"FBI Load"

8

849ACSO

New member
CAUTION: The following post (or a page linked to) includes or discusses loading data not covered by currently published sources of tested data for this cartridge (QuickLOAD or Gordon's Reloading Tool data is not professionally tested). USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

I tried searching the forum, but I didn't see anything immediate related to this.

I've been fiddling with Hornady 158gr Swaged bullets and .38Spl to try and duplicate the old "FBI" load, which if correct, was a LSWCHP driven at about 1050 from a 4" gun, and would still get into the high 800s in a 2.5" gun.

What I'm about to say are loads I have loaded - Use at your own risk -

I managed to get that done in my 66-8 (2.75") with a 5.2gr charge of Unique in .38Spl cases.

I opted to try to get those same speeds from the same bullet and powder using 357Mag cases. No particular reason why, other than they're there.

I got that done with about 5.9gr of unique.

I Liquid aloxed the bullets to help eliminate any leading issues, which seemed to work ok. There's a few smears of lead in the barrel after 75ish rounds.

Anyway - on to my question - I noticed the PERCEIVED recoil with the 357 cases seemed less than with the 38Spl cases. The noise was more "thunderous", but the recoil seemed less sharp. I find this very odd.

Anyone have any insight as to why that would be?
 
All I can think of is that in the larger case, the burn rate is lower in such a way as to produce more of a "push" than a "kick".
 
That was my thought as well, but.............

5.2 in a 38Spl case to about 6.0 in a slightly larger case, with the same bullet speed, would lend to the theory that all should be about the same. Unless the pressure is enough different with the change in case volume vs. powder volume, and the bullet isn't in the gun as long makes the difference. That is what I was thinking anyway.

It's just weird to me the impulse would be noticeably different.
 
849ACSO said:
I tried searching the forum, but I didn't see anything immediate related to this.

I've been fiddling with Hornady 158gr Swaged bullets and .38Spl to try and duplicate the old "FBI" load, which if correct, was a LSWCHP driven at about 1050 from a 4" gun, and would still get into the high 800s in a 2.5" gun.

What I'm about to say are loads I have loaded - Use at your own risk -

I managed to get that done in my 66-8 (2.75") with a 5.2gr charge of Unique in .38Spl cases.

I opted to try to get those same speeds from the same bullet and powder using 357Mag cases. No particular reason why, other than they're there.

I got that done with about 5.9gr of unique.

I Liquid aloxed the bullets to help eliminate any leading issues, which seemed to work ok. There's a few smears of lead in the barrel after 75ish rounds.

Anyway - on to my question - I noticed the PERCEIVED recoil with the 357 cases seemed less than with the 38Spl cases. The noise was more "thunderous", but the recoil seemed less sharp. I find this very odd.

Anyone have any insight as to why that would be?
Click to expand...
Larger case volume, same powder charge, less pressure, less recoil.
 
Larger case volume, same powder charge, less pressure, less recoil.
Click to expand...

That's not what the OP is talking about. He is loading more powder into the larger case. What he has done is matched the velocity of his .38 and .357 loads.

Which means that the pressure is going to be the same.

Now, bearing in mind that we are talking about very small differences in volume and VERY short periods of time, ...

When you start with a "bigger bottle" even though you have increased the powder charge to compensate for the larger case volume, it takes a slightly different amount of time to get to that peak pressure than it does with the smaller case and its powder charge.

This could result in the perception of reduced recoil. Because while the total energy is the same, the force over time is changed. As mentioned, a push, vs. a slap...

as to the bigger muzzle blast, well, you are burning more powder. If my math is right, about 15% more...
 
44 AMP

Yes. Roughly 15%.

Case volume is 1 question. What's the difference in case volume? I haven't H2O checked myself. Standard logic would be more volume. Based on length alone, about 10%, but I've seen some folks saying the 357M cases actually have less volume........?? Dunno.

The other question is the shorter time the bullet is in the gun from the time it starts to move, supposing velocity is the same at the muzzle. If at the muzzle, the speed is the same, then the bullet got to that speed faster in the longer case, as it started it's journey closer to the muzzle, hence, I would think there would be more recoil.

I'm not much of a science guy, but this is somewhat intriguing.
 
You don't need to be a science guy, you just need to know some dimensions and be able to visualize thing a little, and recognize that sometimes what seems like a lot isn't, and some times what seems like a little, is....


The .357 case is (max specs) 0.135" longer than the .38 special case.

HOWEVER, loaded length (w/bullet) the .357 is only 0.040" longer than the .38 Special.

That is slightly less than 1/3 the difference in the case lengths. Using the same bullet, the base of that bullet is NOT .135" farther ahead in the magnum case, it is only .040 farther ahead (closer to the muzzle) than the base of the same bullet in .38 Special brass.

