Assume a 9mm reload calling for 5 grains of powder with a 124 grain jacketed bullet. Would seating the bullet to a 1.00 inch C.O.L. increase the pressure to an unsafe level if the recommended C.O.L. Is 1.125 inches? I realize the seating depth affects pressure but what I don’t know is whether a published load can be made unsafe by seating a bullet too deep (assuming it isn’t so deep the max width of the bullet is below the neck of the case)
How much does it matter?
- Thread starter the45er
- Start date
mikejonestkd
New member
Hopefully someone will be along soon enough with a quickload calculation that shows how much pressure you would be getting by seating a bullet that short in a case.
9mm is probably one of the worst cartridges to try it with- you already have a small case at a fairly high pressure, so there is not a lot of wiggle room before pressure really spikes
9mm is probably one of the worst cartridges to try it with- you already have a small case at a fairly high pressure, so there is not a lot of wiggle room before pressure really spikes
The answer is yes and no. I don't know what bullet length or what bullet construction you are employing. I can tell you that in QuickLOAD, a load of 231 that drives a Hornady XTP seated to 1.125" COL with a peak pressure of 32,000 psi, then has the bullet pushed in to give 1.000" COL, sees that peak pressure jump to 61,600 psi in that computer model. That's unacceptable, of course.
The next question is, does that happen in real life? The answer is, it depends. Frequently, in short powder space cartridges, the primer can unseat the bullet and move it to the throat before the powder burn gets well enough along to do the unseating. In that instance, you don't see that actual peak pressure. Nonetheless, it isn't worth the risk to try it out.
The next question is, does that happen in real life? The answer is, it depends. Frequently, in short powder space cartridges, the primer can unseat the bullet and move it to the throat before the powder burn gets well enough along to do the unseating. In that instance, you don't see that actual peak pressure. Nonetheless, it isn't worth the risk to try it out.
Two thoughts
First,bullet lengths vary.LOA lets you easily replicate seating depth for an identical bullet.It does not work if you substitute hard ball for a hollow point,for example.
A direct answer to your question,deep seating 9mm by .125 will have a significant impact on pressure. I can't tell you how much.but I'll simply advise you don't do that.
Unclenick was faster,we were writing at the same time.
What Unclenick said!!
First,bullet lengths vary.LOA lets you easily replicate seating depth for an identical bullet.It does not work if you substitute hard ball for a hollow point,for example.
A direct answer to your question,deep seating 9mm by .125 will have a significant impact on pressure. I can't tell you how much.but I'll simply advise you don't do that.
Unclenick was faster,we were writing at the same time.
What Unclenick said!!
The answer is a qualified, "yes, maybe..."
It depends on the actual amount of pressure created, and your definition of "unsafe".
Published load data is worked up in a pressure vessel of a known fixed volume (the case with the bullet seated at a specific depth)
The powder charge is tailored so that the pressure obtained within the "standard" size vessel does NOT exceed industry specs for EVERYDAY use.
Change the capacity of the vessel, and keep the same powder charge, you DO change the pressure.
Now, how much do you change is, and is it "unsafe"??
How much is unsafe??? Ok, when the gun goes KA-BOOM yes, but are you unsafe below that? How much below that is safe, and what isn't??
I think that, literally, anything short of proof test pressure is safe. Proof loads are "safe" (the gun survives them intact) However this doesn't mean they should be daily use.
SO, if bullet setback raises pressure to an undesired level, is it unsafe if nothing bad happens? Or just an undesirable and avoidable risk??
The gun plays a significant part, absolutely. Anyone remember the "Glock Ka-booms) that were frequent enough to make a name for themselves?
.40 caliber and often happening with "regular ammo"???
Or the "Super Face"?? Getting peppered with case fragments due to failure of a too high pressure .38 Super in a 1911A1 pattern gun??
These are examples of the principle which is valid, there is an unsafe point. WHERE that point is varies, with the design of the gun.
Again, industry standards are set to things are as safe a possible, in ALL guns of the caliber. Commercial ammo has to be "safe" in supported and unsupported chambers because both are out there in the consumer market.
Things like "Ruger Only" loads are published data, but NOT endorsed by Ruger.
