I had it removed. I would have liked to see how long it would have lasted.,I replaced the barrel because it was the start of my season and I was not wanting to have to be down in the middle of my shooting season to replace the barrel if it did go bad).

I have been told by seveal smiths that they don't like doing it and they won't last very long. Just wanted to share my experience with you on this. Hope it works out for you.

 

[joesr]

The difference here is that the 6CM barrel is only showing signs of normal ware.

Cleaning up the throat of the chamber should not change anything else with the barrel.

The barrel still shoots 1/4 to 1/2 MOA groups and by cleaning up the throat there is no reason not to think that the barrel will last for another 2000 to 3000 rounds.

The rest of the barrel is in great shape.

Joe Hendricks

 

[Rob01]

Ever think about using some Tubbs TMS rounds instead of having to go through the whole cutting back and rechambering? The TMS rounds will smooth out the thraot area and not hurt the rest of the barrel. I use them every 300 rounds in my 300WM and .243 to keep the throat smooth.

 

[Rustystud]

Joel:

I have followed your post for a while now with intrest. My 35 years of rebarreling experience has shown one looses about 40 fps per inch in the barrel length your talking about. My expereience has shown that set backs on .243s and .260s done at the point when the throat errosion is the only sign of wear gives on the average about 700-900 more rounds of usable barrel life. When the barrel heat cracking begins the barrel life is in short order. You have pushed the envelope by using slow powder gas flow friendly shoulder angles and polishing the throad and bore. Your coating obviously adds to the life of the barrel. The military has proved this in a simular way with chrome lined bores. I believe there is a correlation of optimum case capacity, powder burn rate and velocity in the accuracy node. IE 6mm 105-105 shoot best with a 1.7 to 1.85 twist and a velocity between 3000-and 3100fps. This is why the 6mmbrx and 6 Dasher are doing so well. There are many cartridges that can easily push 6mm bullets at 3400 to 3600fps but again barrel life goes away as does accuracy. It will also be interesting to see how the 6 X 47 does with barrel life.

Keeps posted on your findings
Rustystud

 

[chrisj]

I just can't imagine that the 6-6.5x47 will get any better bbl life than the 6xc. Capacity is right about the same. The same poder and amounts of powder is the same. Velocity is about the same. Shoulder angle and neck length is nearly identical. The only variable may be the small primer. Is it possible that temperatures are lower with the small primer?


Chris

 

[joesr]

Joel:

I have followed your post for a while now with intrest. My 35 years of rebarreling experience has shown one looses about 40 fps per inch in the barrel length your talking about. My expereience has shown that set backs on .243s and .260s done at the point when the throat errosion is the only sign of wear gives on the average about 700-900 more rounds of usable barrel life. When the barrel heat cracking begins the barrel life is in short order. You have pushed the envelope by using slow powder gas flow friendly shoulder angles and polishing the throad and bore. Your coating obviously adds to the life of the barrel. The military has proved this in a simular way with chrome lined bores. I believe there is a correlation of optimum case capacity, powder burn rate and velocity in the accuracy node. IE 6mm 105-105 shoot best with a 1.7 to 1.85 twist and a velocity between 3000-and 3100fps. This is why the 6mmbrx and 6 Dasher are doing so well. There are many cartridges that can easily push 6mm bullets at 3400 to 3600fps but again barrel life goes away as does accuracy. It will also be interesting to see how the 6 X 47 does with barrel life.

Keeps posted on your findings
Rustystud

Thanks for your kind words.

One note though....I am not using any coating on the bullet or barrel. I am shooting "naked" bullets.

Thanks,

Joe H