Fillers for Reduced Rifle Loads
October 10, 2018
After I published a column on reduced rifle reloads, several readers asked about fillers and why their use has fallen off. Fillers are non-energetic solids placed in a cartridge to reduce airspace, maintain the propellant’s position, or both. They generally fall into two classes: fiber “puffballs” and granular. I want to talk about the puffballs—to me they are the most troublesome.
Puffball fillers are wads of lightweight fiber and can be natural, like kapok, or synthetic, like polyester fiberfill. Think “pillow stuffing.” Years ago, published reloading information suggested puffball fillers for reduced loads where better ballistic uniformity was needed. You pushed a puffball of the fiber on top of the propellant charge. However, the recommendations rather quickly slowed and, in some cases, stopped.
I knew Dave Andrews, my predecessor at Speer, long before I was hired to fill his shoes. At a trade show in the early 1980s, I asked him why the puffball fad had faded so dramatically. “Ringed chambers” was his short answer.
Andrews said the rings were in the range of a quarter-inch to a half-inch wide and usually found mid-chamber. No catastrophic failures of firearms or cartridge cases heralded the appearance of the rings. Andrews said most were discovered when a cartridge case that otherwise appeared undamaged was hard to extract.
My quandary is this: I participated in a forensic exam of the sad remains of a custom .257 Weatherby Magnum bolt-action rifle built on a high-quality commercial M98 Mauser action. The owner had, we eventually concluded, destroyed the rifle by confusing a full case of IMR 4064 for the slower IMR 4350, creating pressures we estimated to be over 80,000 psi. (For those who don’t know, the SAAMI maximum average pressure for the .257 Weatherby is 65,000 psi.) Despite the rest of the rifle being “morselized,” the Harry McGowen custom barrel was totally undamaged. It and the buttplate were the only parts of the rifle that survived in reusable condition.
Careful examination showed the chamber was still comfortably within specifications and was not ringed. Thus, a rifle-shredding load did no damage to a chamber, but reports said puffball loads were creating rings in chambers with very modest propellant charges. This happened without causing the cartridge case to fail or even show other than normal stress. The single common denominator was that ringing was limited to chambers that had fired puffball filler loads. This didn’t add up. How do you put a ring in high-strength steel without first losing integrity of a much weaker brass case?
Although symptoms suggest exotic collisions of pressure wave fronts, I don’t have a definitive answer to this one. I always felt like a biologist during my career as a ballistician, capturing something for study in the lab. If I could assess the problem in a transducer barrel configured for time-pressure output, I could learn a lot. Unfortunately, the chamber-ringing mystery required experiments I could not afford. In 2002 I was paying $700 to $1,200 for one SAAMI-compliant pressure barrel. A couple of ringed chambers would mean less money for loading manual development. If ringing took out the conformal transducer too, that was another $700 in the “Oops” column.
So we have a little problem that is not unlike the Loch Ness Monster. Suggestions of Nessie’s existence continue to surface, but we’ve never managed to get one into the laboratory for a good look-see and a poke or two.The Ballistician’s Concerns
I’m reticent to guess about something I can’t test. Rather, I prefer to present issues I see with puffball filler loads that don’t have to ring a chamber to trigger my ballistician’s red flag. The first is consistency and repeatability. It is quite hard to get the same amount of “puff” in every case and just as hard to come up with a consistent tamp method. As handloaders, most of us embrace the idea of doing everything to make each cartridge as much like its lot mates as possible. To me, the inconsistencies of puffball filler assembly are a step in the wrong direction.
My second concern is stability. Puffball proponents never advised filling the case, rather using the fiber to wedge the propellant charge against the case bottom leaving airspace above. Even were the case filled with a puffball, it would not be stable. Smokeless propellants are much denser than compressed fiberfill material. Any bump can cause the dense propellant to unseat the ultra-light puffball. Once the filler shifts, the propellant can mix with it, reducing the effectiveness of the charge. That could cause a bullet in the bore. Even driving the puffball cartridges to the range in your vehicle can reduce any semblance of uniformity to rubbish before the first round is fired. Likewise, the recoil of one round in a repeating rifle will dislodge the puffball in all the remaining cartridges in the magazine.
Another issue is residue. I’ve examined cases fired with polyester fillers that showed heavy black deposits inside where the shoulder meets the neck. Yes, a heavier propellant charge might have been able to combust more of the residue before it deposited, but it still concerns me. I don’t want that stuff going down my rifle barrels.
Granular fillers work very differently but are still no cure-all. The best is a natural one: farina, a semolina wheat product used for hot “creamed wheat” cereals. Relatively fine grains and a rough texture help the granules grip each other under pressure, making it easier to compress. Still, it is not an easy chore to consistently load and compress farina to give full confidence that filler and fuel won’t mix. It also needs to fill the case after compression, adding mass that requires charge weight adjustments. It’s not worth the trouble; I use farina for where it shines: case-forming blanks. Any time you need to neck up a cartridge, say the .30-06 to .338-06, the filler-charged case-forming blank will do it with consistency and a fraction of the defects an expander ball can induce.
I am content with foregoing fillers and enjoying the excellent selection of today’s propellants that are engineered for reduced charges, such as Accurate 5744 and Hodgdon Trail Boss.