RepackboxRotoMetals2WidenersLee Precision
Titan ReloadingMidSouth Shooters SupplyInline Fabrication

Results 1 to 9 of 9

Thread: Seating Deeper Reduces Pressure? April 2019 Handloader

  1. #1
    Boolit Grand Master

    jonp's Avatar
    Join Date
    Feb 2013
    Planet Reality

    Seating Deeper Reduces Pressure? April 2019 Handloader

    Brian Pierce writes this paragraph on page 15 in response to a letter about a 6.5-300 Weatherby:

    Usually, but not always, seating a bullet deeper in large capacity bottleneck rifle cartridges will reduce pressures slightly so my deep-seated loads should not be of concern in this application

    This is contrary to everything I thought about pressure vs volume. Seat the bullet deeper and you decrease the internal volume the powder has to burn in which increases pressure. Seat the bullet deep enough and you begin compressing the charge which can increase the pressure spikes.

    Is he making a reference to slow burning powders only? Decreasing the volume would cause an incomplete burn?
    NRA Benefactor Life

    Government is the great fiction, through which everybody endeavors to live at the expense of everybody else.
    The further society drifts from the truth, the more it will hate those that speak it
    George Orwell

    Crux Sacra Sit Mihi Lux
    Tu Ne Cede Malis, Sed Contra Audentior Ito.

  2. #2
    Boolit Grand Master

    dragon813gt's Avatar
    Join Date
    Feb 2012
    Somewhere in SE PA
    Paging Larry Gibson. Iíd like to see some actual pressure results before I believe this. Not saying it canít be true. Just that w/ no pressure data itís conjecture.

  3. #3
    Boolit Master RED BEAR's Avatar
    Join Date
    Oct 2011
    1 mile from chickahominy river ( swamp)
    This is a new one on me????

  4. #4
    Boolit Grand Master

    M-Tecs's Avatar
    Join Date
    Apr 2008
    In some cases it is true. Large volume cases are not effected as much by deeper seating. Deeper seating does increase pressure, however, more distance to the bullet engaging the lands reduces pressure. That is why Weatherby used such long throat. Hard/soft seating bullets into the lands will normally be the highest pressures in a cartridge like the 6.5-300 Weatherby.

    The best example I have is a 308 Palma loaded I used. I soft seated the bullets on these and they shot outstanding until the temps got above 90 degrees than they started having pressure issues. This load also shot second best with .035" jump. Same load seated .035" didn't have any pressure issues above 90 degrees.

    On the other end of the spectrum I have seen 9mm cases blown from bullets that deep seated due to recoil.
    Last edited by M-Tecs; 03-14-2019 at 08:13 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  5. #5
    Boolit Master
    Join Date
    Jul 2009
    Think about the percent reduction in capacity. .100 deeper in a 9mm could be a 25% reduction in capacity. The same in that 6.5mm neck is maybe 1%. Neligable vs the decrease gained by adding to the effective freebore.
    ďYou donít practice until you get it right. You practice until you canít get it wrong.Ē Jason Elam, All-Pro kicker, Denver Broncos

  6. #6
    Boolit Master
    lefty o's Avatar
    Join Date
    Dec 2012
    seating deeper in an actual weatherby chamber probably wont do squat as weatherby's have long throats to start with.

  7. #7
    Boolit Master OnHoPr's Avatar
    Join Date
    Oct 2011
    With large volume cases and slow powder there really wouldn't be a case/powder/bullet issue as many of them are/can be compressed loads. It would even help with to far of a reduction in powder charge. Thus seating the bullet deeper you get a longer jump before the bullet starts into the lands actually reducing pressure.

    With small volume cases and fast powder like the 9mm, 45 acp, 40 s&w, etc it seems or I have read that it can increase pressure, even dramatically. Those cartridges headspace on the mouth and I am not sure of the different manufacturers lead from model to model. But, with general bullet types and weights with barrels ranging from 2 to 6" it would be good to get more knowledgeable input from those scenarios to see if the lead plays a role in the increase of pressure.
    May you hands be warmed on a frosty day.

  8. #8
    Moderator Emeritus

    Join Date
    Mar 2005
    SW Montana
    Seating a bullet 0.005" off of the lands results in less pressure than if the bullet is jammed into the lands.
    [The Montana Gianni] Front sight and squeeze

  9. #9
    Boolit Master
    JSnover's Avatar
    Join Date
    Dec 2007
    Bensalem, PA
    Quote Originally Posted by MT Gianni View Post
    Seating a bullet 0.005" off of the lands results in less pressure than if the bullet is jammed into the lands.
    ^That! It's more accurate to say seating deeper affects the pressure curve. Seating longer will reduce pressure unless you seat into the lands. In that case, the bullet has to overcome it's own inertia + neck tension + the leade. Lead boolits are more forgiving but you get a spike with either
    Warning: I know Judo. If you force me to prove it I'll shoot you.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check