I've been reloading for close to 15 years and go 100 percent by what the reloading manuals say. There is a lot I don't understand about burn rates, compressed loads, case capacity......etc, but by following the load data in the manuals, I have never had an issue. I came across something today that confused me. Any time I have loaded a particular caliber with a particular powder using two different sizes of bullets, the smaller bullet always called for more powder. For example, if I'm loading .45 colt with Unique powder using 200 grain and 250 grain bullets, the load data will show that more powder is used in the 200 grain load. Recently I loaded some 240 grain .454 casull using IMR 4227. The manual called for 33 grains of powder. I then loaded some 150 grain .308 using IMR 4227 and the manual called for 24 grains. I would think that the .308 being a larger case and smaller bullet, would call for more powder than the .454 casull. I'm just curious as to why this was the case. The load data is coming from the Hornady and Lee manuals. And don't get off on the, "why are you using IMR 4227 powder in these calibers when there is better powder out there." I have quite a bit of IMR 4227 and just wanted to see how it performed. Thanks.
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Explain something to me
- Thread starter AL45
- Start date
The answer is the sectional density of the 150-grain .308" bullet (ballistic sd=0.226) is greater than the sectional density of the 240-grain .451" bullet (ballistic sd=0.169). Sectional density determines how much pressure is needed to produce enough accelerating pounds of force on the bullet base to achieve a given rate of projectile acceleration.
.454 casull has max. Pressure of 65k psi, which is higher than 62k psi of .308 win. The chamber is stronger.
The bigger diameter of the .454 of the projectile also make difference. For the same distance it travels down the bore, the containment volume increases more. That helps taming how fast and how high pressure peaks.
When .454 is shot out of a revolver, I believe that limits the pressure too. The throat in the cylinder is not exactly gas tight, and it is longer than the throat in a rifle. Some gas leaks around the bullet and vents out through the cylinder gap.
It is indeed surprising to see what you saw. But after digging into it, it is not unreasonable.
-TL
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The bigger diameter of the .454 of the projectile also make difference. For the same distance it travels down the bore, the containment volume increases more. That helps taming how fast and how high pressure peaks.
When .454 is shot out of a revolver, I believe that limits the pressure too. The throat in the cylinder is not exactly gas tight, and it is longer than the throat in a rifle. Some gas leaks around the bullet and vents out through the cylinder gap.
It is indeed surprising to see what you saw. But after digging into it, it is not unreasonable.
-TL
Sent from my SM-N960U using Tapatalk
Happy to help. The interior ballistic relationships are a collection of interacting factors. For example, the .308 case is a lot bigger, but the bullet in the .454 has to go forward less than an inch for the space behind it to equal the volume in a 308 case (high expansion ratio), and because the sectional density is lower, it will go an inch sooner than the .308 bullet will. So, basically, the difference in starting space doesn't last very long and is not long enough for the extra powder involved in loading the .454 to exceed pressure limits.
Homer Powley, who invented the Powley Computer (a sort of cardboard slide rule for determining rifle loads with IMR powders), and who wrote extensively on the subject said:
Homer Powley, who invented the Powley Computer (a sort of cardboard slide rule for determining rifle loads with IMR powders), and who wrote extensively on the subject said:
"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity."
.454 casull has max. Pressure of 65k psi, which is higher than 62k psi of .308 win. The chamber is stronger.
If you are saying the .454 Casull chamber is stronger than the .308 Winchester chamber, because the rated max working pressure of the .454 is slightly less than 5% greater, I believe you are in error.
The chamber is only stronger (IF it actually is) at blow up level limits, which are not relevant to anything other than blowing up guns.
Guns are made to be strong enough to do the job, and have a margin of safety beyond that. ALL are strong enough to safely contain more than their cartridges max working pressures. (think proof loads)
Differences in "Strength" result from different designs, materials and manner of construction. Not a 3K psi difference in industry max working pressure limits.
Well, if you are building chambers to withstand SAAMI maximums only just barely, you could argue the Casull chamber is stronger. But many 308 Ws are in rifles with room to chamber wider and higher pressure cartridges, meaning the rifle is actually over-built for 308. Revolver cylinders don't usually have a lot of extra steel on the outside of the cylinder, so I see them as running closer to the edge.
I see the point, so I should rephrase.
