OAL, reloading Manuel vs factory

Machineguntony · July 18, 2013, 01:59 AM

I am a bit confused by this. Perhaps I can get some input.

So I've been loading 9mm according to the hodgdon guide and some other info on the Internet. I am using 115 grain bullets. In most manuals, it says to make the OAL 1.10 inches, like in the hodgdon data site.

I've been loading to 1.15 because all the factory rounds that I've measured have an OAL of 1.15.

There seems to be a difference visually, as the 1.10 appears significantly shorter than the 1.15 loads.

Is there a reason why factory loads have a longer OAL?

It's not just one factory load. I measured four factory loads, and they all are around 1.15.

I'm using Longshot, btw.

Grizz12 · July 18, 2013, 04:51 AM

which bullets are you using and in what gun?

chiefr · July 18, 2013, 07:42 AM

OAL is one of those things (just like crimping) that confuses many reloaders and there are many different answers.

All OALs vary, even with the same weight bullet. A box of R-P will have a different OAL than a box of FC. European carts are all over the place with OALs. Most manuals list the minimum acceptable OAL for function thru virtually any firearm.

SL1 · July 18, 2013, 07:59 AM

From the bullet weight, I will infer that you are loading a 9mm Luger cartridge and shooting it in an auto-loading pistol. (It would help to always say that when you are asking a question.)

In short cartridges that operate at high pressure (e.g., 9mm, 40 S&W), the depth that the bullet intrudes inside the case (called bullet seating depth) determines how much space is left for the powder. The amount of space that the powder has when it ignites (and a lot of other factors such as the amount of powder and the bullet's weight) determine the peak pressure that the gases reach as the powder burns. Therefore, bullet seating depth is important to the pressure that a load creates, and thus to safety, and that is why the manuals include the cartridge length used to create the load data WITH A PARTICULAR BULLET.

What confuses a lot of people is that the cartridge overall length (some call it COL, others OAL) is not the sole parameter that determines the seating depth and thus the amount of space left for the powder - - the other parameter is the length of the particular bullet that is being loaded. The manuals always specify a bullet too (except Lee's which only copies a part of the data from the powder manufacturers' manuals, often giving a COL without telling you which manufacturer's "jacketed" bullet was used). But, even the bullet manufacturer's manuals don't tell you the length of their bullets.

Bullets of the same weight but with different shapes (e.g., round nosed, hollow pointed, etc.) can have substantially different lengths. Even when two bullets with the same weight are loaded to the same COL (or OAL), they may have different seating depths and thus leave different amounts of space for the powder. Especially in 9mm, even "round nose" bullet noses can be of such different shapes that the bullets have substantially different lengths.

What we really want to know when we need to substitute a different bullet (from what is in the data) is the seating depth used for the data. That can be calculated by adding the case length to the bullet's length and subtracting the COL listed in the manual. But, we don't have that bullet length from the manual. If you don't have one of the manual's bullets to measure, you can ask for help from people on this forum, or maybe even call the bullet's manufacturer and ask them. Of coourse, you have the bullets you are going to load, so you can measure those yourself. With that information, you can match seating depth to the data, which will give you similar pressures (assuming that you are subsituting bullets of the same construction type, not jacketed for lead, or solid copper for jacketed).

Another wrinkle on all this is that the case length is a little ambiguous. SAAMI specifies a maximum length, and manuals usually specify a "trim to" length that is 0.010" shorter than that max length. But, especially with short auto-loader pistol cartridges, it is not unusual for cases used multiple times to shorten to less than the "trim to" length. So, there is often an ambiguity in the length of the case that exceeds 0.010" That seems like not much difference, but, for 9mm cartridges, it can mean differences in peak pressure that amounts to thousands of psi. So, when doing the substitution calculation for a couple of bullets, that ambiguity can be bypassed by changing the manual COL directly by the difference in the lengths of the two bullets. For example, if the manual says they used a bullet that is 0.600" long and you want to use a bullet that is 0.630" long, you will get the same seating depth if you load the substitute bullet that is 0.030" longer to a COL that is 0.030" longer than the COL in the data.

Compared to the data, loading THE SAME BULLET to shorter COL raises pressure and loading to longer COL lowers pressure. But, you really can't tell what you are doing with pressure simply by comparing COLs from two cartridges with different bullets until you know the lengths of the two bullets.

