Rules for altering powder charge

[Marturios]

I have a noob question about powder charges. I decided to turn some of my cast bullets into hollow points using a case trimmer method I've seen others use. I have already worked up a load for the bullets as-cast that performs well, but I'm wondering how/if I need to alter my recipe for the drilled boolit. Are there some basic rules that would apply for deciding how to alter the powder charge?


I heard from one person that I would need to increase the charge for the lighter round, but this doesn't seem quite right. Obviously, drilling the hollow point will lighten the boolit, but it will not change the external dimensions of the boolit, the seat depth, or (accordingly) the case capacity. My understanding is that powder charge is a function of pressure, which is in turn determined by friction, inertia (a result of the mass of the boolit itself), and case capacity. Lighter bullets do tend to have higher powder charges, but I understood this to be primarily because, all things being equal, heavier bullets seated to comparable depths take up more of the internal volume of the cartridge, and accordingly, the same powder charge with a heavier bullet might compress the load. Also, all things being equal, a heavier bullet has more inertia and slower acceleration than a lighter bullet, and accordingly, will produce more pressure given the same amount of powder.


Given that the material and the case capacity will not change, I don't think there will be any change in pressure due to friction or compression, leaving only the decrease in the mass of the boolit, and the lower pressure created "moving" it. I think I could increase the powder charge without spiking the pressures, but is it necessary? And, on a hot load, wouldn't this run the risk of compressing the load since the case capacity will not have changed?

Any advice or input is welcome. Also, feel free to correct me if I'm making some false assumptions in the above.

[unique]

My suggestion is to shoot it with the previous powder charge which will be safe assuming your previous load was safe and you are seating to same depth. Note that seating depth can have a major effect on pressure. If you are reaming a very large cavity then you can weigh the reamed bullet and find corresponding load in reloading book such as lyman cast book.

Friction will not be a factor.

All your questions are good so feel free to ask away.

[plainsman456]

How much weight did you remove?
Might just shoot some with the load you already worked up and if not to your rifle's liking change it up.
I have not had any problems doing this.

[Marturios]

I'm not sure how much weight will be removed yet. I still need to drill some and weigh them. They are approximately 124gr 9mm from the mold. My guess is that after drilling I will be looking at 105-110 grain, but that's just a guess.

I'm glad to see you guys confirming my gut instinct of starting with the load I already have. I'm nowhere near compressed at this point, but I see no need to back the charge down, and I hesitate to move it up since I'd rather start on the light side anyway.

[paul h]

I think you'll find the round will work just fine with the previous load. Unless you really hogged out the bullet, you probably only removed 5-10 gr.

Assuming an autoloading pistol, if your load was on the light side you might find the pistol won't function with the reduced recoil of the lightened bullet and at that point I'd consider adding a few tenths of a grain of powder to get the load to function the pistol.

[Outpost75]

Drilling 10 grains out of a 125-grain 9mm is ALOT.

I had an Accurate 36-125T FN mold modified to drop 114 grains and the cavity is HUGE.
I load it in .380 ACP and shoot the same charge of Bullseye with both bullets

Does yours look anything like this?

155288

[Marturios]

Outpost, thanks for the visual reference. I probably won't be dropping that much after all. Somewhere between 5 and 10 grains, probably.

What kind of alloy are you using, and have you tested the expansion?

[RogerDat]

Heavier bullet has more inertia, pressure builds until the projectile moves and increases the space causing a reduction in the rate that pressure increases. Also the burn rate for a given powder is generally faster the greater the pressure so the heavier bullet during the initial ignition increases the burn rate more than a lighter bullet.

If you look in a manual for a caliber and look at the same powder for each bullet weight you will see powder load for the same powder goes down as weight goes up. This means you can generally use the load data for a heavier bullet to safely load a slightly lighter bullet of the same caliber. As long as you don't go so far down you lack the pressure to send the bullet out of the barrel.

Weigh the final bullet. Use load data for a powder for that weight or a slightly heavier bullet in the same caliber.

[scottfire1957]

Simply, there are no "rules." There is the information provided in reloading manuals, and some "guidlines."

Figure out what your hollowpoints weigh, and go from there. No point in speculating what you might need for something you have not figured out you need.

