Bridging
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Bridging is when propellant or shot sticks in the drop tube.
Bridging is caused by a lot of different things, but coarse powder (flake or stick), high humidity, rough drop tube, etc. contributes toward it. Shot size large for the drop tube diameter will cause it on the shot-drop side as well as the factors I mentioned on the propellant-drop side.
Bridging is caused by a lot of different things, but coarse powder (flake or stick), high humidity, rough drop tube, etc. contributes toward it. Shot size large for the drop tube diameter will cause it on the shot-drop side as well as the factors I mentioned on the propellant-drop side.
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"Bridging" is the act or process of forming a bridge. 
There's nothing complicated or unusual about it. It happens all the time in various substances.
Did you ever dig tunnels in the sand when you were a kid? Did you observe how the sand from above didn't fall down into the tunnel even though there was nothing (that you could see) supporting it? That was an example of "bridging". 8)
The bridging usually takes the form of an "arch" bridge in which the bottom center of the material falls away (or is removed) and the material above the arch remains.
What physical properties or conditions allow bridging to occur? The main two properties are "friction" and "lateral support" of the archway. Particle size, shape, and density of compaction of the material also play a role.
End of lesson. :wink:
There's nothing complicated or unusual about it. It happens all the time in various substances.Did you ever dig tunnels in the sand when you were a kid? Did you observe how the sand from above didn't fall down into the tunnel even though there was nothing (that you could see) supporting it? That was an example of "bridging". 8)
The bridging usually takes the form of an "arch" bridge in which the bottom center of the material falls away (or is removed) and the material above the arch remains.
What physical properties or conditions allow bridging to occur? The main two properties are "friction" and "lateral support" of the archway. Particle size, shape, and density of compaction of the material also play a role.
End of lesson. :wink:
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It can cause variable powder drops. One hull may have a light drop due to bridging, the next hull can then end up with an overload of powder drop into it. ie; the powder from the first hull that was retained in the drop tube (by the bridging), drops along with the full load. With some bulky powders this can be noticed when your shot is dropped, and fills the hull to the brim.parshal said:
Fine powders can sometimes allow the hull still to crimp. This is where a dangerous situation can develop with an overload.
Happens with shot too, although usually the jiggling of the press loosens the shot just about the time you pull the hull out from that station, and as mentioned... spills all over the place.. :roll:
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So what is the recomended way to prevent this? i have a strip of Anti Static paper towel (Dryer Sheet) in my powder bottle that is supposed to eliminate static electricity. Which is a combination of factors, Temp, humidity, friction, etc. Should we clean out the powder drop tube (MEC Grabber) periodicly? V/R TonyG
The only time I've ever had powder try to bridge off, a guy came in to see my loader setup and told me I had my dryer sheet on wrong, I should have it suspended in the bottle rather than wrapped around the outside. Within 100 rounds I had clumps of powder in the bottom of the bottle, whatever is on those sheets had gotten the powder oily or whatever it does.TonyG said:
I wasn't having any problems whatsoever, even with high winds and single digit humidity with the sheet around the outside, and probably the last time I listened to anyone regarding my loader :roll: :x
Are you really convinced that dryer sheet wrapped around the bottle actually absorbs static electricity?TexasTon said:
I put one on the top of the powder once for awhile and didn't seem to notice any difference.
Damned dry around my territory, too, especially this year, which is actually a drought.
In this chilly weather, I get zapped every time I touch metal getting out of the pickup.
Yep, without it I can run a finger up the side of the bottle and powder will just fly inside, with it there is no action inside, and that is with the loader grounded, still takes all the effort to stop it.
You think you are dry, we've had negative dewpoints, I didn't know that was possible but I guess it is. We just got about 10 inches of wet snow (.52 worth) and our last measurable precip was also snow, first of April.
Gotta try that sheet around the bottle trick.
I've never really had a noticeable problem with static electricity and powder, but I notice the International has a tendency to cling to the insides of a AA-HS hull, whereas I've not noticed that with other powders.
Maybe I just wasn't looking.
My pond's the lowest I've ever seen it, but I know our drought is nothing to compared to what you guys have.
I've lived in the hot, dry, windswept hellhole of Western Oklahoma and want no further part of it.
I've never really had a noticeable problem with static electricity and powder, but I notice the International has a tendency to cling to the insides of a AA-HS hull, whereas I've not noticed that with other powders.
Maybe I just wasn't looking.
My pond's the lowest I've ever seen it, but I know our drought is nothing to compared to what you guys have.
I've lived in the hot, dry, windswept hellhole of Western Oklahoma and want no further part of it.
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Really interested ? Google up "Angle of Repose" and click on the obvious .
