Maybe someone can splain this

M

Mike Marcelli

Guest
A big burly machinist who's been following the threading posts, but who hasn't posted on the Board -- yet -- called me last night and asked that I post this question.

This gent took a piece of 6mm barrel stub, a Krieger I believe, .875" in diameter and about 3/4" long. He took his Deltronic pin gauges and found that a .2372" guage would fit in the bore, but a .2373" guage would not.

He then proceeded to chuck this itty bitty chunk of barrel in his Buck chuck, with the .2372" Deltronic Pin sticking out and began cranking on the allen screws of the Buck chuck with an 8" T-bar.

Now this particular fellow is not small in stature and he relates that he put all of his 340lbs, ex-professional wrestling might, into cranking on those Buck chuck allen screws -- until sweat was beading on his brow.

Being assured that he could crank no more, he gave a tap on the Deltronic pin, expecting it to be wedged solid, but low and behold, it popped right out.

There have been some recent posts about the effect of cranking down on a sleeve, or otherwise being able to change the interior dimensions of a barrel, and being able to detect a change in in the bore. I myself have "thought" I could detect a tight spot in a barrel, while cleaning, caused by overtightening the barrel v-block on my rail. (Indeed, the gun shot better when I loosened the pressure from around 30 in lbs to 20 in lbs on the block's screws.) But, I seriously doubt that a patched cleaning rod passing through a diameter change of less than .0001" could be detected, and there surely was far in excess of 30 in lbs on the Buck chuck screws at issue, so what gives?

If I got any of the facts wrong, perhaps our bashful gunsmith will correct them, but I'm sure I have the gist of the test correct.
 
Mike Marcelli said:
A big burly machinist who's been following the threading posts, but who hasn't posted on the Board -- yet -- called me last night and asked that I post this question.

This gent took a piece of 6mm barrel stub, a Krieger I believe, .875" in diameter and about 3/4" long. He took his Deltronic pin gauges and found that a .2372" guage would fit in the bore, but a .2373" guage would not.

He then proceeded to chuck this itty bitty chunk of barrel in his Buck chuck, with the .2372" Deltronic Pin sticking out and began cranking on the allen screws of the Buck chuck with an 8" T-bar.

Now this particular fellow is not small in stature and he relates that he put all of his 340lbs, ex-professional wrestling might, into cranking on those Buck chuck allen screws -- until sweat was beading on his brow.

Being assured that he could crank no more, he gave a tap on the Deltronic pin, expecting it to be wedged solid, but low and behold, it popped right out.

There have been some recent posts about the effect of cranking down on a sleeve, or otherwise being able to change the interior dimensions of a barrel, and being able to detect a change in in the bore. I myself have "thought" I could detect a tight spot in a barrel, while cleaning, caused by overtightening the barrel v-block on my rail. (Indeed, the gun shot better when I loosened the pressure from around 30 in lbs to 20 in lbs on the block's screws.) But, I seriously doubt that a patched cleaning rod passing through a diameter change of less than .0001" could be detected, and there surely was far in excess of 30 in lbs on the Buck chuck screws at issue, so what gives?

If I got any of the facts wrong, perhaps our bashful gunsmith will correct them, but I'm sure I have the gist of the test correct.
Click to expand...

Mike, indicating on the end of a Deltronic pin sticking out of the bore is just indicating on the extension of whatever curve is in that particular bore. Think about it, you are just extrapolating the error!

And yes, you can feel the barrel vise pressure in the bore with a tight patch. Slug the bore with a lead slug and it will STOP at the vise if it is very tight.

As to why the pin fell out. I'd guess the pin was not within the range of the jaws or he had just proceeded in straightening the bore where the pin was hung.
 
All this discussion about how much the bore changes as you apply pressure to the outside is very easily solved by applying a simple equation for stress. You can look in any strength of materials text book and find this equation for thick walled cylinders. I could give the equations here but have found shooters reading these posts pay little attention to this kind of stuff. ANY pressure applied to the outside diameter causes the bore to restrict. Whether or not you can measure it depends on how high the pressure is and how accurate your measuring method is. An interesting bit of knowledge is that if you apply the SAME pressure to both the O. D. and the I. D. you will still cause the bore to become smaller.
 
