Today I was told that lengthening your COL would increase pressure, if all things were equal to a shorter COL. I was always under the impression that by increasing your COL, you were increasing case capacity (from primer to base of bullet) and thus leaving more room for the same amount of powder to expand. To me, that would mean that your pressures decrease. I recognize that if you shove the bullet into the rifling lands with your COL, that would increase pressure, but that's an extreme. So as I believe, there is a limit to how much you increase your COL. I loaded some bullets .005" longer than the manual instructed me to do, and I was told that it was a dangerous practice. Please help if you can explain it simply.
Need help with a reloading concept.
- Thread starter Jbotto
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m&p45acp10+1
New member
There are several factors involved.
Also there is a huge difference between rifle, and hand gun. With straight wall pistol do not go shorter than the lowest number listed. With small low capacity high pressure rounds this can greatly spike pressures to the dangerous level. (Just as an example (.40 S&W, and 9mm Luger.)
Unclenick or some one else will be along to give a way better explanation that I ever will be able to.
Also there is a huge difference between rifle, and hand gun. With straight wall pistol do not go shorter than the lowest number listed. With small low capacity high pressure rounds this can greatly spike pressures to the dangerous level. (Just as an example (.40 S&W, and 9mm Luger.)
Unclenick or some one else will be along to give a way better explanation that I ever will be able to.
With any case reducing the capacity by seating the bullet further in can increase pressure. As mentioned above with smaller cases a slighty shorter overall length takes up a greater percentage of the space. In a large case that same shorter length uses up less space. .020 less in a pistol could be %7 of capacity where in a rifle it could be a negligible %1 etc.
Seating rifle bullets longer can increase pressure if it is jammed into the rifling/throat to start, where a shorter length is not. Usually if a person starts the load and works up at any length they will be ok staying at that length until seeing pressure signs or reaching the max book charge.
If you want to change the length closer to the rifling or jammed, you would start the powder charge low and work up again.
Seating rifle bullets longer can increase pressure if it is jammed into the rifling/throat to start, where a shorter length is not. Usually if a person starts the load and works up at any length they will be ok staying at that length until seeing pressure signs or reaching the max book charge.
If you want to change the length closer to the rifling or jammed, you would start the powder charge low and work up again.
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It looks like you have two concepts in your head and are trying to get a handle on them. On the one hand, you know that a shorter COL causes more case pressure, due to a reduced case volume (which is true), and on the other hand, with a rifle cartridge, for example, when you start creeping that ogive out towards the lands you are reducing the "jump" and not letting the bullet get the same "running head start" as compared to a load where the COL is shorter. The bullet is hitting the lands sooner, before the pressure can build enough to help it drive into the barrel and smoothly build pressure, so you can see a pressure spike.
Say you have a bullet that sits.030" from ogive to lands at a particular COL with a given powder charge. Say the pressure is "X". Now keep the charge the same and increase the COL by .030". That will place that bullet right at the lands. Two things have happened- you have increased the case volume, which in theory should reduce the pressure, but because the bullet now is facing much more resistance, earlier, you are going to be building pressure faster than before, possibly too fast.
Pressure is all about time in reloading. Until the bullet leaves the barrel you basically have one continuously expanding "chamber". Depending on where the 2 given bullets are at the beginning of the process, and during the process, you will see a different pressure curve even if both bullets started with the same charge behind them.
Say you have a bullet that sits.030" from ogive to lands at a particular COL with a given powder charge. Say the pressure is "X". Now keep the charge the same and increase the COL by .030". That will place that bullet right at the lands. Two things have happened- you have increased the case volume, which in theory should reduce the pressure, but because the bullet now is facing much more resistance, earlier, you are going to be building pressure faster than before, possibly too fast.
Pressure is all about time in reloading. Until the bullet leaves the barrel you basically have one continuously expanding "chamber". Depending on where the 2 given bullets are at the beginning of the process, and during the process, you will see a different pressure curve even if both bullets started with the same charge behind them.
Thanks AllenJ. It is forums like this (probably this one) that helped me get my head around the concept to begin with. That and Lee's Modern Reloading 2nd Edition (no snickering anyone, its a good manual) and the ABCs of Reloading of course.
FYI- for anyone who has an Amazon Prime membership the ABCs is available for to read free on any device using their lending library and a free Kindle Reading App. Well worth the read for any new reloader or seasoned reloader as well who hasnt read it.
