Why Deep Chamfer on Barrel Chamber?

[Carl S]

Just break the edge and a polish

 

[AckleymanII]

Mike, after the Case rupture, I used a tad bit of grease on the bolt face, cut a tiny piece of thin Solder and placed it in the grease. Then checked the thickness of the piece of solder.

There was .032 clearance between the bolt face and the cone in the barrel, way too much.

I checked every rifle I had, and seemed like .007-.013 was what I came up with.

 

[GenePoole]

Mike, after the Case rupture, I used a tad bit of grease on the bolt face, cut a tiny piece of thin Solder and placed it in the grease. Then checked the thickness of the piece of solder.

There was .032 clearance between the bolt face and the cone in the barrel, way too much.

I checked every rifle I had, and seemed like .007-.013 was what I came up with.

I use a rounded tip micrometer as the solder tends to curl.

 

[AckleymanII]

Thanks for the Tip Gene! I see you hit your number on the button!

Mind me asking how thick is that piece of solder you are using?

 

[linebaugh]

Wow. I thought the first pic was bad, that 300 whisper chamber is insane.

Seems this is becoming more common and everyone thinks they are gunsmiths. I've seen some cringeworthy youtube videos that prove this unfortunately.
I shoot for .005 bolt clearance and .003 or less on chamber. I typically break the edge and polish with 320.... and I am a hobbyist.

 

[GenePoole]

Thanks for the Tip Gene! I see you hit your number on the button!

Mind me asking how thick is that piece of solder you are using?

Not sure. It is an ancient roll of solder that came with the shop. I believe it is electronics solder, not plumbing solder. I'll check next time I'm at the shop.

 

[AckleymanII]

Thank you Gene! I am sure that it is electronic solder.

Firing pin hole is an approximate, but will do a google search to find the size.

 

[Scott-ak]

Mike, after the Case rupture, I used a tad bit of grease on the bolt face, cut a tiny piece of thin Solder and placed it in the grease. Then checked the thickness of the piece of solder.

There was .032 clearance between the bolt face and the cone in the barrel, way too much.

I checked every rifle I had, and seemed like .007-.013 was what I came up with.

Do any smiths use plastigauge to make this measurement? It's made for just this kind of thing. https://www.plastigaugeusa.com/plastigauge.html

 

[jackieschmidt]

That chamfer is a good .040 deep
A PPC case is solid for about .150. This is off of a Panda. On these, there is .135 case protrusion plus bolt to bbl clearance. Kelblys tenon print allows .007-.010 for this clearance and at that, it would have .145 unsupported case protrusion..all solid.
This much chamfer does nothing good and leaves a great deal of thin unsupported brass protruding. I usually just polish that edge with 320 grit paper on a small rod. Never a feeding issue nor scratched brass.
View attachment 1349355

That is ugly.

On PPC cases and BR cases, I just polish the corner, especially on my early Farley’s like this 30BR chamber.

 

[Tim Singleton]

View attachment 1349403

I got one like this a few years ago.
One of the reasons I do my own work

 

[tobnpr]

Do any smiths use plastigauge to make this measurement? It's made for just this kind of thing. https://www.plastigaugeusa.com/plastigauge.html

Yep, I do.

 

[davidjoe]

This is the result of to much clearance. He said the first round seemed a little hot because the bolt opened a little hard. This was the second shot.
This was in a Borden action 6 PPC , 68g bullet and 28+ grains of H 4198.

Joe

I’ve seen a rupture like that at a match. The rifle was ported on the side that put the “unused” eye and cheek in the cone of escaping brass and powder. It was scary and bloody.

I’m at the end-user not production side of match shooting but I really noted a few things from that episode,

a) Savages’ nearly-unique in the industry blind lugs behind the functional lugs aren’t there just to look awkward;

b) not everyone realizes there are two extremely different kinds of “case head separation”; and,

c) an excessively-unsupported case by itself can never be detected by go and no-go-gauges, nor even just by comparing the bolt nose to the face and the lugs’ gap to tenon.

