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  #1  
Old 07-09-2018, 04:20 PM
aslap

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Advice for a dinged cone breech



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I have a barrel with a coned breech that I dinged with a dry fire incident. Actually the problem runs deeper than just a single dry fire issue but the result is the same. The gun started to have failures to fire every once in a while and then it started doing it every shot. Pulling the barrel showed a divot out of the edge of the cone where the FP hits the rim of the round. After re-cocking the gun would always fire so I surmise that the first hit of the firing pin wound push the round into the rim defect but not crush it and the second FP drop would finish the job.

The cone has a scallop taken out of it that measures around 0.080" wide by roughly 0.015" deep. I have tried to roll back the peened metal but that hasn't/isn't working at all.

The question is whether I can just get the barrel on a lathe and face off the defect until I'm back to a flat surface on the face of the cone. The barrel is a Rock Creek that was used by a guy who shoots competitively and was chambered by a well known RF gunsmith.

I'd think that the extra 15 thou wouldn't do much other than get the round a little deeper into the rifling. Right now the round engraves about to the end of the first driving band on a Lapua Center X round so there is room to move the round forward some. It's a screw in barrel so I don't have the luxury of it in and out and I'll have to recut the shoulder to get the headspace corrected.

Opinions? I was even thinking abut getting a little TIG weld on the defect and reshaping the cone but that sounds more and more to me like a recipe for disaster. The lathe would make it a quick job.

Thanks for any input.

Tony S.

PS - the reason the defect is so big is that I have a FP that is too long. I use the yellow wall anchors as snap caps and the FP was driving then hard enough into the rim of the cone to bend it back. I should have seen this way sooner than I did.
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Old 07-10-2018, 07:10 AM
Hi-NV Shooter
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aslap,

I assume this is a custom build, my advice don't fix it using short cuts have it done correctly.
also too late now, but this is the reason I use fired shell casings and not those plastic anchors or snap caps.

Lee
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Old 07-10-2018, 09:01 AM
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gcrank1

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Barrel needs to be set back and you will need to decide what reamer to use to fine tune the ‘throat’.

Last edited by gcrank1; 07-10-2018 at 06:30 PM.
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Old 07-10-2018, 01:14 PM
cdiver2
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Originally Posted by Hi-NV Shooter View Post
aslap,

I assume this is a custom build, my advice don't fix it using short cuts have it done correctly.
also too late now, but this is the reason I use fired shell casings and not those plastic anchors or snap caps.

Lee
How? I have never been able to get a fired case back in. In fact I have twenty ECI,s and tried to drill out fired case,s and put the ECI, in but they would not re chamber.
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Old 07-10-2018, 06:28 PM
Dennis D
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So, if you have a lathe you can pull the barrel, put it in a 4 jaw and center it perfectly and use a mini boring bar to just clean up the chamber. Or if your more ambitious since it's a cone breach you could also take about 5 thou. off the shoulder and the cone and set it back a little to reclock the barrel too. That's assuming of course that you have the extra cam to chamber a round.
In any case I'd fix the firing pin so it doesn't wack the barrel again.


Dennis
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  #6  
Old 07-10-2018, 08:22 PM
Hi-NV Shooter
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Originally Posted by cdiver2 View Post
How? I have never been able to get a fired case back in. In fact I have twenty ECI,s and tried to drill out fired case,s and put the ECI, in but they would not re chamber.
are you using the same fired brass that came from the rifle? some chambers may be tighter from different rifles.
also single shot or mag-fed
I only have single shot so just laying the fired brass on the loading tray and pushing it in works for me, sometimes I do have to wiggle them in but have always been able to use fired brass
FYI I stuff tissue in the brass so the residual won't get into the clean chamber and barrel

Lee
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Old 07-10-2018, 11:37 PM
cdiver2
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Quote:
Originally Posted by Hi-NV Shooter View Post
are you using the same fired brass that came from the rifle? some chambers may be tighter from different rifles.
also single shot or mag-fed
I only have single shot so just laying the fired brass on the loading tray and pushing it in works for me, sometimes I do have to wiggle them in but have always been able to use fired brass
FYI I stuff tissue in the brass so the residual won't get into the clean chamber and barrel

Lee
Tried on a single shot bolt action and a Martini, brass from same rifles.
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  #8  
Old 07-11-2018, 07:55 AM
aslap

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Thanks for all of the tips!

The lathe made short work of the ding. After measuring things out, I removed 0.014" from the end of the cone. Step next is to set the barrel shoulder back by that amount and I should be in business. I had a round that I had previously used to check the engraving of the bullet when the whole rig was new. Inserting a round all the way into the barrel now shows, as expected, a longer engraving path but still well ahead of the case mouth. I don''t think I'll do anything to the chamber at this point.

Dennis - Yes, indeedy. The FP is now set back considerably from where it was. When I built this thing I should have been aware of the FP protrusion but just wasn't.

Hi-NV - It's a custom in the sense that it's a Russian MTs-12 receiver that I bought as a spares unit for my other MTs-12. I bought it because I was concerned about never finding parts for the trigger if anything ever went South on me there. Don't you know that maybe a month after I got the receiver, a bolt assembly turned up on eBay! I bought that baby immediately figuring that I would use it a spares thing, also. Long story short, before I knew it I had the bolt repaired (extractor broken and springs missing; firing pin tip broken off) and the receiver fixed up (worn sear that I had TIG welded and reshaped; ejector broken) and the two mated together and working. You can't leave a thing like that alone especially considering that the other MTs-12 is an absolute hammer!

I was teaching myself how to use a CNC lathe here at work so I bought the Rock Creek barrel from a guy and made the bushing to go from the M25x1.25 original threading to the normal 3/4-16 thread and fit the barrel to the receiver. Shot great until this problem but it looks like this should fix things right up. I'll do the shoulder work on Saturday or Sunday and will report back if everything went as planned.

Thanks again!

Tony
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  #9  
Old 07-24-2018, 06:35 AM
aslap

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A quick post to end the thread

Set the shoulder back and screwed it all together and it shoots every time, first time now! The second good thing is that the shoulder cut moved the firing pin impact point to a nice, fresh, thick spot on the cone.

I had to file things back a bit around the extractors to get them to work but going slowly and checking things every couple of file passes has them working fine.

The bolt is a bit harder to close but I am shoving the round another 0.015" into the rifling. Checking a chambered round, the rifling is cutting back into about the middle of the second driving band of a Lapua CX round. Nothing is hitting the case and the engraving is clean and consistent all around the bullet.

So it looks like God smiles on the stupid once again. Even though the firing pin is now where it should be, I think I'll just leave the bolt out of the gun until I'm ready to shoot it.

Tony

PS - In my next post, you can almost guarantee that I'll be crying about losing the bolt!!!!
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