Grains/pressure calculator

[Altcaliber]

Attached is a spreadsheet calculator I made and shared on another reloading forum. We had some great discussion and I just wanted to share it here also, for anyone that may find value.

When loading lead bullets, the bullet hardness and desired pressure calculations are often known (1422 x BHN x .9, etc...), but there isn't an easy method to derive an estimate of grains powder needed to equal that desired pressure from the reloading manuals (you typically get max pressure, sometimes a start pressure).

This calculator answers the question: I know the bullet hardness, I know the pressure I want, now what are the grains of my powder to get that pressure (staying under the max listed grains, of course)?

So far, the results have been excellent. Maximum power matching the lead bullet with great accuracy, and without leading. Of course, bullet fit is paramount before doing any of this. Poor bullet fit, and all bets are off.

To use this calculator, it needs data from one of the reloading manuals that has BOTH starting and max pressures, along with the normal starting/max grains data for your powder/bullet combination. At this time, both Lyman's reloading manual and Hodgdon's online database have this information; but there may be others.

[attached is an excel spreadsheet to do all the calculations fast and easy...]

[ylexot]

This is a nice little calculator, assuming pressure increases approximately linearly with powder. How much tweaking to your loads have you done to get your loads just right, or have they been good enough to satisfy from this calculation?

I'm still getting my head around all the parameters involved and am a total neophite to reloading and casting just starting to learn . I think I saw your post on another forum, but have lost it to the ether that is webcrawling. On your other post, I thought I saw something about over obturation negatively impacting accuracy. If I have it right, the name of the game here is to identify the desired velocity and determine the powder charge to provide the right pressure, within specs, to push it and then match the bullet's hardness to match.

thanks

[geargnasher]

Looks similar to what Richard Lee did when researching reduced powder data. The data that he actually published was all verified, but he did derive and publish a formula that will get you "ballpark" with a powder that's reasonably well-matched for the load.

Gear

[Altcaliber]

Thanks for the feedback.

Still finding myself questioning what I do, and just last week I was testing the pressure theory again.

Ruger Blackhawk: 41 Magnum. 215 grain SWC from Missouri Bullet. BHN 18.

The calculator, using Lyman data for start/max pressure and start/max grains for Unique, gave me 7.9 grains as the ideal load for that weight and hardness of bullet.

My Lee auto-disk measure throws 7.5 grains of Unique, and that is what I have been using. Outstanding accuracy, good power, and no leading. Zero zip nada.

Being one to explore the other side of the fence, I switched up to the next disk measure size, which throws 8.1 grains of Unique and loaded some for that.

I shot a dozen of those. Still saw great accuracy, power was hard to tell the difference between previous load, but I found leading chasing the grooves down the barrel. It cleaned up with a brush just fine, but still amazed me how the calculations were that close.

There are several parameters that can affect leading, and bullet fit to barrel(throat in revolvers) is right at the top. Lube is up there too, but not as critical in handgun loads as it is in the rifle arena.

On the other side of the spectrum: I shoot a standard load of 6.5 grains Unique in 44 special. This is a low-pressure load ~15kpsi, but I use a very very hard Oregon Trail Laser-cast 240 grain bullet. Zero leading! The pressure is supposedly way too low for that hard of a cast bullet, yet the bullet fit is excellent and no leading. It's also the most accurate load/gun I have in my inventory too.

If you use my calculator, just make sure you have start/max data for both pressure and grains. Hodgdon and Lyman both have this data. Obviously, don't go over max with any powder. Double-check your work. Don't take the calculator as gospel. If you look at the formulas in the spreadsheet, you can see what I'm really doing. Nothing more than ratio calculations being applied.

[Altcaliber]

Here is the original discussion thread: http://www.reloadersnest.com/forum/topic.asp?TOPIC_ID=15058


Yes, all of this was inspired by Richard Lee's work in his 2nd edition book. I just needed a tool that ties the pressure desired to the grains of powder needed. A hand-calculator works too, but the spreadsheet is faster on the what-if questions.

There's a lot of leeway (different barrels, alloys, etc...) in finding the exact match of powder. It puts you in the ballpark faster, instead of just treating it all like a black art.

[fredj338]

SInce pressure seldom increase in a linear fashion, I doubt you can determine pressure per grain of powder. Faster powders increase more quickly as they reach the top end, some can even spike, so a linear progression just isn't possible IMO.