I.E. Your bullets, as cast, should be ~125gr. If you only bore out 2-3gr, making your bullet lighter by only 2-3, why would you not just use 125gr load data?

Then, if your drill takes out ~10gr from a 125, there are a lot of 115gr loads for 9mm.

Figure what you have, then ask the question, or refer to a few reloading manuals.

[Marturios]

Scottfire, no need to be grumpy.

I have the information from reloading manuals. If that's what I wanted, then I wouldn't have bothered to ask you fine gentlemen for advice. Also, "rules" or "guidelines" or whatever you want to call them are by their nature general, and can be given without immediate reference to specifics. They are also, due to that fact, useful in a variety of situations. I could, of course, ask you for an opinion on this specific bullet, with this specific change in weight, but I'm looking for information that would be useful in this situation and in any other similar situation where I might decide to hollow out a bullet. That's why I asked for rules, specifically, and not just for a powder charge for this round.

Thanks for your input, but please, do not see it as your responsibility to lecture me simply because you do not appreciate the value of the question as it was asked.

[Outpost75]

Outpost, thanks for the visual reference. I probably won't be dropping that much after all. Somewhere between 5 and 10 grains, probably. What kind of alloy are you using, and have you tested the expansion?

For pistol bullets up to 1300 fps I use 1:30 tin lead, which expands well down to 800 fps if the cavity geometry is correct.

Above 1300 fps up to about 1800 fps alloy of 12-14 BHN works well.

155298

[scottfire1957]

Scottfire, no need to be grumpy.

I have the information from reloading manuals. If that's what I wanted, then I wouldn't have bothered to ask you fine gentlemen for advice. Also, "rules" or "guidelines" or whatever you want to call them are by their nature general, and can be given without immediate reference to specifics. They are also, due to that fact, useful in a variety of situations. I could, of course, ask you for an opinion on this specific bullet, with this specific change in weight, but I'm looking for information that would be useful in this situation and in any other similar situation where I might decide to hollow out a bullet. That's why I asked for rules, specifically, and not just for a powder charge for this round.

Thanks for your input, but please, do not see it as your responsibility to lecture me simply because you do not appreciate the value of the question as it was asked.

.

I'm not grumpy at all. You asked for information on a bullet of which you have not all the specifics. You know it's 9mm, but you don't know the final weight.

All I suggested was get your data before you asked.

Edit: Everything you asked, has been asked before, and answered. Would you like me to search it for you? I'm willing, and able. Be happy to do it for ya!

Edit: I now realize you wanted me to do the research before I answered. I apologize.

[Marturios]

No Scott, I did not ask about a bullet. I asked about general principles, or rules.

It is true that I hope to use that information to develop a load for a specific bullet in the near future, but I did not initially mention the bullet for a reason. I appreciate your suggestion, but it's not helpful. If I wanted to ask the question you think I should have, I would have asked it. But I asked a different, more general, question.

[Marturios]

Scottfire, if you would like to provide a link to where this has been discussed that would be appreciated. It's quite possible I missed it when I was searching.

Of course, it is not true to say that I wanted you to do any research before answering. I did not want you to do anything. But if you have some research and you would be willing to provide it, I'm more than happy to thank you for your efforts and give it a look.

[scottfire1957]

They are approximately 124gr 9mm from the mold. My guess is that after drilling I will be looking at 105-110 grain, but that's just a guess.

That is a quote.

Edit: As you stated, a guess. Obtain more specific data, then you will get better answers.

[Marturios]

Scottfire, I have already received a number of great answers. Again, you do not seem to understand what I am looking for. No matter.

[Marturios]

Outpost, those look great. Again, thank you for providing the picture.

[scottfire1957]

Yes, you have. You chose to challenge me. I have no idea why, my advice is solid.

Figure your final bullet weight, use a reloading manual. Good luck.

[vzerone]

I would just like to add an analogy. Say your are loading jacketed for a rifle that limits the OAL of the cartridge because of the magazine. A good example would be an AR15 in 5.56/223. Say that you had been using 63 grain semi point Sierras and then you change the bullet to a lighter one like a 45 grain of whatever brand. The 45 grain will be shorter and you won't have to load it as deep into the case. Then the load you had used for the 63 grain bullet would be safe with the lighter bullet. In fact it may not get the lighter bullet up to the speed it could really do.