 

[Walt Krafft]

6BR and 6PPC I don't run the barrel cone all the way to the chamber. I go straight out to the diameter of the bolt face plus .01 then start the cone. Repeaters work fine this way. Saw a BR blowup Sat that had the cone all the way to the chamber. Worked fine for a couple hundred rounds then it didnt. Shooter is ok but rattled. Lens was completely peppered. Would have been bad if he wasnt wearing safety glasses.

 

[dnellans]

6BR and 6PPC I don't run the barrel cone all the way to the chamber. I go straight out to the diameter of the bolt face plus .01 then start the cone. Repeaters work fine this way. Saw a BR blowup Sat that had the cone all the way to the chamber. Worked fine for a couple hundred rounds then it didnt. Shooter is ok but rattled. Lens was completely peppered. Would have been bad if he wasnt wearing safety glasses.

Can you provide a visual on this? I’m not sure I get what you mean.

 

[gunsandgunsmithing]

Can you provide a visual on this? I’m not sure I get what you mean.

I'm with you. I'm guessing he's done something like the pic I'm about to post. Stiller did this on some of their actions. But the bolt nose had a small flat on the end instead of going to a full cone nose and it used a snap in remington style of extractor so that the full nose diameter wasn't compromised anywhere.

I'm not picturing how it can reduce unsupported case unless done pretty much just like Stiller did his, with the flat nose on the end of the bolt. He also used a very shallow cone angle, fwiw.

Sorry for pic quality but the original is even worse. Lol!

 

[LVLAaron]

c) an excessively-unsupported case by itself can never be detected by go and no-go-gauges, nor even just by comparing the bolt nose to the face and the lugs’ gap to tenon.

Yep. You can headspace perfectly and have a poorly supported case. For the chambers I've done for other people, I have taken photos and recorded measurements to keep "on file" just in case... but it's something you should always check on your own before firing a new barrel.

 

[Dusty Stevens]

I'm with you. I'm guessing he's done something like the pic I'm about to post. Stiller did this on some of their actions. But the bolt nose had a small flat on the end instead of going to a full cone nose and it used a snap in remington style of extractor so that the full nose diameter wasn't compromised anywhere.

I'm not picturing how it can reduce unsupported case unless done pretty much just like Stiller did his, with the flat nose on the end of the bolt. He also used a very shallow cone angle, fwiw.

Sorry for pic quality but the original is even worse. Lol!

That was for the drop ports. A rem extractor is the only safe way to have a drop port so it doesnt have a fully exposed extractor in your face

 

[gunsandgunsmithing]

That was for the drop ports. A rem extractor is the only safe way to have a drop port so it doesnt have a fully exposed extractor in your face

Right. I shot one for a long time and liked it. Had to have another one so I bought a Borden not long ago, in a dp. That's another extractor design that doesn't compromise the bolt nose. Pretty good design. A little like a 1911 extractor design.

 

[jackieschmidt]

I'm with you. I'm guessing he's done something like the pic I'm about to post. Stiller did this on some of their actions. But the bolt nose had a small flat on the end instead of going to a full cone nose and it used a snap in remington style of extractor so that the full nose diameter wasn't compromised anywhere.

I'm not picturing how it can reduce unsupported case unless done pretty much just like Stiller did his, with the flat nose on the end of the bolt. He also used a very shallow cone angle, fwiw.

Sorry for pic quality but the original is even worse. Lol!

The Stiller Drop Ports were extremely critical in the nose to barrel clearance On the BR and PPC chambers. They have a Remington Style bolt nose and extractor, and with the case chambered, the forward end of the extractor groove was actually Inside the bolt nose a tad.

it all worked, you just had to hold the dimensions within .005 or so.

 

[jackieschmidt]

The Stiller Drop Ports were extremely critical in the nose to barrel clearance On the BR and PPC chambers. They have a Remington Style bolt nose and extractor, and with the case chambered, the forward end of the extractor groove was actually Inside the bolt nose a tad.

it all worked, you just had to hold the dimensions within .005 or so.

sorry, Dusty, we were typing at the same time.