Chamber cast for new barrels?

[Chism G]

Chamber Cast

I've done two chamber castings with Cerrosafe. Its easy to do with the barrel off the action. Never tried it any other way. Lube the chamber area. Block the bore about a half inch in front of the chamber with cleaning patches. Melt the cerrosafe. Carefully pour it into the chamber,keeping a watch on the level so it doesn't overflow out the chamber. It sets fairly quickly. insert a cleaning rod(with jag removed) from the muzzle end of barrel. Push out chamber cast. Its simple to do,even for a non-machinist like me.

Now the flip side. The Cast measurements just gets you in the Ball Park of the exact chamber dimensions. I will never do it again. Trust your Gunsmith or reamer when it comes to chamber dimensions. Take your rifle,with new barrel installed to the range and let the target tell you if you got a good barrel. You should reach a decision fairly quickly. If not,the chamber castings wont help much at all. Been there,done that.



Glenn

 

[Gene Beggs]

I'm not Jackie but here's my .02 worth

Lapua 220 Russian brass is .4400 at the solid head as it comes from the box.

The chamber dimension at .200 ahead of the bolt face which I usually refer to as 'the pressure ring' should be .4420 minimum and .4430 is not excessive at all. Ask me how I know this and I'll say,

"It cost me several thousand dollars and much frustration to learn this while developing the 220/6mm Beggs cartridges."

FWIW

Gene Beggs

 

[adamsgt]

Lapua 220 Russian brass is .4400 at the solid head as it comes from the box.

The chamber dimension at .200 ahead of the bolt face which I usually refer to as 'the pressure ring' should be .4420 minimum and .4430 is not excessive at all. Ask me how I know this and I'll say,

"It cost me several thousand dollars and much frustration to learn this while developing the 220/6mm Beggs cartridges."

FWIW

Gene Beggs

OK Gene, now I'm thoroughly confused. Sounds to me that you want the case to develop a slight bulge after it's fired. How would your reamer cut a chamber with a smaller diameter at the case head after cutiing a larger diameter before that?

 

[Gene Beggs]

Yep, that's what I'm sayin'

OK Gene, now I'm thoroughly confused. Sounds to me that you want the case to develop a slight bulge after it's fired.

(GB) Bingo! That's exactly what you want to happen. That way the sizing die has something to squeeze back down making chambering and extraction smooth with no 'click-at-the-top.' The solid case head does not expand; in the case of the Lapua 220 Russian, it remains .440 like it came from the box while the case body forward of the solid head does expand. If everything is right with either the 6ppc or my 220/6mm Beggs cartridges, the pressure ring of the fired case will measure around .4410 to .4420. Run it through the proper sizing die and it will be squeezed back down to about .440.

How would your reamer cut a chamber with a smaller diameter at the case head after cutiing a larger diameter before that?

Okay, now I see where the confusion is. You're thinking there must be a step in the chamber at the junction of the case body and the solid head. NO, the chamber walls are straight from the shoulder which is usually .4310 on the PPC to the pressure ring just in front of the extractor groove which I specify as .4420. The chamber, at the bolt face, will be close to .4430 which is not excessive at all.

If you section a new Lapua 220 Russian case as it comes from the box you will find that the solid head of the case is .160 thick. This does not expand when the case is fired; it remains .440. Expansion begins forward of the solid head as the case walls begin to taper.

Hope this helps. Let me know if I haven't made myself clear. We're getting there.

Gene Beggs

 

[adamsgt]

Okay, now I see where the confusion is. You're thinking there must be a step in the chamber at the junction of the case body and the solid head. NO, the chamber walls are straight from the shoulder which is usually .4310 on the PPC to the pressure ring just in front of the extractor groove which I specify as .4420. The chamber, at the bolt face, will be close to .4430 which is not excessive at all.

If you section a new Lapua 220 Russian case as it comes from the box you will find that the solid head of the case is .160 thick. This does not expand when the case is fired; it remains .440. Expansion begins forward of the solid head as the case walls begin to taper.

Hope this helps. Let me know if I haven't made myself clear. We're getting there.

Gene Beggs

Gene, you didn't spec the chamber diameter at the case head in your original explanation, hence my confusion. I understand what you're saying now. So, both you and Jackie are telling me that my new "Pure Magic" reamer is still going to be too small. I'm having Larry Baggett do the chambering and he's probably done the barrels already so I'll just have to see how they work out. Thank goodness that I laid in a good supply of Lapua .220 brass years ago before the crazy price jump.

 

[mks]

Lapua 220 Russian brass is .4400 at the solid head as it comes from the box.

