Simulating distortions when chambering?

Butch Lambert said:
Bob,
I have tried on purpose to chamber an out of round chamber and have not had any success. How can you do it with out have a tool holder that operates as a cam and goes in and out while boring. Or you have a tailstock that sways back and forth in time with the barrel while running the reamer in.
I think that it may be oversize, but not out of round.
Butch
Click to expand...


I have a barrel here at the house that has a badly off center chamber. I removed from the ass of the ass that chambered it this way. You don't even need more than the naked eye to see how far off the chamber is to the od of the barrel, but it is not and out of round chamber. However the asses head is some what out of round from having the barrel laid over his head repeatedly.

Of course the up side to this was the justification for me buying a lathe, even my wife could see that it was off center.
 
Reamers can be made to flex. Not unlike a small endmill that is pushed to hard.. Such is the case with an 1/8 long endmill can cut a slot that is
hooked at the bottom. Hard to believe. When ever a reamer is not operating
on the centerline axis it increases diameter in the base end. A barrel
true at breach and out of line towards the muzzle added to some misalignment
in tailstock can cause the reamer to flex, more so after some use. You have
many forces working here. Floating reamer holders are really overated
 
I think that the way one could get an out-of-round chamber is to have the barrel fixed and turn the reamer with side pressure on the shank.
Reamer held in granspa's brace, barrel in blacksmith's vise or tied to stump. I have my grandfather's brace but no stumps here and left my blacksmiths vise on a bench at my last residence. So, I can't prove my theory.

Jay, Idaho
 
If the bore is running eccentric and the reamer is supported on tailstock center, the chamber will be out of round at the rear.
If the bore is running true but the reamer is held offset, the chamber will be oversized but concentric and round.
The only way I can think to produce a chamber which is eccentric to the threads is to cut threads which are eccentric to the bore; then chamber in line with the bore. OIr chamber the barrel then set up eccentric to thread.
Very often, a chamber which is perceived to be eccentric is not. The start of the threads only make it appear so. That the chamber is eccentric to the OD of the barrel is largely meaningless anyway. Even a certain amount of eccentricity to the threads is probably of no consequence from a performance standpoint (say .010TIR). Not the ideal for sure but probably still workable.
Jay,
I have at least 25 acres of potential stumps here. Bring your brace and some rawhide to attach the barrel to the stump and see what you can do! I heard you had moved down to the Moscow area. That so? Some nice stumps at my in-laws place in Potlatch. Regards, Bill
 
If you have ever watched a novice machinist tapping threads by hand,
you have seen tapered threads and broken taps. I have seen this often.
The cause of this is unequal force applied to one side of the tap, causing it to flex.When a reamer is supported by tailstock center, and driven by a
wrench against the compound or other ridgid place, you have the same
lateral suport, which is to one side. Being perpindicular to the axis. This
is no different than when you tighten a bolt .With this exception, the reamer
is also being supported by the barrel, resisting the force that wants to make it flex as a tap does. It still does to some degree. Lots of odd forces
at work here. Finishing chambers with a crescent wrench to drive the reamer
can get you an out of round chamber, much the same as a Bit and Brace.
One of the quickest ways is to polish a chamber that is not running true.
 
Distortion?

Many old time gunsmiths used to finish the chamber with the barrel torqued into the receiver. They would leave just a few thousandths short headspace, assemble, and cut final headspace by hand. It was normal for the reamer to shave a little at the back of the chamber before it started to cut at the shoulder. Of course, they tightened them about as tight as possible, so there was likely to be more constriction than we experience with our puny little 30 foot pounds or so. Constriction, not distortion. I can see where this could become an issue if one starts with a custom reamer, sized to cut an extra tight chamber, and takes all precautions to prevent reaming oversize, and then torques the barrel a little extra tight. I know from experience the problems caused by a too small chamber.

This is all probably a moot point most of the time, but I wouldn't count it out completely.

Scott Roeder
 
I'm feelin ya Bob

Bob, I'm with ya, so we'll stand before the firing squad together.

