After having researched this reloading consideration until my eyes are bleary and my head hurting from the contradictory holdings of various respected authors, I've come to the momentous decision that no one knows whether it's a good or bad practice! Sure generates a lot of verbage on each side of the issue, though!
Adding to the skimpy material on hand, Kragman 71 was kind enough to forward a goodly selection of comments he has accumulated over the years on the subject. I suppose he is just about as confused as I am with the opinions.
OK - it's a crap shoot whether you should use case fillers for insufficiently filled cases or when assemblying reduced loads using cast bullets (hereinafter referred to as CB's).
Folks have used a multitude of articles as case fillers - cork, cardboard, waxed milk cartons, dacron, kapok, cotton, tissue paper (never said whether 1 or 2 ply!), grain cereals (one of the very best uses of grits I have ever heard of - not fit for human consumption, otherwise), plastic and ground polyethylene, to name a few.
In the olden days, black powder loads were judged best when the powder filled the case and the seated bullet applied a slight compression for proper ignition. Sometimes a full charge wasn't desired so artificial material was used to complete the case filling and get the compressed powder. Wads of various materials, similar to those used in shotgun shells were stuffed in and worked fine. Remember, most old blackpowder cartridges were of the straight walled type and everything blew downbore with little restriction, again similar to a shotgun. Also, CB's were the primary projectile in these cartridges.
Today, with smokeless powders we have a different situation is presented. The powders vary in burn rate from extremely fast to extremely slow. Projectiles are both CB's and jacketed. Jacketed bullets offer far more resistance to being engraved with the rifling and will develop higher pressures than a CB of similar weight. BE CAREFUL not to interpose the two thinking the same powder load is OK for both.
We still have folks that like to shoot CB's in bottleneck cases using reduced powder loads using primarily fast burning pistol powders. The trick is to always have consistent ignition of the powder to provide consistent velocities and accuracy. Most powders are position sensitive, in that if the propellent is not held in the same place inside the case, the burn, and therefore pressure, will be erratic.
What to do?
The most obvious and best answer is to fill the case as near as possible with the slowest burn rate powder available to achieve the desired reduced velocity. Believe me, this is much preferred to the addition of fillers.
Since this doesn't work in all cases, we now decide to use a fast burn powder in a reduced load that only partially fills the case. NEVER REDUCE SMOKELESS POWDERS MORE THAN 05% BELOW THAT LISTED IN THE MANUALS - IT IS DANGEROUS. a situation known as double detonation (will not be explained here) can occur causing much mayhem. Follow the manual's recommendations for reduced powder loads and remember the difference with the CB's and the jacketed bullets.
The quandry of powder positioning can be solved in several ways.
1) The use of a "position insensitive" powder (AA5744 is touted as such)
2) The old "elevate and lower" method. Elevate the muzzle of the chambered round to past 45 degrees from the horizontal, then slowly and without bumping, lower the rifle to the shooting position. This should cause the powder to back up against the inside base and remain there until firing. Not recommended for rapid firing events!
3) Stuff something into the case that will assure the powder will remain against the flashhole.
Would strongly advise no's 1 and 2 be used. If still persistent in the desire to use fillers, then OK - here's more to ponder.
It has been reported that both straight walled and bottlenecked cases having fillers placed between the propellent and projectile have "ringed" the chambers. A ring is a bulge in the barrel metal, usually in the place where the bullet base resided when excess pressures developed. This ring will always be there and in some cases is so severe as to cause very sticky extraction of future cases. The necks fireform into the barrel/chamber bulge and are stuck.
I personally ringed the barrel of a fine old pre-Garcia Sako Forester L579 in .243 Win some years ago. Being an impressionable youngster and reloading my own ammo, fell victim to a sage old gun writer advocating the use of cornmeal as a case filler. Decided to top off the charge of Hodgdon H380 that nearly filled the case to the shoulder with a helping of cornmeal up to the bottom of the neck. The Nosler Partition 85 gr semi-spitzer (wonderful bullet) was seated to just at the neck bottom. First shot and the rifle didn't sound right. Bolt lift was heavy, to say the least. The primer was blown from the pocket and the case base was formed to the bolt head. Shoving a cleaning patch down the bore, a peek revealed the dreaded dark "ring" at the chamber neck. My personal belief is that there was a slight compression of the filler which packed, or caked, and that upon firing it acted as a plug in the bottleneck, bridged off momentairly and caused a tremendous buildup of pressure. That was the last time a cereal was used for a filler in any case, regardless of type. If using cereals or other dry forms for fillers (sawdust, etc) be aware of not compressing the stuff and that the added filler MUST be weighed and taken into consideration with the load. The added weight the propellent has to push is the same as using a heavier bullet for the same load, which we all know gets reduced the heavier the projectile.
The present day fillers seem to be cotton, dacron or kapok (if you're able to find an old life jacket still having it). Most advocate just a pinch of it, around .5 to 1.0 grains worth, to stuff it into the case with a blunt pointed instrument (extra decapping rod, sans the pin will do, or a blunt ended pencil if the case is big enough) to push the carded (fluffed) whispy bit of filler material lightly down onto the powder and allow it to naturally spring back. DO NOT make a tight pill or wad of the material and tamp down tightly. This could act as a secondary slug or plug with sufficient strength to hold the powder momentairly as it begins burning and then let go with a force that slams into the bullet base that can cause the aforementioned ringing effect.
Now, I've used the cotton/dacron (can't find the kapok, either!) methodology on some lightweight handgun loads and rifle loads when firelapping bores. Everything has gone well so far, but then again, tomorrow is a different day. When I do, a very minimum of the stuff is used - just enough to assure the powder will remain against the flashhole with careful handling and not enough to begin to fill the complete case.
Ground polyethylene, such as Super Grex, the stuff used to buffer shot in cups when loading shot shells, has been advocated. Not sure I'd try it, because I know for a definite fact that polyethylene melts at 425 degrees. Can just envision the mess it would leave in a bore, not to mention the hydraulic effect that could be pushed as a molten goo against the bullet base.
A product on the market for the past several years called Puff-Lon is said to be a valid filler. Among it's other ingredients are molybdnum disulfide and teflon. It is a very light weight powder to volume and said to be effective. Again personally, I've worked my buns off de-molying my barrel tubes of the moly previously used with abandon when it became the rage in the shooting fraternity. Became dissolutioned with it and have since gotten all the bores scrubbed back to pristine condition. Don't need a product that will re-introduce it, IMHO.
There you have it - danged if you do, danged if you don't.
The gist of this little article is to try and use full, or nearly full, propellent loads to avoid having to possibly use fillers in the first place. If fillers are still desired, use a very minimum amount of space filling naturally springy stuff like cotton or dacron. Watch closely for any increased pressure signs.
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