The chamber dimension at .200 ahead of the bolt face which I usually refer to as 'the pressure ring' should be .4420 minimum and .4430 is not excessive at all. Ask me how I know this and I'll say,

"It cost me several thousand dollars and much frustration to learn this while developing the 220/6mm Beggs cartridges."

FWIW

Gene Beggs

Gene,
I am curious, after your expensive learning process , how much clearance do you recommend between new brass and the reamer diameter at 0.200" ahead of the bolt face? 0.443 - 0.440 = 0.003, is this what you are saying?

Seems like Jackie is suggesting that we are ordering our reamers too small. (JS, please correct me if I am wrong.)

Thanks,
Keith

 

[Wilbur]

Nothing personal there!

"CCBW, please don't take this personally but I've always heard "The good Lord takes care of fools and idiots"!! "

Plain truth! That I'm old, kind of adds value to the statement...

 

[Gene Beggs]

Gene,
I am curious, after your expensive learning process , how much clearance do you recommend between new brass and the reamer diameter at 0.200" ahead of the bolt face? 0.443 - 0.440 = 0.003, is this what you are saying?

(GB) Keith, I settled on .4420 for the chamber dimension at .200 ahead of the bolt face. The sizing dies Hornady makes for me are .4400 at this point.

I've regularly polished out chambers with 320 and a split dowel to .4430 to .4440 at the back and they work fine; no 'click-at-the-top' extraction. Most of the 6ppc reamers in use today are too small at the back (.440) which causes great difficulty trying to find a sizing die that will work.

Seems like Jackie is suggesting that we are ordering our reamers too small. (JS, please correct me if I am wrong.)

Thanks,
Keith

Gene Beggs

 

[Dave Tooley]

Gene,
I am curious, after your expensive learning process , how much clearance do you recommend between new brass and the reamer diameter at 0.200" ahead of the bolt face? 0.443 - 0.440 = 0.003, is this what you are saying?

Seems like Jackie is suggesting that we are ordering our reamers too small. (JS, please correct me if I am wrong.)

Thanks,
Keith

I can tell you from my expensive quest to match up the brass, finish reamer and resize reamer you need at minimum .003"clearence between virgin brass and the finish reamer. If I have confidence that brass will remain the same size in future lots I order the finish reamer +.003" at .200" from the bolt face and +.004" at the shoulder over virgin brass. I order the resize reamer at the same time and it matches virgin brass dimensions. This is for cases larger and longer than a PPC but at these tolerances we're splitting split hairs. I'd rather be a .001" big than a .001" small on the finish reamer.

 

[Gene Beggs]

Yes sir!

I can tell you from my expensive quest to match up the brass, finish reamer and resize reamer you need at minimum .003"clearence between virgin brass and the finish reamer. If I have confidence that brass will remain the same size in future lots I order the finish reamer +.003" at .200" from the bolt face and +.004" at the shoulder over virgin brass. I order the resize reamer at the same time and it matches virgin brass dimensions. This is for cases larger and longer than a PPC but at these tolerances we're splitting split hairs. I'd rather be a .001" big than a .001" small on the finish reamer.

Beautifully stated Dave. I agree 100%!


kGene Beggs

 

[mks]

I can tell you from my expensive quest to match up the brass, finish reamer and resize reamer you need at minimum .003"clearence between virgin brass and the finish reamer. If I have confidence that brass will remain the same size in future lots I order the finish reamer +.003" at .200" from the bolt face and +.004" at the shoulder over virgin brass. I order the resize reamer at the same time and it matches virgin brass dimensions. This is for cases larger and longer than a PPC but at these tolerances we're splitting split hairs. I'd rather be a .001" big than a .001" small on the finish reamer.

Gene and Dave,
Thanks so much for these guidelines. So do you figure that the case will spring back during resizing in the die matched to virgin brass up to +0.002" at the base and shoulder, which then leaves 0.001" clearance at the base and 0.002" at the shoulder between the sized case and the chamber? Is this about right?

Thanks,
Keith

 

[Dave Tooley]

What I've experienced is as the brass ages/work hardens I get less than .001" reduction in diameter from sizing on fired brass. So I'm working in the larger .002" diameter area. I guess in a perfect world you might get by with.002" clearance on virgin brass but the risk/reward ratio is high. An extra .001" clearance won't show up on the target. Again we're splitting split hairs here so err on the side that works each and every time. We can write numbers on a piece of paper and say it should work but very few reamers are exactly what we order. I believe that if the sized body dimensions are managed properly you can reduce the amount of shoulder movement during sizing. Is that important? I believe so.