I've never tried it in a 38-55 but it makes a world of difference in my 28-30 using IMR4227 and Rem. 2 1/2 primers. I plan to try it in my 33-47 soon. 

I use the green, dry floral foam and have been advised that it does no harm at all to the barrel.

Give it a try, you may like it.

Jerry_H

Per the guru (to me anyway) on the use of fillers vs. wads (as they are NOT the same!) from Mr. Larry Gibson, from the Cast Boolits website:

"By L. Gibson (Cast Boolits post):  Does the 38-55 "need" a filler? No it doesn't, but unless you want to raise the muzzle before each shot you will have powder position sensitivity, inconsistent ignition and probable vertical stringing. I would definitely use a Dacron filler with 18-grns IMR4227 & 16-grns 2400 under a 250-gr cast bullet. Use just enough Dacron fluffed to fill the air space between the powder and the base of the bullet."

FWIW my Dad shot thousands of 38-55 smokeless loads in his later years, all with a ~3/8" square tuft of Dacron 'pillow stuffing' over his 4227 or 4759 (preferred) charge and never an issue arose. And he knew all about BP and duplex loads, as he had started shooting at the old Walnut Hill Range, we he had once met and shot with Mr. Pope. Towards the later end of his shooting life, it was nothing but smokeless loads for him. It is, what it is (or was) ... but at least he was still shootin'!

That same load put 4 shots into one ragged hole, just over bullet diameter and counting the 5th, all went into a ~1/2" group @ 100-yards last week on my new CPA wearing that new Davis 12X scope I had just picked up. If I wasn't hunting the flintlock only season after Xmas, I'd be printing her @ 200Y .

If BP loads, then I've digressed, sorry . Sadly, I wasn't into BP cartridge shooting then and did not discuss BO loading much with my Father, who's since passed.

QuestionableMaynard8130 wrote on Dec 23^rd, 2013 at 12:39pm:

Hmmm........... thought that keeping the powder from falling out into the action was a nice secondary benefit rather than the primary purpose. Understood that the primary purpose was to get the powder up around the primer for good, complete ignition. With that thinking, have you ever tested the two different wad locations? One down near the base of the case as opposed to one near the mouth?

You will need to test for best location, what works for one does not work for all. My 28 Darr does not like it at the mouth of the case or down hard on the powder. It likes it backed off the powder a tad and then you have Jerry H shooting a couple of benches down shooting his 28 with the FF having a half crush on the powder shooting an extraordinarly small group at 200yds.

JLouis

there are twotypes of FF that I see in use at EG   one is "wet" and one is "dry"   not sure which is which.

I use the very very fine grain Very frangible type   I think it is the "wet" kind.  I get it at the craft dept at Walmart a couple bucks buys a 3 brick bag of it, enough for a couple seasons. (Not fond of WM but going into the big box craft stores--who also carry it---gives me the creepy hives) It appears to be the most common I see in use by far.
the other, which I think is the "dry" kind is a whole lot more like styro-foam. It has a much larger "grain" and is a lot "crunchier"  some guys may be using it but not as many as are using the finer grain type. 
  

I know of one of our shooters who practically ruined a barrel using plastic overpowder wads.  on an almost brand new Hurst engraved rifle to boot. I'm not sure but I think he was using the kind the BPCR guys were using cut from the "right kind" of milk jugs.  it was the Ldps or Hdps. (as I recall) stuff one is OK and one is bad, and I think with the vision problems he was having he may have cut his wads out of the wrong kind of plastic--whichever it was.   It really crapped up the inside of the bore, ended the match for him.  He stopped making the drive up shortly there after and I don't know if he ever got it cleaned out or not.  Maybe 40-Rod and I are talking about the same incident, maybe not.  
  I know a lot of guys DO use the fine grade FF with no problems. But most, myself included are using it in the mouth of the case not as a deeper seated over powder wad.  
For that matter it may not even be a plastic. I'll have to find a way of checking.
They are now making bio degradable packing peanuts out of an expanded foam made from corn starch.  That product [i ]might[/i] make a good overpowder wad material

Amen Boats, break a piece off, stick it on the end of a tooth pick, light it and if it turns to 100% ash you are good to go. 

JLouis

Wikipedia had some info and the MSDS.  (You need to Login or Register to view media files and links);  

The stuff is known as Oasis floral foam and it is a phenolic foam.  Some are concerned about the constituents but the quantities we use are very small.  It has some barium sulfate in it but I don't know if this is a reaction product (they might use barium peroxide as a reactant) or if barium sulfate is just a filler.  It is probably fine as bug dust so it won't cause any harm.

I've used the stuff for a few years with good luck.  I leave the wad at the case mouth but some seat the foam to the powder.  I've only used this with smokeless.  I use Walters Wads with black powder.

I cut the foam about 1/8th inch thick or a bit less.  I need to make a jig to get more even thickness.   

Dave