Benefit of max COL?

[galaxieman]

I am new to reloading and have heard a lot about COL and am wondering if there is an accuracy advantage to maxing the COL. Let say that your particular rifle has a deeper throat and can handle longer COL. is it best to have the bullet as close to the rifling as possible? or is some "jump" best?
I realize that pressure is lower if it can jump but does that hurt accuracy and or velocity?
Or is is really just part of a much more complicated formula?
I'm Confused?

[Ranch Dog]

I'm Confused?

No reason to be. In a perfect world, a chamber cut to the SAAMI spec for the SAAMI specified bullet is going to be a perfect fit. Even with "this" perfect fit you throw in the variables related to ignition, which is called initial start pressure, variables in the very changes you mentioned; rises in pressure with contact at the start or a lower pressure with no contact followed by a "spike" in pressure with the initial contact. All this affects the bullets accuracy performance to some degree or another. This is one of the items that many reloaders enjoy investigating. It is no different than examining the accuracy performance in difference of a few grains of powder. Just take detailed notes and explore what is best for your firearm.

That is a nutshell view but here are the caveats of cartridge overall length. Using an OAL shorter than that recommended for the data you are using will result in cartridge pressures greater than stated. Your firearm might dictate the OAL; typically the max is a design limitation to keep the rifle compact but shorter OAL might not feed well due to the ramp on the arm.

I'm sure others will join in, please continue to ask questions and give us some of the details you are working on

[galaxieman]

Well my COL for this 444 will be decided by what will cycle through the action. I set up a dummy round that was long on purpose to see if it contacted the rifling. (about 2.65) and it dropped all the way into the chamber with no restriction, but would not cycle. It will cycle 2.59 which is longer than most 444 ammo. I loaded almost 40 rounds and the jacketed rounds ended up right at 2.59 which is great but both the 240 and 265 grain cast ones seemed to push in a little more when crimped so they came in more at about 2.52 but there should be no issues as I am nowhere near max loads. Time will tell.

[TCups]

Some suggested reading for you:

http://www.bergerbullets.com/effects-of ... to-part-1/
http://www.bergerbullets.com/effects-of ... to-part-2/
http://www.bergerbullets.com/getting-th ... our-rifle/

[Ranch Dog]

Thanks TCups, the three pages are an excellent, concise reference on this subject and I've saved them to my favorites!

[quote="Berger Bullets"}Load 24 rounds at the following COAL if you are a hunter (pulling a bullet out of the case with your rifling while in the field can be a hunt ending event which must be avoided) or a competition shooter who worries about pulling a bullet during a match:
1. .010 off the lands (jump) 6 rounds
2. .050 off the lands (jump) 6 rounds
3. .090 off the lands (jump) 6 rounds
4. .130 off the lands (jump) 6 rounds[/quote]

The only thing I would would add is concerning cast bullets. I would bring the choices down two if the OAL did not result in cartridge feed issues.
1. On the lands
2. .005" off the lands

The problem with the jump and cast bullets as the freebore that you have created with the "jump" allows the combustion gases to get ahead of the bullet prior to the bore being sealed. That "flame thrower" and the particulate matter that is pushed ahead does a great job of damaging or etching the bullet as it starts to make contact with the lands. This erosion is what creates "leading". "Leading" is a bit of misnomer, the barrel isn't "leading", the structure of the bullet has been etched and once started the etching continues as the bullet continues down the barrel. As it continues down the barrel, the bullet is being destroyed by combustion gases. That's what "leading" really is. Really is nothing to do with the barrel other than the barrel establishes the criteria for overall bullet diameter. Step defines front band requirements, and the throat defines ogive. So much time is spent by fellows fretting over lubes when what matters is bullet fit. You get a "lube star" at the muzzle when the bullet fit well and nothing got out ahead of the bullet as it traveled down the barrel. The previous statement is valid when the alloy matches the requirements of chamber pressure. Lube is used as a patch when the bullet isn't a perfect match for the specific requirements of the barrel.

As far as a pressure bump goes with ogive contact on a lead bullet, the initial start pressure are about 2K to 5K less than jacketed bullets because of the differences in the alloy strength.

Above, my comments read "The only thing I would would add is concerning cast bullets. I would bring the choices down two if the OAL did not result in cartridge feed issues." If the OAL you need is longer than what your rifles magazine feed with allow or in the case of the 444 Marlin or other lever gun, the carrier feed, you need to "plug" the chamber further back in the throat with bullet diameter.

TLC432300RF_Marlin_444P_444Marlin_Cutout.gif

In this image which is generated by a chamber design software package, it shows the chamber of my 444P as rendered by a chamber cast. The position of the lands in the barrel are represented by the position of the arrow labeled "Bore" at the bottom of the image. The position is quite a bit ahead of what the carrier OAL would allow for any bullet. The only alternative for great cast bullet fit is to match bore diameter back toward the step and then rolling the ogive over to match the angle of the throat. This is also why one cast bullet will work well with one cartridge and not another of the same caliber. It becomes a bit of a "dance" with the computer aided design in that as you make this "fit" you are constantly changing the overall length requirements of the cartridge. When I first started this work using a drafting pad against the chamber cast it might take me up to five mold cuts to get it right. Of course the computer brought it down to being right the first time.

[galaxieman]

That is really interesting stuff. I will probably read it several times. However in my 444 it will be pointless to get a COAL that is longer than it will cycle and I already know that to get close to my rifling would be too long to cycle. I will however monitor what COAL seems to give the best results.

[TCups]

I presume a "444" is a lever gun. To load with bullets touching the lands in my CZ 550 Varmint in 308 Win means that the cartridges cannot be loaded from the magazine. They are much too long. Moreover, the CZ, being a Mauser action, should always be loaded from the magazine for the Mauser's "claw" to engage the case properly. It is possible to single load, however, by placing a cartridge in the action, then pushing it down and back into the magazine with the magazine already in place.

I now do this even when I hunt. Then I put the safety on. Then I load two shorter "follow up" rounds in the mag, just in case. So, it can be done with a bolt action, even if the COL exceeds the length of the magazine. And with Berger 168 VLDs, the extra effort is worth it in mr rifle.

[galaxieman]

It is a Marlin lever gun. I am not looking for super long range accuracy. Just minute of deer. Besides this is more of a Bunkerbuster than a surgical strike weapon.
Gman

[Missionary]

Good morning
More powder capacity especially using slow burning powders.
Example.. back in 1982 was shooting a Dan Wesson caliber 357 10 inch barrel with 180 gas checked bullets at those "Sillywet" steel critters. The DW revolver cylinders are longer than most other manufactureers. I figured out I could crimp in the upper grease groove and pick up .10 inch in COL. That translates into about 10% powder capacity. Now a powder like 296 really excels when more can be added in a long barrel.
My load went from iffy knocking over rams if hit more than half way down to never fails to knock down a ram even if hit 2/3 rds of the way down.
That load will NOT fit in a S&W, Ruger or Marlin chamber. But in the DW that extra COL help make that revolver a Revolver AAA contender.
Mike in Peru