[Altcaliber]

SInce pressure seldom increase in a linear fashion, I doubt you can determine pressure per grain of powder. Faster powders increase more quickly as they reach the top end, some can even spike, so a linear progression just isn't possible IMO.

I would agree 100% with that statement. But that's not what I'm doing. What I'm doing is working between the start and max loads. Nothing is going above maximum. Everything is staying within the start and max loads defined by the load sources. In this case, Hodgdon and Lyman.

The pressure ratio is calculated between those points. If you enter the data into the spreadsheet, you can 'walk' the BHN numbers up and see the pressure calc increase from start to max. The numbers will match exactly when you reach the max charge. If Hodgdon and Lyman did the actual measurements on pressure for starting and max loads, then I trust their published data.

Most important point: The cast load calculations are actually going to hover around the starting load numbers most of the time, since that is where the pressures are that match the hardness of typical cast bullets. The spreadsheet warns you if you try to exceed a max charge.

Hope that helps.

[Altcaliber]

This shows where the calculations can be helpful:

- Let's say I want to reload a 44 Magnum with a 240 grain, BHN 18, cast bullet using Unique.

- Standard BHN formulas show I should aim for around 23k of pressure for a good pressure match to the hardness of this bullet. The bullet was already measured for good fit, and has a good lube.

- The Lyman 49th edition gives the following data (note the valuable start/max pressure data):

Powder Suggested_start Pressure Max_load Max_Pressure
Unique 10.0 25,300 11.7 37,900

OK. Just putting all that spreadsheet and ratios discussion aside: A look at this Lyman data tells me that something around the suggested starting load is going to be close to the pressure I'm seeking, 23k. (Notice no mention of velocity data is being discussed here.) It also looks like I could use a bit less powder just under the suggested start, but it might even work with the starting load just fine too. So I go from there and discover and load and test...

On the other hand, looking at those two pair of data points, it wouldn't take much to figure out right away how many grains of powder around the start load affects the pressure to some degree.

It turns out that 9.7 grains would roughly put you at 23k for pressure by just figuring some ratios on a hand calculator. Again, that's pretty close to the start load already and either may work fine. But it does help you to zero in on the load before even loading up your first cartridge.

Sometimes the pressure desired is a little farther away from the start, or you want to switch to a different hardness bullet. That's where the calculations and a spreadsheet help more, and do it faster. For a BHN 24 bullet, I would be looking around 10.7 grains of Unique. You can calc that fast on a spreadsheet. Again, we're never going near or over max loads here.

[MtGun44]

Or you could just know that 10 gr of Unique is a fantastic load under a 250 Keith in .44 mag
and has worked well for many users. :-)

Extrapolation in the middle of the range is useful. Get anywhere near the ends (which are
hard to know in advance) and things start to go non-linear, so all bets are off. Fun game,
but I think I'll stay with the books when I can. When there is no data, this kind of method
is WAY better than guessing, but still is theoretical, and theory often fails to match reality.

Good stuff if used carefully.

Bill

[Altcaliber]

Or you could just know that 10 gr of Unique is a fantastic load under a 250 Keith in .44 mag
and has worked well for many users. :-)




LOL ! So true. In fact that type of info helps confirm what many have found through trial and error.


Fun game,
but I think I'll stay with the books when I can. When there is no data, this kind of method
is WAY better than guessing, but still is theoretical, and theory often fails to match reality.


Agree 100%. But note again, I'm just using the data already provided by the books. Nothing is going over max loads listed in the books. Ever. It's just applying what is already there from a pressure view to guide the cast bullet load selection.

[Bret4207]

Interesting. I note you're only going by Bhn. What effect do you think various alloys have on all this? That is a HTWW boolit at 25 Bhn isn't going to react to pressure the same as an air cooled 25 Bhn made up of a babbit alloy high in antimony and copper. How much effect do you think that might have?

[Altcaliber]

Interesting. I note you're only going by Bhn. What effect do you think various alloys have on all this?

My understanding is that hardness, strength and brittleness are not one and the same thing. However, when it comes to metals, these three qualities often do go hand in hand.

BHN revolves around the concept of elasticity, or it's ability to deform under load. You are testing that elasticity when you perform a BHN test, like the calibrated BHN tester from Lee where you measure the indentation.

Then, there is the lube equation and how that affects leading too.

I'll stop right there because I'm in no way claiming to be an expert on any of this; just an experimenter like many of us are here.

