Case length ???

toad67

June 26, 2009 11:14

Why is there a difference between max case lenght and trim length?? If cases should be trimed to a certain length should that not be the max case length?? Thanks.

Todd

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  PA Shootist

  June 26, 2009 11:22

  Usually the case becomes a bit longer each time it is fired. Trim-to length is a minimum length; max is to prevent problems like jamming into the lands, the case's contribution to overall cartridge length for feeding, etc. In most cases, if the cases are of uniform length or nearly so, between the min and max you're OK. Some shooters will be more precise, and want every case to be exactly the same, so that crimping, bullet pull etc. will be absolutely identical. The more uniform, the better chance of increased accuracy. Sometimes I have felt the variation between max and trim-to were pretty big numbers, .010" and even more. And I usually don't trim way back to minimum, rather trim to a uniform length based on the shortest cases in my batch.

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  partisan

  June 26, 2009 13:16

  +1 with PA SHOOTIST!

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  Tailgunner1954

  June 26, 2009 15:22

  Actually there are 3 case lengths (there are a couple of exceptions to that), MIN, Trim-to and MAX
  Min & max are usually .020 apart, with the trim-to being in the middle. On the exceptions I mentioned, Min and trim to are the same, with max being .020 longer.
  
  Now, your free to trim every time, and with some cartridges you may have to, but most of the time it takes 3-5 firing cycles before the case "stretches" out to the Max dimension.
  
  Letting your cases grow beyond Max can cause the mouth to pinch down onto the bullet. Pinching will cause you to see the effect of severe overpressure rather quickly [:0][B)]

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  zimmden

  June 27, 2009 11:32

  After testing many cases in 6 different calibers, I find that shooting causes very little stretch ( lengthening ) of the case. Full length Resizing causes the most stretching when the expander ball on the depriming rod is withdrawn. By neck sizing only with bushing dies there is almost no case lengthening. Bob

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  sandwarrior

  June 27, 2009 12:34

  quote:Originally posted by zimmden
  After testing many cases in 6 different calibers, I find that shooting causes very little stretch ( lengthening ) of the case. Full length Resizing causes the most stretching when the expander ball on the depriming rod is withdrawn. By neck sizing only with bushing dies there is almost no case lengthening. Bob
  
  
  +1
  
  Or using a collet type die where the case mouth is resized around a mandrel.
  
  I also lube the inside of the necks a smidge to help slow down case stretch. This also adds a step of cleaning it out once the cases are sized. Lube in the neck during the powder drop stage can make big messes (amazing how many directions 40 little grains of powder can go) and safety issues. And, in most instances, can make your powder perform sub-par.

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  benfishin

  June 27, 2009 19:13

  So, when does one use a case guage? Would that be when you are just neck sizing? I don't see the point if you use a full sizing die and calipers. Does it help check the diameter of the round for use in a revolver and if so do you need to do that for a semi-automatic?
  Thanks

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  zimmden

  June 28, 2009 06:59

  Case gages are useful for setting up 7/8-14 sizing dies, checking headspace, base and mouth diameter and rim thickness and OAL of cases.

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  JustC

  June 28, 2009 08:19

  if you trim all the cases in a new bag to the shortest case in the lot's length, you will virtually never have to trim again. I try not to FL size unless a semi-auto is being used.

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