RCBS Uniflow Powder Measure trouble with small volume charges

[Land_Owner]

I broke my Piggyback II progressive reloader yesterday throwing a 3.3 grain charge of IMR 700X (flake powder similar in shape to WIN 748).  It seems that below a certain threshold, the Uniflow Measure begins to shear and grind the powder into thickened clumps rather than smoothly transfer the measured load to the case.

The powder measure adaptor tube broke in two as the case detection push rod attempted to raise the cylinder handle of the measure.  There was an audible "crack" and the measure fell to the side taking the upper half of the adaptor tube along with it.

I disassembled the measure and so far, with no powder, the measure works "fine".  With the small volume charge however, the force necessary to operate the cylinder handle is 10X to 100X the unloaded force.

Something is definately not right about that.  RCBS is warranty sending me replacement parts no charge and I asked for two of the broken part as I fully expect to break another one trying to determine the problem.

Anybody else had this issue with a powder measure?

[LaOtto222]

Are you using the small drum or large drum? I have an old Uniflow (cast housing). I never experienced any thing like that, but I don't think that I used any thing under 7 grains of Unique. It came with both drums and I used the small one almost exclusively. I do not have a progressive, I still use a single stage press, so now days I use an RCBS Charge Master 1500, of course it would not work for a progressive.

[Graybeard]

I quite honestly don't comprehend what you are talking about. You lost me when you started to compare 700X and 748. One is a flake shotgun powder and the other a ball rifle powder. I've used both extensively and to me they have about as much in common as apples and oranges.

I have no clue how progressives work as I have and always will load on a single stage press and use my measures to drop the powder into individual cases one at a time while they are in a loading block or tray.

I've never experienced anything like powder being ground into lumps as you mention. Now I've seen powders clump a bit when they have sat in cans a long time likely from moisture getting in with them. The only time I've had a problem with an RCBS Uniflow not dropping properly is when static electricity built up and the powder grandules clung to it rather than dropping. A dryer sheet or two down in there and rubbed around usually clears up that.

[Land_Owner]

700X is not ball or cylindrical.  It is tiny round flat flakes - as you noted GB.  There are a bunch of these flakes in a 3.30 grain charge.

At this charge weight the measure binds.  That binding feels like a function of "clogging" or "binding" of the flake powder in the rotating charge drum against the knife edge of the fixed portion of the measure.  It is not unlike a measure "chopping" cylindrical powder grains.  That would be a similar feel. 

When the 700X charge is thrown, there are clumps (wedges) of compressed flakes in the case.  Clumps as if some portions of the powder got caught in a compactor. 

There are no clumps in the powder resevoir. 

Based on LaOtto's comment about "small drum", I just called RCBS and have purchased the small drum, which I do not have and was not using.  RCBS was well aware of the "binding" problem using the large drum for a small charge.

Hopefully - problem solved.

[Graybeard]

OK I think I better understand. Yeah with the large drum dropping such tiny volumes of powder is not easily done. Doing it by hand one at a time I'd relate it more as grating or grinding and when taking the measure apart you can see that there is contact between the moving plunger that determines cavity size and the body of measure if you try to throw too small a charge in the large drum. It really doesn't work well at all at tiny powder volumes.

[necchi]

Why not just get a bigger gun? 

[Land_Owner]

Why not just get a bigger gun?   

Good one.  LOL.  I have many of those too!    

Right now I am loading for plinking and to really use (finally) my Colt/Walther PPK in 380 Auto (such an unusual combination that Colt/Walther thing).  The Walther just sits there while the Ruger SP101 in 357 Mag, Super Blackhawk Convertable in both 45 ACP and LC, Colt Defender in 45 ACP, and Thompson/Auto-Ordinance 1911 in 45 ACP get banged away routinely.

[Lloyd Smale]

 700x is a poor powder to use in progressive loading with small cases. Ive yet to find a powder measure that is accurate with it. If i were youd id give serious consideration to switching to bullseye unless you want to weight each charge of your 700x.

[Steve P]

You certainly need the drum with the smaller metering rod.  YOu may also need to put a second baffle in your powder measure if your 700x is "clumping".  The powder baffle is supposed to keep the weight of the powder in your measure from compressing on itself.  This is what allows it to meter evenly into the orifice of the drum.  If you do not have a powder baffle in place in your powder measure, you certainly need one of these also. 

Good luck....you will get there......

Steve

[Land_Owner]

I purchased the small drum and powder baffle yesterday.  They are on the way.

I had lightly "crushed" or warped some of the 380 Auto cases and while setting the progressive up.  They functioned through the action of the Walther, but I was interested to see if they would fire. 

Happy to report they all fired - and I lost all of those cases and then some in the leaves at the range.  Now I am really going to be happy with the rest of the rounds that I made.

I made the consciencious decision to reload hand gun rounds with IMR 700X and Hodgdon Clays for their clean burning and highly energetic properties.  I use IMR and Hodgdon relaoding manuals for the bullet caliber and weights.  If the powder manufacturer says they load and test those, then I am good with that.

Getting a powder measure to "accurately" throw a small charge is problematic.  If I can't get the Uniflow to do the job right every time, then it will be Bullseye or other powder to prevent me from blowing something up that is not intended.  Also, the 3.3 grain charge of 700X fits nicely in that little case.

[cybin]

Like GB I don't use a progressive press--but do use a RCBS uniflow measurer---I drop 3 grains of Bulleye all day long with no problems, no matter the level in the measurer. The RCBS uniflow measurer is the best one out there IMO.
My nephew just a few weeks ago bought a Lyman turret press with the Lyman powder measurer--don't know the model number but it looks like a smaller copy of the old Lyman model 55---it is a POS. The press is good--but nothing else he bought.

Good luck--let us know when you get things working right and what you did to get it right.

cybin