H4350 Burn Rate Change?

Discussion in 'Reloading' started by aggie99, Sep 17, 2013.

  1. aggie99

    aggie99 Well-Known Member

    Messages:
    169
    Joined:
    Sep 16, 2008
    I have been loading 165gr NP's ove 58.5 grains of H4350 for a few years and getting velocities in the area of 2950 fps. I started on a new 8lb jug and started low to rework the load. The best accuracy was at 57.5 grains. I built a few more to get velocities and was suprised to see an average of 3090 fps. OAL, gun, primer, bullets, and chronograph are the same. Drops seem to match the velocity at 620 yards. Any ideas why the velocities suddenly jumped?

    The brass does not show signs of excess pressure. Bolt lift is normal.
     
  2. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,264
    Joined:
    Aug 10, 2003
    All powders vary by lot, and it's good that you were cautious.
    But it's hard to say anything about anything with so many changes going on at once.
     

  3. Catfur

    Catfur Well-Known Member

    Messages:
    160
    Joined:
    Jan 31, 2012
    As best I've been able to determine H4350 is mythical, and therefore any burn rate changes are strictly theoretical.

    Seriously though, lot to lot variation? Remember H414 and W760 are actually the exact same thing, though I've seen burn rate charts put them several powders apart.
     
  4. aggie99

    aggie99 Well-Known Member

    Messages:
    169
    Joined:
    Sep 16, 2008

    The only change was 1 grain less powder. I may have to find someone who can loan me a different chronograph to check my results.
     
  5. FAL Shot

    FAL Shot Well-Known Member

    Messages:
    289
    Joined:
    Oct 9, 2010
    Bright sunny day and cloudy day causes about a 100 FPS difference in my chronograph. Bright sunny day is consistent, where cloudy day is not. Sensor screens need a consistent lighting. I do ALL chronographing for load workups on a sunny day, and shield the sensor slots from any direct intrusion of sunlight, which also makes a difference.

    A load worked up on a sunny day and then rechecked on a cloudy day will show a velocity change.

    Low sun angles on bright sunny days are also to be avoided. The first couple of hours and last couple of hours are not for chronographing.

    A precharched pneumatic air rifle that is pumped up to the same pressure every time is consistent in velocity with match grade pellets. Unlike firearms, as long as air pressure is the same it is the same, as measured by an accurate gauge. Air can be added or bled off if there is a big temp change. Air pressure is air pressure is air pressure. When pumping up a PCP, the air chamber gets hot, and pressure will reduce in a few minutes. I take a couple of extra minutes and add air as pressure drops as the air chamber settles to ambient pressure.

    If you have a high quality PCP air rifle (Benjamin Marauder, BSA, Daystate, FX, Air Arms, etc.), then it is a very accurate checker of your chronograph.

    A string of a half dozen shots will vary by about 3 FPS in my BSA Lonestar .25 cal.

    Powder can vary significantly from lot to lot, but I have not found that to be the case with Hodgdon powders lately. Liability issues and modern manufacturing practices make canister powders quite consistent.

    Primers can change from lot to lot . I bought a lifetime supply of WLR primers during a short time period some time ago. That's one problem I don't have to contend with. Winchester primers of today are not the same as years ago, just like their brass.
     
    Last edited: Sep 18, 2013
  6. aggie99

    aggie99 Well-Known Member

    Messages:
    169
    Joined:
    Sep 16, 2008
    "Low sun angles on bright sunny days are also to be avoided"

    This may be a large part of the problem. It has been very hot and I was shooting early in the morning. I'll try a few later in the day when the sun's angle is a little less acute.
     
  7. bullfrog

    bullfrog Well-Known Member

    Messages:
    156
    Joined:
    Jul 27, 2010
    I have switched lots of H4350 with all other components identical with identical powder charge and blew primers. Had to pull the other bullets. I now back off and work up every time I change powder lots.
     
  8. Trental

    Trental Well-Known Member

    Messages:
    53
    Joined:
    May 12, 2011
    I've had the same experience. I now try to buy H4350 at least 16lbs at a time (2 8lb in the same lot).
     
  9. Engineering101

    Engineering101 Well-Known Member

    Messages:
    1,010
    Joined:
    Jan 29, 2013
    aggie99

    The velocity change you got while dropping 1 grain of powder is pretty normal. I just cracked the seal on a new 8 lb jug of H4831SC and had to add 2 grains to get back the lost velocity. I can’t think of a lot change I’ve made where there wasn’t a change in burn rate.
     
  10. ArchAngelCD

    ArchAngelCD Active Member

    Messages:
    42
    Joined:
    Sep 1, 2013
    When loading H4350 in the 30-06 with a 168gr bullet I have found:

    With a 22" barrel I get the highest velocities with a 57.0gr load and slight lower velocity from a 58.0gr load.

    From a 26" barrel the numbers are more what I would expect, I get the highest velocities from the 58.0gr load and slightly lower velocities from the 57.0gr load.

    Accuracy with all 4 loads is very good.
     
  11. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,264
    Joined:
    Aug 10, 2003
    ArchAngelCD
    A 30-06 packs a slug of powder behind the bullets, which isn't burned at all in a short barrel until released at the muzzle.
    This contributes to increased recoil, ES, reduced accuracy(compared to better designs), and as you found, adding more powder beyond burn reduces velocity -with a 30-06(not with most cartridges).
     
  12. aggie99

    aggie99 Well-Known Member

    Messages:
    169
    Joined:
    Sep 16, 2008
    Thanks too all for the food for thought. I am trying to find a second cronograph to check my results but since I am not seeing any pressure signs I think the load will be safe in my gun.
     
  13. Lefty7mmstw

    Lefty7mmstw Well-Known Member

    Messages:
    4,280
    Joined:
    May 13, 2012
    All I can say is WOW. I usually buy rl in 5# bottles, but I've been buying rl25 in #ers lately as the 5# jugs are higher per pound. I haven't noticed a bit of difference even with stuff that was packaged a couple of years apart. I don't buy enough H to know any better I guess, though it seems when I do buy it I'll but a 8#keg (to keep from getting ripped off locally) so I don't really have multiple lots to deal with.
     
  14. Ridgerunner665

    Ridgerunner665 Well-Known Member

    Messages:
    553
    Joined:
    Sep 15, 2008
    58 grains of H4350 seems pretty consistent in my 06...24" barrel...2,862 fps average for 7 shots. ES was 18, SD was 7...and this was with Winchester brass.

    2,873
    2,861
    2,861
    2,873
    2,855
    2,861
    2,855