.45-70 loads have been classed in 3 levels depending on what gun they are to be used in, and its been that way since the 70s when modern single shots (Rugers) and converted bolt actions became common. Before that, you find Trapdoor and 1886 Winchester loads.
So, yes, specific features of gun design do matter, they make a difference WHERE (at what amount) the pressure goes from safe to unsafe.
Aguila Blanca
Staff
There's one other piece of information missing from the question:
If you know the case volume and the seating depth, you don't need QuickLoad to do a rough-and-ready calculation. The burning of gunpowder produces a gas, and it's the gas that exerts the pressure. I still remember from high school physics (unless it was chemistry) the formula for gas pressure:
P1V1 = P2V2
T1 . . . . T2
Where P = Pressure
V = Volume
T = Temperature
Since we're doing rough-and-ready, and since the temperature will be generated by the combustion and probably won't be significantly different for the two cartridges, it boils down to P1V1 = P2V2. #1 is the published load, # 2 is the load with the increased seating depth. We want to know P2:
P2 = P1V1/V2
I wouldn't bet the farm on the accuracy of this quickie calculation, but if P1 is anywhere near max and P2 is at or over max ... I think this is close enough to convince me that it's not a good idea. If P2 is borderline-ish, then maybe you find a friend who has QuickLoad and run it through that ... but even QuickLoad is only an approximation (albeit a much better one than my off-the-cuff computation).
Is the 5 grains of powder (unnamed) the starting load, the maximum load, or somewhere in between?
If you know the case volume and the seating depth, you don't need QuickLoad to do a rough-and-ready calculation. The burning of gunpowder produces a gas, and it's the gas that exerts the pressure. I still remember from high school physics (unless it was chemistry) the formula for gas pressure:
P1V1 = P2V2
T1 . . . . T2
Where P = Pressure
V = Volume
T = Temperature
Since we're doing rough-and-ready, and since the temperature will be generated by the combustion and probably won't be significantly different for the two cartridges, it boils down to P1V1 = P2V2. #1 is the published load, # 2 is the load with the increased seating depth. We want to know P2:
P2 = P1V1/V2
I wouldn't bet the farm on the accuracy of this quickie calculation, but if P1 is anywhere near max and P2 is at or over max ... I think this is close enough to convince me that it's not a good idea. If P2 is borderline-ish, then maybe you find a friend who has QuickLoad and run it through that ... but even QuickLoad is only an approximation (albeit a much better one than my off-the-cuff computation).
Ask a question on this forum and you get good feedback! Rare these days. Too many smart crackers trying to earn an online living by stupid remarks.
Thank all of you for the considerate feedback. Rest assured I'm not going to load any 1.0" 9mm's. In fact, I just looked closely at the load I had loaded up with 4.9 grains of IMR 7825 and 124 grain Berry's RN bullets. The load I used called for a C.O.L. of 1.125". My loads were 1.120", hardly enough to cause much of an overpressure if any. I looked at the bullet and concluded that even if you tried to load a 1.00" C.O.L. length, the bullet would seat down so far that the depression around the rim of the casing would be noticeable. I'm not sure you could even taper crimp it.
Anyway, thank you all for the good responses. Shoot well and be safe!
Thank all of you for the considerate feedback. Rest assured I'm not going to load any 1.0" 9mm's. In fact, I just looked closely at the load I had loaded up with 4.9 grains of IMR 7825 and 124 grain Berry's RN bullets. The load I used called for a C.O.L. of 1.125". My loads were 1.120", hardly enough to cause much of an overpressure if any. I looked at the bullet and concluded that even if you tried to load a 1.00" C.O.L. length, the bullet would seat down so far that the depression around the rim of the casing would be noticeable. I'm not sure you could even taper crimp it.
Anyway, thank you all for the good responses. Shoot well and be safe!
Have not heard of IMR 7825. Is this an old powder?
LOL that's what I get for typing without my glasses! IMR SR7625
Aguila Blanca
Staff
the45er said:
Where did you get your load data? Looking on the Hodgdon web site, for a 9mm 124-grain bullet with IMR SR7625, there's only one recipe, and that calls for a C.O.A.L. of 1.150", not 1.125". The charge range is 4.3 grains to 4.9 grains.
