RCBS Uniflow problem...........

[3006guns]

I've owned my RCBS Uniflow since the very early seventies, when I first began reloading in earnest. It's always thrown powders pretty much "dead on" plus or minus perhaps a tenth.......very reliable.

Yesterday I was setting up to throw 16 grain charges of 2400 for a military cartridge. As is my habit, I always throw the first 3 -5 charges in my scale first, this being my minimum to verify everything's all set.

Suddenly the charges began weighing 15.6 to 16.2......? Repeated weighing got 16 grains (dead on) a number of times, then a repeat of the error. Note: The scale (an RCBS 505) is level and checks out.

I finally grabbed a box full of spare Uniflow parts and swapped out the powder drum for a brand new one. This time I got 16 grains, and then suddenly a repeat of the error. I adjusted it several times and got the same results.

I'm stumped. Is it possible that the error has been there all these years and I just never noticed before? Could it be the powder? I had this happen years ago and it turned out that I left the "small" funnel in the measure, which caused the stick type powder to bridge. Not the case here though.....large funnel is in place and 2400 usually meters beautifully. Any suggestions gratefully accepted!

[popper]

Had that problem few yrs back. Fine powder dust collected and hardened above the rotor, finally broke off and bridged so I got overflow usingH335 in 30/30.

[Taterhead]

The throws you describe are +/- 0.3 gr. A little high

My process of elimination would start with the scale. You say that it "checks out". Does that mean that it was verified with 16 grains of check weights? And is that repeatable? I.e. if the weighted tray is removed and re-placed a few times does it give the same reading?

The 505 does drift from impulses to the workbench.

The size of the metering cylinder doesn't change in the Uniflow unless the dial is turned. If the scale is ok, then I'd disassemble the measure and look for obstructions that would cause hangups or bridging. Popper has good advice in this regard.

Lastly 3 tenths, might be on the outside of expected variances. A bit of more consistent technique in metering could clean that up somewhat. 2400, being a small extruded powder, won't meter like an Accurate No. 7.

I like my Uniflows. I make good use of all 4.

[3006guns]

Thanks for the advice guys. I'll disassemble the measure again, take it out to the shop and blow some compressed air through all the openings. I'll also verify the scale with check weights, something I should have done in the first place.

As for my technique, I've always made it a habit to raise the handle with a gentle but authoritative "thump" at the top, and the same "thump" when dropping the powder. In other words, uniformity of motion for each measure.

After all of the above, I'll report back with any info that may be of help to others. Thanks again!

[3006guns]

Okay, I set up my scale and carefully leveled it to where the pointer was EXACTLY on zero. I then set the balance weights to 16 and selected the correct Pacific check weights that add up to 16, then placed them in the pan. The balance came to rest on zero immediately. I then removed the pan several times and replaced it with the same results. I even "bumped" the beam in order to make it oscillate, only to have it go back to zero each time.

I'd say the scale is accurate.

Something popper said reminded me.......when I was replacing the rotor, I noticed the cavity below the hopper (and above the rotor) looked clean but somewhat "frosty". I wiped my finger around the cavity, but got no material out. The "frosty" appears to be like a fine, rough casting. Is that cavity supposed to be machined/polished? The rough casting MIGHT cause variances with a fine powder like 2400 and I've been measuring away in blissful ignorance!

Edit: Okay, I just checked my spare Uniflow and indeed, the inside above the rotor is a bit rough and complete with RCBS green paint! Maybe I'll try gently "thumping" the entire full measure on my bench a couple of times and try that.

Headed for the range right now to try these 303 Brit loads...........

[gwpercle]

Been using it since the early 1970's ???
Maybe you just wore it out.... If the "thumping" fix doesn't work it just might be time for a new one. Most things don't last forever .
Gary

[poppy42]

I would suggest disassembly wash it with dishwashing soap and water once it’s dry go over it with alcohol see if it makes a difference I doubt very much it’s wore out. I have issues over the years with you and the flow and usually fine if it’s something insignificant and once cleaned it returns to operating parameters. I also wiped the hopper gently with a used dryer sheet to eliminate static charge. Just some things I’ve done in the past hopefully my suggestions are helpful

[Valley-Shooter]

Try another powder and see if it happens again.
Maybe your 2400 has gotten lumpy.

Sent from my HTC One M9 using Tapatalk

[3006guns]

Try another powder and see if it happens again.
Maybe your 2400 has gotten lumpy.

Sent from my HTC One M9 using Tapatalk

Bingo! I just got back from the range and decided to try a load of 12 grains/Unique. Set everything up and started throwing charges. Maximum variation this time was around a tenth, or what I would expect from a Uniflow. The 2400 looks perfectly normal, no lumps or warts, so my Uniflow just doesn't like 2400 for some reason!

