Unsupported case, again.

[Dusty Stevens]

I see this type stuff quite often with new age gunsmiths. Most cater to the prs crowd and i guess the reasoning behind it is trying to fix feeding issues. I think they used a wood counterbore on that one. This is a danger on prefits as well- the counterbore vs. headspace is luck if its right. As you can see it doesnt take much to be in dangerous territory

 

[Edd]

That print does not tell you how much unsupported case you will have.
The BATS I have played with do not make me nervous.

If the bottom of the print wasn't cut off it would show that you would have about .160".

 

[Clark]

1) I have overload worked up 223 many times.
2) I have overload worked up 9x19mm many times with 0.180" feed ramp intrusion with a 0.160" thick case web and a 0.015" thick case wall. That is good enough case support for overloading until the primer falls out.

3) But I have never overloaded a 223 with feed ramp intrusion.

4) My guess is that if Doug has 0.009" of unsupported case wall 0.040" thick, the primer pocket enlarging will still be the weakest spot in the brass

 

[Clark]

This case failure in a new Rem700 223 caused and eye injury that required medical treatment.

 

[boltfluter]

I see this type stuff quite often with new age gunsmiths. Most cater to the prs crowd and i guess the reasoning behind it is trying to fix feeding issues. I think they used a wood counterbore on that one. This is a danger on prefits as well- the counterbore vs. headspace is luck if its right. As you can see it doesnt take much to be in dangerous territory

As Dusty said, I have seen some very large chamfers on the end of a lot of Remington chambers in the last five years. Many are playing with fire and do not even realize it! Sooner or later they will get bitten.

Paul

 

[dnellans]

I'd like to see some pics of the kinds of barrel and chamber edge chamfer that guys here are putting on their work.

I've never seen a barrel with that kind of multi-angle chamfer shown a few posts back that looks almost like a saucer dish. That first angle is so shallow that I don't even see how it could help with feeding, the bullet tip is still going to ram into that sucker.

I've typically been using a 30 degree chamfor on mine but its "small" compared to these examples. Why 30? simply because the compound is set there so it makes it quick and easy, though I know others that just manually free hand a 45'ish onto it.

 

[DaveTooley]

I normally put a .020" -025" 45 on mine. Saves polishing in a radius.
I do some barrels that have a wide shallow angle with a good size radius entering the chamber. No problems.

 

[Clark]

I put just enough chamfer on the chamber orifice to get the case mouth edge to slide up.

 

[McFred]

This case failure in a new Rem700 223 caused and eye injury that required medical treatment.

Is it known if the shooter was wearing eye protection?

 

[pdhntr]

I'd like to see some pics of the kinds of barrel and chamber edge chamfer that guys here are putting on their work.

I've never seen a barrel with that kind of multi-angle chamfer shown a few posts back that looks almost like a saucer dish. That first angle is so shallow that I don't even see how it could help with feeding, the bullet tip is still going to ram into that sucker.

I've typically been using a 30 degree chamfor on mine but its "small" compared to these examples. Why 30? simply because the compound is set there so it makes it quick and easy, though I know others that just manually free hand a 45'ish onto it.

If you are referring to the PDF in post 6 of this thread, the drawing is a cross section of a barrel face for a coned BAT bolt. The bolt cone to barrel face is .007 +/- .003

Jim

 

[McFred]

I'd like to see some pics of the kinds of barrel and chamber edge chamfer that guys here are putting on their work.

I'm an amateur, not a smith, and none of the ones I've done are "prefits." They're all shouldered. As long as it feeds, and doesn't scratch up brass, I don't see a reason to go nuts on a chamfer. The "8-groove" was done professionally by an unknown gunsmith, but it's not out of line with factory examples.

 

[Clark]

Is it known if the shooter was wearing eye protection?

No. He was shooting prairie dogs and ran out of ammo. He grabbed someone else' ammo with 15 gr blue dot powder and 33 gr Vmax. Blue dot is known for uneven metering.

 

[mr45man]

That print does not tell you how much unsupported case you will have.
The BATS I have played with do not make me nervous.

Well if the smith machines to the drawings and not to “what difference does it make then there will be zero unsupported.

 

[tobnpr]

As Dusty said, I have seen some very large chamfers on the end of a lot of Remington chambers in the last five years. Many are playing with fire and do not even realize it! Sooner or later they will get bitten.

Paul

Zombie thread but WTF...
I agree 100%.
There's a fairly popular online blog (I won't name it), where they guy chronicles his gunsmithing/rifle builds.
Not a pro smith.
Most of the time, his methodology is fine. Maybe not how I do it, but we all know there's many ways to get from "A" to "B".

But I noticed on one M700 build, he used a cutter to put a radius on the counterbore and at the entry to the chamber. Matters not what you do on the counterbore (within reason of course)- but the radius at the chamber mouth was HUGE. Apparently, oblivious to the fact that the larger that radius, the more unsupported case he created. Yeah, it'll feed well, until it goes kaboom...

 

[dnellans]

zombie thread? most active gunsmithing thread in months!

fairly popular blog? never heard of it... link it?

... and a big thanks to all the real 'smiths that are willing to take the time to illustrate, educate, and intrepidate all us hobby home turners. i'm not sure there is a better gunsmithing community on the web right now!

 

[Alex Wheeler]

Just did a cadex in 6.5 creed. Followed the print other than I fitted the bolt face clearance to .005". Had .175 of unsupported case. I changed to cone angle until I got it to under .160. With the original print I would not send it out of here. A solid case head for lapua 6.5 creed is .175" thick. Check everything...

 

[dnellans]

What does the print for a cadex call for? I can't find a print for them online.

I just did a surgeon 591 and their clearance is .155 (-0 +.005) that doesn't leave much room to put a chamfor on if you don't want anything over .160

 

[Alex Wheeler]

It doesnt give a spec for exposed case. I just cut the cone angle to spec but set it up as tight as I could and it was about .175 exposed case. Probably would be fine, but I was uncomfortable, so I changed the cone angle until I got to .160". It still fed fine. I think you could get into trouble on those if you put a big chamfer at the back end. I dont chamfer the back end of chambers, just hold a little 400 emery on them to knock the sharp edge off. Never had a feeding issue.

 

[Dusty Stevens]

Some of these newcomer actions are rediculous in their engineering

 

[338 Mollett]

I like to shoot for 5 thou.clearance all the way around,and take a small file to the chamber edge and sand paper to just knock the edge off.But I do cheat and go about a 1/2 degree flatter on the cone.