Why do I need faster powders for cast boolits?

[famdoc2892]

I have hand loads worked up for 150-gr j-word bullets using IMR-4895 in all 3 calibers, and I was surprised when all the powders listed in the Lyman #49 manual for my 170-gr 311291 CBs are faster on the burn rate charts than the 4895.

Can anybody who knows their internal ballistics explain to me why a heavier, slower boolit needs a faster powder? I predicted a slower powder...

[felix]

A boolit moves away from the chamber quicker than a condom, and the powder burn needs to keep up to keep the pressure curve somewhat equal, during the first half of the burn anyway. ... felix

[paul h]

You didn't mention what calibers you are loading for. I'm going to assume that the cast bullet loads are at lower velocity than the jacketed bullet loads. What I've found is that slow powders when loaded at lower pressures generally don't burn that consistantly, which generally produces poor accuracy. The get a more consistant burn, going to a faster powder, and a smaller charge of it, gets the powder to burn at a pressure where it will burn more effectively.

For many centerfire rifles, cast bullets are loaded to velocities that are far less than the rifles are capable of achieving, or another way to say that is the case capacity is larger than needed for the job we ask cast bullets to perform. When downloading a case, results tend to be better when using a faster powder.

[famdoc2892]

Sorry, when I re-worded my question, I eliminated the detail that I'm loading for 30-06, 308 and 30-30! Hope that helps.

[Bret4207]

You can use the slower powders, while keeping SEE in mind, but it requires some extra work and possibly (likely?) the use of fillers to help with the burn rate and pressure curve. Faster powders are just easier to work with and you usually need less of the powder too which helps economically.

[famdoc2892]

Thanks, Bret, but SEE? Help me out on that one.

[sav300]

Secondary Explosion Effect or a explosion not a controlled burn.

[excess650]

4895 should be an excellent powder for those cartridges if using "heavy for caliber" boolits at velocities towards the upper end of what the rifling twist will accomodate. With an excellent boolit fit, good alloy for the application, and a good lube you should be able to go full throttle in the 30-30 (assuming 12" twist).

I'm working with 4895 in the 30-06 and 7.5x55 under the 205gr 311299. The 30-06 is 1-10" twist and 7.5x55 1-10.6"(?) so should be capable of handling a bit more velocity with all else being equal.

4895 loaded in the upper 1/3 of charges listed for similar weight jacketed should be OK. Slower powders like 4350, 4831, or even harder to ignite ball powders, not as friendly.

SEE is a term relating to a secondary explosion. Slow powders (relative term)seem to need higher loading densities to prevent SEE. The easy way to think of SEE is to envision the boolit moving forward from primer blast and stopping to become an obstruction. The powder has not properly ignited and then does suddenly, causing the secondary explosion with a plugged barrel. This may not be exact, but gives you an idea.

[famdoc2892]

I appreciate the explanation. I have leaned away from fast powders in the past because one of my primary goals in hand loading is recoil reduction. I understand the economy, but also suspect that faster powders are more temperature- and position-sensitive. For the 30-06/308 cases, where do you start seeing these problems crop up using faster and faster powders?

[excess650]

The 308 and 30-30 cases will be more forgiving in regards to powder position due to their smaller capacity than the 30-06. I've had excellent results in the 30-06 with AA5744 and H322 in addition to my higher vleocity loads with 4895. The 30-30 and 308 will also give excellent results with the same powders, and add 2400 into the mix as well. I've not had as good results with flake powders like Unique and Red Dot, but haven't concentrated on them because I was working towards higher velocity.

Red Dot and Unique are bulky and easily ignited, so shouldn't be particularly position sensitive(or temperature).

In that I try to keep my loading simple, I don't use dacron filler, but do elevate the muzzle prior to shooting.

[10 Spot Terminator]

You can use slower powders but it is tricky in that pressure when firing is the key issue to control with casts and near impossible to calculate on your own. There is a formula to figure max pressure allowed for any given bullet based on the actual BHN rating of the alloy used. This is the BHN # ( say 15 as in Lyman #2 alloy ) times 1422 to get max pressure in PSI ( not CUP ). 15x1422 = 21330 PSI. This is part of the rub as CUP is the more dominant listing given in published reload data and unless the load research was done specifically with casts the charge tables start out too high to be of any use to you . There are those who have endeavored to try this on their own with some good results but ran the risk of squibs or turning their barrels into a lead melting tube which some have shared these expieriences. It would be nice to have access to a gun lab with a pressure barrel for all the calibres out there to run casts through but the $$$$$ just isnt there for the research and lead is going under attack more and more each day to help complicate things even further.