.454 casull is rated 65k psi and has been proof tested as such, whereas .308 win is 62k psi.
Are you saying the 454 takes more powder than the 308 because the 454 load produces higher pressure?
.454 can take rifle pressures. Unlike pistol ammo, say .357 magnum, powder charge close to rifle ammo is expected. Plus other factors, larger bullet diameter being one, it ends up with the load data you got. We can safely assume that load is below 65k psi and is safe.Are you saying the 454 takes more powder than the 308 because the 454 load produces higher pressure?
-TL
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.454 casull is rated 65k psi and has been proof tested as such, whereas .308 win is 62k psi.
It could be a rifle in .454 casull. No way to know the safety margin in the particular design.
SAAMI proof test standards are generally between 130% and 150% of the max working pressure.
What this means is that the proof test load (rifle OR handgun) for a given cartridge is somewhere between 1/3 and 1/2 MORE (higher) pressure than the max working ammo load pressure.
For a cartridge with a working load max limit in the 60K+ psi range this means that the guns are proofed with loads in the 90K psi range, OR MORE.
The guns survive proof testing. They survive this without damage. No, they aren't built for a constant proof level pressure use, but they do take it when "proofed" without failing.
This means that the 3Kpsi difference in the working load limit pressure between a .308 Win and a .454 Casull is piffle, in terms of stressing the chamber or any other load bearing part of the firearm.
Are you saying the 454 takes more powder than the 308 because the 454 load produces higher pressure?
Something being missed here is that for the ONE load mentioned, using IMR 4227 in the .308 Win is what that load actually IS. I don't mean the 25gr charge weight, that is clear from the OP, but what isn't clear is WHAT that load in .308 does, and is intended to do.
What is the velocity of the 150gr .308 slug using 25gr of IMR 4227?
I don't have that load listed in my manuals, in fact none of them list IMR 4227 I'm sure it would be considered a "reduced load" compared to the full potential of the .308 round.
While useable for reduced/gallery level loads IMR 4227 is to fast a rifle powder to produce full power performance in the .308. It is useable, but its not suitable for full power .308 loads.
SO, AL 45, what is the velocity listed in your data for the 25gr IMR 4227 150gr .308 load. I'm guessing it is at or below 2000fps, please provide the information, if possible.
.454 can take rifle pressures. Unlike pistol ammo, say .357 magnum, powder charge close to rifle ammo is expected. Plus other factors, larger bullet diameter being one, it ends up with the load data you got. We can safely assume that load is below 65k psi and is safe.
It seems like you're implying the OP's 454 load produces more pressure than the 308.
In order for this to apply to the OP's post, it must mean the 454 load produces more pressure than the 308 load, or more pressure than typical 308 loads. Right?
So, what is the pressure of the OP's 454 load?
If the OP's 454 load doesn't produce more pressure than the 308, then all this talk about pressure limits is irrelevant to the OP's post.
Something being missed here is that for the ONE load mentioned, using IMR 4227 in the .308 Win is what that load actually IS. I don't mean the 25gr charge weight, that is clear from the OP, but what isn't clear is WHAT that load in .308 does, and is intended to do.
What is the velocity of the 150gr .308 slug using 25gr of IMR 4227?
I don't have that load listed in my manuals, in fact none of them list IMR 4227 I'm sure it would be considered a "reduced load" compared to the full potential of the .308 round.
While useable for reduced/gallery level loads IMR 4227 is to fast a rifle powder to produce full power performance in the .308. It is useable, but its not suitable for full power .308 loads.
SO, AL 45, what is the velocity listed in your data for the 25gr IMR 4227 150gr .308 load. I'm guessing it is at or below 2000fps, please provide the information, if possible.
Velocity is not the issue. Pressure is. While it might be a 'reduced load' with respect to velocity, it might be a max load with respect to pressure for that powder and bullet.
That's what all the noise about pressure is about.
No it wasn't my intention. I don't know whether those 2 loads are max. And I was trying to list out factors to explain the op's observation.It seems like you're implying the OP's 454 load produces more pressure than the 308.
In order for this to apply to the OP's post, it must mean the 454 load produces more pressure than the 308 load, or more pressure than typical 308 loads. Right?
So, what is the pressure of the OP's 454 load?
If the OP's 454 load doesn't produce more pressure than the 308, then all this talk about pressure limits is irrelevant to the OP's post.