And based on the shorthand nomenclature on the Hodgdon site, I believe the recipe is for using Berry's Bullets Hollow-Base, Round-Nose, Thick Plate bullets ("BERB HBRN TP"). That's Berry's #15143. Berry's calls for loading that one to 1.150". But Berry's has another 124-grain round-nose, the #76848. That one isn't a hollow base bullet. Berry's suggests loading that one to a C.O.A.L. of 1.160".
I think reducing either of those to a C.O.A.L. of 1.00" would increase the pressure significantly.
Last edited:
"0mm, 124gr bullet"??? 
Thinking Aguila didn't have his glasses on either..
Possible that the45er got his data from another source?
Berrys, or Lyman perhaps?
Lets not forget that different sources come with often different data.
Hence the reloaders mantra of "This is for MY gun, Your gun is different".
Along with the always sage advice of start low, work up.
Thinking Aguila didn't have his glasses on either..
Possible that the45er got his data from another source?
Berrys, or Lyman perhaps?
Lets not forget that different sources come with often different data.
Hence the reloaders mantra of "This is for MY gun, Your gun is different".
Along with the always sage advice of start low, work up.
Please look on page 56
My load data source:
http://pdf.textfiles.com/manuals/FIREARMS/imr_reloading.pdf
My load data source:
http://pdf.textfiles.com/manuals/FIREARMS/imr_reloading.pdf
Last edited:
That data is obsolete at this point. Some of it is still valid and some isn't. In particular, I believe SR 7625 was dropped from their line last year or so, but Hodgdon still lists data for it. IMR is distributed by Hodgdon now, which is why they have the updated load data. They actually list the 124-grain HBRN Berry's seated to 1.15" COL with 4.3 grains as the starting load and 900 fps from their 4" test barrel, and 4.9 grains as maximum, getting 1,054 fps from their 4" barrel. So that one didn't change a lot. 800X on the other hand, gave a maximum of 6.5 grains in your data, while the current Hodgdon data puts 5.7 grains as the current maximum.
Another thing the Hodgdon data has for you are some 125-grain bullets (close enough not to matter) that are blunt shapes that need shorter seating, like the Hornady HAP. They seat it to 1.069", but the maximum load listed with your powder is just 3.8 grains. That should give you a concrete example of the difference seating shorter makes.
Powders can change with which plant they are made in and by what process. Also, testing has become computerized and better standardized than it was when that manual was written and occasionally they find some pressure spikes or other issues they couldn't see in the past. Also, a lot of old data was developed firing production guns rather than SAAMI standard-compliant velocity and pressure test barrels, and so you have data you know worked in one person's gun, but was not really made standard. Bottom line: always try to find current data.
Another thing the Hodgdon data has for you are some 125-grain bullets (close enough not to matter) that are blunt shapes that need shorter seating, like the Hornady HAP. They seat it to 1.069", but the maximum load listed with your powder is just 3.8 grains. That should give you a concrete example of the difference seating shorter makes.
Powders can change with which plant they are made in and by what process. Also, testing has become computerized and better standardized than it was when that manual was written and occasionally they find some pressure spikes or other issues they couldn't see in the past. Also, a lot of old data was developed firing production guns rather than SAAMI standard-compliant velocity and pressure test barrels, and so you have data you know worked in one person's gun, but was not really made standard. Bottom line: always try to find current data.
Aguila Blanca
Staff
But that shows a Remington 124-grain "MC" (Metal Case) bullet, which is different from either of the two Berry's bullets you might have. You haven't yet identified which one you have, and it does make a difference. One has a hollow base, the other doesn't. And Berry's recommends a different C.O.A.L. for each of the two.
And that doesn't call for 5 grains, it calls for 4.9 grains. The way the data are presented, that's the maximum safe load so, if we assume the data are still valid, anything that would increase the pressure should be assumed to be unsafe.
Going back to the high school science class formula for gas pressure, P1V1/T1 = P2V2/T2. Since the two we would be comparing both involve burning gunpowder at a high temperature, for simplicity let's assume the temperatures are approximately equal and ignore T. So we want to compare the pressure change from the specified load to one with the bullet seated deeper. So the variable is the volume.