10 Spot

[Larry Gibson]

Can anybody who knows their internal ballistics explain to me why a heavier, slower boolit needs a faster powder? I predicted a slower powder...

Because each powder has a specific minimum psi where it burns efficiently. At the much slower velocities most cast bullets are shot the pressures are much lower than the pressures with jacketed bullets. Thus, faster burning powders are used that will burn efficiently at those lower psi's. Most cast bullet rifle cartridge loads with GC'd bullets run in the 18,000 - 30,000 psi range with the larger % of those in the 20 - 25,000 psi range. Faster, more easily igniteable powders are needed. One can use a heavy for cartridge cast bullet and slower powders like 4895 for excellent loads in many cartridges. Even the slow burners can be used in some circumstance.

However, best powders for most cast bullet shooters in rifles is the faster burning powders from 5744 or 4198 on down.

Larry Gibson

[geargnasher]

You don't, if you shoot your cast boolits at jacketed bullet velocities. But if you shoot your cast boolits at milder pressures and velocities, you need to match the burn rate to the pressure.

Due to the nature of nitrocellulose and nitroglycerine powders, there are some trade-offs. It would be nice to be able to shoot heavy cast boolits at less than 2K fps in an '06 with a powder having a burn rate of 4350 and the ability to completely burn at 25K PSI. But that isn't going to happen, unfortunately, because the retardants that slow the powder to that sort of burn rate need much more pressure than that to fully and consistently combust. So the compromise is to go with a less-retarded powder that builds pressure faster, but burns better with less pressure overall.

Gear

[Bret4207]

You can use slower powders but it is tricky in that pressure when firing is the key issue to control with casts and near impossible to calculate on your own. There is a formula to figure max pressure allowed for any given bullet based on the actual BHN rating of the alloy used. This is the BHN # ( say 15 as in Lyman #2 alloy ) times 1422 to get max pressure in PSI ( not CUP ). 15x1422 = 21330 PSI. This is part of the rub as CUP is the more dominant listing given in published reload data and unless the load research was done specifically with casts the charge tables start out too high to be of any use to you . There are those who have endeavored to try this on their own with some good results but ran the risk of squibs or turning their barrels into a lead melting tube which some have shared these expieriences. It would be nice to have access to a gun lab with a pressure barrel for all the calibres out there to run casts through but the $$$$$ just isnt there for the research and lead is going under attack more and more each day to help complicate things even further.

10 Spot

I mean no offense, but go back and re-read what the originator of that formula says. All that does is give you a probable point for the boolit obturating. IME that formula is just another over sold answer to a problem that isn't as much of a problem as people think.

[Char-Gar]

My understanding of the issue goes like this; Lead alloy bullets being much softer than jacketed bullets, will deform much easier when the pressure smacks them on the butt. To much pressure to fast, will cause the bullets to "accordian" and accuracy will suffer.

Therefore, With loads that produce pressure which produce velocites (talking 30-30 and 30-06 here) at or below 1.8K fps, faster powders are the ticket. When the pressures goes much above that, you get to quick a blow to the base with bad results.

So, if I want to go much about 1.8 to 1.9K fps, I choose a slower medium power which will deliver a slower shove to the bullet. I am talking powders in the 3031, 4895, Varget, H335 etc.

If want to go with really slow powders like 4350, 4831 and even slower like the ball machine gun powders, you need a case full of the stuff to avoid the possibility of SEE/Kaboom. You can get great cast bullet accuracy in the 30-06 (not so much the 30-30) with these slow powders, but expect to find some unburned powder in your barrel.

That is the way my somewhat simple mind understands this stuff.

[leadman]

Also if you want a lower recoil load use the faster powders. With the slower powder part of the powder that has not yet burned becomes added weight the charge is moving so there is more recoil.

[Jeffrey]

Slug your bore with a lubed pure lead boolit then with a jacketed bullet. (Don't really slug your bore with a bullet). See which one moves down the barrell easier. The higher resistance bullet is more resistant to 'getting out of the way' of the powder burning, thus the need for 'slower burning' powder.

[canyon-ghost]

Gear, it only took you one small paragraph to shine a light on it :

Why do I need faster powders for cast boolits?

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You don't, if you shoot your cast boolits at jacketed bullet velocities. But if you shoot your cast boolits at milder pressures and velocities, you need to match the burn rate to the pressure.

[famdoc2892]

As usual, you've given the kind of answers that point out the basic concepts, not just the "cookbook" sort of fluff. Thanks for your insight, and keep up the good work!