velocity difference with fill

[Nora]

I'd recently tried adding Polly Fluff pillow stuffing as a fill to my 54R load with some promising results. In working up loads with it I thought it would be fun to try different amounts to see how they may effect the pattern size in my Carcano carbine. I crono'd the rounds and found a bigger surprise in the velocities. All other things being the same It showed that the more fill used, reduced the fps, and seemed to also have an effect on the consistency in speed. This will definitely need further work, as I don't consider 12 rds each target to be fact but is interesting just the same. I didn't position the powder for any of the rounds, it was just loaded and fired.
Any way, here's how it played out.

Rifle used: M91 Cavalry Carbine with 17.5" barrel
All thing constant: 6.5x52 Carcano. Prvi brass, Rem 9 1/2 primer. 10 gr Unique, topped with a 140 gr 266469 gc'd (Hornady) and lubed with LLA.
Polly measured in grains

FPS............High.........Low..........Av....... ... SD
No Fill........1364........1324.........1347...... 40.15
.5 Fill.........1347........1322.........1335...... 24.74
1 Fill..........1336........1305.........1317...... 30.72

[Harry O]

My experience with fill is that the weight is more important than the amount. I started with "Cream of Wheat" way back when. I did not have a chrono back then, but filling a 32-20 case to the top (about 2/3 to 3/4 of it filler) increased the report and the recoil. I have no doubt that it also raised the speed and pressure.

I tried a few other things, but in recent years, I have used the tiny plastic beads that are used for shot fill. It does improve the consistency and does not raise the speed (and I assume, does not raise the pressure). However, it is still extra work and messy besides.

[243winxb]

Kapok was the fill used many years ago, my testing in a 1903 showed accuracy was just as good not using a fill. Iron sights , groups ran around 3" @100 yards, that was with the new barrel installed. Fill can be very dangerous depending on the type used.

[Larry Gibson]

Nora

While I always recommend dacron for a filler you've just found out why I do not recommend it with the faster powders such as Unique. It is not necessary with such powders especially when using a medium to heavy weight bullet for caliber as you are.

Larry Gibson