First we need to calculate the case volume. For the 9mm, Wikipedia lists a case volume of 0.862 cubic cm. That's .05260 cu. in.
Case length is (per Wikipedia) .754 in. Using the Berry's bullet from the on-line Hodgdon/IMR data, Berry's gives us a bullet length of .612 in.
The case length of .754 plus the bullet length of .612 adds up to 1.366. Hodgdon and Berry's call for a C.O.A.L. of 1.150", which means the bullet will be seated to a depth of 1.366 - 1.150 = .216 inches.
Bullet diameter is .356. Bullet cross sectional area is .10462 square inches.
.10462 times the seating depth of .216 means the seated bullet occupies .10462 x .216 = .02260 cubic inches. The remaining case volume is therefore .05260 - .02260 = .03000 cubic inches.
Now let's seat the same bullet to a C.O.A.L. of 1.000 inches. 1.366 - 1.000 = .36600" seating depth. Off the top of your head you can see that's a 50% increase in seating depth. So how much difference does that make?
.10462 x .366 = .03829 cubic inches, our new seating volume. So the new case volume behind the bullet will be .05260 - .03829 = .01431 cubic inches.
Again right off the top we can see that the new case volume (behind the bullet) is less than half what it was before. The formula is linear: Ignoring temperature, P1V1 = P2V2.
P2 = P1V1/V2
So the new pressure will be:
P2 = P1 x V1/V2
P2 = P1 x .03000/.01431
P2 = P1 x 2.09644
It's a rough calculation, that starts with the assumption that the combustion temperatures of the two loads will be close enough that we can ignore the effect of temperature. I'm comfortable with that assumption. What we see is that this "small" change in seating depth DOUBLES the pressure.
This is why (a) we don't exceed published load maximums, and (b) why it's so important to read and understand the complete load recipe. If the bullet you want to load is longer than the bullet in the published recipe and you load it to the same C.O.A.L., then you will be increasing the seating depth, which reduces the available case volume behind the bullet and increases the pressure.
Class is dismissed. Don't forget to turn in your homework assignments on the way out the door,.
Aguila Blanca
Staff
Heh, heh.44 AMP said:
Proof loads are "safe" IF the gun survives. The whole purpose of a proof round is to be right on the ragged edge of "safe" so that a gun with a defect won't survive firing the proof load(s). That's a bit like saying it's "safe" to pull the pin on a hand grenade with a 10-second fuse and hold it in your hand for nine seconds ...
Aguila Blanca
Staff
Digging a bit deeper into that old IMR loading manual. From the Handguns section in the front:
Note: "The powder charge weights specified represent loads that developed Maximum Allowable Chamber Pressures ..."
What we typically find today is load data giving a starting load and a maximum load. Here, IMR didn't provide a range, so it's up to the individual to follow accepted practice and work up to the maximum load. Generally, you would begin at 10% less, so where they listed 4.9 grains (not 5 grains) as the maximum, a starting load might be 4.4 grains. So IMR didn't "call for" a load of 5 grains. They didn't "call for" a load of 4.9 grains. They said "Do not exceed 4.9 grains."
Note: "The powder charge weights specified represent loads that developed Maximum Allowable Chamber Pressures ..."
What we typically find today is load data giving a starting load and a maximum load. Here, IMR didn't provide a range, so it's up to the individual to follow accepted practice and work up to the maximum load. Generally, you would begin at 10% less, so where they listed 4.9 grains (not 5 grains) as the maximum, a starting load might be 4.4 grains. So IMR didn't "call for" a load of 5 grains. They didn't "call for" a load of 4.9 grains. They said "Do not exceed 4.9 grains."
Now I’m told the first “hit” I had when looking up loads is obsolete. Well, the powder is old too! The Berrys bullets are solid based. The 4.1 grain loads won’t cycle the Ruger. I’ll go ahead and back the load down a grain or two but based on the experience shooting so far, I. I’m really not worried that I’m flirting with disaster here. I have a chrono that I use for archery that will handle bullets too. I’ll chrono some tomorrow and make sure I’m not exceeding Berry’s recommended velocities.
Aguila Blanca
Staff
Berry's velocity recommendation is not related to safe working pressures. It's provided because their bullets are plated, and if you over-drive them the plating may start to peel off.