The rest of the .357's "extra" case length is on the outside of the bullet, reaching up further on the bullet than .38 brass does (which is why some designs have two crimp grooves) and it does so only to prevent chambering in .38 Special guns.

SO, the additional powder space in the magnum case is a flat cylinder, the diameter of the case interior and 0.040" high (at max specs)

I'm not going to hurt my head today trying to remember high school geometry, but feel free to calculate the volume of that "cylinder" 0.040" high and compare that amount as a percentage of the total available volume.

Now, to further complicate matters (and do remember essentially what we're talking about is how many angels can dance on the head of a pin ;)) modern smokeless powders are "progressive". The effect is most pronounced in rifles and their large powder charges, but it happens in pistols, too.

What this means is that the powder is formulated to burn at a given rate, producing X amount of gas over a specific period of time, AND do that as the pressure in the case goes from relative "zero" (standard air pressure) to thousands of PSI in a very, very short time.

In effect, as the pressure inside the case goes up, (and this is well before the bullet begins to move) the powder has to burn "harder" to overcome the increasing pressure and release more gas to keep increasing the pressure up to the point the bullet moves, and THEN keep going as the volume of the case increases with the bullet moving forward, until complete combustion/peak pressure is reached.

AND, keep that pressure up long enough to send the bullet down (and out of) the barrel. Specifically how the powder makers figure that out gets very detailed and a bit tricksy chemistry, but the principles are understandable, easily enough.

The other question is the shorter time the bullet is in the gun from the time it starts to move, supposing velocity is the same at the muzzle. If at the muzzle, the speed is the same, then the bullet got to that speed faster in the longer case, as it started it's journey closer to the muzzle, hence, I would think there would be more recoil.
Click to expand...

recoil energy is exactly the same as the energy that comes out of the muzzle. (Newton's 3rd law, equal and opposite reaction, etc.) But its not exactly the same as the bullet's ME, its slightly more, due to the powder gas mass and speed and a bit of the venturi efffect of the gas itself adding a little bit of energy. For practial use, you can consider it the same as the bullet ME.

SO, the force coming back is the same as the force going downrange.

BUT, that force coming back is converted into "felt recoil" in your mind. Many factors influence "felt" recoil. Gun weight, grips shape/fit to your hand. Relative speed of the recoil impulse, are just a few.

Another point to consider (a couple actually) since we're talking shooting .38s and .357s from the same gun barrel length becomes a fixed reference. so no fair comparing speeds from other barrels.

In BOTH .38 and .357 loads, your bullet is still accelerating when it gets to the end of your 2.5" barrel. Now, since the .357 bullet could only be as much as 0.40" ahead of the .38 bullet, the length that bullet travels is that much shorter than what the .38 does. BUT is that something significant??

both are going from zero to your desired high 800s fps at the muzzle. So, the .38 slug has to go 0.04" farther to get to the muzzle (at most). If you have the lab instruments to measure it, I expect you would find a slight difference in the "barrel time" between the .357 and .38, but since both your loads leave the muzzle at the same speed, what does it matter?

There are many many things where there is a measurable but not a significant difference. I think this is one.

Further complications involve the fact that both are accelerating as they move down the barrel. and while the acceleration rate might be slightly different, when both exit the muzzle, it becomes irrelevant.
Doesn't it? :rolleyes:

Felt recoil is what you feel. It involves an entire can of worms as factors, PLUS how you personally interpret the sensations.

Someone else, firing your gun and your loads might have a much different impression of the recoil they feel.

Clear as mud yet?? :rolleyes::D
 
44 AMP said:
You don't need to be a science guy, you just need to know some dimensions and be able to visualize thing a little, and recognize that sometimes what seems like a lot isn't, and some times what seems like a little, is....


The .357 case is (max specs) 0.135" longer than the .38 special case.

HOWEVER, loaded length (w/bullet) the .357 is only 0.040" longer than the .38 Special.

That is slightly less than 1/3 the difference in the case lengths. Using the same bullet, the base of that bullet is NOT .135" farther ahead in the magnum case, it is only .040 farther ahead (closer to the muzzle) than the base of the same bullet in .38 Special brass.

The rest of the .357's "extra" case length is on the outside of the bullet, reaching up further on the bullet than .38 brass does (which is why some designs have two crimp grooves) and it does so only to prevent chambering in .38 Special guns.

SO, the additional powder space in the magnum case is a flat cylinder, the diameter of the case interior and 0.040" high (at max specs)

I'm not going to hurt my head today trying to remember high school geometry, but feel free to calculate the volume of that "cylinder" 0.040" high and compare that amount as a percentage of the total available volume.

