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End of chamber area...

gunsandgunsmithing

M.Ezell
Gold $$ Contributor
Well, it's cold out so I'm bouncing a couple of things that I've been considering for a while off of the vast knowledge base on here.
Right now I'm thinking about the area of the chamber between where the case ends and the throat begins. It's that 45° area at the end of the case mouth of the chamber.
Just thinking here and again, wondering if others have tried it or just what your thoughts on this are.

Any point like this that is fairly abrupt or has sharp angle changes becomes a heat sink area. We almost all have a borescope of some type these days and it's pretty clear that firecracking begins right there...and it makes sense that it would. Lets focus on this area for a minute. Exact neck diameter can affect the exact numbers but you'll get my thinking pretty fast, I think. In a pretty typical, say .272 6mm neck chamber, this 45° bevel is about .015 long..so it's short and abrupt, right?
I understand that very short freebores won't always work here but lets say we make that area 15° instead of the standard 45°. So, instead of it being about .015 long, it's now about .045 long, so you have to have at least that much freebore before you can even really consider this.

Bottom line, we've smoothed that heat sink down a lot. Will that help bbl life and will it affect accuracy in the short term? Logically, I see no reason accuracy should change either way but I see a very big potential for increasing useful barrel life.

Years ago, when Smith came out with their then new 500S&W revolver, they had pretty significant issues with flame cutting of the top strap portion of the frame. One of their engineers told me how they fixed it and it WORKED....they polished the inside of the top strap!! No rough edges to serve as a heat sink. The flame traveled smoothly over the smooth surface and didn't cut into rough areas, proliferating the whole issue as it grew and grew. I look at barrel break in pretty much the same way but that's a different subject.

So what are your thoughts. I think it has huge potential in regard to bbl life without any negative aspects as long as you have enough freebore in the given chamber design/bullet length etc. Maybe this should go in the gunsmithing forum but I'm mostly interested in competition gunsmith and shooters' opinions. Fire away. I think it's worth discussing unless someone that's done it can shoot it down. Thanks!--Mike
 
Manson Fullbore .223, & I believe, .308 reamers are cut exactly this way. I’ve cut a few chambers with the .223, and they shoot well. I can’t say at this point if they last longer.
Are you sure we're talking the same area? I'd love to see a print from either of those. It has nothing to do with "fullbore"

edit and my apologies. You're correct. I only looked at the 223 fullbore but it's exactly that...15° rather than the .45°
I have to think there is a very substantial increase in bbl life. I'm still interested in any feedback. Thanks Doug
 
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We often hear of some pretty phenominal bbl life with both of those cartridges in their respective games. Any input fro Doug or anyone else in that regard? I'd like to discuss any pros and cons that anyone has. Thinking short range BR stuff but I think anything is good info.
 
We often hear of some pretty phenominal bbl life with both of those cartridges in their respective games. Any input fro Doug or anyone else in that regard? I'd like to discuss any pros and cons that anyone has. Thinking short range BR stuff but I think anything is good info.
I believe Ray Gross designed these so he is the real authority. But IIRC he told me that the idea of laying that transition angle down is to maximize the corner and hence minimize the localized heat build up on that corner that then tears out over time leading to rough freebore entrance.

The T15 FB 223 is 15 degrees and the 2019 308 FB is 30 degrees.
 
I believe Ray Gross designed these so he is the real authority. But IIRC he told me that the idea of laying that transition angle down is to maximize the corner and hence minimize the localized heat build up on that corner that then tears out over time leading to rough freebore entrance.

The T15 FB 223 is 15 degrees and the 2019 308 FB is 30 degrees.
That's my thinking too. I just have to wonder why it's not done more. I haven't seen a downside yet.
 
That's my thinking too. I just have to wonder why it's not done more. I haven't seen a downside yet.
As with anything engineering related there is a balance or trade off. What that is in this case I am not entirely sure. I don’t know if there has been a side by side A vs B study done to quantify the change. I have to believe in a long FB chamber like the T15 the bullet May never even notice. If it was a short FB like a CLE or Wylde meant to fire mag length ammo then results might be different.
 
@Ray Gross 30 SPRC ST RG0 (30-6.5 PRC) was also designed with a 30° angle at that point. I asked him about it in the 30-6.5 PRC thread. He said it was an ongoing experiment.

 
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@Ray Gross 30 SPRC ST RG0 (30-6.5 PRC) was also designed with a 30° angle at that point. I asked him about it in the 30-6.5 PRC thread. He said it was an ongoing experiment.

It seems just about everything has been tried. Not much conclusive here so far. Perhaps there is nothing gained but to my mind, it's hard to see it not helping.
 
Have you considered calling out a radius at the top of the angle where the freebore starts? If it was polished I think that it might help without doing as much damage as a long angle might.
 
Have you considered calling out a radius at the top of the angle where the freebore starts? If it was polished I think that it might help without doing as much damage as a long angle might.
A radius certainly is another option and has been brought up offline. I'm not sure if one way is better than the other. I'm not concerned about damage per se but the radius method would work with a shorter freebore. I suppose you could do both in a reamer design that utilizes sufficient freebore length.
 
Have you considered calling out a radius at the top of the angle where the freebore starts? If it was polished I think that it might help without doing as much damage as a long angle might.
I had this conversation some time ago with Ray and the feedback I received was that the area was so small that it didn’t really matter if it was called out as a sharp corner or radius. You weren’t going to get much if any radius let alone a consistent one.
 
A few years back there was a "bore rider" reamer that got popular
then was'nt. I have a barrel that was givin' to me by Gary Smith
that he used at Ridgway for the 6.5-284. Not sure if this is anything
in the equation, but the fire cracking in it is a good several inches
down the bore and looks like a recently plowed field !!
 
A few years back there was a "bore rider" reamer that got popular
then was'nt. I have a barrel that was givin' to me by Gary Smith
that he used at Ridgway for the 6.5-284. Not sure if this is anything
in the equation, but the fire cracking in it is a good several inches
down the bore and looks like a recently plowed field !!
They re quite different than this but they won some matches. I was not a fan of the idea so I didn't buy into it. It won its share though so I wonder why it fell out of favor.
 

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