chamber throat angle

[VA_XTC_Shooter]

Relevant PS article I recently came across

 

[gunsandgunsmithing]

Relevant PS article I recently came across

Interesting article.

 

[spclark]

Interesting article.

Yeah I thought so too. Worth noting changes over the years.

 

[tom]

My experiences with 6mm heavies we typically use. I just ordered my 8th BRA reamer. Number 1 and number 7 are great. They are 1.5 and I would recommend looking somewhere else. Hopefully I just saved you some $$$$ and time lol.


Tom

 

[johara1]

Jim, like I said in my original post I'm trying fix something that doesn't need fixing. Well maybe, LOL!
Enjoy that new barrel.

I'm more concerned with free bore diameter and length than the angle..... jim

 

[orkan]

Number 1 and number 7 are great. They are 1.5 and I would recommend looking somewhere else.

This would appear contradictory. Did you mean to say "wouldn't?"

 

[gunsandgunsmithing]

I'm more concerned with free bore diameter and length than the angle..... jim

Angle directly affects length

 

[johara1]

Angle directly affects length

So will my 1.5 degree .2438 throater..... jim

 

[tom]

This would appear contradictory. Did you mean to say "wouldn't?"

Would not look elsewhere from the 1.5 yes.( 1.5 good)

Tom

 

[dnellans]

My experiences with 6mm heavies we typically use. I just ordered my 8th BRA reamer. Number 1 and number 7 are great. They are 1.5 and I would recommend looking somewhere else. Hopefully I just saved you some $$$$ and time lol.


Tom

what is the difference between a wheeler 1 and 7? inquiring minds want to know

 

[tom]

what is the difference between a wheeler 1 and 7? inquiring minds want to know

Hopefully nothing up front, it was intended to be a replacement as far as the front end, but with my own body specs.

Tom

 

[Walt Krafft]

The original 6XC used the typical 1.5 degree lead. Then it was changed to .75 degree. That is what the CIP standard shows. The latest 6XC reamer I got from Manson has it back at 1.5. I am guessing that over time it was decided it didn't make any improvement.

 

[VA_XTC_Shooter]

I am reviving this thread instead of a new one because there was a lot of good information in here.
I continued to look at ways to better understand the affects of freebore length and leade angle on the pressure of the cartridge, but also accuracy and barrel life considerations.

I was recently introduced to the work of Jeff Siewert - bulletology.com (I have his book on order to read, but have read through his work available on his website. One article in particular, Gun Barrel Considerations Gun Barrel Configuration Info v2.pdf (storage.googleapis.com)
touches on some of these aspects. There are multiple barrel aspects discussed in this article, I would like to keep this thread focused on the leade angle, what he calls force cone angle. I will make other threads to discuss other aspects of this article for better housekeeping and reference.

Starting on p. 7, Mr. Siewert discussed Forcing Cone Angle. He compared the engraving pressure on the bullet that entered a 1.2* forcing cone vs a 2.5* forcing cone. What is interesting is that the 2.5* forcing cone has a lower engraving pressure, opposite of what I would have expected. However, the standard deviation of the 1.2* forcing cone was lower than the 2.5*, thus more consistent muzzle velocity.

What is not addressed and would need further testing is, what is the life of the forcing cone angle? Obviously, this is cartridge dependent, but which angle would last the longest?

 

[VA_XTC_Shooter]

I found the complete study Siewert conducted for ARDEC
Complete Engraving Force Study

 

[gunsandgunsmithing]

What is not addressed and would need further testing is, what is the life of the forcing cone angle? Obviously, this is cartridge dependent, but which angle would last the longest?

Sorta related...I have a new reamer on order that I changed one area on. The very end of the chamber neck is typically 45°. I am having that angle layed down to 15°. The sole thought being toward better bbl life, due to a smoother flame travel, err heat sink. Anyone that's ever looked at a bbl with a borescope knows that's the area where fire cracking seems to begin. We'll see in time how it works out. I don't expect any change in accuracy but maybe a little less carbon, possible small increase in velocity but the main goal being less erosion at that starting point....fwiw.

 

[VA_XTC_Shooter]

I am not aware of any other actual data on throat angle

Sorta related...I have a new reamer on order that I changed one area on. The very end of the chamber neck is typically 45°. I am having that angle layed down to 15°. The sole thought being toward better bbl life, due to a smoother flame travel, err heat sink. Anyone that's ever looked at a bbl with a borescope knows that's the area where fire cracking seems to begin. We'll see in time how it works out. I don't expect any change in accuracy but maybe a little less carbon, possible small increase in velocity but the main goal being less erosion at that starting point....fwiw.

I am also interested in the reamer neck length. It appears many are 15 thou longer than the spec case length. To me, you are just inviting carbon build up between case mouth and the transition you are referring to. I would like to see only 5-8 thou longer than case neck and perhaps a different angle to into the freebore, those combined may decrease carbon build up. I visualize that section as a turbulent section of hot gases and with the hard angles, almost an eddy created allowing carbon to deposit easier.

 

[gunsandgunsmithing]

I am not aware of any other actual data on throat angle

I am also interested in the reamer neck length. It appears many are 15 thou longer than the spec case length. To me, you are just inviting carbon build up between case mouth and the transition you are referring to. I would like to see only 5-8 thou longer than case neck and perhaps a different angle to into the freebore, those combined may decrease carbon build up. I visualize that section as a turbulent section of hot gases and with the hard angles, almost an eddy created allowing carbon to deposit easier.

I agree about the carbon. A while back, due to availability issues, I used 220r brass to make into 6 Grendel. I never could get the neck to grow enough to suit me but it shot just fine. Still, it did leave about .020 extra area between the end of the case mouth and end of the chamber for a carbon ring to develop. I think it would just be a matter of diligently staying on top of that carbon ring if need be. Fortunately for me, I found and bought some Grendel brass to hold me for a good while.

 

[LCazador]

Since I started this post I have ordered a new reamer with a 1.75 degree throat angle. I've been shooting now for two years and there isn't much difference in accuracy or wear. I do see a slight difference but not enough to warrant the cost of a new reamer. This is a 6X47 40 degree chamber with .290" neck. About 400 rounds down the barrel. At first I thought it made a difference in group size but I've since tweaked that load a number of times on bullet tension and jump. Maybe a couple of hundred rounds more will make a difference. Nothing scientific about my experience, just satisfying my curiosity.

 

[VA_XTC_Shooter]

Between 1.5 and 1.75, I don't think I'd expect to see a difference.