Superior Powder Measure Design?

Discussion in 'The Ammo & Reloading Forum' started by Brian Albin, Aug 16, 2012.

  1. Brian Albin

    Brian Albin New Member

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    After reading that some powder measures throw charges more accurately than others, I am thinking of trying to design and build one. Could some of you who have tried several different models tell me what features contribute to accuracy?
  2. aa1911

    aa1911 Active Member

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    Belding and Mall (spelling?) bench mount. Design is such that the weight of the powder in the tube does not push on the loading chamber so it throws very consistent charges into the drop tube. This is my favorite and most accurate measure! and the oldest....

    [​IMG]

    closer up, sorry it's sideways...
    [​IMG]

    I have powder baffles for my MEC shotgun reloaders, those are supposed to help also with metering charges. Basically, any device that removes the weight of the powder in the main holding chamber to isolate the charge chamber will contribute to better accuracy.

    Why are you building one? Just curious, sounds like a cool project. Are you a machinist by chance?
  3. Brian Albin

    Brian Albin New Member

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    Hello, aa1911. Thank you for the reply.
    I am not a professional machinist, but would like to be a hobby machinist. I learned some of the use of the lathe and vertical mill in High School in the 1970s but have done none of it since.
    My main reason for wanting to make one is because I read so many complaints regarding the models currently on the market; it strikes me as a challenge to come up with something better.
  4. LDBennett

    LDBennett Well-Known Member

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    Brian Albin:

    There are a couple of ways to measure powder that have been used, such as a bar that fills with powder by gravity feed and is pulled out to deliver it to the case and a rotary cylinder with a small cavity that fills by gravity and is rotated around to dump the powder into the case. Some of the rotary ones have a rounded bottom in the cup in the rotor or a series of rotors for various gross volumes with an adjustment to modify the volume of the cup finely. The bar type change the volume with an adjustment but again may have gross volume difference between selectable bars.

    The gravity feed is one of the features that has to be held constant so many use a baffle in the bottom of the powder storage tube (reservoir) to keep the weight of the powder (the head in mechanical speak) constant. The baffle supports all the weight of the powder while the powder below it is always constant until the baffle is exposed when you then must fill the reservoir again.

    The hard part is metering the log shaped powder kernels. They want to be cut by the rotor or the bar as it moves to dump the powder. Some manufactures claim that no kernel are cut by this action. I have no idea how they do that...it may just be sales talk or maybe they chamfer the edge of the rotor or bar (??).

    Another area that can give better accuracy is the fit of the bar or the rotor to the powder measure body. Get it too loose and the spherical powders can get in the loose clearance and either make the effort excess or stick the rotor or bar. The fit has to be tight but free to move.

    Many of the measures on the market have plastic reservoirs that gather static electricity and keep the powder from flowing smoothly. Eventually the tube gets covered with graphite from the powder, making the surface conductive and killing the static buildup. At least a couple of reservoir of powder have to go through the measure to get any kind of a coating on the plastic tube. Some measures have a brass tube which kills the static build up immediately but does not allow you to see where the powder level is during reloading.

    These are only some of the challenges with making your own power measure. Then there is the challenge of machining it.

    I too took some machine shop classes in my younger days. When I retired I bought a Smithy Chinese lathe/mill. I found I forgotten more about machine than I remembered. The depth of the cuts to use, the precision of the finished cuts, and the surface finish of the cuts, are tough to master. The mill part of the machine is tougher yet as it really is not massive enough to do precision milling. The point? To do your task you are going to need a real separate mill and a good lathe not made in China and cheap. You will probably need a precision hone as well. The Smithy worked fine for my motorcycle parts but anything that needs precision is not easily made on the Smithy without great concentration and effort (lots of tiny cuts and extremely well held down parts to be milled). If I had it to do over again I'd find a used machinery dealer and buy a good used professional lathe and separate mill that have been verified to be accurate enough and not totally worn out.

    Good luck with your project but personally I would NOT take it on myself and I've been practicing for the last 15 years on my Smithy.

