RCBS - Inconsistent Powder Throws

[jackstrawIII]

Hey all,

I have an RCBS Uniflow powder dispenser that I've just started using. I'm having a heck of a time trying to get it to throw uniform charges. I mean, it's bad.

I'll dial it in at 40 grains... but it will shoot 39.7, 40.2, 40, 40.4, etc on consecutive throws of the lever. I'm trying to work the lever as consistently as possible (as I've heard that can affect it).

Otherwise, what can I do to make this thing work? I feel like I won't be able to develop decent loads if I can't even throw consistent powder loads. It's pretty frustrating.

Thanks gang.

 

[mkl]

Two thoughts come to mind:

1) install a powder baffle to keep the weight of the powder above the volumetric cylinder consistent.

2) Use the "double tap" method with the charging handle. On the upstroke bring the handle to a stop with a smart tap. Lower the handle about 1/3 of the way and then up again with a good firm tap. This settles the powder in the chamber evenly. On the down stroke (powder dump) hit the stop firmly, raise the handle about 1/3 of the way an bring down again with a firm tap. This assures the chamber is completely empty.

My RCBS Uniflow throws very accurate charges using the above methodology.

 

[Sure Shot Mc Gee]

No mention of the type of powder using. i.e. Ball_ stick_ flake_ or granular?
If you want a truly consistent powder charge weight. Beam scale each charge or consider one of those electronic measure's.

 

[walnut1704]

Static maybe? Wipe the hopper out with a dryer sheet before loading it with powder. It is winter.

 

[jackstrawIII]

MKL, I'll try the double tap and see if that helps.

Regarding the type of powder, I was using Varget, which is an extruded powder. I'll also be using H1000 (also extruded), RL 17, and Ramshot TAC for the various cartridges I plan to load.

 

[Unclenick]

Mainly it is technique trying to get the powder to dispense without altering the bulk density of the powder by having different powder column weight over the metering chamber and not exposing the power column to different levels of vibration from one throw to the next. Powder baffles address the first issue and tapping or knock are for the second. Some folks have gone to the trouble to use big rubber bands to attach an aquarium air pump to the side of the powder hopper and put a momentary pushbutton switch on it and push that to vibrate the hopper the same amount for each throw. Others have a screwdriver and tap the measure housing with the plastic handle once or twice before each throw. You get the general idea: make the powder packing match.

Here is a link to my do-it-yourself powder baffles template and instructions. The last page has some brand-specific baffles. However, the makers keep modifying things, so double-check that the narrow diameter of the cutout template is slightly under the ID of your hopper.

Edit: Stick powders are subject to a lot of packing issues, and when you cut the grains with the drum, the sharp vibration that action causes can pack the powder in the hopper down more for the next throw.

The extra baffles should help. You will find Varget is not very sensitive to charge errors, having low velocity per grain in the usual rifle peak pressure range, and that ±0.2 grains (0.4 grain spread) is perfectly fine for match grade loads if your load is on a sweet spot. Twice that is likely fine for hunting accuracy, as long as your upper charge in the range doesn't go past maximum. This is because more tightly packed stick grains tend to ignite a little more slowly, so there is some degree of self-compensation in this.

 

[higgite]

In addition to what others have said, two more suggestions, in case you haven’t already tried them.
1) Run a hopper or 2 of powder through the Uniflow, since it's new, to coat its innards with graphite from the powder.
2) Every time you fill or refill the hopper, tap it a number of times and drop 20 or so charges to settle the powder.

 

[jackstrawIII]

Unclenick and Higgite,

Thanks for the tips. I am using a baffle, but haven't been working hard to uniform the packing or pressure. I'll give the dispenser an extra tap/shake between charges to see if that will help.

Also, I did run a bunch of powder through it towards the end of the night just to see if it needed to break in or something. That did seem to help a bit.

 

[Unclenick]

If you read my baffle file, look at the two-baffle arrangement. It's like adding an extra stage to a noise filter. It makes you replenish the hopper more often because of the space it takes up, but placed with its drop slots perpendicular to the those of the lower baffle, it really does tighten the throws.

If you ever decide to upgrade to a better measure for stick powders, the JDS Quick Measure is the most consistent stick measure out there. I never see more than 0.2 grain error with it and usually it is within 0.1 grains. It's more trouble to adjust and costs more, though, so you will do best to stick with your RCBS until you find the limit of what you can make it do. The RCBS will do best with spherical propellants because they don't pack down under vibration to the extent that sticks do. I currently have both RCBS and Redding measures doing spherical duty and the Quick Measure doing sticks, as it has no precision advantage over the other two with sphericals.

 

[edfardos]

thats plus or minus one percent. thats not bad for stick powders. you must trickle by hand if you need better imho.

