Barrel install Question on an N frame

[Gun 4 Fun]

You guys are missing it. You are crediting the bullet with torque, or spin of it's own. If it had it's own spin, then yes, it would pull the barrel back into itself and tighten the barrel.
However, the bullet has no force or torque of it's own, and therefore when the bullet is forced down the bore, the walls of the bore acts as a drag. This drag causes resistance to the movement of the bullet, creating torque in the direction of the rifling, which makes the barrel want to unscrew.

The truck analogy is inaccurate because the transmisission parking pawl holds the gears from turning while in park. This is what causes the engine to want to rotate in the opposite direction. When in gear, that same torque is put to work rotating the wheels. Yes, the engine will still want to torque away from the direction of rotation under acceleration simply because the mass of the truck is much greater than the mass of the engine itself.

 

[Rancher]

OK, it seems to be time for an experiment. Who wants to loosen a barrel slightly, fire a round or two, and then report on whether the barrel loosened or tightened?

 

[tomcatt51]

Equal but opposite reaction. Bullet goes forward, gun comes back. Rifleing causes the bullet to rotate clockwise, barrel (and frame etc) rotates counterclockwise.

 

[Gun 4 Fun]

Originally posted by tomcatt51:
Equal but opposite reaction. Bullet goes forward, gun comes back. Rifleing causes the bullet to rotate clockwise, barrel (and frame etc) rotates counterclockwise.

This is still assuming that the barrel is tightly fitted to the frame and unable to move. If the barrel is loose in the frame, the rotational torque will make the barrel want to follow the bullet due to drag.

To put it another way, if the barrel was screwed into the frame with a 1-20" pitch thread equal to a .44's rifling, the bullet would simply stick in the barrel and the expaning gasses woud shove the whole unit forward and unscrew the barrel. It's the same thing, only the threads are much finer, and it would take many firings to completely unscrew the barrel. The drag/torque effect would eventually do the job as long as there were no other issues ie; having the BC gap getting bigger, the bullet jumping that gap and hitting the forcing cone with a more damaging impact, possibly peening the rear face of the barrel etc.

Yet another way of demonstrating this would be if you took a barrel that wasn't threaded and force fit it to the frame (press fit), then fired the gun. What do you think would happen?
To start, the force of the bullet slamming into the rifling would blow the whole unit off. If you could watch it in slow motion with high speed photograghy, you would see that unit leave the rest of the gun in a spiral motion following to the rifling twist rate. This is because the bullet having a high inertia level when it engaged the rifling, would still make it partway down the bore before drag brought it to a halt in the barrel. That is assuming that the press fit wasn't so tight that the bullet could actually make it through the barrel before the barrel left the frame. Even if that happened, the barrel would still follow the direction of the rifling due to the drag of the bullet as it passed through the bore.

 

[pred]

This is all very interesting to me, I ave concidered myself "smart" in the past...
I guess the big question is,,, How could the barrel wound up a few degrees tighter than it should be on a used gun? The ser# says it is a 3" barrel gun,,, What i dont know is.... Did someone swap a longer barrel on it in the past, then put the 3"er back on it???
The rear sight was adjusted to the left to accomidate the over tightened barrel...
I wonder if someone here has shot a barrel loose or tight ? ? ? ? ? ?
Peter.

 

[Gun 4 Fun]

I can't remember if it was on this forum or The Firing Line, but I recently read about that very thing happening to someone.

In this section I believe, a guy wants to take his 6" barrel off and mount a 3" barrel on his 29-3. He wants to save his 6" though and re-install it when he sells the gun. This is a fairly common occurence.

 

[john traveler]

That's correct. Repeated loosening and tightening of barrels or changing barrels will result in front sight realignment, even for original barrels re-installed.

Most rebarreling is done by the Mk I "Eyeball" method. The correct way is to use a machinist's table or at the least, a milling vise and indicators to check alignment.

 

[tomcatt51]

I suspect most barrels are just visually checked for index. John's absolutely right about "best" way. It's easy to be off just a little. You can also have frame issues which will have the rear blade moved way over even with the barrel correctly indexed.

I really doubt the torque reaction from the bullet in the rifleing loosens or tightens barrels. It's just like any other threaded fastener. If you don't torque it sufficiently for the loads it will see, or use LocTite, it will come loose.

 

[Pvt.Joker]

Originally posted by Gun 4 Fun:
I can't remember if it was on this forum or The Firing Line, but I recently read about that very thing happening to someone.

In this section I believe, a guy wants to take his 6" barrel off and mount a 3" barrel on his 29-3. He wants to save his 6" though and re-install it when he sells the gun. This is a fairly common occurence.

That is probably my post you are referring to, and yeah, I'd like to have the ability to have the "either/or" choice. I know to clean the threads and add a drop of red loctite; is there anything else I need to be aware of?

 

[john traveler]

For that short 3" barrel, I would be especially careful to align the front sight vertically. You should have access to a machinist's surface plate, machinist's vise, try square, and indicators. Eye-ball alignment will be twice as hard to do as for a 6" barrel. Hold frame in the machinist vise using paper to prevent scratching. Index the barrel visuallly and check for verticallity. The new barrel may need fitting for 0.004"-0.006" barrel-to-cylinder gap. The replacement extractor rod and center pin may need fitting too, and should snap into place and provide a close fit of crane to frame. The locktite has about a 10 minute setting time, so that will allow you to make adjustments if needed.