Smokeless powder in black powder cartridges (such as the 45-70 and the 38-55) leaves a lot of air space and can produce a larger extreme spread in velocity due to poweder position. Some sort of filler can help solve this problem. I was reading about some interesting research done by Charlie Dell. Apparently, he could ring a chamber at will with certain normal loads and in certain cartridges by simply pointing the rifle straight up and pulling the trigger. The phenomenon seemed to be caused by the powder all being completely back against the primer and perfectly flat across the base, since it was pointed straight up. The result was a pressure wave that ringed the chamber around where the base of the bullet was. Some have reported a ring at the same location when certain types of filler were used, particularly with straight walled cartridges.

It is hard to know for sure without testing, which I do not plan to do, but it may be the case that if a filler both kept the powder perfectly back against the primer AND was fluffy enough to permit a shock wave to hit the base of the bullet, that the same ring could be produced with the rifle in a normal horizontal shooting position. Some have suggested to leave a space between the base of the filler and the powder so that the powder sloped when being fired.

Here’s my thinking: Cotton, dacron and kapok can both keep the powder nicely and flatly against the primer, and be fluffy enough to possibly permit a shock wave to ring the chamber exactly as might happen if no filler was used at all but the gun pointed straight up. Polyfiller does not do both. It holds the powder pack perfectly, but I think the polyfill dampens out the shock wave as it compresses, which is why it seems to be safe (though I’ve never used it). Toilet paper does neither, at least not the way I’ve used it for thousands of rounds. It sort of holds the powder back nicely, but not perfectly, as some powder can easily work forward a bit into the butt ends of the loosely rolled and folded TP.

I could not see how adding a loose, low density filler into the load could increase pressure in such a way as to ring a chamber, but Charlie Dell’s work makes sense to me and maybe turned on a light.

Bottom Line: With certain powders and certain cartridges, it may be possible to ring the chamber by either using no filler and pointing the gun straight up or by using certain types of filler, re-creating the same powder position in a horizontal orientation. The bottom line is to avoid any type of filler that might recreate both the powder position and the shock wave that pointing the gun straight up could cause.

Conclusion: It seems to me that toilet paper loosely rolled and folded is safe, since it does not perfectly position the powder against the rear primer. It also seems to me that polyfill would be safe because although it does perfectly position the powder against the primer, it compresses and dampens out the shock wave. The danger may be in cotton, kapok and dacron with certain loads. I know that Sherman Bell has done strain gauge testing at the case neck with all these kinds of filler and found that the pressure was entirely within the safe zone, but who knows how it would work with different powders, especially faster ones. I would think that slower powders will be less likely to create the nice shock wave.

Personal Recommendation: After reading about Charlie Dell’s work and thinking on this, I’m inclined to think that we should not use cotton, dacron, or kapok as filler. If filler is required, I’m feeling that toilet paper, loosely rolled and folded or polyfill should be fine. I’ve used toilet paper in a few thousand rounds and in different calibers such as 38-55, 45-90, 45-70 and 44-40 with never the faintest hint of a problem. I have been using cotton filler more recently, but after reading about what Charlie Dell found out, I’m swearing off cotton filler. I admit I’m erring on the side of caution, and a lot of fellows use this with no problem at all, but I think Charlie Dell’s findings make a lot of sense, at least to me. No more cotton filler for me; it positions the powder too perfectly against the back of the case to risk re-creating the effects of a non-filler, vertical shot.

Alternative: With 5744, I have found a Winchester Magnum primer gives me the same velocity in my 38-55, but a lower extreme spread. So it makes a filler unnecessary.