 

[HiBC]

I move relatively slow through my stroke Taking a wild guess,about 0.7 second each way.Deliberate.I "thunk" a bit on the stop.I dwell at the stop maybe a second.No extra motions.If I stumble a bit crunching grains,I reject that charge and the next,back in the hopper.
Give the powder time to flow.Introduce a bit of consistant shock.Redo anything that feels different.Add powder when level gets down to 1 in or so.Some float a fender washer on top.
I get ammo that will outshoot me by a lot.

 

[Steve in PA]

I've been using the Uniflow for 26 years now and it works great.....with ball or flake powder. However, when I use extruded powders, I always set it up to throw a little on the light side, then use a powder trickler to finish the weight.

 

[reynolds357]

Use a scale and a trickler.

 

[GeauxTide]

1) install a powder baffle to keep the weight of the powder above the volumetric cylinder consistent.

2) Use the "double tap" method with the charging handle. On the upstroke bring the handle to a stop with a smart tap. Lower the handle about 1/3 of the way and then up again with a good firm tap. This settles the powder in the chamber evenly. On the down stroke (powder dump) hit the stop firmly, raise the handle about 1/3 of the way an bring down again with a firm tap. This assures the chamber is completely empty.

Used a Uniflow for almost 40 years and always had the trickler ready when using stick powders.

 

[serf 'rett]

If I recall correctly, the Uniflow can be set up two ways. Handle down with fill cylinder down or handle down with fill cylinder up (powder filling the cavity) as I have mine set. With the fill cylinder facing up with the handle at rest, a slight double bump serves to fill the cylinder better, allowing simple handle rotation to drop the charge. Handle to charge cavity orientation makes a difference.

 

[brasscollector]

I move relatively slow through my stroke Taking a wild guess,about 0.7 second each way.Deliberate.I "thunk" a bit on the stop.I dwell at the stop maybe a second.No extra motions.If I stumble a bit crunching grains,I reject that charge and the next,back in the hopper.
Give the powder time to flow.Introduce a bit of consistant shock.Redo anything that feels different.

^^^This is exactly how I do it with my uniflow as well. I have loads that consistently chrono with ESs below 10fps. I think part of finding the perfect powder load for a rifle is finding the powder charge that throws the most consistent from your measure. In other words my best loads are the ones my measure throws the best. Rifle would likely shoot a lower or higher charge just as accurately but my measure doesn't throw those charges as good...at least that's my theory.

 

[Heavy Metal 1]

FWIW I stopped using mine a few years ago. I have the lg and sm drums, the so called micrometers.

At present I use the Lee Perfect Powder Measure and find it to be excellent in throwing both ball and stick powders. It is significantly more consistent than my RCBS thrower. I will sell my RCBS unit at my someday yard sale.

 

[noylj]

1) Did you completely clean the measure before use? You should disassemble, per instructions, and clean with Hornady One-Shot Cleaner and Dry Lube (do not wipe off the cleaner/dry lube, just let air dry). Plastic parts can be washed in soapy water and air-dried (do not rinse)
2) After adding the powder, give the measure a few gentle shakes to settle the powder.
3) Always throw at least 10 charges before you EVER start to weigh any charges. You may need to weigh as many as 10 charges at times to get the measure settled. When you adjust the metering setting, you need to throw at least three charges before weighing any.
4) If you are manually cycling, be sure to raise the arm all the way and go "tap, tap" and when you lower the arm, you again go "tap, tap." Consistency is important.
5) Baffles may help. Sometimes they hinder.
6) Some use aquarium pumps or mini-vibrators on the measure to keep the powder consistently settled.
7) If the measure uses a large and small rotor, be sure you have the large one installed for rifle rounds and the small one installed for almost ALL pistol rounds.
8) Buy a powder dispenser and forget the measure all together.

 

[mkl]

noylj has an excellent point in his #7 item.

I just looked up the current version of the RCBS Uniflow and note that there is an option for a large or small measure. This would refer to the cylinder (drum) size that was shipped with the powder measure.

My Uniflow came with both the large and small volumetric charge cylinders. For your purposes you need to be using the "large" cylinder. If you are using the small one, it will not be as accurate for the 40+ grain charges you want.

I mostly use the small cylinder for my handgun loading and seldom exceed fifteen grains of powder. It is very accurate in the 0-15 grain range that I use, even with extruded powders.

I have not used the large cylinder that came with my Uniflow very much, but it did seem to give accurate charges for the 47.5 grains of IMR4831 I use for my .243 Win. with a 75 gain bullet.

I don't shoot a lot of rifle, so most of the time I just weigh the powder as oppose to throw it with the Uniflow.

Even though RCBS says the small drum (cylinder) will throw up to 50 grains, it will be less accurate than if you were to use the large size drum for the size of charges you want to throw (40+ grains).

 

[roashooter]

I concur with the others....the consistency will depend on the type of powder..and the technique of tapping...

been using the same RCBS Uniflow since 1974....