Best Filler Material For 45-70

I have for many, many years found dacron (polyester fill) to be the best “filler". I use a filler only when appropriate. Many think I always use a filler with every powder....I DO NOT!!!! The use of the filler can cause problems if not used correctly and when appropriate. If the powder is not correct for the bullet/cartridge combination then the filler is not going to make it “right". Many want to use a specific powder for a cartridge because the powder is “cheap” or because “they have a lot of it". There are lots of powders that are not only poor choices to use but that can be dangerous if used in an inappropriate bullet/cartridge combination. Do yourself a favor if you are wanting to use an inappropriate powder (usually “no data” available is an indication the powder might be inappropriate) and get an appropriate powder. You will save yourself a lot of frustration. The use of the dacron filler only makes an appropriate powder perform better. The dacron filler will not make a silk purse out of a sow's ear.

I don't use the dacron filler or a wad with the fast to medium burning “fast” pistol /shotgun type powders. I find one of these fast burning powders that is fast enough to ignite and burn efficiently at the velocity I want and avoid using a filler with them. I almost always use the dacron filler in rifle cases with the slower “fast” burning powders (4227, 4759, 5744, 4198, etc. with lighter medium weight bullets for the cartridge; i.e. 140 - 165 gr bullets in .30/.31 cals of 30-30 through '06 case capacity), the medium burning powders (RL7, 3031, 4895, etc.) up through the slow burning powders (RL19, AA4350, H4831SC, RL22, 3100, etc.) that give around 80% or less loading density under medium to heavy weight bullets for the cartridge; i.e. 170 - 220+ gr bullets in .30/.31 cals. Those examples are for the .30/.31 cals but the same guidance applies to other calibers. The dacron filler is used only between the powder and base of the bullet.

The “dacron” is polyester fill as commonly found in pillows and toys. It also comes in sheets called “batting”. It can be obtained very reasonably at most any fabric store.

The dacron batting comes in various thicknesses. I prefer that which is about 5/8” thick. My wife recently bought me 10 yards which will give many, many thousands of cast bullet loads. With this current batch of batting I cut it initially across the width into strips about 3/4” wide. I then “eyeball” cut 1/2” wide chunks which is close to 3/4 gr.

A smaller chunk is cut for 1/2 gr and larger for a larger amount. I've cut some chunks that weight 1/2, 3/4, 1, 1 1/4 and 1 1/2 grs and have them in a “snack” baggie stuck on a poster board above my loading bench for quick reference when I need to cut new chunks. The batting will run thin and thick throughout the sheet so I again just “eyeball it” based on the thickness of the batting when cutting the chunks.

Pretty extensive tests have demonstrated that the weight of the filler does not have to be exact, only close. What is important is that there is enough so that it “fills” the space between powder and bullet. A little too much hurts nothing but too little poses problems. That's why I have the different size “chunks” so I can use the right size for the case capacity I am filling. For example; with most medium burning powders (3031, 4895, 4064) in and '06 to function an M1 a 3/4 gr dacron filler is about right. With slower powders that give a higher loading density like 4831 a 1/2 gr filler is about right.

I use a section of .22 cal cleaning rod in cartridges of .30 - .375 cal to push the Dacron chunk inside the case just so it is all in. The 6 to 10” section gives plenty to hold onto and sufficient “feel". Merely hold the chunk of dacron over the case mouth and shove it in with the rod. Sometimes it takes a couple three pokes to ensure all is inside the case mouth. I poke the chunks in until all the dacron is at the bottom of the neck or at least all in the case. It doesn't matter exactly where just so long as you don't tamp it down on the powder as a wad and leaved a space between the base of the bullet and the dacron.

What you want to do is push it in to let the base of the bullet finish pushing it down and adding any compression against the powder. Thus I do not push it down on the powder but let the bullet do that when the bullet is seated. Using the right size chunk of dacron this method then provides a “filler” in the air space between the powder and base of the bullet.

A small length of coat hanger works for the .22-7mm cartridges and an unsharpened pencil works well for .45 cals. With the charged cases in a loading block I simply hold the chunk of dacron over the case mouth and push it in with the rod. It is quite easy and a lot of “precision is not required, just get the dacron into the case and let the bullet finish pushing it down.

With regards to the OP's question using a 350 gr cast bullet over 4227 powder and keeping the loads down to “trapdoor” levels I would suspect a Dacron filler would be beneficial. However, that bullet weight with that powder in the 45-70 cartridge is what I consider “borderline” for the use of a Dacron filler. A lot depends on what the OP considers “trapdoor” levels. If he is referring to velocity level of 1400 fps or less then the Dacron filler will probably be beneficial. If the OP refers to psi levels then enough 4227 may be used so that the Dacron filler isn't beneficial (that isn't saying it will be harmful BTW). Only way to really know is to try it both ways; work up a load to the expected “trapdoor” level with both the Dacron filler and without.

LMG