FYI- for anyone who has an Amazon Prime membership the ABCs is available for to read free on any device using their lending library and a free Kindle Reading App. Well worth the read for any new reloader or seasoned reloader as well who hasnt read it.
wncchester
New member
Military arsenal tests of the .30-06 showed a reduction in chamber pressure as bullets were seated deeper until they were about .25" inch deeper than normal - a quarter inch, and that's a LOT deeper than many of us would go. And the pressure didn't 'spike' (I hate that meaningless term, chamber pressure IS a spike) even when they went that deep, it just started going back up.
Not sure what conclusions you are trying to draw in regards to the .30-06 test WNC. How the seating depth of a .30-06 bullet effects pressure in a rifle is going to be far different than how the seating depth of 9mm bullet effects a handgun, for example. Forget about .25"- even a .025" decrease in OAL could have very bad results in a 9mm load that was already at max.
Regarding the term "pressure spike"- if you have a .30-06 load that is at max pressure .050" off the lands and you suddenly increase your COL by .055", how would you describe the violent pressure increase you are going to see?
Regarding the term "pressure spike"- if you have a .30-06 load that is at max pressure .050" off the lands and you suddenly increase your COL by .055", how would you describe the violent pressure increase you are going to see?
Wow guys keep it coming! I am talking about rifle rounds. I've always loaded a touch longer than book lengths on .223 and now the .243. I am starting to grasp this concept though. But with my lengthening the .243 by .005" I just did not see that I was going to get to excessive levels by doing this.
10 Spot Terminator
New member
+1 on the explanations given by tkglazie. I take this concept one step farther using a Stony Point ( now Hornady ) bullet comparator to measure my seating depth of the cartridge from the length measured at the ogive of the bullet as oal of the bullets can vary quite a bit in just one box let alone in different lot numbers in a given manufactures bullet . Over time throat errosion in the barrel may be a tell you come accross using this form of bullet seating in conjunction with the readings you get with a coal measuring tool by the same companies. If accuracy starts to drop off this can be the culprit and send you back to the bench to tweek your loads accordingly. Its all part of the game seeking the "ultimate perfoming" round for your rifle .
One thing that is helpful when loading for accuracy in any rifle is to make up an ogive gauge using a dummy case with slits in the neck and whatever bullet you are planning to use. You place the bullet in the modified case very long then chamber it fully by hand or using a dowel. This pushes the bullet back into the modified case. Carefully remove the dummy cartridge, measure the resulting COL and compare that to whatever COL you are using or planning to use (do this a few times until you are sure your reading is true) Here is a good example of one such gauge, courtesy of larrywillis.com.
You can make one of these up for all of your bullet profiles. Well worth the effort. Note that this info is only going be as accurate as the variance in the ogive to bullet tip for whatever particular bullets you are using, so I wouldnt recommend using this as a way to get your bullets a couple of thousands off the lands or anything like that. Think of it instead as just one more piece of data to help you understand what is going on and improve your chances of loading safe, accurate rounds.
(10 Spot- I was typing this post when yours was posted and I didnt see it- looks like we are discussing the same theory. Your method is clearly the more precise one)
You can make one of these up for all of your bullet profiles. Well worth the effort. Note that this info is only going be as accurate as the variance in the ogive to bullet tip for whatever particular bullets you are using, so I wouldnt recommend using this as a way to get your bullets a couple of thousands off the lands or anything like that. Think of it instead as just one more piece of data to help you understand what is going on and improve your chances of loading safe, accurate rounds.
(10 Spot- I was typing this post when yours was posted and I didnt see it- looks like we are discussing the same theory. Your method is clearly the more precise one)
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jbotto, I am the fan of the running start, I want my bullets to have a jump, backing the bullet up into the case for the jump at the running start can cause a small increase in pressure. If I should decide to seat the bullet out to the lands I could cause a small increase in pressure, seems the bullet starts to move with the running start before hitting the lands, then, hitting the lands can cause the bullet to slow down while the pressure is building, back to the part where I do not seat to the lands, I do not want my bullet setting still and jammed into the rifling while the pressure builds, time is a factor.
I know, it sounds cute “I seat my bullets .001” off the lands...etc..”
I am also the fan of transfers, standards and verifying measurements. I drill the flash hole/primer pocket out of the head of the case, I then full length size the case to get all the bullet hold I can get, then seat a bullet, remove the bolt, chamber the modified case, then with a push rod, I push the bullet out of the case and into the rifling, when the bullet stops against the rifling I remove the modified case and use it to set up my seater die. The only thing I have to keep up with is when the seater plug is adjusted down to the bullet the seater die is adjusted for .000 off the lands (and head space as in the length of the chamber from the bolt face to the shoulder of the chamber, the bolt was removed (remember), so my adjustment if .000 off the lands plus the difference 9in length between the case and chamber from the usual places.