Mike , I am in your corner. I think this is a bunch of horse hockey stuff. All have theorys but has anyone really done it other then your "friend"
 
Mike
But he did have to tap on it as opposed to simply grab it with his fingers like it went in. So there was some grip on it - the bore had become tighter on the pin. Maybe not as much as he had expected, but some distortion had taken place. It would be interesting to see if the barrel stub, once removed from the chuck, would still not let the .2373 go in.
 
I know if you hold a barrel in the barrel vice over the chamber area tightly as you would to remove or install this barrel that you just chambered, a chambering reamer will not fit in the chamber while the vice is tight... and that outside diameter is about 1.2"...
 
Paceil----stress equations

I'd appreciate it if you'd post these stress equations.

I have zero background in strength of materials and no reference info but am not reluctant to deal with a little arithmetic.

With a little luck and help from EXCEL, I'd hope to build a spreadsheet that would simplify and quantify some of this.

Thanks.

A. Weldy
 
Vibe said:
Mike
But he did have to tap on it as opposed to simply grab it with his fingers like it went in. So there was some grip on it - the bore had become tighter on the pin. Maybe not as much as he had expected, but some distortion had taken place. It would be interesting to see if the barrel stub, once removed from the chuck, would still not let the .2373 go in.
Click to expand...

Poor choice of words. He could have pulled it out, but tapped on it instead. The .2373 would still not go in after the stub was stressed.
 
Mike

There is no doubt that you can compress a cylinder by exerting force on the OD. In some propellar shaft applications on large vessels, we use keyless couplings. The coupling slips onto the shaft with about .002 clearance. A heavy, tapered sleeve is then compressed on the OD of the coupling body. This exerts temendous tonnage, closing the bore to what would amount tp a .010+ shrink fit.
The big question concerning our application is, can the flimsy things we call tuners, lightly cinched with two rather small 6-32 screws on a very fine thread, exert enough force to close a bore.
I say if it does, it is not enough to make any difference, and I have the match reports to prove my point.
There seems to be a rather large contengent that thinks I am wrong, and are going through all sorts of "fixes" to avoid doing what many of us are doing now.
But, we will just keep shooting, and watching these developments. If something better comes along, that is practicle in The Competitive Arena, I will certainly want to know about it........jackie
 
Early on, when I first started barreling I would indicate the muzzle in with a pin and final adjust in the grooves with a indicator.. The muzzle end was held in a 4 screw spider, those screws were and are 5/16'' in diameter and without undue effort I did make the deltronic pin impossible to remove with my fingers.. I didn't use a pin in the muzzle after that or anywhere else for that matter!
 
Not long ago - -

There was discussion about deliberately putting "choke" at the muzzle end of a barrel, in fact, I think Bill C. might have advocated doing it. If adding a slight bit of "Choke" in the muzzle end with a clamp of any kind, that might be a good thing, No ? Conversely, making a Blunderbus out of 'er would not be a good thing; even to a small degree. I think this may be where Bill is coming from; Choke GOOD, Blunderbus- BAD.
 
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Pat B. said:
Early on, when I first started barreling I would indicate the muzzle in with a pin and final adjust in the grooves with a indicator.. The muzzle end was held in a 4 screw spider, those screws were and are 5/16'' in diameter and without undue effort I did make the deltronic pin impossible to remove with my fingers.. I didn't use a pin in the muzzle after that or anywhere else for that matter!
Click to expand...


ok...
i see this a bit defferent.
its a pin....not a single point/plane.
its probable that the screws bent the bbl, not as much of a constriction. the pin is in over a length and is fairly tight in that length, bend the bbl over that length..and guess what...one of three things can happen.
nothing.....not enough change to notice;
the pin is loose.....you straigthened the bbl over the length of the pin;
and
the bbl bends binding the pin in place....not constricted, but bent over the lenght of the pin.

things to ponder

mike in co
 
I was at my gunsmith's garage this afternoon and we decided to see if there was anything to this theory that threading the outside of a barrel opens up the bore.