.454 casull is a pistol round, .308 win is a rifle round. With same powder, I would expect .454 charge be lighter, as pistol rounds are lower pressure. I looked it up and found .454 actually has higher max pressure.
The other 2 factors are as in my post.
-TL
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44 AMP, you are correct in that it is a reduced load and the Lee Manual lists it at 2,000 fps. I was looking for a lighter recoiling round for plinking. I also have a reduced load using Trail Boss, but it is extremely reduced with somewhere around 1400 fps as I recall. I'm using it in a Ruger scout rifle with a red dot, so I'm not looking at a long range or extremely precise round with this load. I took this to the range today and it did what I was desiring. There is no magnification on the red dot, so my aging eyes can't speak to how accurate the round is. AT 25 yards from an unsupported standing postion, firing at a steady pace, I was "quart paint can" accurate and from 100 yards off a sandbag, I was "gallon paint can" accurate.
44 AMP, you are correct in that it is a reduced load and the Lee Manual lists it at 2,000 fps.
And there is your answer why the Casull load used more powder. 33gr IMR 4227 is a full power (at, or near max) load for the .454 while 25gr is a reduced load in the .308 Win.
And there is your answer why the Casull load used more powder. 33gr IMR 4227 is a full power (at, or near max) load for the .454 while 25gr is a reduced load in the .308 Win.
According to the Lee Manual #2, for a 150 grain bullet, the max load with IMR4227 is 26.0 grains and produces 51100 CUP. That charge weight is still well below the max 454 load which is 34 grains for a 240 grain bullet for a pressure of 48700 CUP in the Lyman 50th load manual.
To summarize my previous posts, the lower sectional density and the bigger diameter of the Casull bullet are the important differences. The lower SD bullet will accelerate faster at a given pressure. The wider bullet doesn't have to move as far to add a given quantity of bore volume to the combustion space behind it. Both of these factors mean that in the OP's example, the 454 Casull needs a larger quantity of powder burning than the 308W does in order to make gas fast enough to achieve a given pressure in its faster-expanding combustion volume. This is regardless of what value in the pressure curve you are looking at.
I admittedly am not the expert, but my view is as follows. In your 45 caliber
pistol cartridge, the limiting factor is pressure. A heavier projectile creates more resistance, driving up pressure. To keep the pressure in the safe and sane category a reduction of propellant is required.
pistol cartridge, the limiting factor is pressure. A heavier projectile creates more resistance, driving up pressure. To keep the pressure in the safe and sane category a reduction of propellant is required.
Mule,
Go back and read the OP. It is the lighter 308 bullet that is getting less powder in the databook. Weight only works for comparison in this context when the bullets you are comparing are the same caliber.
The above is true because what matters is not absolute bullet weight but sectional density. If you stick with the same caliber, sectional density always goes up and down with weight, but when you change caliber, that matching relationship is gone. Sectional density is how much weight you have per square inch of bullet cross-sectional area*. Since pressure is the number of pounds of force you have per square inch of bullet cross-sectional area, it follows that pressure and sectional density combine to tell you how many pounds of force each grain of bullet weight has working to accelerate it down the tube. If the large diameter and small diameter bullets were the same weight, a lower pressure would give the larger diameter bullet the same acceleration as a higher pressure did the small diameter bullet. The larger diameter has a greater cross-sectional area to act on, and thus it takes less pressure to give the larger bullet the same total amount of accelerating force (force=pressure/area).
Go back and read the OP. It is the lighter 308 bullet that is getting less powder in the databook. Weight only works for comparison in this context when the bullets you are comparing are the same caliber.
The above is true because what matters is not absolute bullet weight but sectional density. If you stick with the same caliber, sectional density always goes up and down with weight, but when you change caliber, that matching relationship is gone. Sectional density is how much weight you have per square inch of bullet cross-sectional area*. Since pressure is the number of pounds of force you have per square inch of bullet cross-sectional area, it follows that pressure and sectional density combine to tell you how many pounds of force each grain of bullet weight has working to accelerate it down the tube. If the large diameter and small diameter bullets were the same weight, a lower pressure would give the larger diameter bullet the same acceleration as a higher pressure did the small diameter bullet. The larger diameter has a greater cross-sectional area to act on, and thus it takes less pressure to give the larger bullet the same total amount of accelerating force (force=pressure/area).