duplex loading WC 870

[wmitty]

This powder is available at a rather attractive price from Jeff Bartlett ($40/8lb): and I suspect I'm not the first to try and make practical use of it by placing a small charge of a faster burning powder next to the primer and filling the remainder of the case with the 20 mm propellant. I have access to a chronograph and .0001" micrometer to detect case head expansion; and am cheap in that I don't like ruining brass due to excessive pressures opening primer pockets. I intend to begin loading with H 4198 starting with a 1.0 gr kicker and increasing in one grain increments, while filling the remainder of the case to the base of the 311407 Mod (.30-06) seated into the lands. I'll load three rds at each charge wt and check the velocity and case head expansion.

My question is, will the velocity range become less as the kicker charge wt is increased? Will the increase in pressure be linear in relation to the increasing charge wt of the kicker; or will the decrease in the volume (mass) of the 870 throw in an unforeseen variable?

[aspangler]

Just use data for A8700. It is almost identical.

[Jailer]

Velocity will increase with an increasing kicker charge. I've not tried duplex loads in 30-06 but my 45-70 loves 5gr of H4198, 48.5gr WC867 compressed with a 405gr boolit.

I can't stress enough that the powder column must be compressed enough to keep the powder from moving and mixing.

I would be very surprised if you could get enough 870 in a 30-06 case to cause excess pressure. You just have to make sure you have 100% case volume fill to keep it from moving and mixing with the kicker charge.

Did I mention you don't want the powder charge to move at all????

[wmitty]

I meant to ask if the standard deviation of the velocity would become smaller as the charge wt of the 4198 was increased. I had hoped it might. I also was hoping the increase in pressure would not suddenly spike for a small increase in charge wt.

Jailer: I will take your advice and make sure to compress the powder column to prevent mixing.

[45 2.1]

I meant to ask if the standard deviation of the velocity would become smaller as the charge wt of the 4198 was increased. I had hoped it might. I also was hoping the increase in pressure would not suddenly spike for a small increase in charge wt.
Jailer: I will take your advice and make sure to compress the powder column to prevent mixing.

To a degree...... your boolit weight is under what really needs to be used to accomplish that well. The very slow powders with a booster charge in this cartridge respond better when you're above 210 gr. boolit weight (it varies with cartridge) or so. You will find the booster charge will give poorer accuracy and increasing recoil, above what you experienced before, much above 7.5 gr. of your booster powder you've chosen (it will be apparent and a warning to go not too much further in booster charge weight). As far as powder mixing, as long as your in the shoulder of the case enough, you should have little problem on that. As a test, take a plastic tube about the size of the cartridge and place a normal booster charge, then your slow powder up to about 3/8" of the end, cap the tube and shake........then tell us how much is mixed........................

[Jailer]

Heed the advice posted by 45 2.1 he knows much more about this than I do. My experience is very limited with duplex loads and I only shared what I've found through my experimentation.

[wmitty]

45 2.1

Thanks for the input; I was wondering where the limit as far as weight of the booster might be. In you opinion, does the loss of accuracy come from erratic velocities or pressure exceeding the alloy hardness or something else I don't recognize? Is there a better choice of powder to use as the booster?

[45 2.1]

45 2.1 Thanks for the input; I was wondering where the limit as far as weight of the booster might be. In you opinion, does the loss of accuracy come from erratic velocities or pressure exceeding the alloy hardness or something else I don't recognize? Is there a better choice of powder to use as the booster?

The problem is dealing with a slower burning powder meant to used in a much larger combustion chamber. It takes a certain amount of powder to ignite and burn itself at it's intended pressure. In use, the 30-06 case really doesn't have enough room to do that with lighter boolits (even heavy ones at times) and less barrel friction......... so, you're helping it to ignite itself better with a booster. That is a balancing act in which just how much fuel (booster) do you use to start the fire so it (the slow powder) burns consistently. Accuracy comes from getting the boolit straight down the bore every time with a consistent equal push. The question about booster speed is more involved, so I'm not going to answer that now. I can answer in a general way like this, but an in depth answer won't make a whole lot of sense to you until you have quite a bit more experience with it so you can see the problems involved.

[wmitty]

45 2.1

Thanks for your comments; perhaps the .375 H & H would be a better candidate for this experiment. I have a 350 grain plainbase Lyman I have been paper patching in a Rem 700 in this chambering.

[Elkins45]

So is there any problem with using WC 870 without a booster charge? I have some and I have figured out that a 308 case will be filled to the bottom of the shoulder with 45 grains of it.

Is there any danger in shooting this load with a Lyman 311299 (195 grains as checked and lubed) on top?

[45 2.1]

So is there any problem with using WC 870 without a booster charge? I have some and I have figured out that a 308 case will be filled to the bottom of the shoulder with 45 grains of it.

Is there any danger in shooting this load with a Lyman 311299 (195 grains as checked and lubed) on top?

In a modern proofed for caliber firearm....no....other than a dirty bore with straight WC 870 if the case is full to the boolit base. Broaching the subject of how to use boosters on an open board assumes that people follow instructions.....and most do not. Amounts and types change with caliber and boolit weight so you have to realize something of what you're doing and how the load reacts.