The locking bolts do not engage into the frame's "locking table" very far, and from what I have seen over the years, if they only engage just enough to release the hammer block safety and permit the frame to fire, this minimal engagement will wear and thus round the forward edge of the locking table. Once the locking table is rounded, it will be more prone unlocking when fired. If after what follows here has been addressed, a barrel or barrels still fly open, then send the frame back to TC for inspection and probably replacement.

     This minimal engagement will be caused either by the height of the locking bolts being too high for the given frame or it will be caused, as you noted, by cases sticking out of the chamber too far due to not being sized correctly. (This is one reason why I harp on the subject of size die adjustment and highly discourage neck sizing for these break open guns. Continued firing of rounds that interfere with lock up can cause undue wear on the locking table.)

     The cure is to either get a set of undersize locking bolts from TC or learn how to adjust a size die to get the correct headspace. The latter is a pretty simple concept, but the majority of shooters have been dumbed down by what they read and hear and just can't quite put it together in their minds. I don't mean this in a disparaging way, since I have also "been there, done that" trying to figure out what in blue blazes is going on. Look at it this way. I have probably made just about every mistake you guys can make and then some, and I also have a pretty good clue what your problems are getting through puzzling situations.

     You have to go through a process of elimination. With the barrel empty, you can get some idea, though not 100% conclusive, about the engagement by holding the hammer back and pulling the trigger with the barrel closed. If the hammer block safety is not dropping... you got a problem, and need lower locking bolts.

     But just because the hammer block drops, this does NOT mean you have adequate engagement. For one, the mating surfaces between the hammer block and the interlock (the little butterfly shaped gipper the locking bolts turn when the barrel is locked up) can be worn and permit the hammer block to drop when it shouldn't, as in when the barrel is not fully locked up.

     You still need to degrease the tops of the locking bolts, ink them with a felt tip pen, and then open and close the barrel in a normal manner several times. This will leave a "signature" on the locking bolts by marring the ink where the locking bolts are in contact with the locking table. This marring should show on the locking bolts approximately 1/32" forward of the "U" shaped notch in the locking bolts. It need not extend to where the main locking surface meets the angled surface forward of it, but it should be close to it.

     If the marring goes all the way to the way to this angled surface, it may also indicate the top surface of the locking bolts is too low, and the lock up may not be tight enough. So don't get alarmed if the marring does not take up the entire engagement surface on the locking bolts. But it must be noticeably forward of the "U" notch.

     The point has been made elsewhere that the locking bolts should be left dry, and this is true, especially in marginal situations. But if the locking table surface is as it should be and the locking bolts themselves have not been polished, lubrication will not cause the barrel to open. Face it, day in and day out I test fire barrels that go from the lathe to the parts cleaning tank, which is a combination of some diesel fuel and lots of oil. For mostly rust preventive qualities, I add some cosmoline and "STP" like goop to the diesel fuel. Locking bolts that come out of the wash tank are well lubricated. But I cannot remember now when the last time was that a Contender flew open test firing it. While the locking bolts are best left dry, LUBRICATION ON THE LOCKING BOLTS IS NOT THE CAUSE OF THE BARREL FLYING OPEN.

     With adequate engagement as described above, if the barrel will unlock when fired, oiled or not, then either the locking table is worn and the frame needs to be replaced, or the tops of the locking bolts have been "dinked with" and are either polished too smooth or the top "draft angle" on the locking bolts has been altered to a more vertical plane.

     In other words....DO NOT POLISH THE TOPS OF THE LOCKING BOLTS WITH THE IDEA OF GETTING IT TO UNLOCK EASIER, ETC. The tops of the locking bolts can be lowered to get a proper lock up engagement and easier unlocking ok, but the surface should remain textured, not polished.

     With locking bolts in good condition engaged into the frame adequately and the locking table in the frame in good condition, mechanically, there is no reason for a barrel to unlock unless the loads being fired are excessively hot, but even hot loads will not necessarily cause the barrel to unlock. With things mechanically "right," the cause of unlocking frequently is then due to cases being too long from head to shoulder and interfering with lock up.

     There are all sorts of ideas about how the barrel feels or sounds when it is snapped shut "guesstimating" whether the size die is set right or not, but the only way to do it, in my opinion, is to first find out what the barrel to frame gap measures, then with the barrel OFF of the frame, drop a sized case into the chamber and measure how far it sticks out compared to what the actual barrel to frame measurement is. Do the same thing with loaded rounds. Seating bullets out to contact the rifling creates a round that is too long also, and can interfere with lock up.

     In summary, we have all done things with Contenders particularly for years that were rather dumb, or at least ill advised, and gotten away with it, sometimes with great success. But it is a lack of understanding of what is going on that rears its ugly head and causes problems such as misfires and barrels flying open, the continuing bain of those who have not looked quite far enough into how these guns work. Hopefully my efforts will help get the word out and make these problems a thing of the past.

     Final comment. One nice thing about Contenders and Encores is that the standing breech, small as it is, acts as a shield that deflects cases flying out of the chamber up over the top of the shooter's head. While it definitely gets your attention, usually the worst it does is nick the top of your cap as it does its "auto eject" thing flying by. However, someone standing directly behind a shooter when a barrel does fly open could be at risk if a hot flying case hit him in the eye. They come out with some force, but usually not enough to cause severe damage unless something like an eye is hit. A barrel flying open is NOT a good thing, and definitely not something to permit continuing to happen, but it is not normally a severe hazard either. I have had it happen a number of times, once while being filmed for television even. Talk about embarrassing. So, yes, I have "been there, done that."