Here are three responses from my friend Mic McPherson when we got to talking about using filler materials, such as dacron. I thought that you would want to see it.
ADD-ON: I asked him about COW and CM fillers too, pointing out the danger of decreasing the effective case capacity, relative to the given propellant charge. Here's what he indicated:. . . The use of any synthetic filler such as Dacron is only asking for a destroyed gun. Just a matter of time before the chamber is either ringed or the gun is completely destroyed. THIS IS A MONUMENTALLY DANGEROUS PRACTICE.
I once wrote of this problem in a PS (Precision Shooting Magazine) article. Within one week of that piece's being published, I had three calls from experts who "had been doing that for decades... and never had a problem." Within three weeks thereafter, two of those guys called me back to apologize for they had just ruined a gun by ringing the chamber. A ringed chamber is exactly one infinitesimal step from a failed gun -- the classic detonation.
Thanks, Mic
Now, most folks have opinions, but Mic is the fellow who wrote the algorithms for the popular QuickLOAD software. He really knows what he is talking about, when it comes to internal ballistics. He's a very private fellow, so please don't bother him by e-mail except to arrange for him to do work on your lever action rifles. His essential "fix" is to use florist foam for a filler, which is cheap and readily available. You'll get LOTS more by reading his articles and book. That is the best way to obtain, and make use of, his input.Organic fillers are monumentally less dangerous. However, no one can predict the ballistic consequences -- the filler might very well decrease chamber pressure! Why? Because it might promote primer induced bullet movement. However, any such filler has some percentage of rather abrasive inclusions. The only well proven safe filler is florist's foam -- it is cellulose based and crushes to produce dust that is not abrasive. Using anything else is just foolish.
Why is Dacron and such so dangerous? Because it compresses to almost no volume when the primer blast hammers into it. Then is melts. Both processes absorb a huge amount of heat from the primer blast, leaving less to ignite propellant. Also, the entire charge is then located at the bullet end and. Inadequate ignition is responsible for all detonations and the Krupp commission proved in its 1888 tests that any cylindrical cartridge with a partial case filling charge located at either end of the chamber and then ignited will always generate a standing wave -- whether the peak of this standing wave grows narrow enough so that the force at the center of the peak exceeds the strength of the chamber depends upon an entire hoist of variables but the potential is always present. So, synthetic fillers are doubly dangerous and it amazes me that folks do not know this!
Mic
Thanks, Zeek