The guy running a local reloading supply shop guy says to definitely not clean with ultrasonic when seeking precision/accuracy with 6.5 Creedmoor (Ruger Precision Rifle, bolt action). He says one needs a layer of carbon buildup inside the brass to insulate from the flash of primer and burn of powder.  He says squeaky clean brass will absorb too much of flash/burn but that tumbling will allow a desirable carbon layer to remain inside the brass and provide for a more consistent burn of powder.  I have been using ultrasonic for my pistol and .223 loads but now for first time with this 6.5 I'm really striving for accuracy at distance. Should I abandon the ultrasonic and tumble instead? I like ultrasonic because it certainly cleans well and there's no dust to deal with.  I'm wondering how many people accept that with all things being equal ultrasonic hurts accuracy compared to tumbling brass.  Thank you.

Call some ammo companies.

I can guess what they would say - don't they use brand new, shiny brass?

As long as the chamber is clean and dry, and the brass is clean and dry, the pressure of the firing cycle will press the brass into the surface texture on the chamber and hold the case as a gasket for the next millisecond or so.

You need to listen to your friend less.

This.

I highly doubt they fire ammo just to load ammo.

Just saying.

Thanks everybody.  Doesn't seem like there's a great consenus againt the ultrasonic cleaning.  I searched for information on it and the only thing I found was some people talked about this in terms of neck tension saying that a little carbon left inside the case acting as lubrication was good for consistent neck tension.

With so many things to chase and explore in reloading I think I will for the time being keep cleaning with ultrasonic and concentrate on other areas.  I can always come back to this later.

Do a test.  Report the results.

My ultrasonic cleaner didn't get my brass clean enough so I switched to wet tumbling. 
I've noticed no change in my accuracy, MV or luck playing the lottery 

I've read that carbon on the inside of the neck can act as a lubricant when seating bullets.  If that is the case, it makes sense that a process which yields proper neck tension when reloading dry tumbled cases would yield too much tension with squeaky clean brass.  This can obviously be adjusted for, but I think it might be a good idea to avoid switching up the cleaning method used for any given load.

I was doing some "neck tension" internet research recently and stumbled on a similar article (LINK - ultrasonic cleaning specifically mentioned in bullet point #3!)...  and I think you're right that consistency is the key.  Reloading for "precision" applications is largely about controlling as many variables as possible.

Yes, seems like consistency is the key.  So that makes me wonder whether it's easier to have more consistent conditions with slightly sooty conditions inside the brass or with squeaky clean obtained from either ultrasonic or wet tumbling.  I'm new to all this but it seems to me that maybe the squeaky clean condition would be easiest to replicate each time.  The reason I asked this question is to obviously get the opinions of you guys which are more experienced and have possibly tried both methods.  Thanks for your response.

I'm not the guru you seek, but honestly, I doubt this is a first or even second order factor unless you are already doing everything else possible (neck turning, annealing, ect...) for prepping your brass, and you are looking for that last little thing that will give you a < 10fps extreme spread and/or < 1/4 moa groups.  I personally bought a wet tumbler because I like how it cleans the primer pocket.

Patrick;

I don't think that your cleaning methodology will make much of a difference either way...  but what I think doesn't really matter!!!  If you want real proof, set up an experiment!.  Take 10 cases and load them the way that you normally do...  divide the group into 2 groups of 5 and mark the cases in 1 group to make them easily identifiable.  Then shoot 2 groups of 5 and save the results (both groups should be indistinguishable).  Then load and shoot the 10 cases as many times as you like (say 10?) with the only difference between the groups being the way that they are cleaned...  One group you will clean with your ultrasonic cleaner and the other group you will not clean at all other than to wipe loose crap off the outside with your hand or a paper towel if necessary - do your best to be otherwise "reasonably nice" to the cases so don't drop them in a mud puddle for example.  After several firing/loading cycles, take the 2 groups out and repeat the shooting of 2 groups you did at the beginning of the experiment and see if anything is any different after not cleaning cases...

Caution: Doing this experiment may result in your questioning why you spent however many dollars on whatever cleaning equipment/supplies you now have.

Side note: When I was a young man in the 1970s, my cousins and I reloaded all sorts of rifle, pistol, and shotgun cartridges.  We were young, ambitious, had more time than money, and did a lot of shooting of various sorts.  We reloaded initially to save $...  We never cleaned a case other than to wipe surface dirt off the outside of the case by hand (if a case was too dirty/grungy we just tossed it!)...  and we had no problems producing good quality ammunition.  To be fair, we did not reload for the type of precision shooting that is the subject of these (precision rifle) forums although taking woodchuck worked pretty well out to about 350 yards with our hand loaded 220 swift ammunition (50-ish grain flat bottom bullet @ ~4,000 fps!).  The limiting factor at that time seemed to be the optics on the rifle (optical magnification/clarity (not great by today's standards); simple crosshairs - no duplex, no BDC, no adjustable turrets)...  just sayin'...  

Thanks so much for the information. That sounds like a good test.  I may do exactly that.

You're welcome.  If you do the test, be sure to report back with details and findings...  

Best,

- R -

The problem, is with the inside of the neck getting too clean. Two differing metals will tend to "bond" over time, creating deviations in neck tension.

Bare brass, mated to bare copper, will bond over time. Leaving some carbon in the case neck is supposed to prevent this.

http://www.longrangehunting.com/forums/f19/bullets-cold-welding-cases-184346/index2.html

Am considering this true.  Also lubricates the expansion ball when expanding a case neck after sizing, if that is the method u are using.

I think one could argue that without getting the brass as clean as possible each time could cause differing neck tension. If you let carbon build up inside the neck then eventually you will have cases that have a bit more than others which could cause more or less neck tension. I doubt you will see a ton of difference either way but that is my thought on it.

Personally I tumble in ss pins to get inside the case and primer pockets clean, also so that my Templaq has something to stick to so I can gauge temperature when I anneal my cases.