take down rifle question

[nekshot]

I am working out the plans for making a takedown rifle out of a vz-24. I am currently using the rifle as a switch barrel between my 50-80 and a 7mm mauser barrel. info and pict of 50-80 on black powder cartridge section. As I was freezing in my deer stand this morning I get a grand idea. I have always wanted to convert one of these's vz's to a takedown and the thought came to incorperate the 2 barrels into seperate forearms as a way to quickly switch barrels rather than take action out of stock. My question is this, when I make the locking lever that locks the 2 pieces together would it be be of any good value to have the lock push the threads forward towards muzzle or to pull the threads back into action. And before you get wild ideas of wopply threads forget it , all threads are very firm and tight. I have alot of research into this and I am committed to a plan or copying a metal workers rifle I saw in a book.

[lefty o]

imo if the threads are tight (which they need to be), its not going to matter. in theory pushing apart would give you that .001" of play into the headspace right out of the gate, vs. pulling which would show that added headspace upon firing. precision machine work has to be the key, without it, its not ever going to shoot well.

[scb]

Pushing back toward the bolt will tend to tighten headspace. Toward the muzzle loosen - increase headspace.

[nekshot]

I don't think there is enough room in the threads to change headspace of any detriment, what I was really wondering which side of the thread of barrel takes the force of ignition- I assume the front but I have been wrong often before and I really think I am over thinking this thing but the cold can do funny things to the noodle!

[justashooter]

agreed that you want to have a jamb nut or some other device that pushes the barrel forward to pre-load the front of barrel threads, or they will move forward on cartridge firing and compress whatever device that you are using to tension them rearward...

[John Taylor]

Had a Griffen and How ( spelling) come in that was made from a Winchester model 70. They interrupted the threads so it would come apart with 1/4 turn and a spring loaded detente ball to keep it from coming loose. I made three more barrel for the rifle in different calibers. The customer complained about the original barrel not shooting as good and I remembered it was not as tight as the new barrels in the action. I told him to take the spring out of the detente ball and put a spacer in then tighten the screw that was used to hold the spring in. This applied pressure on the threads pushing the barrel away from the action and taking all the slop out. The rifle shot much better with the barrel tight as it should. There is a plate about 1/8" thick attached to the front of the action and shaped to match the cut off stock and another plate on the barrel to match the forearm. The one on the action had a small screw head sticking out and the plate on the forearm had a groove that the screw head fit into. the end of the groove acted as a stop so the barrel would be lined up to the action and the spring loaded ball was under the barrel and inline with it.
I have another rifle in to do the same thing but i don't like interrupted threads so the barrel will need to be unscrewed all the way. Also thinking of a more positive lock to keep things tight.

[W.R.Buchanan]

Interrupted threads scare me on a high power rifle. All right for a .22 or a Shotgun like a M12 Winchester which are both relatively Low Pressure systems. High Power Rifles are another story entirely and I think using full threads would be the smart thing to do.

The best takedown systems I have seen are well machined but they are also adjustable for slack. The kicker is that as the barrel comes into it's 12 o'clock home position all slack must be out of the threads. This also the position the barrel should be head spaced at. At this point the threads will be loaded on the forward side of the barrels threads and the rearward side of the receivers threads. just like they would do at firing if there was any movement. IE: the gun tries to blow itself apart each time it is fired, but the threads won't allow it.

All of the High Power Takedowns I have seen have some kind of a base plate on the barrel fore end section that either butts up against a plate on the front of the rear half of the gun, or in the case of the Leverguns I have seen, it butts up against the front of the receiver.

The best one of these that I have seen used a two piece end plate that could be adjusted to take up the slack. You would set up the guns takedown assembly having as little slack as possible and then on final assembly you would use shim stock between the plates to adjust for final fit. The shims are made to the full profile of the end plate so if brass was used a tasteful gold line separated the two halves. Thus it could be adjusted for wear, which is inevitable.

This whole assembly is press fit or silver soldered onto a step turned onto the barrel just behind the threads and the rear face of the plate would be in the same position as the step on the barrel that butts up against the receiver. Obviously the step turned onto the barrel would be the same length as the thickness of the takedown plate.

There also has to be some kind of a locking system to keep it screwed together in it's proper place. On Leverguns it typically is the magazine tube. And the tube usually has a sleeve on it that closely fits the hole in the receiver or it threads into threads in the receiver itself. The tube must be retracted before the barrel can be unscrewed and I have seen no less than 6 different ways to lock the tube in place on the barrel. I really like the Winchester one currently being used on the current batch of M92 takedowns.

The Browning BLR uses a "Key Latch," that locks the barrel into the receiver, but since there is no forward thrust on the barrel, as the bolt locks into the rear of the barrel like an AR15 works, the only requirement as far as strength is concerned is to make sure the whole thing doesn't flop around and stays tight. This is also why they can have aluminum or plastic receivers and not blow up. This could work on a bolt action system as well as long as the barrel assembly had a positive stop as it threaded into it's final position. Then the latch would only prevent the barrel from unscrewing as the stop would prevent it from screwing past it's 12 o'clock position.

This is pretty much everything I know about Rifle Takedown systems, but there are plenty more ways to do it and I see new ones several times a year. Blaser Rifles have interchangeable barrels, and there are several that the zero on the rifle doesn't change even though the scope is mounted on the receiver. I believe Thompson Center now has a bolt gun with interchangeable barrels. Most of this is the product of better and more precise machine work from automated machinery. However there have been Takedown Guns with interchangeable barrel sets for at least 125 years so none of it is new.

I think they are one of the high points of the gun makers art, and there is a lot to learn here.

Randy