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Why 1.250?

Discussion in '10mm Reloading Forum' started by gofly, Apr 14, 2012.

  1. gofly

    gofly pistoleer

    Feb 29, 2012
    All the drawings I've seen specify 1.260" as the oal. Why then is it more popular to assemble at 1.250?
  2. Jitterbug


    Aug 27, 2002
    Sometimes 1.250" feeds better...each chamber, bullet nose profile and ramp geometry is different, but this doesn't mean to deviate very much from published data, too short will increase pressure...this is true of any cartridge, some are more sensitive then others, .40 S&W comes to mind.

    For example if load data calls for 1.260" then that recipe at 1.250" will generate more pressure, so as always work up carefully.

    The "sweet spot" for feeding is generally between 1.242"-1.260"

    Most of my old Double Tap loads measure 1.242"

  3. gofly

    gofly pistoleer

    Feb 29, 2012
    Ah Ha, Makes sense.

    I was aware of the pressure implications, which is what had me puzzled.
  4. WeeWilly


    Nov 12, 2011
    My G20SF seems really insensitive to OAL with regard to feeding. The only feed issues I have had on the gun was when I intentionally loaded some rounds up super light to test the lower bounds of my spring setup. As I have started loading into the hot zone with my 10mm rounds, I use 1.260" all the time.
  5. gofastman


    Jan 29, 2010
    I aim for an oal of 1.255"

    The only time I have heard of it being necessary to get down to the 1.240-1.245" range is with the wide-flat-nose hard cast bullets, they tend to not feed as well because they arent as pointy as a standard jacketed bullet
    Last edited: Apr 15, 2012
  6. Jitterbug


    Aug 27, 2002
    Often times when working up a "new load" I'll make a couple of dummies at 1.250", 1.255" and 1.260" and see which cycle best through the gun. Just don't put a primer or powder in the cartridge.

    I'm also checking for setback when I do this, I want to see the load cycle 3 or so times with zero setback and little to no deformation of the nose profile.

    This can be enlightening especially with used brass, or loading a lighter (shorter) bullet into a case that's previously fired a heavier bullet...something you really want to avoid.

    To simply things I've taken to loading mild, 170-180 grain .401" cast bullets in all my 10mm used brass.
  7. nickE10mm

    nickE10mm F.S.F.O.S.

    Apr 13, 2004
    Wichita, KS
    I have always used 1.26 OAL unless I have feeding issues with a particular setup. 1.25-1.26 is the accepted range, with some manufacturers and handloaders going to 1.24-1.25" for reliability or other reasons.
  8. _The_Shadow

    _The_Shadow Ret. Fireman

    Jul 23, 2007
    Southeast, LoUiSiAna
    Most of the original 10mm bullet designs and cartridges were designed around the 1.2500" spec. therefore the magazines and chamber free bore were designed around that spec also. The magazine may allow for longer COAL such as the 1911 which were designed around the 45ACP @ 1.2700" +, so some have experimented with the longer seated bullets to take advantage of more powder space.

    Some chambers are cut such that the feed angles of long seat rounds can cause issues, this can be because of bullet nose shape and length outside the casing in relation to the chamber. Most freebore of the 10mm guns are good to 1.270, but only measuring can tell if the bullet will come in contact with the end of the freebore and jam into the rifling.

    My S&W 10xx series and Glock 29 will work with 1.260", but I seat them to 1.250" - 1.255". Like others I have see where mostly HP's and WNFP styles have been seated at 1.242" to help feeding issues!

    This is one reason I handload my own stuff...
  9. Taterhead

    Taterhead Counting Beans

    Dec 13, 2008
    Boise, Idaho
    I load lightweight bullets to 1.25 rather than 1.26" to give a bit more bearing surface to increase bullet pull. I load heavier bullets longer. All seem to feed fine in my G20.

    I have noticed that factory manufacturers often seat between 1.24 to 1.25. My guess is to ensure feeding reliability in the widest range of platforms.
  10. nickE10mm

    nickE10mm F.S.F.O.S.

    Apr 13, 2004
    Wichita, KS
    Strangely enough, I have problems when I load certain bullet profile in my Fusion 10mm 1911 to 1.26". The rounds will stick in the mag (nose & tail jam). If I load to 1.25 they work great. I can load nearly ANY length in my G20, however.

    Handloading is "where its at". :cool:
    Last edited: Apr 17, 2012