As the former production manager of Nesika Bay Precision's rifle dept and the entire Dakota Arms, Inc barreling operation I'd like to think I have constructive input.

My experience in the machine shop began in autoracing working for an NHRA Competition Eliminator team that contracted an engine builder in SOCAL. Richard Conley. When Richard wasn't binge eating 200 piece McDeath nugget meals, he could build one hell of an engine. (think Jabba the Hut)

Anyways. I have always felt that cranking a barrel onto an action has to impart some kind of stress. I can't begin to describe what kind, how much, or if its enough to even matter, but I know its there. It has to be. Well, with engines valued at over $80,000.00 we went to great lengths to mitigate these same kind of fastener induced distortions.

Anyone who's been around hot rod or racing engines knows what a torque plate is. So, I started chambering a few guns this way just to see what happens. All my personal guns and all the rifles I built for high end competitive shooters were done this way. I made a "torque plate" for the barrel tennon and I cram the reamer in there with the tennon under tension.

Cathy Winstead won a world smallbore silhouette championship with her rifle done this way and so did Kyle leibertrau with his during the 2007 world Palma championships.

It may not do a damn thing, but it sure doesn't seem to be hurting anything either. FWIW I had to buy a new B/S best test with a .0001" resolution to be able to detect chamber runout. Not saying this particular process made it more accurate, but having an 80K Harrison CNC tool room turning center built with class 9 tapered gamut spindle bearings sure made for nice chambers.

How's .000175" for TIR?

Someone light my cigarette before the order to fire comes.

Cheers!

CD
 
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Nesika Chad, did you know James Anderson at Dakota? On your double throw down lathe, how did you hold the barrel and indicate it in? What happened to loaded 6ppc ammo after Kokesh bought the rights from Palmisano and Pindel?
Butch
 
Chad,
"How's .000175" for TIR?"

Just a question: How did you measure that fine? To .000001"?

Regards, Ron
 
A .0001 indicator tells ya by the spaces between the graduates. You can see half, you can see 3/4.

It'd move one tenth and then about 3/4's of a tenth. I guess I could say I was getting just over a tenth of runout but .000175" looks so much more impressive.
 
bob3700 said:
OK, there have been discussions concerning the fit of the bbl threads into the action. Some like them very tight and some very loose.

There are engineers out there that will tell you if you fit the threads between the bbl and the action tight, you can alter the dimension of the finished chamber walls. The chamber is said to have it's final dimensions altered by the stress of torquing the bbl to the action. Some smiths will finish reaming the chamber with the action torqued in place to get a perfect chamber.

What if? You manufactured a false receiver ring. Take a piece of steel and drill and cut threads just like a receiver ring. Then mill a couple of flats on it to be able to torque it to the end of the bbl tenion. Install and torque the false receiver ring to the bbl. Now you have pre-stressed the chamber end of the bbl and simulated the action being torqued in place. Now chamber the bbl up.

Would this not provide a chamber of more accurate final dimensions?

The concept is used on racing engine blocks. High performance shops torque thick steel plates to the cylinder block to induce the distortions and stresses that the cylinder heads do. They then bore and hone the block for a more accurate/round/consistent dimensioned hole.

Seems like the same concept being applied. Am I barking at the moon here?

Bob
Click to expand...

The distortion could be calculated, although it is probably less of a dimension change, then say......5 or 10 degrees F ambient.

So, would you load differently for a match that was 75 vs 80 degrees F?

Or, in the chambering process, would you headspace different if your shop was 5 degrees one way?

Ben
 
Novice ?

OK lets say we have a rifle that has a slightly out of round chamber. Might it be prudent to index the cases so that when they reenter the chamber they encounter the same conditions?

I am thinking that an action that has the recoil lug in the threaded area might create an unequal distribution of compressive force on the chamber.

Also what happens to these type of actions/chambers as the rifle changes temps. as far as chamber shape. ( Uneven mass around the chamber? )

Sorry too much coffee this morning.

Jackie! just realized my old "Sebastian" has about 6'' of spindle sticking out
the back that serves no purpose. I am now down to about a 20" spindle.:p Yea

Aloha, Les
 
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