.357 Dia 9mm Overpressure

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  • Kelson1066

    Ultimate Member
    Jul 31, 2012
    1,028
    Frederick County
    Question for those with a lot more reloading experience than me.

    I recently acquired a box of XTreme Bullets 9mm 147gr RN with a diameter of .357 during one of their sales. Using the Alliant Manual I put 4.0 grains of Unique in the case. I use the same load for my 147gr HP and 147gr RN both have a diameter of .355.

    Yesterday when I was shooting at TMGN I observed signs of over pressure in the cases that were loaded with the .357 bullets. I could see the firing pin strike and a small rectangular dent around it (I'm using a Gen 3 G17). I know I will have to back off the load for safety reasons but my question to the group is:

    With all things being equal why do I have over pressure with the .357 and not the others?

    Google has not yielded results that satisfy my curiosity. Most answers direct me towards information about 9mm +P.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,281
    HoCo
    You put a copper plated bullet that is .002 over sized into a 9mm?
    I think you have the answer there.

    Ruger makes a convertable pistol that is 357 and accepts 9mm. But the bore is designed for the bigger 357 bullet so 9mm will shoot but will shoot like an undersized bullet.
    Going the other way around is a whole other story I think.
     

    Kelson1066

    Ultimate Member
    Jul 31, 2012
    1,028
    Frederick County
    You put a copper plated bullet that is .002 over sized into a 9mm?
    I think you have the answer there.

    Ruger makes a convertable pistol that is 357 and accepts 9mm. But the bore is designed for the bigger 357 bullet so 9mm will shoot but will shoot like an undersized bullet.
    Going the other way around is a whole other story I think.

    Thanks,

    I guess it's a case of let the buyer beware.

    Though I wonder who would use .357 I guess someone shooting competition.
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    Picture of the primer(s)?

    Both of my Gen 3 .357 SIGS (31 & 32) will leave a rectangular 'box' around the pin strike, with factory Speer ammo. If the primer still has a radius to the edge, you may be seeing a little bit of flow back into the opening of the slide for the striker.

    I'll see if I can snag a pic of my brass, so you can see if it's identical to yours.

    20180213_171913.jpg

    **FWIW, I've had plenty of plated bullets for .45ACP (ideally .451") that measured in from .452" to as much as .453.5", they weren't an issue as long as I didn't try to push them at a max charge. A quick look around, 4gr of Unique is still safely under a max charge.
     

    Kelson1066

    Ultimate Member
    Jul 31, 2012
    1,028
    Frederick County
    My primer has the same appearance though the dent is a little deeper. I assumed there was an issue because the .355 loads had a simple round strike mark.
     

    Seabee

    Old Timer
    Oct 9, 2011
    517
    Left marylandistan to NC
    As already said, the extra .002" is simply the plating. This is normal as they take a normal .355" bullet and plate it. Always back off your load and start over when changing bullets. Also, if possible, find data for the bullet you are using. I also have xtreme bullets that are slightly oversize for my 45 ACP. They shoot great but I had to back off more than usual because of the plating.
    If I may, what is your load?
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    As already said, the extra .002" is simply the plating. This is normal as they take a normal .355" bullet and plate it. Always back off your load and start over when changing bullets. Also, if possible, find data for the bullet you are using. I also have xtreme bullets that are slightly oversize for my 45 ACP. They shoot great but I had to back off more than usual because of the plating.
    If I may, what is your load?

    Maybe so with other bullet makers, but not necessarily true with Xtreme Bullets. They offer several different diameters in the same caliber and same weight so it would be wise to read what you are ordering.

    https://www.xtremebullets.com/9mm-s/9666.htm
     

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    Kelson1066

    Ultimate Member
    Jul 31, 2012
    1,028
    Frederick County
    As already said, the extra .002" is simply the plating. This is normal as they take a normal .355" bullet and plate it. Always back off your load and start over when changing bullets. Also, if possible, find data for the bullet you are using. I also have xtreme bullets that are slightly oversize for my 45 ACP. They shoot great but I had to back off more than usual because of the plating.
    If I may, what is your load?



    147gr bullet
    4.0 gr Unique
    CCI 500 primer
    Once fired brass
    COAL is factory standard


    Sent from my iPhone using Tapatalk
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    I normally run cast bullets that are 1 - 2 thousandths over the nominal bore size.

    NOT with jacketed.
     

    ken792

    Ultimate Member
    Sep 2, 2011
    4,480
    Fairfax, VA
    I shoot my Xtreme 147gr slugs with 3.4gr Titegroup or 4.6gr Longshot. Both are very good loads and I've had no issues. Mine also measure 0.356", as they advertise.
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    I've been reading that the wider 0.356-0.357 bullets are meant for older European barrels that tend to have wider bores. Stick with the 0.354-0.355 bullets.
    This. Had tons of issues trying to load coated .356 into my 9x19 bores, and eventually gave up on the practice. .355 is where it's at.
     

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