It is not uncommon for people to adjust the COL to make the auto-feeding process reliable in their particular pistols. Some do that and even substitute bullets without taking into account the effects on pressure, and will post defenses of that practice on this forum. Others will always go to the trouble of quantifying the effects on powder space and adjust the powder charges accordingly, at least when loading near maximum. (As you can guess, I am in the second category.) At least learning HOW to think about COL and pressure PROPERLY is helpful in avoiding trouble. It IS possible to blow-up a gun when handloading, and that is usually followed by a confused handloader trying to figure out what happened. Nobody INTENTIONALLY blows-up a gun while holding it in their hands; they just missed something, sometimes because they did not understand something properly.

One related issue that I will mention is "bullet setback" which is a change in COL that occurs during the auto-feed process when the slide bangs the bullet into the feed ramp while feeding a cartridge from the magazine into the chamber. There is a surprising amount of force involved, which can push the bullet back into the case. That has the same effect on pressure as if you intentionally seated the bullet much deeper at the loading bench. So, making sure that your case grips the bullet tightly is another important aspect of handloading. In auto-loading cartridges that headspace on the case mouth, that canNOT be achieved with the crimp; it is a matter of using the proper expander die plug diameter. But, this reply is already long, so I will leave that subject to other threads.

SL1

buck460XVR · July 18, 2013, 12:21 PM

Factory load OAL has nuttin at all to do with OAL of the rounds you load yourself EXCEPT as a reference to how they feed in your autoloader. Bullet profile has much to do with what OAL feeds best in your gun. If revolver rounds then OAL is determined by the position of the cannelure and the length of your cases. You reload to the specs in your manual for the powder and bullet. If you need to adjust your OAL for proper feeding, you adjust the loads appropriately.

wncchester · July 18, 2013, 08:17 PM

Factory ammo was loaded to the proper pressure for their powder and charge. Manual ammo was loaded to the proper pressure for their powder and charge.

July 18, 2013, 01:59 AM	#1
Machineguntony Senior Member Join Date: June 22, 2013 Posts: 1,277	OAL, reloading Manuel vs factory I am a bit confused by this. Perhaps I can get some input. So I've been loading 9mm according to the hodgdon guide and some other info on the Internet. I am using 115 grain bullets. In most manuals, it says to make the OAL 1.10 inches, like in the hodgdon data site. I've been loading to 1.15 because all the factory rounds that I've measured have an OAL of 1.15. There seems to be a difference visually, as the 1.10 appears significantly shorter than the 1.15 loads. Is there a reason why factory loads have a longer OAL? It's not just one factory load. I measured four factory loads, and they all are around 1.15. I'm using Longshot, btw.

