The Firing Line Forums - View Single Post

keys85 · September 29, 2008, 09:17 PM

I noticed several members found COL critical to attaining best accuracy with their pistols. This variable is going to vary from pistol to pistol. However, when providing load data, many posts do not include COL. Shouldn't this be an important ingredient to the recipe, along with firearm make/type?

According to a post (shown below) by a senior member, changing the COL will effect chamber pressure. Chamber pressure is related to velocity. Consistency of a particular velocity in your firearm is related to accuracy. So, my question is, if seating a bullet deeper and raising pressure - wouldn't that be the same as keeping a longer COL and using a (minor) larger powder charge (and vice versa)?

When developing a load, the COL must be within a certain spec for reliability with the particular bullet design...however, I never had to seat to minimum COL to get a round to chamber right. But this is what the load data is written for. In such a case, if using a longer COL, I'd be able to most likely push the max load a bit?

What is more critical to accuracy...powder charge vs. seating depth?

Once a powder charge is found to be accurate, then is COL fine tuned, or should COL be a deciding factor in the load development that is as important? Think about missing a "sweet spot" should you seat deeper, raise velocity, and open groups versus first starting out with that shorter COL than a longer one, and working up the powder charge as the secondary procedure...

Sometimes it is necessary to seat deeper than max COL. Why seat longer than what the load manual states if the min. COL chambers reliably?

Is there a "guideline" or procedure when developing a load as to COL? Such as, starting at max or whatever chambers and playing a bit to see if it effects accuracy OR would it make sense to seat at min. COL, then work the powder charge, and because a deeper COL raises pressures, be utilizing less powder?

"As to pressures, seating depth makes a lot of difference in the .45 ACP because its powder space is short and fat. This means small changes in how deeply the bullet base seats into the case can change chamber pressure rapidly. Taking a standard hardball military load equivalent, 230 RNFMJ, seated to 1.275" OAL over 5.0 grains of Bullseye, the peak chamber pressure is only around 16,000 PSI. If you seat the bullet a tenth of an inch deeper, to 1.1750" OAL, the availabe powder space decreases 30% and peak pressure leaps up to 24,000 PSI; well over the +P limit of 21,000 PSI. This is why it is very important that bullets in this, or any other stubby, straight wall cartridge case be firmly seated and be unable to shove back into the case when driven up the loading ramp or recoiled against in the magazine. Fortunately, the .45 ACP case has one safety feature built-in: The case web (the wall) thickness increases below the depth hardball is normally seated to. This means seating deeper fattens the cartridge by pushing that thicker brass outward, and if you go 1/10" deeper, the cartridge usually won't chamber. Just don't try to prove this the hard way, in case your chamber has extra room in it or you got an oddball brand of case not made with normal internal dimensions."

September 29, 2008, 09:17 PM	#1
keys85 Junior member Join Date: September 21, 2008 Posts: 199	1911 Accuracy: Powder Charge vs. COL I noticed several members found COL critical to attaining best accuracy with their pistols. This variable is going to vary from pistol to pistol. However, when providing load data, many posts do not include COL. Shouldn't this be an important ingredient to the recipe, along with firearm make/type? According to a post (shown below) by a senior member, changing the COL will effect chamber pressure. Chamber pressure is related to velocity. Consistency of a particular velocity in your firearm is related to accuracy. So, my question is, if seating a bullet deeper and raising pressure - wouldn't that be the same as keeping a longer COL and using a (minor) larger powder charge (and vice versa)? When developing a load, the COL must be within a certain spec for reliability with the particular bullet design...however, I never had to seat to minimum COL to get a round to chamber right. But this is what the load data is written for. In such a case, if using a longer COL, I'd be able to most likely push the max load a bit? What is more critical to accuracy...powder charge vs. seating depth? Once a powder charge is found to be accurate, then is COL fine tuned, or should COL be a deciding factor in the load development that is as important? Think about missing a "sweet spot" should you seat deeper, raise velocity, and open groups versus first starting out with that shorter COL than a longer one, and working up the powder charge as the secondary procedure... Sometimes it is necessary to seat deeper than max COL. Why seat longer than what the load manual states if the min. COL chambers reliably? Is there a "guideline" or procedure when developing a load as to COL? Such as, starting at max or whatever chambers and playing a bit to see if it effects accuracy OR would it make sense to seat at min. COL, then work the powder charge, and because a deeper COL raises pressures, be utilizing less powder? "As to pressures, seating depth makes a lot of difference in the .45 ACP because its powder space is short and fat. This means small changes in how deeply the bullet base seats into the case can change chamber pressure rapidly. Taking a standard hardball military load equivalent, 230 RNFMJ, seated to 1.275" OAL over 5.0 grains of Bullseye, the peak chamber pressure is only around 16,000 PSI. If you seat the bullet a tenth of an inch deeper, to 1.1750" OAL, the availabe powder space decreases 30% and peak pressure leaps up to 24,000 PSI; well over the +P limit of 21,000 PSI. This is why it is very important that bullets in this, or any other stubby, straight wall cartridge case be firmly seated and be unable to shove back into the case when driven up the loading ramp or recoiled against in the magazine. Fortunately, the .45 ACP case has one safety feature built-in: The case web (the wall) thickness increases below the depth hardball is normally seated to. This means seating deeper fattens the cartridge by pushing that thicker brass outward, and if you go 1/10" deeper, the cartridge usually won't chamber. Just don't try to prove this the hard way, in case your chamber has extra room in it or you got an oddball brand of case not made with normal internal dimensions."