Bob:

Good responses from Tinker and Curl. Use the Dacron. Always err on the side of too much, rather than too little.

I've used Dacron in double rifles for 20 years and have heard warnings of dire consequences for doing so from theorists (rather than double rifle shooters) the entire time. Whenever damage is reported, it virtually always turns out that a tiny little tuft was pushed down on top of the powder instead of filling the remaining air space up to the point of compression. I've never once heard of an instance where damage (such as a ringed chamber) occurred when dacron was used properly. Because of the necessity of fillers in the large flanged Cordite rounds and BPEs, dacron has been used in this role for decades now, and the does and don'ts are long since settled.

In the Cordite rounds, Kynoch uses their foam wads in virtually all of their factory ammunition over .375 caliber, and I've never had a report of a hiccup. However, Ross Seyfried HAS reported ringed chambers from the use of multiple foam wads in Nitro for Black applications. Again though, I've never had a single credible report regarding dacron in NfB loads, when used as you describe (12-14 grains in a .450 BPE), and it's been done that way for a long, long time.