    LDBennett
    Last edited: Aug 16, 2012
  5. Clipper

    Clipper Active Member

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    I am comfortable with my RCBS bench mounted flask. I do weigh each charge for the first ten, then weigh every 10th charge until I load the first 50, then go for production, checking only every 25 or so. So far, I have not had a single problem throwing over/under in my .45's. I do check all the cases before fitting the projectile with a small flashlight. I also don't ever load maximum loads for any of my handguns (well, maybe just a few for the Blackhawk .357)
  6. Brian Albin

    Brian Albin New Member

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    My Powder Measure Design

    Inaccuracy seems to come partly from using gravity feed. I may use a horizontal hopper pouring into a visible metering chamber by means of a screw augur or a conveyor belt driven with a handle until the metering box appears well filled. A scraper then slips off the excess into a holding tank where it accumulates until the hopper is empty. It can then be poured back into the hopper.

    The next complaint is rod shaped powder kernels being cut. My top scraper pushes away the excess when I think the granules are not under load. So the powder has more inclination to slide away than to resist motion and thereby be cut.

    “Another area that can give better accuracy is the fit of the bar or the rotor to the powder measure body. Get it too loose and the spherical powders can get in the loose clearance and either make the effort excessive or stick the rotor or bar. The fit has to be tight but free to move.”

    I think mine will dump through a hinged door or dbl flap doors on the bottom of the chamber. A funnel under the doors allows room for the doors to swing, and then guides the powder into the drop tube. The powder slipped off the metering box is by this funnel excluded from the drop tube.

    The handle motion would be a 90 Degree “L” shape. First pulling the handle toward me to load powder from the hopper into the metering box. Then tipping the handle outward to first scape the excess, then dump the box contents into the cartridge. This second motion may be more pleasant to use if fitted with a return spring. How to then get the handle back to position 1 for the next charge I have not yet determined.

    “Many of the measures on the market have plastic reservoirs that gather static electricity and keep the powder from flowing smoothly. Eventually the tube gets covered with graphite from the powder, making the surface conductive and killing the static buildup. At least a couple of reservoirs of powder have to go through the measure to get any kind of a coating on the plastic tube. Some measures have a brass tube which kills the static build up immediately but does not allow you to see where the powder level is during reloading.”

    My positive drive defeats this failure to feed due to static cling. But I do not like plastics and will use a brass hopper or glass.
  7. aa1911

    aa1911 Active Member

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    I know some people don't like stick powders (IMR mainly) but I love them; they make a delightful crunch in my powder measure! Especially when I'm loading 70gn charges or even 42gn for .308, a couple of cut extruded powder granules don't seem to affect anything.

    Best way to do 'benchrest' or max accuracy loads is to just undercharge and use a trickler on a digital scale to get consistency by weight vs. volume.

    But I'm curious to see what you come up with and more importantly if you are able to create something with better consistency than what's available.
  8. LDBennett

    LDBennett Well-Known Member

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    I know there are a lot of reloaders out there who measure loads to the last tenth of a grain.

    Testing by experts (certainly not me but noted gun writers with connection to powder makers) show that it is not necessary as all the other variables swamp out any inconsistency in powder volumes within several tenths of a grain. Perfection is nice but it can be wasted.

    I throw all my loads from a powder measure directly except for my 50BMG rifle stuff which I have no powder measure for, that is big enough. I scoop it onto the scale with a spoon and get it close, then dribble in grains off the spoon. I get it within a couple of tenths of a grain either way but the charge is 220 grains of very slow powder. I only get it that close because I can, not because it is necessary.

    The bottom line: precision weighing of every load is not necessary and is laborious. Errors of charge from a powder measure within a couple of tenths is not discernible in real life shooting, according to the experts (not just me). Almost any power measure made by almost anyone will meet these requirements if you operate it exactly the same every time.

    LDBennett
  9. Brian Albin

    Brian Albin New Member

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    Me too. This is mostly a challenge to me; a puzzle to see if something better can be done.

    This I did not know. If existing measures are good enough, then my experiment becomes merely a bit of play. But it still appeals to me as a game, to see what I can come up with; so I think I will press on.
  10. blackhawk44

    blackhawk44 New Member

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    Check out the designs of both the Harrell and the Quick Measure. They are among the most accurate especially with stick powders.
  11. Brian Albin

    Brian Albin New Member

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    That Harrell measure is sure fancy looking with it's polished body. RealGuns http://www.realguns.com/Commentary/comar63.htm did not find it to be more accurate than an RCBS Uniflow, except in the "Moderate Charges - Extruded Powder" & "Very Heavy Charges - Extruded Powder" tests. While "Heavy Charges - Extruded Powder" The RCBS was superior. With spherical powder they mostly tied.
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