doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com choke tube blow out

Here is Mike's info:

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Pete

Any time a choke tube "blows out", it's likely it was either not screwed in tight or was a bad installation that left the tube protruding into the bore, so the wad and load caught it. That and pressure behind will do it. If the installation is correct and the tube is scewed tight against the shoulder in the barrel, there's no reason the above should happen. I would bet the Perazzi installation was correct(assuming it was from the factory). I would not be quick to bet on a correct installation from a Mossberg or their imports.

Jakearoo, a couple of years ago, one of the members at our club
had the bottom barrel choke tube portion of his high end German gun part company very quickly. He believed that the choke tube lossened, backed out partially, and caused the mishap.

He had the barrels shortened and retubed. After the work was done,he lost confidence in the gun and traded it off.

Gunny,
I explained that my choke had been neglected (briefly, I swear.) and left some rust in the threads which I cleaned and did all the right stuff to. (Great grammer there, eh?)
A very knowledgable friend suggested that the choke tube was damaged and not flush in the barrel. That it was ripped out by that edge getting caught on the wad.
I don't think so, but be VERY careful with your gun at this point. Make SURE that choke tube fits absolutely flush as it should. Make sure the threads are tight and good. I will continue to investigate. But, it is obvious that there is lots of downstream force when that shot and wad are thrown out.
Guns, ya just gotta keep workin' on em.
Jake

As a mechanical engineer, I am curious as to how choke tubes can blow out without, in some cases, at least, shearing off the threads of either the tube or the barrel.

It seems as if the barrel must expand outward enough to permit the tube to pass forward without thread shearing. One way that comes to mind might be substantial pressure leakage into the volume in-between the tube and the barrel around it. This pressure would cause the barrel to expand radially, while the tube would not expand, since it would experience approximately equal internal pressure (as usual) and external pressure due to the leakage. If the barrel expanded enough, radial clearance between the tube and barrel threads could occur. This would allow tube threads to slip past the barrel threads and the tube to blow out.

With information on the thickness of the barrel wall remaining after the threads were cut, tube and barrel thread dimensions, and an estimate of pressure, some simple calculations could determine if my guess as to how, and why, tubes sometimes blow out is reasonable.

If it is, keeping tubes tightly seated to prevent leakage would be particularly important. Without leakage, choke tubes are forced outward against the inner barrel wall, forcing tube and barrel threads firmly into contact and making slippage impossible.

In any of the cases observed, did shearing of the threads permit the blow out to occur? It certainly seems to have not been the case with the Mossberg in which the tube was re-installed and continued to function.

Unfortunately, as with many educated guesses, calculations using some typical dimensions do not seem to support mine. Anyone have any better ideas as to what might be physically happening?

If the tube became stuck as a result of rust, it is most likely that removing it required some considerable pressure and possible that the rust and force ever so slightly changed the tube enough to let gas behind. It may also be possible that the tube had been dropped at some time slightly damaging the sealing wall. It is recommemded by all choke tube manufacturers that if a tube is damaged in any way buy a new one and destroy the old tube, I suspect that this is what happened, next time let the moths out of your bill fold, it's much cheaper than a new set of Perazzi barrells. I have seen tghis happen before and the owner had been playing around with the gun, if i remember correctly the choke was origionally frozen in. he had the bottom barrell shortened and fitted an extended choke tude

Hotrack

On the Mossberg the tube had a dent on the leading edge, now I don't know if it happened when it hit the ground or thats what caused it to fly 20 yards out. It fits flush and tight now.
I can't envision how something like that happens except maybe the dent was there first.

Whether the choke tube is flush or not is not the important factor. What's important is that the rear of the tube is bottomed out, tight against the shoulder in the barrel at the back of the hole, so gas can not get between the tube and the barrel. The front of the tube may or may not be flush with the muzzle. Extended tubes will not be flush with anything but the important part is that they are tight against the barrel shoulder. I put mine in with a wrench and remove them with a wrench. Something waxy like bee's wax or Door Ease is much better than a light oily lube. You don't want to make it easy for them to become loose and back out a bit.

I use a good bearing grease and keep them tight. There is no reason for a tube to blow out if it and the barrel are undamaged and it is properly installed (that is, kept tight in its threads and in contact with the shoulder, as pointed out earlier).

Screw choke barrels are shot tens of thousands of times each week and this is a relatively uncommon (although not unheard of) occurance. Hardly the Emperor with no clothes, I should think.

Cheers

I have a three year old Beretta 687 Sporting Clays II with choke tubes that seem to loosen by themselves. I tighten them every so often when I am out on the course. The exterior smooth section of the choke tubes is about 2" long and is often dirty after shooting. I have been a bit concerned since I bought it but now I am real nervous that I am heading for trouble.