Cartridge OAL

lesterg3 · Posted: Mon Dec 08, 2008 11:25 am Post subject: Cartridge OAL

Hey Guys, (and Gals, if there are any)
Got something new ruining my sleep. As I read in several manuals, including the most recent Lee, I understand that in developing accurate loads that the cartridge OAL is important in that the bullet should touch or nearly touch the rifling in the cartridge chamber. What the book(s) have not described is how to develop that measurement. The load data gives a trim length and or an overall length.

While I am a hunter, I also love accuracy, and besides the obvious cost saving, the next thing I am interested in is developing the most accurate load I can for each caliber I shoot. Another reason I can think of for reloading is stockpiling all the components so the new government won't know what I have, Oh did I say that out loud? Crying or Very sad

Anybody worrying about this too?

Anybody know a way to determine the best OAL of the cartridge?

Thanks

Pumpkinslinger · Posted: Mon Dec 08, 2008 12:07 pm Post subject: Re: Cartridge OAL

Lester, there are a few threads on the subject of seating depths, etc. already on this site. Look in the Reloading forum for more than I've included.

www.huntingnut.com/ind...pic&t=4927

www.huntingnut.com/ind...pic&t=4931

Elvis · Posted: Mon Dec 08, 2008 12:40 pm Post subject: Re: Cartridge OAL

the best way is lots of shooting. oh yeah thats lots of fun too. I dont worry too much and just use a factory round that works well to give me a starting point. good luck and just remember that" its a new load and i need to try it dear" is a valid reason to leave the lawns till later.

Grumulkin · Posted: Mon Dec 08, 2008 1:45 pm Post subject: Re: Cartridge OAL

If your gun has it's chamber, throat and barrel in good alignment, then how much the bullet jumps to get to the lands isn't as important as when these alignments are off. In other words, seating a bullets to it's just off the lands makes up for defects in how the throat, etc. is cut.

Lore has it that for most bullets it's best to seat them just off the lands. An exception is Barnes bullets that allegedly need some jump for good accuracy. Also, many times, the length of the cartridge that will fit in the magazine is the limiting factor on COAL.

The way I seat bullets in those instances where I want them just off the lands is to attempt to chamber them when they're a little long. The lands will make marks around the bullet. I then seat the bullet deeper until the lands no longer makes marks on a bullet. Since the bullet will be marked up by the lands I load successive cartridges with the bullets a little deeper until I get them where I want and then seat them all to the same depth.

In loading for Encores/Contenders it's even easier. I just seat the bullets deeper the action closes easily. There are also various chamber gauges you can buy to make the appropriate measurements but I've never used one.

Dawgdad · Posted: Mon Dec 08, 2008 2:04 pm Post subject: Re: Cartridge OAL

Ditto on what Pumpkinslinger already posted. If you have specific questions after reading down those threads, ask away. A quick answer is there is a low tech cleaning rod method and a fancy tool made by Hornady that will measure the value you are looking for. What that value actually is will vary from gun to gun load to load.

The questions you are losing sleep over now will only be intensified if you atart to include chamber tolerances, bullet manufacturing variability differences in ogive from one stule of bullet to another of the same caliber Shocked

But in the end most of that is for splitting hairs and squeezing the nth degree.

wncchester · Member Joined: Apr 08, 2006 Posts: 160

"I understand that in developing accurate loads that the cartridge OAL is important in that the bullet should touch or nearly touch the rifling in the cartridge chamber. "

Yeah. That's part of what a lot of web and book experts agree on; it ain't true but they do tend to agree. It's sort of like the assurances that we will get "better accuacy" if we neck size only or weight each charge to .1 gr., it all sounds reasonable but just ain't so! NO fixed rule applies to all rifles but that one applies to very few.

That method of seating come from BR shooter's methods. They use for much different rifles than ours and they can load in ways that aren't practical for those of us with factory sporters. Neither rifle type is "better" than the other but each is quite different from the other because of different end needs.

The real reason BRs shoot at or into the lands is that their cases have so little neck tension they need the resistance of a bullet in the lands to help get ingniton pressures up to consistant levels. It's NOT for better alignment of the bullets in their very tight chambers! Their alignment is near flawless to start with. Nor is seating into the lands likely to help US obtain better bullet alignment.

Our much higher bullet tension means our ammo gets better ingnition when the bullet is allowed a bit of a running start before it impacts the rifling, from as little as .020" to as much as .100" in my rifles.

Those of us who do need a little more neck tension are the ones who benefit from bullet crimping, not seating into the lands. Crimping works for some rifles, not for others. Meaning, again, no fixed rule applies to all rifles.

woods · Member Joined: Oct 15, 2005 Posts: 89

The most common way to "find the lands" is with the Hornady tool

www.midwayusa.com/epro...mid=570611

You will also need a modified case

www.midwayusa.com/epro...mid=761522

which you thread onto the end of the gauge. Put a bullet into the neck of the modifed case which is large enough to let it move inside

It has a plastic rod that travels inside the tool that you can push the bullet into the lands with

you lock the rod in place and then you can measure the COAL

Subtract the distance you want to seat off the lands, .020" is a good spot.

gelandangan · Posted: Mon Dec 08, 2008 8:55 pm Post subject: Re: Cartridge OAL

What a bunch of pretty pictures..