F. Guffey
I know, it sounds cute “I seat my bullets .001” off the lands...etc..”
I am also the fan of transfers, standards and verifying measurements. I drill the flash hole/primer pocket out of the head of the case, I then full length size the case to get all the bullet hold I can get, then seat a bullet, remove the bolt, chamber the modified case, then with a push rod, I push the bullet out of the case and into the rifling, when the bullet stops against the rifling I remove the modified case and use it to set up my seater die. The only thing I have to keep up with is when the seater plug is adjusted down to the bullet the seater die is adjusted for .000 off the lands (and head space as in the length of the chamber from the bolt face to the shoulder of the chamber, the bolt was removed (remember), so my adjustment if .000 off the lands plus the difference 9in length between the case and chamber from the usual places.
F. Guffey
wncchester
New member
"Not sure what conclusions you are trying to draw in regards to the .30-06 test WNC. How the seating depth of a .30-06 bullet effects pressure in a rifle is going to be far different than how the seating depth of 9mm bullet effects a handgun, for example. Forget about .25"- even a .025" decrease in OAL could have very bad results in a 9mm load that was already at max."
I stated a fact, leaving you to draw your own conclusion and I'll leave it at that. But I cited .30-06 rifle ammo, not handgun, so I don't quite understand what you don't understand. But, since you raise the issue of handguns, specifically the 9mm, it and the 10mm are recipricals of rifles because they are very small, low volume cases with high pressure loads that use very fast burning powders. What applies with that combination really doesn't apply to rifles or revolver cartridges but some people seem to think it does; is that confusing?
"Regarding the term "pressure spike"- if you have a .30-06 load that is at max pressure .050" off the lands and you suddenly increase your COL by .055", how would you describe the violent pressure increase you are going to see?"
I say jamming into the lands with an established load will produce an increase in pressure while seating deeper (extending bullet jump to the lands) will decrease pressure. Indeed, that was the whole point of the published military findings I cited! But it won't be a 'spike' in the way spike gets used on the web; the whole pressure:time thing is quite high and very brief so a quite normal pressure curve is a spike when graphed; how do we spike a spike? Calling a rise in pressure a 'spike' suggests some unexpected, strange or weird event, which it certainly is not.
Your senerio of "suddenly" jamming into the lands and inducing a "violent pressure increase" is meaningless unless the loader is a fool. No one should ever make such a drastic change without standard work up proceedure and if a loader will does something that stupid he will do other stupid things too - so what conclusion are you trying to draw from your hypothetical (and irrational, IMHO) example??
What do you call a 'max pressure' load; do you mean a standard SAAMI factory load, or a proof load or a load that is barely below bursting? That matters because what would actually happen in your senerio depends on which max pressure definition you're assuming, along with what bullet and powder is being used. All meaning what would actually occur is not as simple as you seem to assume.
I stated a fact, leaving you to draw your own conclusion and I'll leave it at that. But I cited .30-06 rifle ammo, not handgun, so I don't quite understand what you don't understand. But, since you raise the issue of handguns, specifically the 9mm, it and the 10mm are recipricals of rifles because they are very small, low volume cases with high pressure loads that use very fast burning powders. What applies with that combination really doesn't apply to rifles or revolver cartridges but some people seem to think it does; is that confusing?
"Regarding the term "pressure spike"- if you have a .30-06 load that is at max pressure .050" off the lands and you suddenly increase your COL by .055", how would you describe the violent pressure increase you are going to see?"
I say jamming into the lands with an established load will produce an increase in pressure while seating deeper (extending bullet jump to the lands) will decrease pressure. Indeed, that was the whole point of the published military findings I cited! But it won't be a 'spike' in the way spike gets used on the web; the whole pressure:time thing is quite high and very brief so a quite normal pressure curve is a spike when graphed; how do we spike a spike? Calling a rise in pressure a 'spike' suggests some unexpected, strange or weird event, which it certainly is not.
Your senerio of "suddenly" jamming into the lands and inducing a "violent pressure increase" is meaningless unless the loader is a fool. No one should ever make such a drastic change without standard work up proceedure and if a loader will does something that stupid he will do other stupid things too - so what conclusion are you trying to draw from your hypothetical (and irrational, IMHO) example??
What do you call a 'max pressure' load; do you mean a standard SAAMI factory load, or a proof load or a load that is barely below bursting? That matters because what would actually happen in your senerio depends on which max pressure definition you're assuming, along with what bullet and powder is being used. All meaning what would actually occur is not as simple as you seem to assume.
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