Am I on the right track?

[ShadeTree]

Need some pointers from those that have gotten into the nitty gritty of chamber dimensions and how everything works to see if I'm thinking correctly.

Ran into an issue late last fall when shooting Pop's model 71 348. Was shooting a couple shots right before season started and was also double checking things with the chronograph. Was getting WILD velocity swings with just a couple shots and I quit. We are talking like 150 fps.

I put it away and figured I'd figure it out later. One day just sitting around I got an idea to check something.....I took the cases I'd just fired last time (not resized) and tried by hand to put one of the Swift A-Frame bullets I was shooting into them. They are TIGHT. Basically will not start in without a LOT of force. I then tried the same bullet in once fired cases that I had been shooting Hornady 200 grain bullets in. Extremely TIGHT.

I then took a 200 gr Hornady bullet and tried the same thing in both the cases that had the Hornady's fired through them, and the ones that I'd fired the Swift bullets through. TIGHT.

I'm thinking there is a carbon ring built up in the neck area of the chamber restricting the neck brass from expanding and causing spikes in pressure and velocity. Any other non sized, fired case in any caliber, I can take any bullet for that cartridge and it will fall into the case until you resize the neck.

 

[gbflyer]

I’d say you’re on the right track. You need a good fitting bronze brush, maybe .358 or .375. It’s not going to be easy being it’s a lever gun. Not sure but I doubt that foamy cleaner stuff will cut it but may be worth a try.

 

[ShadeTree]

I’d say you’re on the right track. You need a good fitting bronze brush, maybe .358 or .375. It’s not going to be easy being it’s a lever gun. Not sure but I doubt that foamy cleaner stuff will cut it but may be worth a try.

I'm gonna test some of the Hornady's again, just to see. But even if I don't get the same velocity swings with those, it still doesn't mean it's not a culmination of the same problem, but I'll have to see.

The Swift's are I believe a harder copper.......I'm using a Lee factory crimp die set to the same setting for both bullets, so the crimp might be holding on harder to the Swift bullet. Still wouldn't explain though why the necks on fired cases are not expanded out to where it's loose.

 

[truck driver]

You can take a bore mop and load it with Kroil and let it soak in the chamber with the muzzle pointed down so the oil doesn't drain back into the action Leaving it sit over night, Then take a over size bronze bore brush and scrub the chamber.
Gunzilla is also good for cleaning carbon and won't hurt the metal but don't get it on the wood since it will remove the finish.

 

[Blkram]

Just a thought..
But have you mic'd the bullets to check actual diameters, and mic'd the brass to check neck thicknesses?
Perhaps necks need to be turned? (might eliminate/mitigate neck wall thickness and tension variations, or at least eliminate that variable???)
Have you checked the dies? Are they of proper interior dimensions? (clean and/or free from some crud or deviation?) Had a friend who was having problems and in the end after lots of frustration, found his dies had a defect inside that was causing the issue. Manufacturer replaced without delay.

 

[mjcmichigan]

I’d verify the case trim length as well.




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[ShadeTree]

Case trim length is within specs and on the ones that were loaded numerous times when they grew to maximum length were trimmed accordingly. Actually on these because they're getting crimped, I pay special attention that they're all the same length so the crimp is applied the same.

Dies are new and took them apart when I got them and cleaned any residue/metal filings out by spraying them with gum cutter. Even if they were squeezing the necks too hard and causing pressure spikes (which would be bad), once fired the necks should still be expanded out to chamber size?

I will double check bullet diameters, and I don't own a micrometer but have a good set of calibers, and will see if I can verify that case neck thickness is within specs. Be hard to believe the whole lot of them are outside of spec but I guess it's possible.

 

[gbflyer]

My guess is the case neck thickness is fine. You’d have a hard time finding a neck turning mandrel for a .348 I bet.

Those old rifles got cleaned from the muzzle down and all the carbon went into the chamber. I bet it’s pretty built up after all the years. You might have luck with a chamber brush setup like the GI version for an M14 if you could find a brush of some kind that is tight. Otherwise you’ll probably have to pass a cleaning rod down the bore then attach a big bore brush to it as it’s sticking out of the chamber then pull it into the chamber. It would be good to have a way to spin it once you get the brush in the neck. Might take some “MacGyver-ing.”[emoji1]

 

[cloverleaf]

My guess is the case neck thickness is fine. You’d have a hard time finding a neck turning mandrel for a .348 I bet.

Those old rifles got cleaned from the muzzle down and all the carbon went into the chamber. I bet it’s pretty built up after all the years. You might have luck with a chamber brush setup like the GI version for an M14 if you could find a brush of some kind that is tight. Otherwise you’ll probably have to pass a cleaning rod down the bore then attach a big bore brush to it as it’s sticking out of the chamber then pull it into the chamber. It would be good to have a way to spin it once you get the brush in the neck. Might take some “MacGyver-ing.”[emoji1]

Really truly not trying to disagree with the above suggestion. Its sounds like a plan given the action type you are talking about.... and then the warning bell went off in my head... if you spin that brush with a rod attached aren't you running the risk of damaging the crown? For me I'd pay to have a good smith bore scope the thing..... Just thinking.... "DANGER WILL ROBINSON..." But I could be wrong....what do I know? I think I'd try a full can of Wipe Out or Kroil or something before I resorted to mechanical means in a place I cant see. That there is one cool rifle, if I recall correctly. All the best. CL

 

[ShadeTree]

CL. I haven't decided for sure how I'm gonna approach it yet. But one thing I do know for sure is that I'm gonna wait until I have plenty of time and am not rushing it. I might just tear it down where the lever and bolt is removed so I can access the chamber from the breech end.

I will definitely have to wait until I got lots of time and can carefully study how things come apart if I go that route.

 

[gbflyer]

The crown is a valid concern. It could be protected with a rod guide, again similar to the ones they make for Garands and M14.

The real way to do it is to pull the bolt. I’ve done 92’s, it’s not that big of deal with good directions and the right tools. A gunsmith would be a good suggestion [emoji1]

 

[ozarkpugs]

Clover leaf's comment gave me a chuckle , not that I disagree because he is 100% right about protecting the bore its just that the last chamber I polished was with clover leaf lapping compound .

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[lhsako]

My guess is the case neck thickness is fine. You’d have a hard time finding a neck turning mandrel for a .348 I bet.

Those old rifles got cleaned from the muzzle down and all the carbon went into the chamber. I bet it’s pretty built up after all the years. You might have luck with a chamber brush setup like the GI version for an M14 if you could find a brush of some kind that is tight. Otherwise you’ll probably have to pass a cleaning rod down the bore then attach a big bore brush to it as it’s sticking out of the chamber then pull it into the chamber. It would be good to have a way to spin it once you get the brush in the neck. Might take some “MacGyver-ing.”[emoji1]

Really truly not trying to disagree with the above suggestion. Its sounds like a plan given the action type you are talking about.... and then the warning bell went off in my head... if you spin that brush with a rod attached aren't you running the risk of damaging the crown? For me I'd pay to have a good smith bore scope the thing..... Just thinking.... "DANGER WILL ROBINSON..." But I could be wrong....what do I know? I think I'd try a full can of Wipe Out or Kroil or something before I resorted to mechanical means in a place I cant see. That there is one cool rifle, if I recall correctly. All the best. CL

Dr. Smith is my gunsmith....lol