FWIW....the folks concerned that I'm putting something out there that is experimental or questionable; look at it this way:



- A guy posts a load he uses with so many grains and a bullet on this forum.

- You look the data up in your reloading book and confirm it's safe and decide to use it.

....................................or...

- A guy posts a spreadsheet he uses that allows you to input your own reloading book data on this forum

- You look the data up in your reloading book and confirm it's safe and decide to use it.


Doesn't sound that much different. Not trying to be defensive or directing this at you, just sharing what has been working great for me. Maybe someone will find some value in it too. The Lee 2nd edition book is highly recommended. :)

[MtGun44]

Not knocking the method, it is useful. Just being aware that a whole lot of newbies are out
there lurking and want to be sure everybody stays safe, esp those with a bit less experience
or theoretical knowledge. Used to be that most on the site were old hands, or at least
moderately experienced. The jump in ammo cost has pushed many to start loading and
start casting, so the audience contains many more inexperienced loaders and casters. I
try to remember this when I am posting.

Bill

[BLTsandwedge]

Interesting Altcaliber. Why is (1422*.9)*BhN true?

[Altcaliber]

Not knocking the method, it is useful. Just being aware that a whole lot of newbies are out
there lurking and want to be sure everybody stays safe, esp those with a bit less experience
or theoretical knowledge.

All is well. :)

Was a busy day when I posted that. Just wanted folks out there to know that I'm not going 'off-the-cliff' with some sort of new reloading data outside of the published books. Everything is working within published load data limits (grains and pressure).

Hard not to do something useful with that pressure data when it's listed in the latest manuals. :p It was only recently that more sources have come out with starting pressures. That's valuable information to have.

Speaking of things that affect cast bullet performance besides just bullet hardness: I'm working with one of those Buffalo Classic 45-70 rifles. It shoots jacketed bullets just perfect at any speed, yet does terrible with cast :sad:.

What I'm finding out about is how shallow the rifling is in that barrel (think Marlin micro-groove situation). I've used 405 grain Laser Cast brand cast bullets which are supposed to be around 24 BHN (sized .459), but when pushed to any reasonable level they shoot a pattern like a shotgun. The barrel slugs .456-.457.

Looking through my past reloading notes, I find that I did at one time show some promise with cast, but had the loads down around 1300-1400 fps using black powder and also using Varget. Apparently it's stripping of the bullet in those shallow grooves? I'm at wits end with this rifle because it shoots jacketed so well, yet cast has been a fail. To me cast and 45-70 go together. So, I'm going to back off the loads of RL-7 down to the 1300-1400 range, if possible, and retest. My spreadsheet calculator isn't helping me here. :p

[Altcaliber]

Interesting Altcaliber. Why is (1422*.9)*BhN true?

That's taken from Lee's book chapters on obturation and ultimate compressive strength. Same information found on other sites. I believe Missouri Bullet has a tech section explaining the same.

The times .9 is just "reducing 10%". Same as 'give me 90%'. It's setting the load at 10% below the ultimate compressive strength of the bullet. Lee shows that as the ideal spot where accuracy is maximized. I don't see it as a hard and fast rule though, because many have found they can push pressure right up to the ultimate compressive strength of their alloy, and sometimes a bit beyond with good results.

Lee has that very cool example in his book where he walks the pressure up on several loads in a rifle, and then reports the accuracy. You see the accuracy improve right up before the ultimate compressive strength, and then fall off rapidly just after. Depending on the lube, alloy, bullet fit/design; I'm sure that can shift the results around.

For me, it's exactly what I've seen play out though; at least in my revolvers. I tumble-lube a thin coat of alox on all my bullets, even though they may be purchased and already have lube rings filled from the caster. When I cross over that compressive strength point, I start seeing leading follow the grooves in the barrel. Push it further, and I get a molten mess coating the barrel.

Now, with Laser Cast BHN 24 bullets I haven't yet found their limit. With other BHN 18 bullets purchased, I have found it...every time. :o

[Altcaliber]

........ Apparently it's stripping of the bullet in those shallow grooves? I'm at wits end with this rifle because it shoots jacketed so well, yet cast has been a fail. To me cast and 45-70 go together. So, I'm going to back off the loads of RL-7 down to the 1300-1400 range, if possible, and retest. My spreadsheet calculator isn't helping me here.

