Hypothetical load guesstimation.......

[bigbossman]

So - I'm just sitting around with nothing to do, and I thought I'd tinker in the garage and pull down some milsurp 8mm I have laying around. I bought a case of 1,000 rounds years ago when this stuff was practically free, just for the bullets and powder. I wanted to avoid the corrosive primers, so I planned on knocking out the bullets and powder and re-loading them into my commercial brass with new non-corrosive primers.

Now, that's easy enough to do. The bullets are 200g (heavy ball) and the average powder charge per case is 44gr. So, just load new cases with 44grs of the mystery powder, seat a bullet, and call it good.

Well - OK. But it got me to thinking........ could I figure out a SAFE way to extrapolate powder charges for the same mystery powder and lighter bullets?

For instance, I looked up the load data for known powders and 200gr bullets, and came up with 2 candidates that have 44gr charges within their range for 200gr jacketed bullets:

IMR 4895 Min 39.0gr 34,900 CUP max 45.0gr 48,500 CUP
Hodgdon H4895 min 38.0gr 36,800 CUP max 45.4gr 49,200 CUP

So - here's the hypothetical question....... would it be SAFE to assume that the mystery powder is of a similar burn rate as these two powders, and therefore would be OK to substitute the load data of these known powders with lighter bullets for the mystery powder I pulled down? Does it work that way, or am I missing something?

Now - I want to stress that I'm not seriously considering doing this. Since I already have a 1:1 relationship with the pulled bullets and power charges, I will stick to my original plan...... but it got me to thinking (which is always dangerous).

Opinions? Thoughts? Advice? Ridicule? Discuss.

[ar15barrels]

So - here's the hypothetical question....... would it be SAFE to assume that the mystery powder is of a similar burn rate as these two powders, and therefore would be OK to substitute the load data of these known powders with lighter bullets for the mystery powder I pulled down?

No.
It does not work that way.

[Pauliedad]

Thinking too much defiantly has caused me some grief in my experience. I'm not going to ridicule since there will be plenty of others for that but I think the question deserves a more complete answer so I'll hang around and see what comes next.

[bigbossman]

Thinking too much defiantly has caused me some grief in my experience. I'm not going to ridicule since there will be plenty of others for that but I think the question deserves a more complete answer so I'll hang around and see what comes next.

I was hoping for just that, a discussion on why or why not from experienced reloaders that have experience with these things. Always trying to learn something.........

We'll see what develops.

[MongooseV8]

Why dont you just use the 44 grains of mystery powder under a lighter bullet? Guessing when reloading is a great way to drop the number of fingers on your hand.

[bigbossman]

Why dont you just use the 44 grains of mystery powder under a lighter bullet? Guessing when reloading is a great way to drop the number of fingers on your hand.

Well...... like I stated in the OP - this is a hypothetical exercise, I am not going to actually do it. I'm just trying to start a discussion on how this things get puzzled out, how loads get developed (or if they even can) when there is an unknown to deal with.

So far, I'm failing.....................

[JMP]

Just look up applicable 8mm loads.
For the mystery powder you could measure the specific impulse with a strand burner.
But, really, just shoot the corrosive stuff. It's no biggy if you clean the gun. The "corrosive" byproducts are generally KCl or NaCl, basic water soluble ionic salts. Folks act like it's sulfuric acid that's going to instantly melt away your barrel.

[Sunday]

Shoot them as is and clean the barrel with soapy water .

[bigbossman]

OK - so, I'm assuming from the responses I'm getting that I didn't make myself clear about what I was wondering about, or that no-one has had any experience experimenting with what I was wondering about.

I'm not asking about how/whether to shoot and then clean after using corrosive ammo - I know about that.

Like I stated in the OP - this is a hypothetical exercise. I'm just trying to start a discussion on how this things get puzzled out, how loads get developed (or if they even can) when there is an unknown to deal with.

[JMP]

Like I stated in the OP - this is a hypothetical exercise. I'm just trying to start a discussion on how this things get puzzled out, how loads get developed (or if they even can) when there is an unknown to deal with.

For the mystery powder you could measure the specific impulse with a strand burner.

I already answered what I believe to be your question. Yes, you can do this, but you need the right equipment. The chemical engineers that work in the industry test the powders for these various properties. If you have the equipment and knowledge of thermodynamics and physical chemistry to understand propulsion, you can do it. If you do not, then it isn't advisable. You will not be able to get the correct values needed, and it has the potential to be very dangerous.

[bigbossman]

I already answered what I believe to be your question. Yes, you can do this, but you need the right equipment. The chemical engineers that work in the industry test the powders for these various properties. If you have the equipment and knowledge of thermodynamics and physical chemistry to understand propulsion, you can do it. If you do not, then it isn't advisable. You will not be able to get the correct values needed, and it has the potential to be very dangerous.

Yes, you did. Thank you expounding a bit on your previous answer.

So, let me adjust my question if i may........ how then do folks come up with new, 'wildcat' calibers? Do they tinker and do a bit of "educated guessing", or do they usually have access to the specialized equipment and knowledge to the work in a more formalized manner?

[MongooseV8]

Many wildcats come from a parent cartridge. Take a 243 for example. Based on the 308, we can reasonably assume a safe load for the 308 will probably be safe for a lighter bullet in the 243 "wildcat."

So 45 grains of x powder under a 150 grain bullet with a case capacity of y creates z pressure. So when we are testing out loads in our new wildcat 243 we can predict that 45 grains of x powder under a 100 grain bullets will create z or less pressure.

Now we test our prediction. Using standard pressure test equipment we find that indeed we have less than z pressure. Now we can test the range of the powder load as it relates to the pressure created by different loads.