We took a 3" barrel stub and found that we could get a .2772 deltronic pin in but the .2773 would only engage by about 1/8". Instead of threading we simply turned 1/8" from the diameter for about 3/4" back from the muzzle. Afterwards the .2772 pin still felt the same and the .2773 would only go in about 1/8". We saw nothing in the real world that supports the theory of the barrel opening up when threading the outside.

Lawrence Weisdorn
 
That's where you went wrong

Lawrence W. said:
..... Instead of threading we simply turned 1/8" from the diameter for about 3/4" back from the muzzle. ........
Lawrence Weisdorn
Click to expand...

You gotta thread it to cause it to open up...simply turning it down caused the remaining stress to multiply exponentially. I'm surprised the hole didn't get smaller.

Had you threaded the piece, the forces would have been spirally confused. As you know, energy can't be destroyed so being confused it jumps off the piece onto the lathe as heat.....the hole gets bigger and so does the lathe. I knew a guy once that had a threading machine that was an inch longer and a half inch taller than when he bought it....
 
Pete Wass said:
There was discussion about deliberately putting "choke" at the muzzle end of a barrel, in fact, I think Bill C. might have advocated doing it. If adding a slight bit of "Choke" in the muzzle end with a clamp of any kind, that might be a good thing, No ? Conversely, making a Blunderbus out of 'er would not be a good thing; even to a small degree. I think this may be where Bill is coming from; Choke GOOD, Blunderbus- BAD.
Click to expand...
Before Ed Shilen retired he was experimenting with tapered bores. He made me one with 0.0005" taper and one with 0.001" taper over the 26" of the blank. Those barrels shot great but I couldn't tell they shot any better that the two straight bore barrels I got at the same time.

Put a 0.002" constriction in the last 1/2" at the muzzle and you can't hit the paper at 25 yards!!!
 
I have heard and seen

JerrySharrett said:
Before Ed Shilen retired he was experimenting with tapered bores. He made me one with 0.0005" taper and one with 0.001" taper over the 26" of the blank. Those barrels shot great but I couldn't tell they shot any better that the two straight bore barrels I got at the same time.

Put a 0.002" constriction in the last 1/2" at the muzzle and you can't hit the paper at 25 yards!!!
Click to expand...

People say the exact opposite. Actually, some makers purposely lap about that much constriction into their barrels! They will want to know where the crown is likely to go. Interesting, isn't it?
 
Pete Wass said:
People say the exact opposite. Actually, some makers purposely lap about that much constriction into their barrels! They will want to know where the crown is likely to go. Interesting, isn't it?
Click to expand...
Pete, all I can report is that I installed a 0.002" shrink for collar 1/2" long on the muzzle of a new Krieger barrel. I had deliberately left this barrel 1" longer than final finish.

I took it to the range and put up a target that was 12" x'12" at 100 yards. Couldn't get on the paper. Moved the target to 25 yards, boresighted again. Still couldn't get on the paper even. Moved it to 10 yards and got 2 perfect keyholes at about 1" apart.

I machined the collar off leaving the barrel muzzle as it was. Reinstalled the barrel and back to the range. That barrel with the cobbled up OD shot great.

I could find no evidence on the 10 yard target that the bullet was coming apart. Just two perfect keyholes. Go frigger???
 
Indeed - -

I have a barrel that came out of a lot of good ones that I wore out trying to get it to shoot. Had the thing trimmed several times, new crowns, etc, etc. Some of em don't shoot.

I think I recall in the article on Kreiger in PS a couple of years ago that they lap a bit of constriction into their barrels. I know of at least one other that has done that on a fairly regular basis and they were the HOT barrel for a couple of years. Of course, I didn't measure any of them !
 
Mike, I wouldn't argue with your assumption.. I will add that the spider screws were over the area of the muzzle where the pin was ie; the last 3/4'' or so...

We can always count on Wilbur for the straight poop----grin.
 
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