Nobody addressed my question:
What causes the barrel to flip open, frame flex or improper fitting locking bolt/s? Or maybe a combination of both? I guess weak locking bolt spring would contribute.
Bottom line, if you've had one flip open, what did you do to correct it and did you figure out what was really wrong?
The first barrel I ever had flip open on firing was a custom eabco, when made by bullberry. The locking bolts were soft and the full power loads peened them just enough to cause the barrel to unlock when fired. I was actually at a woods walk and the bullet was still hitting the target but about the 3rd time it popped open, and the case smacked me in the forehead, I decided it probably wasn't safe to continue. );
So, I think you've nailed most of the points to check, let us know what you figure out.
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I have had 2 barrels that opened on firing a 22 hornet and a 357 mag the 357 mag got my attention times 10 the case self ejected and actually hit my shooting glasses, both barrels I stoned the Latches Bolts Lugs or what ever you choose to call them to fully engage the frame, Problem solved, I have had at least a dozen or more barrels that would not engage enough to cock the hammer again same stoned the latches until they did. Just part of the Contender addiction you may have to put up with every now and then. Some MGM barrels of a few years ago the spring and latches were less than useful and most required fitting or replacing, As of late that is no longer a problem, My last 4 barrels form them fit perfect with smooth closing and latching.
Another cause can be too much oil on the locking bolts, that's what was causing my 30 Herrett opening on firing.
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Under sized cartridge and closing the frame lightly can also cause this.
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I should of noted That I currently only use G2 frames my fingers are to abused to open the Contender frames any longer when I go to the range I shoot A LOT so I want real easy open. One of the three G2s is considerably more difficult to close I refer to it as tighter fitted, 2 are Rochester one from Springfield, one of the Rochester's is the tight one the other had issues with being rather loose sent it to S&W TC and they remedied the problem, When I get a new or new to me barrel I try it on all three to see if there will be any issues, I really learned from the 357 incident,
Not true I have gone to the range with the tight fitted frame that would close and cock but until closing with a round in the chamber then the hammer would not cock, There head space comes to play a case that was not sized for that chamber, So there can be more than just one cause or remedy
Having no one else close to me I have had to figure out these issues on my own on the phone with other Contender nuts or the internet gurus, Some mistakes were made in diagnosing a simple problem, Not very many Gunsmiths know enough about Contenders, David White is no longer here and Mike Bellem is no longer available to send our problem frames to, Mike and David both help me out more than once on the phone try finding that kind of help today, TC for now unavailable too.
OK I think I am done rambling now
You did not say if it was a Contender/G2 or Encore, although I don’t think I have ever heard of this with Encores but I assume it happens. If it is an Encore EABCo makes locking lugs for them from tool steel. That may be an option. Plan on trying a couple sets myself just for curiosity sake.
Sorry, I only have the old style Contender, don't like the Encore of G2 triggers, too hard to work on.
I was just hoping someone had actually measured the bolt engagement and had a real world idea of what happens.
I had the same situation a number of years ago with some mild loads in a 6mm-.223, and it had me baffled. But then I remembered I had taken apart the entire pistol to clean it a few days prior after getting caught in a bit of a downpour.
I try and keep the action free of any excess lube, but I was a little overly-enthusiastic in my cleaning and let the engaging surfaces become slickened with a bit of WD40.
Drying that out took care of my problem.
That's the way I always checked headspace on necked-down cases for fire-forming...I'd neck the case in increments and stop when the action dependably closed, cocked and popped a primer or engaged the firing pin. That way I could ensure that I'd have a perfect fit for the chamber without any excess headspace. Doesn't work with the TCU's though.
If excess is not present Change the locking bolts.
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I was dealing with a action popping open as well. My loads were safe but higher end. I cleaned the locking lugs and installed a heavy duty spring. I’ve also gone down to another load with a lighter bullet. I actually shot a deer this year at 200 yards and had the frame open up. Killed the deer but not where I was aiming.
Also measure your headspace and make sure it’s correct. If that case is to long it won’t let you shut the action properly.
I prefer the Bellm method. Measure the distance from breech to barrel. Remove the extractor and use the chamber for a gauge. IMHO, if the case drags across the breech face when closing, you lose accuracy and if it has >.005 clearance you may get case head separation. I strive for .001-,002 clearance and that takes a lot of measuring.
Case head separation will throw a shot out of the group and inch or two, how far out when the action flips open?
Looks like the magic marker on the locking bolts is the scientific way to check engagement. I've been overthinking again!
Think about it. If the action won’t close fully because the cartridge is too long, that means that the interlock safety will not be tripped by the bolts. If the safety is working properly then the pistol will not fire when not fully closed. If the pistol fires when not fully closed and then pops open there are several things wrong with it and it needs to see a competent T/C gunsmith pronto.
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Check your case lengths. If case is to long it will cause the barrel to unlock.
Lonestar.... makes sense to me!
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