421
421
Ah yes, but if you owned that land and had any of the several hundred Oil/Gas wells that have been drilled in the last 10 years, making 2-5 million cubic feet of gas and 2-600 barrels of oil a day, you could learn to live with it :roll: :lol:Case said:
And compared to where I live, Western Oklahoma is a "Forested Region" :wink:
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the angle of repose.GordonWood421 said:
The difference in the angles of slope of the pile are partly related to the difference between the dynamic friction angles which are relevant to the grain falling on the pile and the static friction angles which are relevant to the pile at the rest. The static friction is related in practical terms to the angle of internal friction which is the angle at which a block moves on a plane surface (Embleton and Thornes, 1979). It is denoted by the symbole Ø and usually associated with the Mohr-Coulomb failure criterion:
tf = c + sn tanØ .
tf is the shear strength of the substance at failure.
c is the cohesion (measured in Nm-2) which is the molecular attraction that binds particle together.
sn is the normal stress (in Nm-2).
Sorry Gordon..it didn't help me.. :lol:
With my experience in centrefire reloading I know that if I dump my powder scale pan in one lump into the case funnel, it can easily bridge. If I pour it slowly, no problem. I suppose if one was to slide the charge bar slower it may help prevent bridging as it would allow powder to slowly drop down the tube, rather than in one lump...
I rub the outside of my powder bottle and drop tube with an anti-static cloth, but don't add any to the powder itself. I have not personaly had a problem with powder bridging, but I have had shot bridging. The anti-static cloth dosen't help for this.
I have added a touch of graphite to shot I've poured in a bucket, and then mixed well. This seems to lessen the problem.
It probably wouldn't hurt if you could polish the inside of your drop tube, perhaps with a drill and a small piece of dowling, with a rag and a little car wax. :idea:
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12GA guy,
Essentially, what the angle of repose offers to such an analysis is that ANYTHING one can do to keep the "hill" forming from a stream of the particular material flowing onto a flat surface as flat as possible will minimize the tendency for that material to bridge an opening .
BUT , just as fluids have a "Reynold's Number", solids also behave in a way related to the "size" of the particulate compared to the "size" of the "channel" (pipe, weir, nozzle, etc) through which they flow .
So , anti-static materials , correctly applied, should help minimize bridging --- The hooker is " correctly applied" . Optimally , if a reloader could make all the powder "flakes" similarly charged , the "flakes" would not want to clump together but would want to create a "quicksand" media .
But , YMMV ,
421
Essentially, what the angle of repose offers to such an analysis is that ANYTHING one can do to keep the "hill" forming from a stream of the particular material flowing onto a flat surface as flat as possible will minimize the tendency for that material to bridge an opening .
BUT , just as fluids have a "Reynold's Number", solids also behave in a way related to the "size" of the particulate compared to the "size" of the "channel" (pipe, weir, nozzle, etc) through which they flow .
So , anti-static materials , correctly applied, should help minimize bridging --- The hooker is " correctly applied" . Optimally , if a reloader could make all the powder "flakes" similarly charged , the "flakes" would not want to clump together but would want to create a "quicksand" media .
But , YMMV ,
421
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Well, guys, all I can say is that with one possible exception I've never had an small-flake propellants typical of shotshell-type propellants to bridge anywhere in the machine.
The one exception, maybe, is a recent experience with some Promo. It would not drop consistently from my RCBS Grand, and I don't mean it was off by a few tenths of a grain. It was off enough to turn the load into a blooper. On the other hand, it never dropped an overcharge. That's the reason I said maybe it was a bridging problem, but I'm not convinced of that. The second "hooker" is that it dropped very consistently from either of my Grabbers and my 9000G.
With shotshell presses, the only bridging I've seen has been with shot. Shot larger than the typical target-type sizes or small drop tubes like on 28 gauge and .410 bore machine.
Propellant bridging and/or kernel cutting in dispensers with long-kernel rifle-type propellants is sometimes frequent. That's why Hodgdon, for example, came out with their short cut propellants such as H4831SC.
The one exception, maybe, is a recent experience with some Promo. It would not drop consistently from my RCBS Grand, and I don't mean it was off by a few tenths of a grain. It was off enough to turn the load into a blooper. On the other hand, it never dropped an overcharge. That's the reason I said maybe it was a bridging problem, but I'm not convinced of that. The second "hooker" is that it dropped very consistently from either of my Grabbers and my 9000G.
With shotshell presses, the only bridging I've seen has been with shot. Shot larger than the typical target-type sizes or small drop tubes like on 28 gauge and .410 bore machine.
Propellant bridging and/or kernel cutting in dispensers with long-kernel rifle-type propellants is sometimes frequent. That's why Hodgdon, for example, came out with their short cut propellants such as H4831SC.
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