And here I am thinking that the "Split case" method is THE most common way to measure OAL.

Heck you only need a case and a pellet to do it.

As example is this from www.larrywillis.com

woods · Member Joined: Oct 15, 2005 Posts: 89

Be careful not to let the lands grab the bullet and pull it out when extracting, that seemed to be what happened when I tried it. Inconsistant measurements.

I also use a tool called the R-P tool shown here with the Hornady

with it you insert down the muzzle to the bolt face (firing pin retracted) and set the rear collet

then insert the bullet against the lands (the Hornady tool makes a great tool for doing this) reinsert the rod back to the bullet tip and lock the front collet

and measure between the collets

with this method you don't have to allow for headspace like with the Hornady or the split case method.

Dawgdad · Posted: Tue Dec 09, 2008 1:45 am Post subject: Re: Cartridge OAL

Great pictures! But wouldn't you measure from the right side of both collets and not in between them?( the sides that touched the muzzle) Confused

Otherwise your bullet jump will be the width of the second collet.

One more caveat to throw in here. Long bullets may exceed your magazine length before you reach the rifling. not a problem if you single load but if you want a follow up shot....it has to fit in the magazine.

lesterg3 · Posted: Tue Dec 09, 2008 10:54 am Post subject: Re: Cartridge OAL

Wow!! Thanks for all the input. It's great. But, Miss Dee says I have to finish the upstairs bathroom before I can build my loading bench, so all the stuff is sitting on the floor in the one room Miss Dee gave me, and I am way too busy hunting right now to finish the bathroom.

I the meantime, I will continue to ask questions as the answers elude me. It's great hearing all the stuff you all have learned and I hope one day to be as knowledgeable as you.

steve4102 · Member Joined: Feb 24, 2005 Posts: 38

Loading to the lands is not always the best place for accuracy. According to Barnes, most rifles have two OAL sweet spots, one up close to the lands and another much shorter. Here is and article by Barnes on OAL and accuracy. Scroll down to "From the Lab".

www.barnesbullets.com/...-bullet-n/

.

huntingstoneboy · Member Joined: Mar 19, 2006 Posts: 32

I always check my AOL with the hornady tool, however many times cartridge length is too long to cycle through the magazine and remain close (5-10 thous.) off the lands. just my 2cents.

woods · Member Joined: Oct 15, 2005 Posts: 89

Dawgdad wrote:

Great pictures! But wouldn't you measure from the right side of both collets and not in between them?( the sides that touched the muzzle) Confused

Otherwise your bullet jump will be the width of the second collet.

One more caveat to throw in here. Long bullets may exceed your magazine length before you reach the rifling. not a problem if you single load but if you want a follow up shot....it has to fit in the magazine.

Does seem counter-intuitive but you do measure as shown above. What you have to consider is that when you lock the rear collet against the bolt face, you have the other collet in between the rear collet and the muzzle. So you have already allowed for one collet width.

Dawgdad · Posted: Wed Dec 10, 2008 9:12 am Post subject: Re: Cartridge OAL

woods wrote:

Dawgdad wrote:

Great pictures! But wouldn't you measure from the right side of both collets and not in between them?( the sides that touched the muzzle) Confused

Otherwise your bullet jump will be the width of the second collet.

One more caveat to throw in here. Long bullets may exceed your magazine length before you reach the rifling. not a problem if you single load but if you want a follow up shot....it has to fit in the magazine.

Does seem counter-intuitive but you do measure as shown above. What you have to consider is that when you lock the rear collet against the bolt face, you have the other collet in between the rear collet and the muzzle. So you have already allowed for one collet width.

OK-I thought you added the second collet after you took the muzzle to boltface measurement. Now that I look more closely at the picture that is out of focus I see the two collets are both in place. It pays to read and look at the pictures too!

Thanks again for posting the pictures. We have had several disucssions on the board (as you probably know) where we have tried to describe these tools and how to use them and a picture IS worth a thousand words.

My final comment is that for most peoples purposes this is probably overkill. I use my hornady OAL gauge and comparator on a competition service rifle to tweak the best accuracy at 600 yards after I have used OCW to pick the ideal powder charge. For most of my hunting loads I find that if I use OCW the groups are real close to 1 moa anyway and the extra time and experimenting with the OAL is mostly academic because the loads hit where I am aiming with a book value for OAL to start with. I could spend that time and money working on my positions and trigger control rather than making another 100 bullets at different jumps from 0.000 to -0.040 off the lands.