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Posted: 2/24/2012 12:58:25 PM EDT
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Went to the range today to try a couple more loads for the mighty 243 Win. I had loaded the last of my Win cases so I grabbed 5 R.P to load. Upon shooting the rounds I had 1 out of 15 Win's that would not chamber and 4 of the 5 R.P's would not chamber. I had measured the Comp OAL so I knew that was ok as the little Remington 788 has a Comp OAL way longer then the mag, if you remember one of my posts a couple months ago had pics of some loaded rounds with the crimp groove way above the case mouth.
Once I returned home I got out the Stoney Point head space gauge and did some measuring. The SAMMI specks on the 243 are 1.630 min and 1.640 max for head space. The 4 rounds that would not chamber measured 1.630. I saved a round that chambered freely to measure which is at 1.625. I measured 13 fresh once fired cases and have a range of 1.626 to 1.628 with an average of 1.626769. My sizer die is knocking the shoulder back to 1.625 on cases I measured a couple months ago. It appears that my chamber is short as a 1.630 case will not chamber and I have once fired cases measuring .004 under theSAMMI minimums, yes / no? Why is it that some brass isn't getting set back as much as others? I look at sizing as mechanical and don't see how one case can get sized to 1.625 and another 1.630. Dose difference have to do with case head or rim thickness, brass spring back? The fix? I measured some other R.P and a couple FC cases that have been resized and head space runs into the to long. I tried loading some of these cases and had hard bolt closure. I checked the press and sizing die to make sure its set and found that I am in fact camming over the press ram fairly stiff right now as is. |
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Not really. The Stoney Point Heaspace gauge uses a "Comparator" to measure headspace. Comparator as in compare your fired brass to your sized brass. It does not land exactly on the datum of the shoulder and cannot be used to compare to SAAMI specs, only to whats on your bench. They are universal and are designed to work with several different cartridges. If the comparator was designed to land exactly on the datum line of the shoulder then Hornady would have to make individual ones for each and every cartridge available.
Fire a round, measure with the headspace comparator, size same round, measure again, done. Forget SAAMI it has nothing to do with this gauge. |
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Quoted:
Not really. The Stoney Point Heaspace gauge uses a "Comparator" to measure headspace. Comparator as in compare your fired brass to your sized brass. It does not land exactly on the datum of the shoulder and cannot be used to compare to SAAMI specs, only to whats on your bench. They are universal and are designed to work with several different cartridges. If the comparator was designed to land exactly on the datum line of the shoulder then Hornady would have to make individual ones for each and every cartridge available. Fire a round, measure with the headspace comparator, size same round, measure again, done. Forget SAAMI it has nothing to do with this gauge. K this makes since but why are some rounds chambering and some are not? How can I size the not chambering rounds when I am already camming over the press, remove material from the bottom of the die. |
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Quoted:
Quoted:
Not really. The Stoney Point Heaspace gauge uses a "Comparator" to measure headspace. Comparator as in compare your fired brass to your sized brass. It does not land exactly on the datum of the shoulder and cannot be used to compare to SAAMI specs, only to whats on your bench. They are universal and are designed to work with several different cartridges. If the comparator was designed to land exactly on the datum line of the shoulder then Hornady would have to make individual ones for each and every cartridge available. Fire a round, measure with the headspace comparator, size same round, measure again, done. Forget SAAMI it has nothing to do with this gauge. K this makes since but why are some rounds chambering and some are not? How can I size the not chambering rounds when I am already camming over the press, remove material from the bottom of the die. What brand of dies and press? Might want to contact the manufacturer. It happens, I have had this issue with all of my Redding AI dies, had to send them back with a couple fired cases to have them fixed. I have also had this issue with one Forster WSSM die, didn't send it back, just remove material off the top of the shell holder. Cheaper to ruin a shell holder than the die, easier too. Also make sure that your decapping stem is not set to deep. Did you apply a little lube to the inside of the necks. It is possible that the expander ball is is dragging the shoulder forward on exit. |
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So I sized some fired cases and it appears that the die is setting the shoulder back .002 to .003. I pulled bullets on two of the cases that didn't load and resized them. They started out at 1.630 and sized back down to 1.628, I sized these the first time 15 years ago so who knows what the deal is there. I chambered a few of the sized rounds and found that cases sized at 1.625 chambered easy, 1.626 I could feel the resistance and 1.627 made the bolt handle very stiff. I happened to have another shell holder which I tried and cut another .001 off the head space.
Press is an old RCBS Rock Chucker with 25 year old RCBS dies. The expander is kinda stiff coming out so it could be draging the shoulder up. I will remove it and try a couple more cases and see what I get. A little polish might be in order? Thanks for the ideas. Removed the expander and nothing changed. Set the sizer die down until there was no camming over and squeezed another .001 off the shoulder but I'm sure thats not the answer. measured a few more cases and most are right at 1.625 which is just on the edge. Looks like I might need to rework a shell holder for the cases that don't get enough set back after initial resizing. Will suck to have to check each case and redo the long ones but one thing about it I shouldn't be over working the shoulder with what I got. Know if I could just get my groups to tighten up. |
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The expander is kinda stiff coming out so it could be draging the shoulder up. I will remove it and try a couple more cases and see what I get. A little polish might be in order? Try lubing the inside of the case necks better. No lube will stretch the shoulder up towards the mouth.Also, try sizing the cases without the expander, and see if they will chamber correctly. That will tell you if it the expander causing the problem.
Polishing the expander won't help unless it's visibly scarred and rough. If you reduce the diameter of the expander, you'll just increase the neck tension. |
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Quoted:
I look at sizing as mechanical and don't see how one case can get sized to 1.625 and another 1.630. It may take 3 firings for the brass to fully expanded to the chamber. I don't see how it happens either, but it does. I just finished about 100 .223 LC 1X cases. Started out checking each one through the RCBS precision mike. I got a spread of -.004 to +.001. I finally got tired of messing with the sizer settings and said to heck with it, they are what they are. Most of the .223 necks and shoulders are very soft. I think the expander retraction messes with the shoulder. I trimmed each one and got another .001 variation in trim length there. I wanted the trim to be consistent because I am going to roll crimp the neck into the "improved" cannelure I made in the 77 SMK w/c 's. |
| Its possible to have a combination of chamber & die that will not work together If you study this article on the 243, you will see its possible.. Link Lee has said on there FAQ that they cut there FL dies to middle of SAAMI specifications. They will make adjustment to a die if needed. Lee makes no small base dies. Just saying about dies in general, as you are using RCBS. Neck size your brass, for a bolt till, you can no longer chamber a round. Now measure your brass, this will tell you the true head to datum line measurement. |
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