Barrel to Cylinder Clearance

[45D]

How about putting a bolt with a karger head, filing the head until it is the same diameter as the arbor then adjusting depth?

That would work but it's a little easier to use the head of a pan head S.S. machine screw (Phillips head) that is the appropriate diameter (#12 for belt pisty,#14 for the horse pistols). You can then use a Phillips bit in a drill motor to spin the head (minus the threaded shaft) against a belt sander to get your thickness (wear glasses ! Lol. ).

Barrel harmonics are not an issue in the short length of revolver barrels however frame, slots (all three of them) wedge shape and lower lug fit do effect point of impact, accuracy and longevity. The arbor doesn't care if it hits bottom or not because all the force at firing is forward away from end load tension of the arbor, if it exists . Loading the end of the arbor in it's well has no appreciable effect on accuracy or longevity and it seems at least Pietta has figure this out!
A gun with proper fit of the mentioned load points will shoot every bit as accurately and as long without any more wear as one will with the arbor bottomed out.

Per your own post, if it doesn't matter, what did Pietta fix . . . (oh yeah, the arbor now bottoms out in the arbor hole!! )


Mike

 

[TrapperDude]

So it would seem that as the projectile enters the forcing cone, the barrel's lug will flex forward to a certain extent from the forward force of the projectile. At that point, it will return to its original position.

I can only guess that because the flex is so rapid and minute, the barrel and lug will return to their original position before the projectile exits the muzzle. If the arbor doesn't bottom out in the arbor hole, it would seem that the barrel could oscillate to some extent as the projectile travels the barrel's length.

If the oscillations are consistent, then the same powder charge and velocity should result in consistent position of the muzzle along the vertical axis as the projectile exits the muzzle each time. However, inconsistent oscillations could result in inconsistent muzzle orientation along the vertical axis.

Moreover, it would seem that a vertically oscillating muzzle would cause a pistol to be hyper sensitive to variations in powder charges because the projectile would leave the muzzle at different points along the vertical axis as the muzzle oscillate.

For these reasons, a properly bottomed out arbor would seem to prevent those oscillations along the verticle axis, resulting in more consistent grouping.

These suppositions, of course, are based on the premise that the barrel is oscillating as the projectile exits the muzzle.

 

[Dude]

TrapperDude "So it would seem that as the projectile enters the forcing cone, the barrel's lug will flex forward to a certain extent from the forward force of the projectile."

Since the barrel is fastened to the arbor, it can't possibly flex when the projectile enters the forcing cone. It's like a teeter totter and the arbor is the fixing point in the middle. For the barrel gap to increase, it would have to dig into the lug.

 

[M. De Land]

That would work but it's a little easier to use the head of a pan head S.S. machine screw (Phillips head) that is the appropriate diameter (#12 for belt pisty,#14 for the horse pistols). You can then use a Phillips bit in a drill motor to spin the head (minus the threaded shaft) against a belt sander to get your thickness (wear glasses ! Lol. ).




Per your own post, if it doesn't matter, what did Pietta fix . . . (oh yeah, the arbor now bottoms out in the arbor hole!! )


Mike

I can tell you have not tried and tested any of what was said . You were taught or told there is only one way and so your doomed to stay right where you are until you decide to try some different approaches and see for yourself.
I have several early Piettas and none of them have an end fit arbor. My overhauled 60 is accurate in the extreme with the new Key and trigger I built from tool steel. The key than fit to both barrel slots and arbor slot . The lapped barrel and re-cut forcing cone and re-crown also help out as did the lug trim and refit to the frame.
I would bet you also think the revolver is out of time if the bolt drops before the lead in slot !

 

[TrapperDude]

TrapperDude "So it would seem that as the projectile enters the forcing cone, the barrel's lug will flex forward to a certain extent from the forward force of the projectile."

Since the barrel is fastened to the arbor, it can't possibly flex when the projectile enters the forcing cone. It's like a teeter totter and the arbor is the fixing point in the middle. For the barrel gap to increase, it would have to dig into the lug.

Well, the barrel is above the part of the lug, which is fastened to the arbor. Again, only an engineer or someone who'se seen analysis of it could say, but it seems there could be some flexing of that lug above the arbor. When/if that lug flexes, it would cause the barrel to pivot ever so slightly at its base, where it is screwed into the lug, along the verticle axis.

If the arbor were short, then the arbor wouldn't perfectly mitigate that pivot because the lug would theoretically be able to rotate farther back than the original resting point since nothing would be there to stop it. Think of taking a long piece of PVC pipe, holding it vertically, and whiping it back and forth. It will flex as it goes back and forth. If, however, you did so standing under the forward edge of a low ledge, the ledge would stop its rearward movement in short order. Under that latter circumstance, a quick whip of the PVC pipe forward would result just in a quick whip forward and a stop against the overhead ledge. Without the ledge, the PVC pipe could keep going back and forth until it ran out of momentum and came back to a rest.

Again, that's premised on an idea of how much flex really happens in a barrel lug.

