velocity to low

Discussion in 'Reloading' started by adamg1986, Jun 23, 2013.

  1. adamg1986

    adamg1986 Member

    Messages:
    6
    Joined:
    Jun 23, 2013
    hey guys, I just posted over in hunting about this but thought it might get more attention here. Long story short, Im loading for a 7mm rem mag. I have no chronograph so I estimated my mv to be around 2950. Shot at 550 yards dialed in 7.5 minutes and was hitting 9 to 10 inches low. Dialed up to 9 minutes and hit. Im loading 66gr H4831sc over a 168gr berger vld. My scope height is 1.75 and at 100 yards my group (.181) was around 2.18 inches high. I am kinda disappointed bc I was hoping to be right at 3000 fps. but it seems im not even at 2800 fps. Anyone have any ideas as to whats going on? Thanks
     
  2. Nimrod

    Nimrod Well-Known Member

    Messages:
    444
    Joined:
    Aug 20, 2006
    Could be a lot of things, book velocity is often not even close. I don't know how you got your estimate but there are a lot of variables that come into play. Even 2 identical rifles will have different velocities, sometimes considerably different. For any serious shooting or load development I consider a chronograph a requirement.

    Bob
     

  3. adamg1986

    adamg1986 Member

    Messages:
    6
    Joined:
    Jun 23, 2013
    Thanks for the reply Nimrod. My manual only list 65 gr of 4831 and 170gr bullet at well over 2800 and it doesn't list barrel length so I was hoping my velocity would be higher but I guess not. I know I need a chronograph but its just one of those things I haven't got around to buying. Ive been looking at reviews on different ones and am scared to buy anything really. Just about all of them have a bunch of bad reviews so I don't know which one to go with. Do you have a recommendation? Also would anyone recommend switching powders. I like the temp stability of the 4831 but it was just leftover from another gun I loaded for and im almost out of it. So now would be a good time to switch if I need to. I was thinking about Retumbo possibly. I know velocity isn't everything but you would thing with a magnum I could at least hit 2900.
     
  4. rinodods

    rinodods Well-Known Member

    Messages:
    249
    Joined:
    Aug 2, 2008
    A book will get you close but you can't count on the velocity across different rifles. A crony would be nice but if you know what the drop is you can use that to figure out what your velocity is. What book were you going by? If I get a minute I will see what bergers book has listed.
     
  5. Nimrod

    Nimrod Well-Known Member

    Messages:
    444
    Joined:
    Aug 20, 2006
    The Oehler 35P is the best chronograph IMHO. I had a Pact that worked great for several years and then it quit. Now they refuse to make good on the lifetime warranty. They have had it for nearly a year, their solution was to offer a 30% discount on a new unit, so the warranty is worthless . I'm saving for an Oehler now.

    There are several powders that will work in the 7MM Magnum among the ones I have used are H4831, IMR 4350, IMR 7828, H1000 and Retumbo.

    Good luck in your quest!
     
  6. westcliffe01

    westcliffe01 Well-Known Member

    Messages:
    1,191
    Joined:
    Jul 6, 2011
    Apologies I listed a 300 Rem load....

    Since you are using Hodgdon powder, why do not use their data from their online web site ? Cartridge Loads - Hodgdon Reloading Data Center - data.hodgdon.com Based on their website, a minimum powder charge is 60gr with a max at 64. At 60gr 24" barrel the velocity is listed at 2731fps and at 64gr it is at 2871fps.

    How did you do your load development ? Usually one works up until you start seeing pressure signs, then backs down. Also check the listed cartridge OAL, usually if it is listed then it is a Sami value, you may be able to load longer which will reduce pressure if your throat allows it.


    162 GR. HDY SPBT Hodgdon H4831 .284" 3.290" 60.0 2731 43,300 CUP 64.0 2871 49,800 CUP
     
  7. westcliffe01

    westcliffe01 Well-Known Member

    Messages:
    1,191
    Joined:
    Jul 6, 2011
    It looks like Retumbo may be good for 100fps more. If you can load longer, might be good for even more.
     
  8. adamg1986

    adamg1986 Member

    Messages:
    6
    Joined:
    Jun 23, 2013
    I started at 62 gr and worked my way to 66 gr in .5 gr increments. Ive found 3 nodes between and 66 gr seems to be the most accurate. Primers are normal, bolt is not stiff so I think its a pretty safe load. My manual lists 170 gr bullet with 65 gr max @ 57000 psi so I think its a conservative load. Hodgdon lists the same but velocity is 2806. I guess my velocity isn't that far off. I figure im around 2770 or so. Im gonna step it out a bit further to see if that is close. Does anyone know how temp sensitive retumbo is. Ive heard that h4831 is pretty stable. Whatever powder I use I want to be able to find a load now and be able to use it this fall and winter without having to work up another mid season.
     
  9. Joe King

    Joe King Well-Known Member

    Messages:
    1,390
    Joined:
    Apr 29, 2012
    You can't really use bullet weight as an indicator, of where you might be at as far as appropriate powder charge is concerned. Take a 160 Nosler Partition, and a 180 Berger Hyrbrid. The listed max charge for the Hybrid with Retumbo is 1.3gr higher than for the Partition in the Hodgdon manual. Why? it's due to differences in bullet construction and material.

    Also I would be very care full about listed loads. If I tried to use the Max load from the Hodgdon manual my case would last about 2 rnds, where as I'm running 0.2gr above Bergers listed max and still 0.8gr below Hodgdons max.
     
  10. westcliffe01

    westcliffe01 Well-Known Member

    Messages:
    1,191
    Joined:
    Jul 6, 2011
    If one reads the berger reloading manual, the key to obtaining the best velocity without excessive pressure is seating the bullet out as far as practical and throating the barrel to suit. If you load to sami length and have a barrel that is chambered the same way, then of course performance will be "typical" at best.

    The downside to this is that one essentially renders the gun useless for shooting bullets that are shorter/lighter since the barrel will behave the same as one that is shot out.

    I have noticed that my Shilen match 243AI barrel shoots significantly faster than my previous Savage barrel, even though the twist rate went from 1:9.25 to 1:8 (which you would think might add drag). The lapping might well be worth some additional velocity as well as the consistency of the diameter.

    I am typically trying to shoot bullets that weight/length wise are at the limit of each caliber so I am not concerned about loss of utility with lighter/faster bullets.