Results 1 to 7 of 7
  1. #1
    Marksman
    Join Date
    Jun 2013
    Posts
    357

    Flat based FMJ VS concave/recessed 9mm bullets for reloading

    Was wondering if there are any difference when using a flat based FMJ bullet vs a concave/recessed bottom bullet to reload with? Will be reloading on a Hornady LnL progressive press.

    Thanks,
    Art.

  2. #2
    Sharpshooter
    Join Date
    May 2014
    Location
    Bloomington
    Posts
    713
    .

  3. #3
    Grandmaster gregkl's Avatar
    Join Date
    Apr 2012
    Location
    Bloomington
    Posts
    5,504
    It would change the pressure but if you are using a loading manual with the proper bullet, the manual should adjust the charge accordingly.

    Bullet weight, type and seating depth all contribute to the final outcome.
    Easy choices, hard life.
    Hard choices, easy life.

  4. #4
    Marksman 55fairlane's Avatar
    Join Date
    Jan 2016
    Location
    Ft. Wayne
    Posts
    612
    Supposedly, both are designed to shoot the same, but in some cases one will shoot better,this is due to the flat base having more bearing surface, I know in rifles for instance, my 22-250 likes a flare case over a boat tail.....you will have to load some of both and see if one gives you better groups

  5. #5
    Grandmaster
    Join Date
    May 2009
    Posts
    11,053
    Besides aiding in seating, I've never understood the whole boat tail concept.
    It would appear a flat base, with a larger bearing surface, would better catch the expanding gasses.
    NRA Instructor/Dormant U.S.Marine/ NRA Benefactor-Life

  6. #6
    Grandmaster Bigtanker's Avatar
    Join Date
    Aug 2012
    Location
    Mishawaka
    Posts
    11,729
    Quote Originally Posted by Mgderf View Post
    Besides aiding in seating, I've never understood the whole boat tail concept.
    It would appear a flat base, with a larger bearing surface, would better catch the expanding gasses.
    The boat tail is for aerodynamics. It closes the air behind the bullet for a cleaner flight. That technology is used in all over the place. Have you seen these on the back of semi's? Boat tails. It really helps close the air in neatly behind the trailer, thus making it more aerodynamic, thus giving the truck better fuel economy.



    Quote Originally Posted by Kirk Freeman View Post
    The N in INGO stands for knowledge.
    Quote Originally Posted by pudly View Post
    FYI- You can make that assumption, but not everyone intends to dicker.
    Quote Originally Posted by rhino View Post
    ***Hey, you be friends with Kirk Freeman and see how it affects you.***
    INGOer # 22951

  7. #7
    Plinker
    Join Date
    Nov 2015
    Location
    Monroe County
    Posts
    74
    My experience loading 9mm: flat based JHP (Precision Delta) are slightly more accurate than concave base FMJ (Everglades). But, not significant enough for my purposes to care. I believe the flat bases are a more consistent Bullet design and even distribution of pressure. Concave bases have more bearing surface but are susceptible to the lead melting/ vaporizing.


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •