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length of brass "updated"

how critical is this length??

there is usually 10-15 thousandths allowed between the "long" and the "trim to length"

I was sent some 17M4 brass to be used in my 17rfb.

I read in "precision shooter" last month, that i could use the brass from 17M4 in my 17rfb but not the other way around.

the trim length on the 17M4 is 1.380 and the 17 rfb is 1.400
is it safe to use these being 20thousandths short??

Comments

  • mrbrucemrbruce Member Posts: 3,374
    edited November -1
    The only way to be sure is to check each chamber for individual trim length.
    Sinclair sells a sintered lead piece that goes into the end of a trimmed
    case that will give you the length your looking for.
    I like to open up the flash hole and just check the length out with my Hawkeye bore scope.
  • glabrayglabray Member Posts: 679 ✭✭✭✭
    edited November -1
    As long as the case shoulder is in the correct location and the difference in length is only in the neck, then use of somewhat shorter cases in a bottleneck cartridge shouldn't pose a safety problem. Use of a too LONG case WILL cause a safety problem if it is so long that the case mouth gets forced past the front of the chamber resulting in a severe crimp on the bullet. It is important to maintain the same case length from case to case. If the neck length varies from case to case, the gripping force on the bullets will vary also which in some calibers can have a dramatic effect on accuracy.
  • OdawgpOdawgp Member Posts: 5,380
    edited November -1
    quote:Originally posted by glabray
    As long as the case shoulder is in the correct location and the difference in length is only in the neck, then use of somewhat shorter cases in a bottleneck cartridge shouldn't pose a safety problem. Use of a too LONG case WILL cause a safety problem if it is so long that the case mouth gets forced past the front of the chamber resulting in a severe crimp on the bullet. It is important to maintain the same case length from case to case. If the neck length varies from case to case, the gripping force on the bullets will vary also which in some calibers can have a dramatic effect on accuracy.


    the shoulders are different the 17rfb is slightly longer and has a steeper pitch, I would essentially be fire forming the 17-223 to match the 17rfb
  • Tailgunner1954Tailgunner1954 Member Posts: 7,815
    edited November -1
    Just in front of the case mouth the chamber steps down in diameter, to just .001-.002 over the bullet diameter. If your case mouth should hit this step, you will pinch the bullet in the case mouth, and you will experance a severe overpressure event (nice way of saying blow your rifle up).

    As a rule of thumb, SAMMI maximum case length minus .010 = trim to length, max - .020 = Sammi Minimum case length.

    The reamer manfactures tend to set this step a little over the max length, but unless you know exactly where it is in your rifle, stick to the specs you know.

    Brass that is shorter than the Min Spec is safe to use, but you may get a little erosion over time, along with (very) slighty lower bullet pull force.
  • OdawgpOdawgp Member Posts: 5,380
    edited November -1
    quote:Originally posted by Tailgunner1954
    Brass that is shorter than the Min Spec is safe to use, but you may get a little erosion over time, along with (very) slighty lower bullet pull force.


    I would imagine that after one or two firings that the neck will lengthen. I usually have to trim cases in most of my other calibers every other or every third time.

    thanks
  • dcs shootersdcs shooters Member Posts: 10,969
    edited November -1
    Just go ahead and fire form the cases and then check the length.
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