July 18, 2013, 07:59 AM	#4
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	From the bullet weight, I will infer that you are loading a 9mm Luger cartridge and shooting it in an auto-loading pistol. (It would help to always say that when you are asking a question.) In short cartridges that operate at high pressure (e.g., 9mm, 40 S&W), the depth that the bullet intrudes inside the case (called bullet seating depth) determines how much space is left for the powder. The amount of space that the powder has when it ignites (and a lot of other factors such as the amount of powder and the bullet's weight) determine the peak pressure that the gases reach as the powder burns. Therefore, bullet seating depth is important to the pressure that a load creates, and thus to safety, and that is why the manuals include the cartridge length used to create the load data WITH A PARTICULAR BULLET. What confuses a lot of people is that the cartridge overall length (some call it COL, others OAL) is not the sole parameter that determines the seating depth and thus the amount of space left for the powder - - the other parameter is the length of the particular bullet that is being loaded. The manuals always specify a bullet too (except Lee's which only copies a part of the data from the powder manufacturers' manuals, often giving a COL without telling you which manufacturer's "jacketed" bullet was used). But, even the bullet manufacturer's manuals don't tell you the length of their bullets. Bullets of the same weight but with different shapes (e.g., round nosed, hollow pointed, etc.) can have substantially different lengths. Even when two bullets with the same weight are loaded to the same COL (or OAL), they may have different seating depths and thus leave different amounts of space for the powder. Especially in 9mm, even "round nose" bullet noses can be of such different shapes that the bullets have substantially different lengths. What we really want to know when we need to substitute a different bullet (from what is in the data) is the seating depth used for the data. That can be calculated by adding the case length to the bullet's length and subtracting the COL listed in the manual. But, we don't have that bullet length from the manual. If you don't have one of the manual's bullets to measure, you can ask for help from people on this forum, or maybe even call the bullet's manufacturer and ask them. Of coourse, you have the bullets you are going to load, so you can measure those yourself. With that information, you can match seating depth to the data, which will give you similar pressures (assuming that you are subsituting bullets of the same construction type, not jacketed for lead, or solid copper for jacketed). Another wrinkle on all this is that the case length is a little ambiguous. SAAMI specifies a maximum length, and manuals usually specify a "trim to" length that is 0.010" shorter than that max length. But, especially with short auto-loader pistol cartridges, it is not unusual for cases used multiple times to shorten to less than the "trim to" length. So, there is often an ambiguity in the length of the case that exceeds 0.010" That seems like not much difference, but, for 9mm cartridges, it can mean differences in peak pressure that amounts to thousands of psi. So, when doing the substitution calculation for a couple of bullets, that ambiguity can be bypassed by changing the manual COL directly by the difference in the lengths of the two bullets. For example, if the manual says they used a bullet that is 0.600" long and you want to use a bullet that is 0.630" long, you will get the same seating depth if you load the substitute bullet that is 0.030" longer to a COL that is 0.030" longer than the COL in the data. Compared to the data, loading THE SAME BULLET to shorter COL raises pressure and loading to longer COL lowers pressure. But, you really can't tell what you are doing with pressure simply by comparing COLs from two cartridges with different bullets until you know the lengths of the two bullets. It is not uncommon for people to adjust the COL to make the auto-feeding process reliable in their particular pistols. Some do that and even substitute bullets without taking into account the effects on pressure, and will post defenses of that practice on this forum. Others will always go to the trouble of quantifying the effects on powder space and adjust the powder charges accordingly, at least when loading near maximum. (As you can guess, I am in the second category.) At least learning HOW to think about COL and pressure PROPERLY is helpful in avoiding trouble. It IS possible to blow-up a gun when handloading, and that is usually followed by a confused handloader trying to figure out what happened. Nobody INTENTIONALLY blows-up a gun while holding it in their hands; they just missed something, sometimes because they did not understand something properly. One related issue that I will mention is "bullet setback" which is a change in COL that occurs during the auto-feed process when the slide bangs the bullet into the feed ramp while feeding a cartridge from the magazine into the chamber. There is a surprising amount of force involved, which can push the bullet back into the case. That has the same effect on pressure as if you intentionally seated the bullet much deeper at the loading bench. So, making sure that your case grips the bullet tightly is another important aspect of handloading. In auto-loading cartridges that headspace on the case mouth, that canNOT be achieved with the crimp; it is a matter of using the proper expander die plug diameter. But, this reply is already long, so I will leave that subject to other threads. SL1 Last edited by SL1; July 18, 2013 at 08:09 AM.

July 18, 2013, 04:51 AM	#2
Grizz12 Senior Member Join Date: December 11, 2012 Posts: 527	which bullets are you using and in what gun?

July 18, 2013, 07:42 AM	#3
chiefr Senior Member Join Date: January 27, 2010 Location: AR Posts: 1,401	OAL is one of those things (just like crimping) that confuses many reloaders and there are many different answers. All OALs vary, even with the same weight bullet. A box of R-P will have a different OAL than a box of FC. European carts are all over the place with OALs. Most manuals list the minimum acceptable OAL for function thru virtually any firearm.

July 18, 2013, 12:21 PM	#5
buck460XVR Senior Member Join Date: December 28, 2006 Posts: 4,342	Factory load OAL has nuttin at all to do with OAL of the rounds you load yourself EXCEPT as a reference to how they feed in your autoloader. Bullet profile has much to do with what OAL feeds best in your gun. If revolver rounds then OAL is determined by the position of the cannelure and the length of your cases. You reload to the specs in your manual for the powder and bullet. If you need to adjust your OAL for proper feeding, you adjust the loads appropriately.

July 18, 2013, 08:17 PM	#6
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	Factory ammo was loaded to the proper pressure for their powder and charge. Manual ammo was loaded to the proper pressure for their powder and charge.