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  1. #1

    Default More Powder, Less Velocity...

    While testing loads yesterday, I had the experience of a .5grain increase in powder producing lower velocities. What does that usually mean? Interestingly, it was also the load that gave me the biggest spread of velocities and the tightest group. I would appreciate any wisdom on this matter.

    Load: .30-06, 180 grain Hornady Interlock Round Nose, IMR 4350, Rem case, WLR, 3.21"

  2. #2

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    chrony giving wonky numbers would be my first guess.
    Cows, not condos

  3. #3
    Join Date
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    There could be a handful of things going on. My 7mmMag did this using cheap Serbian cases due to inconsistent case capacity. The whole lot of brass ended up being junk. I don't suspect that is the issue. I'd wager it's a chronograph issue...move the machine back another 5 feet and replace the batteries then give it a try.

    I'd have to ask is this a 1 shot trend or is it consistent across 3, 5, 10 rounds? Are you weighing every powder charge (what scale)? Are you crimping these bullets? What temp are your rounds being stored at? IMR4350 is a fairly stable powder but major temp changes can affect velocity.

    I don't know much about how powder burns but in some cases adding more powder doesn't improve velocity as it isn't all burnt which could affect the entire load. Somebody that has more experience may be able to add.

  4. Default

    No matter what you think or anyone else thinks, a rifle will do what it's gonna do. We simply try to bring out the best in them. I think we were way ahead of the game before chronographs! Now and then I shake my head at mine!

    Think about what you need to do to kill an animal, large animal, at say 250yds. Practice shooting at 250yds regardless the velocity! What happen's between 0 and 250yds makes no difference!

  5. #5

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    How big of velocity difference did you see?

    Was it colder out when the lower velocities were saw in comparison?


    What chrono are you using? lighting conditions can really create havoc with the hood type chromos.

  6. #6

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    Was the half grain more seated at the same coal as the other loads or was it longer with more of the bullet closer to the lans?

  7. #7

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    Well, embarrasingly, after doing some simple math, I was wrong. The average was a bit higher. Here are the specifics:

    56 grains: 2534, 2525, 2549 (avg. 2536)
    56.5 grains: 2515, 2530, 2588 (avg. 2544)

    All same length, same temp, not crimped. It was a cloudy day, but my Chrono was set up on top of snow. It's a Competition Electronics Pro Chrono Pal. It still seems weird to me that those two were so much slower. I weigh every charge. I do use a smaller, digital scale, but I calibrate before every session and don't load a lot at a time. If it was drifting, I'd think the powder pan would start showing up as under, or over zero. I usually weigh out to the hundreths.

    The other funny thing about this load is that according to Hornady's manual, 56.5 is 2 grains above max and should be giving me 300 mag-like velocities... No pressure signs though and the velocities are pretty darn modest.

  8. #8

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    Quote Originally Posted by Dougfirtree View Post
    56 grains: 2534, 2525, 2549 (avg. 2536)
    56.5 grains: 2515, 2530, 2588 (avg. 2544)

    The other funny thing about this load is that according to Hornady's manual, 56.5 is 2 grains above max and should be giving me 300 mag-like velocities... No pressure signs though and the velocities are pretty darn modest.
    You usually won’t see a large swing in velocity for 0.5 grains of powder inside of safe pressures. That 0.5 grain increase in your load is a little less than 1% difference. Until you get close to or exceed safe pressures for a load you won’t see a dramatic increase in velocity. That’s when the bullet just can’t get out of the way of expanding gasses behind it.

    The 73 fps spread in velocity you measured could be from a difference in quite a few factors; primer efficiency, load density, brass volume variance, neck tension, even letting the round heat sink in the barrel. To see low to single digit extreme spreads in velocity brass prep becomes just as important as powder selection and accurate charge weight.

    You may be seeing lower than expected velocities for a few reasons.
    If your rifle has long free bore it tends to act like a larger case capacity and lowers pressure (lower velocity) since the bullet has a running start before contacting the lands. Also, while IMR 4350 is not as temperature sensitive as a double base powder, you will still see velocity swings from changes in ambient temperature.

  9. #9

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    You do have to remember that sometimes a load will not show pressure sighns, and then if used during a very much warmer temps, it may be way more of a problem.
    But some Chambers will be different enough to allow a load to be safe at powder charges past the book listed max loading.

  10. #10

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    e
    Quote Originally Posted by Rancho Loco View Post
    chrony giving wonky numbers would be my first guess.
    ....have experienced diminished velocity reads with increased boom gram'ge....but have also scratched my head at inexplicable/uncorrectable error codes. I tend to agree with loco.

    I have researched the hell out of chrono's and can't tell a tinkerer's damn difference between any of em spec & review-wise.

  11. #11
    Join Date
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    This is a warning sign, when the velocities seem to stop increasing in line with the powder increase it's due to excessive case expansion. Measure the case after you fire it and compare the dimensions to a case that was loaded with the book max (around 54.3 gr), I'll bet that you'll find that the case head on the hotter loads will be a couple thousandths bigger. Also check for a ridge inside the case just above the head (look inside with a flashlight). If you find that either of these occurs then you are exceeding the limits of expansion for the case and you will get premature case failures. It's unfortunate that so many people seem to think that reloading manuals are to be ignored but generally, when you exceed their recommendations then it's a good bet that you're exceeding some load parameter. I doubt that you are exceeding safe operating pressures for the rifle action but you are most likely exceeding the limits of what the case can handle.

  12. #12

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    Quote Originally Posted by rammac View Post
    This is a warning sign, when the velocities seem to stop increasing in line with the powder increase it's due to excessive case expansion. Measure the case after you fire it and compare the dimensions to a case that was loaded with the book max (around 54.3 gr), I'll bet that you'll find that the case head on the hotter loads will be a couple thousandths bigger. Also check for a ridge inside the case just above the head (look inside with a flashlight). If you find that either of these occurs then you are exceeding the limits of expansion for the case and you will get premature case failures. It's unfortunate that so many people seem to think that reloading manuals are to be ignored but generally, when you exceed their recommendations then it's a good bet that you're exceeding some load parameter. I doubt that you are exceeding safe operating pressures for the rifle action but you are most likely exceeding the limits of what the case can handle.
    Interesting. Where do you think the extra space is, allowing the case to expand so much? Are you suggesting that there's a headspace issue? It's wierd because every load in my test gave me velocities way below what the book called for. It wasn't just the ones over max.

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