Just finished testing some loads at around 1400 fps with the 405 grain RNFP. The Buffalo Classic shot its best cast bullet group ever; shooting 2 MOA with me shaking behind a sandbag. I was doing this initial small load test at 50 yards to see if the load had any hope. Planning on moving out to 100 yards with the next batch of loads.


http://farm4.static.flickr.com/3229/5855191442_f487721456_z.jpg

At 34.8 grains of RL-7 (Lee 2.5cc dipper), the pressure is pretty low; 14-15k. Yet, just a few grains of unburnt powder were found in the barrel.

With this low a pressure, a 10-12 BHN lead might have worked just as well, instead of buying those super hard 24 BHN bullets. The thought was that the hard cast, and slow powder, would fight the 'shallow rifling issue'...which may be a non-issue if I continue to keep the velocity down around the 1400 range. :???:

[45 2.1]

That's taken from Lee's book chapters on obturation and ultimate compressive strength. Same information found on other sites. I believe Missouri Bullet has a tech section explaining the same.

The times .9 is just "reducing 10%". Same as 'give me 90%'. It's setting the load at 10% below the ultimate compressive strength of the bullet. Lee shows that as the ideal spot where accuracy is maximized. I don't see it as a hard and fast rule though, because many have found they can push pressure right up to the ultimate compressive strength of their alloy, and sometimes a bit beyond with good results.

Lee has that very cool example in his book where he walks the pressure up on several loads in a rifle, and then reports the accuracy. You see the accuracy improve right up before the ultimate compressive strength, and then fall off rapidly just after. Depending on the lube, alloy, bullet fit/design; I'm sure that can shift the results around.

For me, it's exactly what I've seen play out though; at least in my revolvers. I tumble-lube a thin coat of alox on all my bullets, even though they may be purchased and already have lube rings filled from the caster. When I cross over that compressive strength point, I start seeing leading follow the grooves in the barrel. Push it further, and I get a molten mess coating the barrel.

Now, with Laser Cast BHN 24 bullets I haven't yet found their limit. With other BHN 18 bullets purchased, I have found it...every time. :o

One should be very carefull of copying/referencing someone else's work. What they write is sometimes not correct. What they call something is not actually what it really is. And, some of the above is not correct................................

[popper]

IMHO, for the last 4 mo. I've been shooting 40SW 180 gr. BHN = pure. 4.8 HP-38. Hodgdon shows 4/23k, 5.1/33k (~800-950fps) for jacketed. If I plug th numbers into the calc, I get a 1.7 gr optimal load (won't even operate the slide). By the calc, I should get extreme leading as I am 3 x the plastic pressure. I don't get leading, hoes are round and groups are < 2" @ 25 yds when my eyes work decent. All I can glean from your calc is that I need to be below 18 BHN for my load to obturate. That equates to AC any alloy but lino and it will work. It might work for rifle loads, I haven't run any of those.

[Maven]

Interesting Altcaliber. Why is (1422*.9)*BhN true?

Great effort, Altcaliber!

For BLT sandwedge, et. al., take a look at the attached article by Steve Hurst from "The Fouling Shot" #131-10:


P.S. I had to use Adobe Reader 8 to open that attachment. If you know a better way, please let me know!

[fredj338]

With this low a pressure, a 10-12 BHN lead might have worked just as well, instead of buying those super hard 24 BHN bullets. The thought was that the hard cast, and slow powder, would fight the 'shallow rifling issue'...which may be a non-issue if I continue to keep the velocity down around the 1400 range. :???:

Nice idea, but really, w/o pressure testing, you are just guessing. Again, powders do NOT build pressures in a linear, predictable fashion. It will vary along hte vel cruve. You would have noobs eleiving they can plug some random numbers in & get useable data. No chronograph, no rpessure testing, it's just educated guessing.:holysheep

[geargnasher]

Heck, its ALL educated guessing until you pull the trigger, as Runfiverun says. Why muddy the waters with a bunch of guesstimated numbers and an exact formula, when you're going to have to shoot it and see anyway?

I can say this because I've tested the BHN/pressure formula pretty thorougly myself and found it works quite well, but also found that most of my favorite loads run at two to three times the maximum pressure the formula suggests. So you can do it both ways. It's easier to use the BHN formula, and it DOES work as Lee suggests, the sweet spot is usually in the 90% range, but that for sure isn't the ONLY sweet spot in the spectrum.

Gear