Not the end of the world..........there's still Lee dippers! :) ..........or my Little Dandy.

[Gofaaast]

That’s one wild uniflow if Unique meters more accurately than 2400! I have a couple uniflows along with a couple Redding’s. Redding’s always have less variation when comparing small drums from each manufacturer. I played with both a coupe weeks back with 11 grains of unique being the charge. The uniflow variation neared that of the Redding’s when I installed a baffle in the uniflow. No baffles in the Redding. 2400 has always metered +- one tenth of a grain for my loads in the teens. I set mine based on 10 charges once I get single charges close and use consistent motion ect.

[BK7saum]

You might try bumping or thumping the measure more to settle the powder. I have had my weights get more consistent once the kernels have all aligned. This shows up with extruded powders, not necessarily with 2400 as I haven't used much of that. Just something else to look out for.

[JimKirk]

I suggest that you place the handle where it dumps the powder on the down stroke(if you're is already setup like this ...disregard).... with the setup this way the powder does not always be exposed to the cavity ... any different vibrations on the bench/powder measure will result in varying charges....
https://i.postimg.cc/T24GGT6k/1828.jpg (https://postimg.cc/K4BCDS4L)

https://i.postimg.cc/65MW8Cnh/1831.jpg (https://postimg.cc/6yGJS2H7)

A stand like this allows the meter stem to pass through the stand ....as does the RCBS Advanced stand.
https://i.postimg.cc/kMBTppyx/Powder-stand.jpg (https://postimg.cc/5jW5HpT0)

https://i.postimg.cc/tR2ZG6n0/31-5-MVAVv-WL-SX466.jpg (https://postimages.org/)

This Uniflow is a 1969 Model I got in late '69....

[remy3424]

Nice dumper stands, never knew about that "advanced" stand, I like it!

[kungfustyle]

Try to throw about 20 charges to settle and fill it up with a funnel still in it. Fill it up so there is powder in the funnel, it will help maintain constant weight on powder and help flatten out the variation. Hope that helps.

[JimKirk]

Nice dumper stands, never knew about that "advanced" stand, I like it!

That first one I built before RCBS came out with the Advanced Stand .... all aluminum except the bolts and nut

[cwlongshot]

I would suggest disassembly wash it with dishwashing soap and water once it’s dry go over it with alcohol see if it makes a difference I doubt very much it’s wore out. I have issues over the years with you and the flow and usually fine if it’s something insignificant and once cleaned it returns to operating parameters. I also wiped the hopper gently with a used dryer sheet to eliminate static charge. Just some things I’ve done in the past hopefully my suggestions are helpful
THIS!!!!

Static can do crazy things and softener sheets are a quick fix.

IT NIT WORE OUT!!! I have 4-5 of them some been running since the 1960’s!! Others are 1980’s and COUNTLESS STROKES thru them!!!

Something I always do it “taps” top and bottom of the stroke. I also like to mount the handles upside down. Meaning I charge the hopper on the up strike and dump powder when I return it to bottom. With “taps” both strokes same every time. These measures are incredabully accurate as long as you are consistent. Baffles help too.

Good luck

CW

[wildwilly501]

Make sure there's not a spider web or bug nest in the lower part of the measure.Mine started doing something similar a couple years ago turn out there was part of a spider web in the drop tube part.Compressed air normally won't blow them out.I used a Q-tip

[country gent]

I would also recommend wiping it down with a dryer sheet to remove static build ups in measure and powder. his affects all powders but the fine grained are more affected. Seen a buddies measure where 231 was actually climbing up the hopper, a quick wipe down fixed it.

Another is a simple good cleaning to remove build ups in the body hopper and rotor. Then look for any burrs on the rotors cavity slide a q-tip around edges if fibers are pulled it needs a little attention. Also look for rounded edges that should be sharp. This can occur from use more so with the stick type powders.

Some measures throw certain powders better than others even in the same make model. "blueprinting" the measure, and tuning it up can make a big difference. This isnt hard to do mainly removing burrs and making sure everything is what it needs to be.

[gnostic]

I use baffles in all powder measures, as my charges were always different without them. My technique may differ from time to time, I try to maintain a standard, but can't say I'm always successful....

[FLINTNFIRE]

I mount so mine fills on upstroke also seems most natural for me , but I do a tap twice on up and twice on down , one of my mentors used the lyman55 and he had a rhythm using the knocker on front on up and down his finger would flip it while charging those loading blocks full of 38 for his bullseye shooting