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Internal ballistics frustration.

 
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  #15  
Old 12-22-2006, 09:18 AM
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Re: Internal ballistics frustration.

I have run into this a bunch in my reloading of big cases (over .515" at the web).

From what I understand of your problem, the brass fits when new, then each successive reloading from there gets harder and harder to chamber and especially extract. If this is the case, I would say that the problem is in your FL die. It is short enough to bump the shoulder back (which if it's an RCBS die is flat out amazing) but it is incorrect dimensionally in the web area of the case. These big cases need clearance in the web area more than smaller cases. If your chamber is small to normal in the "arse" end and your die is large for spec in this area, cases go in snug to fine but are an absolute ^&#*# to come out.

Check the diameter of the web of some virgin brass and then compare it to some that have been fired once and then to some that have been fired twice or three times. Then measure the web of some that have been fired a few times and have also been resized by your FL die. If there isn't much diff in the measurement of the sized brass vs. the 3x fired brass (.001-.002") than you have a chamber dimension to die dimension problem.

Remedy: get a new FL die. Preferably a Redding or custom.
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  #16  
Old 12-22-2006, 11:15 AM
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Re: Internal ballistics frustration.

[ QUOTE ]
then each successive reloading from there gets harder and harder to chamber and especially extract.

[/ QUOTE ]

Almost. After resizing, in all cases the cases chamber perfectly. Its only the extraction on the sencond and third time fired. The case head expands about .002" Slightly less. When I resize them, they remain .002" bigger than a factory new case. The drawing I have on the chamber specs show the head to be .5479" The cases new are .545". When fifed they are .547". After resizing they are .547". Would that contribute to this problem despite them chambering easily?
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  #17  
Old 12-22-2006, 11:27 AM
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Re: Internal ballistics frustration.

[ QUOTE ]
Is it perfectly straight or can you see any expansion bands around the body of the case.


[/ QUOTE ]

From what I can tell. it seems to be straight without any rings.

[ QUOTE ]
Do you have even bolt lug contact and has your receiver been accurized and trued?


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Yes and yes.

[ QUOTE ]
It does seem odd that you need to set the shoulder back that much to chamber easily with a sized case.

[/ QUOTE ]

I never had to set it back that much to get them to chamber easily (.005") They expanded .003" from new and I would set them back .003 to get them to new size + .002" hoping that would allow a little more case expansion for less pressure spikes. The new cases fired once will chamber back in perfectly whether resized or not. In all cases, if I resize them, even just setting the shoulder back .001" from the fired size, they chamber perfectly. I think I am dead wrong in setting them back that much. The reasoning was if the new ones extracted so easily, a lillte smaller would extract even better. I see now that this may be a bad idea. Do you think this could contribute to the problem? Is this creating more pressure than normal?

I am on my way to the range to see if setting them back less will help.

Thanks for all of your guy's valuable input.
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  #18  
Old 12-22-2006, 02:07 PM
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Re: Internal ballistics frustration.

I just got back from the range. I shot 5 rounds with twice fired cases and one 3 times fired case that was a bad offender. After resizing them to just bump the shoulder .001"-.002" instead of .005" helped quite a bit. They all had slightly difficult bolt lift, but not too bad. Slightly difficult meaning that, I can feel some resistance while lifting the bolt, then to get it to pop all the way up, it takes some minor to minorly moderate force. The actual extraction (act of pulling the bolt back and case out) was easy. Just the bolt lift required a little persuasion.

None of them pulled my extractor apart this time. Next I am going to try .0005-.001" and see if that improves it any more.
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  #19  
Old 12-22-2006, 02:15 PM
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Re: Internal ballistics frustration.

Did you shoot them over a chrono, it sounds like your running some higher presures as well. I have heard this with the Nosler cases that their internal capacity is smaller then say a Rem RUM case.

That bolt lift tightness would make me think that. At the top of the bolt stroke is where the mechanical extractor cam goes into effect. Do you need to give the bolt a slight pop to get it to go this last little bit and then the bolt comes back easily, I would check your velocities and see what they are saying with these loads.

On another note, that extractor pulling out would have me a bit worried. When Sako extractor is properly fitted to a bolt, the more pressure back on the bolt should pull the extractor down into the bolt, not out of the bolt. I would look into this as well, that is not right for some reason.

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  #20  
Old 12-22-2006, 02:26 PM
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Re: Internal ballistics frustration.

Why dont you try some just neck sizing?? It may give you a clue.
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  #21  
Old 12-22-2006, 03:17 PM
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Re: Internal ballistics frustration.

[ QUOTE ]
Why dont you try some just neck sizing?? It may give you a clue.

[/ QUOTE ]

This has ocurred in my 300ultra, it did however disappear when I necksized only.
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