belt expansion as pressure indicator

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by rufous, Jan 13, 2002.

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  1. rufous

    rufous Well-Known Member

    Jul 17, 2001
    I read in Hodgdon Manual #27 that measuring case head or belt expansion can be a good means of measuring pressure. It says that for unbelted cases one should measure just in front of the extractor groove and that if expansion is 0.0005" then that would be considered maximum. For belted cases one should measure the belt and it should expand no more than 0.0007". The question I have is should this test only be done on new cases or only on once fored cases or does it matter? I would think only on new cases. Rufous.
  2. Brent

    Brent Well-Known Member

    Jun 12, 2001
    I'm not to sure about this but here's something to consider. My 416 Weatherby factory loaded ammo measures .602" on the belt with calipers and once it's fired is .605" to .606", thats .003"-.004" greater, that's 3 thou, not 3 ten thou.

    But fire a less than max load after that and dia. stays the same. A max load will sometimes produce .0005" more expansion. So I think they refer to after the initial fire form from my experiance.

    I once loaded 400gn X bullets with RL22 at 120gr to get 2700 fps which is the max velocity listed but is 12 grains over maximum Barnes load. The velocity fell to 2500fps with 120.5 gr and bolt lift got a little sticky with belt expansion moving from .606" to .607" in one firing. dropped back to 120gr and no psi signs at all, even belts stayed the same. The next lot of powder was worked up from 105gr and found the exact reaction at 118gr and at 118.5 velocity fell again. I went to the XLC and found even better accuracy with 115gr at 2550fps.

    Hope this helps some.

    [ 01-14-2002: Message edited by: Brent ]