 

[M. De Land]

I have a new Uberti Colt 1862 Pocket Police, and I can not see any clearence between the rear end of the barrel and the front of the cylinder. My other revolvers show a very tiny amount of light between these two surfaces. In fact, when putting the barrel onto the frame, I have to force the barrel back hard in order to start the wedge into place. I understand that there should be .004” to .006” clearance between the barrel and cylinder.How do I go about adjusting this clearance?

Well, the barrel is above the part of the lug, which is fastened to the arbor. Again, only an engineer or someone who'se seen analysis of it could say, but it seems there could be some flexing of that lug above the arbor. When/if that lug flexes, it would cause the barrel to pivot ever so slightly at its base, where it is screwed into the lug, along the verticle axis.

If the arbor were short, then the arbor wouldn't perfectly mitigate that pivot because the lug would theoretically be able to rotate farther back than the original resting point since nothing would be there to stop it. Think of taking a long piece of PVC pipe, holding it vertically, and whiping it back and forth. It will flex as it goes back and forth. If, however, you did so standing under the forward edge of a low ledge, the ledge would stop its rearward movement in short order. Under that latter circumstance, a quick whip of the PVC pipe forward would result just in a quick whip forward and a stop against the overhead ledge. Without the ledge, the PVC pipe could keep going back and forth until it ran out of momentum and came back to a rest.

Again, that's premised on an idea of how much flex really happens in a barrel lug.

If all the pressure points are square, plumb and fit each other at battery you still have the tension and compression of the steel itself under load. That's why the gap one sees and measures with a feeler gauge at battery bears no resemblance to what those same tolerances are under load of firing . All the pressure load on the barrel group is forward away from the cylinder and frame. Because the barrel axis is above the center of the arbor it wants to bend downward and the lower lug fit is the cantilever stop to this direction of movement . The pins arrest the barrel torque and reduce the torsion load on the key and slots.
If the barrel/cylinder gap is even at battery it will open up at the top under load and steel compression at ignition. This is the reason one wants the cylinder gap tighter at the top at battery. The trick to accuracy is to adjust and balance the pressure points to hold square and plumb under the load stress of firing.
When one gets these adjustments right with the proper hardness in the accompanying parts the revolver will be it's most strong and able to consistently repeat it's movements which produces accuracy and longevity.
Most keys are to soft in my opinion and triggers are not as good as they could be on the Pietta's. I've replace mine using 0-1 on the trigger and A-2 hardened tool steel on the key.
Almost all their barrels will show tight spots when checked with plug gauges and can stand hand lapping to true them up..

 

[TrapperDude]

If all the pressure points are square, plumb and fit each other at battery you still have the tension and compression of the steel itself under load. That's why the gap one sees and measures with a feeler gauge at battery bears no resemblance to what those same tolerances are under load of firing . All the pressure load on the barrel group is forward away from the cylinder and frame. Because the barrel axis is above the center of the arbor it wants to bend downward and the lower lug fit is the cantilever stop to this direction of movement . The pins arrest the barrel torque and reduce the torsion load on the key and slots.
If the barrel/cylinder gap is even at battery it will open up at the top under load and steel compression at ignition. This is the reason one wants the cylinder gap tighter at the top at battery. The trick to accuracy is to adjust and balance the pressure points to hold square and plumb under the load stress of firing.
When one gets these adjustments right with the proper hardness in the accompanying parts the revolver will be it's most strong and able to consistently repeat it's movements which produces accuracy and longevity.
Most keys are to soft in my opinion and triggers are not as good as they could be on the Pietta's. I've replace mine using 0-1 on the trigger and A-2 hardened tool steel on the key.
Almost all their barrels will show tight spots when checked with plug gauges and can stand hand lapping to true them up..

Is there any rebound of the barrel before the projectile exits the muzzle?

 

[M. De Land]

Is there any rebound of the barrel before the projectile exits the muzzle?

No. If all pressure points are fit tight, square and plumb the tolerances will hold. This is what produces the consistency and thus accuracy and longevity.
I also have a Pietta 58 Army that has had the same over haul and it is more accurate than my ROA. Solid frame guns are great because they are so rigid unless you get one with the barrel hole through the frame out of co-axis . There really is no good fix that I'm aware of for that.
I have not tested them against each other but if my 60 had as good of sights as the 58 I think it would probably give it a run for it's money in accuracy.
Both have had their barrels hand lapped.
End fitting the arbor hurts nothing as far as I can see if that floats your boat I just don't believe it appreciably aids accuracy from what I have seen. One mans opinion.
If you look down the arbor well of older Pietta's you will see they are not blunt ended but tapered. This is a poor shape for end fitting and a machine screw drilled and tapped in the end of an arbor is a poor adjustable end block, It also weakens the end of the key slot in the arbor that holds the barrel from taking off down range via the key.

 

[Pete G]

End fitting the arbor hurts nothing as far as I can see if that floats your boat I just don't believe it appreciably aids accuracy from what I have seen. One mans opinion.

My experience also.