You are really only changing the bullet weight by hollow pointing it, not the length of the bullet. You OAL won't be changing. The load for the solid bullet should be entirely safe with the same bullet hollow pointed.

[Marturios]

Scott, I did not challenge you. I politely asked you to refrain from complaining because you didn't like my question. You are free to move on at any time. A while ago would have been nice.

[scottfire1957]

I would just like to add an analogy. Say your are loading jacketed for a rifle that limits the OAL of the cartridge because of the magazine. A good example would be an AR15 in 5.56/223. Say that you had been using 63 grain semi point Sierras and then you change the bullet to a lighter one like a 45 grain of whatever brand. The 45 grain will be shorter and you won't have to load it as deep into the case. Then the load you had used for the 63 grain bullet would be safe with the lighter bullet. In fact it may not get the lighter bullet up to the speed it could really do.

You are really only changing the bullet weight by hollow pointing it, not the length of the bullet. You OAL won't be changing. The load for the solid bullet should be entirely safe with the same bullet hollow pointed.

I see your point, however original poster's bullet length shouldn't change, unless he drills really deep. Just the weight will change, but we don't know how much.

[scottfire1957]

Scott, I did not challenge you. I politely asked you to refrain from complaining because you didn't like my question. You are free to move on at any time. A while ago would have been nice.

Show me where I was "complaining" and I will apologize. Seriously.

[Marturios]

Scott, this has grown old. Seriously, it's time to move on.

[scottfire1957]

Scott, this has grown old. Seriously, it's time to move on.


Yes, it has. Get your data, use a manual. It's that easy. Good luck. I wish you well.

[Marturios]

Wish you well, too. I hope you have a good rest of your night.

[leadman]

I read your original posting and the rest and would like to add my comments. You stated your load is nowhere near compressed. I take this to mean you are not compressing the powder? If so I would like to state that a load does not need to be compressed to be an excessive load. Some manuals will code a compressed load in some fashion.
Also some of the slower handgun powder can not be reduced by much, if at all from the manual data. Usually these are the W296/ H110 normally loaded in the magnum cartridges. These same powders may not perform well or safely if bullet weight is reduced.
With a load within parameters listed in a manual can be used with a lighter bullet close to the original bullet weight. In your case the reduction in weight from you drilling a small hollow point in the boolit will have little effect. About the same effect will be caused by a change of alloy sometimes. A heavier bullet should not be used in place of the lighter bullet listed in a manual.
Most of the bullet and powder companies have load data on the internet and most will also help you out if you give them a call. They usually have more data than what is on the website.
It is good that you asked your questions here and want to load safely.

[RogerDat]

good point on some powder do very poorly when used in reduced loads. Seem to recall 2400 might be one of those. If you want to load 44 mag to 44 special for a lighter load the larger case volume can give problems at lower end 44 special loads. Or something along those lines.

Hodgdon during a phone call told me (and I have seen it published) that for cast 60% of max load is a generally safe starting load. Might not be as accurate as you would expect but safe and work as a starting point. That is a guideline or general rule of thumb that I have come across. Can't say I have applied it often as I generally use actual load data so YMMV but that is sort of what you asked for.

Go closest bullet (weight and profile/length) listed in manual or manufacture load data that is not lighter than yours, work up from .6 x max load of that bullet watching for pressure signs etc.

[Marturios]

Excellent feedback, guys. That's why I came here.

[.45Cole]

I use the 454-270-SAA from Miha and the diff between solid and the Penta HP is maybe 10 grains. That is a lot of lead, and I still use the same load. The solids are probable cruising a little faster, but for a pistol out to 100 - 150 yds probably will not make a difference without a scope. Your 9mm HP will probably drop less than 10gr (I would totally guess more like 4-7grns) and that's about 5%. You should be concerned that the holes are drilled concentrically, so as not to destabilize the boolit. Of course all this matters less as the range decreases. If you shoot at pop cans out to 25 feet, I would think all this matters little.

With a fast powder you are not going to notice a difference as long as the volume below the boolit in the case stays consistent. Let us know how they did!