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7mm STW - Stuck cases, at wits end

 
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  #15  
Old 07-28-2011, 07:46 AM
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Re: 7mm STW - Stuck cases, at wits end

We've covered the chamber size so I'll offer something new for you to think about. I presume that you are trimming or at least measuring the brass that you are using.

I mention this because I had this exact same thing (difficult extraction from the chamber) happened to a friend of mine with his 7 WSM. New brass worked fine, but 2X fired brass would not extract (6 out ot 10 would stick in the chamber) from his custom chamber. Turns out the brass would grow between firings 1 and 2 and on the second firing, was just long enough to engage the end of teh chamber and then refuse to extract. I had also suffered from periodic difficult extraction, and yep the brass was right up at the trim length.

Hope you gedt your situation figured out. let us know what you find out.

JeffVN
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  #16  
Old 07-28-2011, 10:54 AM
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Re: 7mm STW - Stuck cases, at wits end

Thanks for all the advise.

Last night we polished the chamber with Flitz. We figured if it needed to be re-chambered we might as well try a quick polish job. We did as much reading as we could find on polishing a chamber. From all our reading we gathered super smooth wasn't what we wanted. We attached a 20 gauge bore mop on a cleaning rod, chucked it in a drill, applied the Flitz and spun it in the chamber for 30 seconds at the most. We test fired two shots. The first was a normal load and the second was hot. Both extracted with minimal effort and neither case had marks in front of the belt. Tonight we are headed to the range to test more loads.

At this point we think there may have been a burr in the chamber where it transitions from belt to case wall.

Has anyone else had issues with burrs?

The reamer is brand new and it was chambered on a manual lathe.
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  #17  
Old 07-28-2011, 11:54 AM
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Re: 7mm STW - Stuck cases, at wits end

I would size the cases one more time, and reload them with one grain less powder. That ring you are seeing is known as a pressure ring, and when you see it it's time to back off a bit. Also you need a better die than what you probably are using to resize the case down by the belt. Look for Larry Willis on the internet as he has the die needed to resize near the belt.
gary
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  #18  
Old 07-28-2011, 12:32 PM
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Re: 7mm STW - Stuck cases, at wits end

Even if a reamer is brand new it can pick up a chip and scratch the chamber wall. I've also seen brand new reamers leave what looks like scratches. I usually polish a chamber with 1000 grit sandpaper and a bit of oil. You have to be careful not to polish clear up in the throat.

Did you remove the barrel to polish it? Did you try measuring the back of the chamber?

Last edited by IdahoCTD; 07-28-2011 at 12:36 PM.
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  #19  
Old 07-29-2011, 12:10 PM
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Re: 7mm STW - Stuck cases, at wits end

Quote:
Originally Posted by IdahoCTD View Post
Even if a reamer is brand new it can pick up a chip and scratch the chamber wall. I've also seen brand new reamers leave what looks like scratches. I usually polish a chamber with 1000 grit sandpaper and a bit of oil. You have to be careful not to polish clear up in the throat.

Did you remove the barrel to polish it? Did you try measuring the back of the chamber?
that bright ring is just ahead of the belt. That's where the case will see it's max pressure. Also the ring runs all the way around the case. Normaly a reamer going south will simply not cut well. Actually a dull reamer often cuts a more accurate hole than a recently ground one. Bad spindle bearings will also effect the finish, but those lines usually run parallel with the axis of the reamer. The dead give away here is the O.D. measurments the poster supplied. The case has expanded several thousandths at the pressure ring area. A normal sizing die has a hard time sizing that area, if it can at all. That's why I suggested a visit with Larry Willis.

I have polished a few chambers in the past with an oil slurrey I made up using light spindle oil (like three in one), and powdered cleaner like Comet. Use a hard maple dowl about four inches long. First polish the chamber with 400 grit black paper wrapped around a wood dowl. Then use the slurrey. If you really want it slick, then after the Comet, try corn starch & oil, and then later dry. It'll look like a mirror. There is an even better compound out there, but think it's illeagle in the U.S. these days
gary
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  #20  
Old 07-30-2011, 06:42 PM
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Re: 7mm STW - Stuck cases, at wits end

i would get the head space checked out on the chamber.
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  #21  
Old 07-31-2011, 12:29 PM
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Re: 7mm STW - Stuck cases, at wits end

Quote:
Originally Posted by TRG300WM View Post
i would get the head space checked out on the chamber.
the head space on a belted magnum is exactly .250." You can set them up to head space off the shoulder, and case head, but the proper way is the belt. If it's a factory chamber or one using a factory type reamer it will head space off the belt unless modified. The headspace being too long will simply not allow the bolt to close. The headspace being too short will create case stretch length ways, and not laterally.

As I said take a brand new case and load the same charge, but about one grain less. See if that works for several loadings. If not, then it's time for a chamber cast. When you touch off the primer and ignite the powder the gasses in the case cause it to expand in all directions. But as the pressure eases the case will retract to where it started from inless you took the metal past it's yield point. The shooter has done this by looking at the O.D. numbers he's posted. I might add here that it's nearly impossable to measure case growth with a conventional micrometer. You at least need a blade mic, and even the width of the blade is still too much. I use both blade mics and a .5135" ring gauge made from a ball bearing with a 13mm I.D. (even an inner race for a 13mm shaft will work very well right out of the box). If the bushing will not slide all the way down the shaft, I know the case needs completely resizing (got a cigar box full of case now)
gary
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