Now, to further complicate matters (and do remember essentially what we're talking about is how many angels can dance on the head of a pin ;)) modern smokeless powders are "progressive". The effect is most pronounced in rifles and their large powder charges, but it happens in pistols, too.

What this means is that the powder is formulated to burn at a given rate, producing X amount of gas over a specific period of time, AND do that as the pressure in the case goes from relative "zero" (standard air pressure) to thousands of PSI in a very, very short time.

In effect, as the pressure inside the case goes up, (and this is well before the bullet begins to move) the powder has to burn "harder" to overcome the increasing pressure and release more gas to keep increasing the pressure up to the point the bullet moves, and THEN keep going as the volume of the case increases with the bullet moving forward, until complete combustion/peak pressure is reached.

AND, keep that pressure up long enough to send the bullet down (and out of) the barrel. Specifically how the powder makers figure that out gets very detailed and a bit tricksy chemistry, but the principles are understandable, easily enough.



recoil energy is exactly the same as the energy that comes out of the muzzle. (Newton's 3rd law, equal and opposite reaction, etc.) But its not exactly the same as the bullet's ME, its slightly more, due to the powder gas mass and speed and a bit of the venturi efffect of the gas itself adding a little bit of energy. For practial use, you can consider it the same as the bullet ME.

SO, the force coming back is the same as the force going downrange.

BUT, that force coming back is converted into "felt recoil" in your mind. Many factors influence "felt" recoil. Gun weight, grips shape/fit to your hand. Relative speed of the recoil impulse, are just a few.

Another point to consider (a couple actually) since we're talking shooting .38s and .357s from the same gun barrel length becomes a fixed reference. so no fair comparing speeds from other barrels.

In BOTH .38 and .357 loads, your bullet is still accelerating when it gets to the end of your 2.5" barrel. Now, since the .357 bullet could only be as much as 0.40" ahead of the .38 bullet, the length that bullet travels is that much shorter than what the .38 does. BUT is that something significant??

both are going from zero to your desired high 800s fps at the muzzle. So, the .38 slug has to go 0.04" farther to get to the muzzle (at most). If you have the lab instruments to measure it, I expect you would find a slight difference in the "barrel time" between the .357 and .38, but since both your loads leave the muzzle at the same speed, what does it matter?

There are many many things where there is a measurable but not a significant difference. I think this is one.

Further complications involve the fact that both are accelerating as they move down the barrel. and while the acceleration rate might be slightly different, when both exit the muzzle, it becomes irrelevant.
Doesn't it? :rolleyes:

Felt recoil is what you feel. It involves an entire can of worms as factors, PLUS how you personally interpret the sensations.

Someone else, firing your gun and your loads might have a much different impression of the recoil they feel.

Clear as mud yet?? :rolleyes::D
Click to expand...
Delete, need more coffee.
 
44 AMP said:
recoil energy is exactly the same as the energy that comes out of the muzzle. (Newton's 3rd law, equal and opposite reaction, etc.)
Click to expand...

Actually, it is the momentum in the bullet and gun that wind up equal and opposite. The recoil energy is much lower than the muzzle energy because the bullet is accelerated to a much higher speed than the more massive gun is by the equal and opposite force, and energy is proportional to the square of velocity. For a 30-06, for example, you can get close to 3000 ft-lbs of muzzle energy but have only about a dozen ft-lbs of recoil energy, depending on the gun's weight. If this weren't so, the shooter would suffer damage from firing the shot.

The lower perceived recoil is interesting. With more powder and the same bullet at the same velocity, there will be more recoil momentum from the heavier load in the longer case. I think one thing that is happening is that because the longer case has more volume (about 11% more in QuickLOAD's database) your expansion ratio is smaller. This means pressure drops less between the chamber and the muzzle so that you get more of the bullet's acceleration occurring later in its travel down the tube, and less is from its position at the pressure peak. Thus, the peak pressure and peak recoil momentum are actually lower using the bigger case when the muzzle velocity matches. The second thing that is happening is that with the 38 Special cases reaching higher peak pressure, when the bullet clears the barrel/cylinder gap the blast from the gas escaping that gap is going to be higher, creating a sharper and louder sound and increasing blast wave that impacts your face. This can help create the overall impression of sharper recoil.
 
I believe you're right, again, of course, and I did say energy, but I was trying to keep things slightly simpler for the comprehension of the OP.

And, I failed at that, too...:rolleyes:

When you've been deeply involved in this for decades, as we have, its easy to forget how beginners can suffer information overload...or, it is for me, anyway. :D
 
No, keep at it, 44 AMP!

While not totally an "old hand", but not a Noob, i like and learn alot from You & Unclenick!

You don't have Unclenicks cool graphs, but your replies still get the gray matter swirling. ;)
 
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