That is a simple version of load development, naturally its much more complex but you get the idea.

The reckless way is guessing. Like we want to invent the 6.5 Grendel and since it has around the same case capacity as the 7.62x39 we can guess it safely use the same powders and same charge weights. Kaboom.

Pressure numbers are mandatory for reliable and safe ammunition development.

[MongooseV8]

Both methods above have been used to create many different cartridges, some are still around and others have died off. Sometimes you have to guess when inventing something new, but pressure standards still need to be a part of development. Most of us dont have that option so we follow published loads.

That being said, sometimes I push the limits of published loads. But that is done with great cunning and dexterity, since there is no way for me to know 100% of the time that its safe. Pressure signs dont always show before you blow a case head or a primer ect.

[ar15barrels]

Many wildcats come from a parent cartridge. Take a 243 for example. Based on the 308, we can reasonably assume a safe load for the 308 will probably be safe for a lighter bullet in the 243 "wildcat."

Absolutely FALSE.

Let's look at Varget under a 155gr Matchking in the 308 and say we run 45gr which would be a moderate load.

Cartridge          : .308 Win.
Bullet             : .308, 155, Sierra HPBT Palma MK 2156
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length      : 26.0 inch or 660.4 mm
Powder             : Hodgdon VARGET

Predicted data by increasing and decreasing the given charge,
incremented in steps of 1.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-10.0   93    40.50   2548    2234   39824   6080     94.3    1.380
-09.0   94    40.95   2574    2281   41082   6151     94.7    1.361
-08.0   95    41.40   2601    2328   42381   6219     95.1    1.342
-07.0   96    41.85   2627    2376   43722   6287     95.5    1.324
-06.0   97    42.30   2654    2424   45105   6352     95.9    1.306
-05.0   98    42.75   2680    2473   46538   6416     96.3    1.288
-04.0   99    43.20   2707    2521   48012   6478     96.6    1.271
-03.0  100    43.65   2733    2571   49530   6538     96.9    1.254
-02.0  101    44.10   2759    2621   51092   6597     97.2    1.237
-01.0  102    44.55   2786    2671   52702   6653     97.5    1.221  ! Near Maximum !
+00.0  103    45.00   2812    2721   54367   6708     97.8    1.205  ! Near Maximum !
+01.0  104    45.45   2838    2772   56088   6760     98.1    1.189  ! Near Maximum !
+02.0  105    45.90   2864    2824   57867   6811     98.3    1.173  ! Near Maximum !
+03.0  107    46.35   2891    2876   59706   6859     98.6    1.158  !DANGEROUS LOAD-DO NOT USE!
+04.0  108    46.80   2917    2928   61609   6905     98.8    1.143  !DANGEROUS LOAD-DO NOT USE!
+05.0  109    47.25   2943    2980   63578   6949     99.0    1.128  !DANGEROUS LOAD-DO NOT USE!

Now lets's drop 45gr of Varget into a 243 winchester (308 case necked down to 6mm) with a 107gr bullet.

Cartridge          : .243 Win.
Bullet             : .243, 107, Sierra HPBT MatchK 1570
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length      : 26.0 inch or 660.4 mm
Powder             : Hodgdon VARGET

Predicted data by increasing and decreasing the given charge,
incremented in steps of 1.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-10.0   93    40.50   3071    2241   70482   9003    100.0    1.165  !DANGEROUS LOAD-DO NOT USE!
-09.0   94    40.95   3096    2278   72727   9054    100.0    1.150  !DANGEROUS LOAD-DO NOT USE!
-08.0   95    41.40   3121    2315   75040   9104    100.0    1.135  !DANGEROUS LOAD-DO NOT USE!
-07.0   96    41.85   3146    2352   77423   9153    100.0    1.120  !DANGEROUS LOAD-DO NOT USE!
-06.0   98    42.30   3171    2389   79880   9202    100.0    1.106  !DANGEROUS LOAD-DO NOT USE!
-05.0   99    42.75   3196    2427   82411   9250    100.0    1.092  !DANGEROUS LOAD-DO NOT USE!
-04.0  100    43.20   3221    2464   85020   9297    100.0    1.078  !DANGEROUS LOAD-DO NOT USE!
-03.0  101    43.65   3245    2502   87711   9344    100.0    1.064  !DANGEROUS LOAD-DO NOT USE!
-02.0  102    44.10   3269    2540   90486   9389    100.0    1.051  !DANGEROUS LOAD-DO NOT USE!
-01.0  103    44.55   3294    2577   93349   9434    100.0    1.038  !DANGEROUS LOAD-DO NOT USE!
+00.0  104    45.00   3318    2616   96302   9478    100.0    1.025  !DANGEROUS LOAD-DO NOT USE!
+01.0  105    45.45   3342    2654   99349   9521    100.0    1.013  !DANGEROUS LOAD-DO NOT USE!
+02.0  106    45.90   3366    2692  102497   9564    100.0    1.000  !DANGEROUS LOAD-DO NOT USE!
+03.0  107    46.35   3390    2731  105746   9606    100.0    0.988  !DANGEROUS LOAD-DO NOT USE!
+04.0  108    46.80   3415    2770  109102   9646    100.0    0.976  !DANGEROUS LOAD-DO NOT USE!
+05.0  109    47.25   3438    2809  112570   9686    100.0    0.965  !DANGEROUS LOAD-DO NOT USE!

Same powder.
Same case volume.
Lighter bullet.
Smaller bore.
The pressure goes from 55,000 PSI to 96,000 PSI.

What your simple comparison is missing is that smaller bores have smaller expansion ratios.
Therefore, you need a slower powder.

[MongooseV8]

Like I said, a watered down random example.