overall case length question

[scooterman27006]

i dont know why i havent asked this question before now but its past time - i have found on more than one of my rifles that if i want the bullet to touch or almost touch the rifling or lands (not sure of the correct term here) then i have to go a little longer than what is in the books - noticed on 204 ruger in remington 700 and also 243 with a ruger 77 - in the ruger i had to go to 2.88 for it to almost touch and its 2.73 for a 243 contender barrel so there is a big difference ------ so my question is should i try to get as close as i can or is it ok to leave them short and just put the COL at what the books say put it at - i noticed on the ruger 243 that there is only 1/3 of the bullet in the brass - it is in far enough it wont fall out but not half way and the 204 heck i had to go with a 50 gr bullet in order to have enough to stay in brass lol and the factory stuff for 204 is way too short if i need to be close to the rifling---- anyhow my question is - is it ok for stuff to sit back in the chamber and not come close to the rifling or is it better to have it as close as can be without being hard to chamber

[denton]

Every gun, and every bullet is going to be different. I have one 30-06 where there is .100" difference in where a Hornady bullet touches the lands, vs. a Sierra.

For each rifle you load for, and each bullet you shoot, you should measure the COL (cartridge overall length) that just puts the bullet out to the lands, and load about .030" shorter than that. You may find that this is longer or shorter than what is in the book. Loading clear out to the lands will cause excessive pressure.

To measure the distance to the lands, fully form an empty case, and cut a slit on both sides of the neck, using a Dremel tool and abrasive cutting wheel. Knock the burrs off. Seat a bullet just barely into the neck. Load it in the gun, and close the bolt. When you extract it, the length of the dummy cartridge will be the COL that puts that bullet at the lands. Do it a couple of times, just to be sure your readings are consistent.

After you have used the case a couple of times, you will have to gently tighten the neck tension with a pair of pliers or something.

[Cal Sibley]

You may have opened a can of worms. Firstly you may not even be able to reach the lands. Todays chambers are very long. Each bullet will have a diffeent maximum OAL. One bullet is rarely the same length as another type and weight. Additionally not all bullets perform best when seated into the lands. Some acually prefer a jump to get there. I use a Stoney Point OAL guage and find it works quite well. You want to merely kiss the ogive lightly, don't force it or you run the risk of very high pressures which can be dangerous. Take your time and regardless of the method employed in finding the maximum OAL length, make length adjustments as required to find the best length for accuracy. Best wishes.

Cal - Montreal

[Rocky Raab]

I'm kind of a maverick in this bullet-land gap thing. I don't care what the jump is.

When I start loading for a new gun or new cartridge, I first set the OAL at the book number. That's set by SAAMI at a point where it will be safe in any gun with a standard chamber.

Then I shoot it and note the group size. I'll work up to a safe load with good accuracy first. Now, I'll try two different seating depths, one a bit deeper and one with a bit longer OAL. Normally, I'll go .020" each way.

Shoot again and see if there's an accuracy change. If there is, I'll try a third batch 0.10" either way off the more accurate depth. Again, if there's a most accurate one, I'll settle on it. (At this point that would be the most accurate of five attampts at OAL, if you follow.)

Now I'll determine the loaded length from case head to a standard datum: the bore diameter. I explain all this on my web page, and it's too lengthy to repeat here. But from here, I can load an accurate depth with ANY different bullet with no trials at all.

[denton]

Yeah, but....

The data I have for a 243 round that I'm working on puts the Barnes X bullet at a certain COL. If I substitute a Sierra HP, at that length, the Sierra is right at the lands.

[scooterman27006]

boy i sure am glad i opened that can - i will play with different col's and see what happens - if i am too long what kind of bad things can happen - i have already loaded several rounds that will touch - now i know not to shoot if i have to get a hammer and beat the bolt down lol but if it is hard to push down what are some of the things i may see - like a primer backed out or worse or maybe i dont want to know this answer but how will i know i have too high a pressure - i really dont think these that i have already loaded are unsafe because i measured all of them with the stoney point gauge and they are either touching or just short of touching its just that some are much longer than recommended - example a tenth of an inch longer another example - in the 243 ruger 77 book calls for 2.71 ocl and for the ruger to come even close with 2.88 now the encore barrel needs to be 2.75 and they both chamber really easy with no sign of being too long but i havent shot any of these yet -- using 80 gr nosler ballistic tips

[Catfish]

Benchrest shooters all load their ammo with in a few .001`s or in the lands. But they all fire single shot guns so they don`t have to worry if they will feed from the magizine. They are alos useing custom chambered thight neck chambers. I do not load for any gun I own that my oal is not considerable longer than SAMMA spec. As previlously stated if you jam the bullet into the lands the presure will go through the roof. Some guns shoot better this way, but I don`t recomand even trying it with a factory chamber. I like to start about .005 off the lands but with many factory chambers you can`t even get close to that. I then back off .005 at a time but usually find that I get my best accuracy up close, not always though. The Ojive of the different bullets can make the oal of the bullet vary greatly for the same jump. It is definately worth playing around with if your looking for the best possible accuracy from a rifle.

[Rocky Raab]

denton, that's because the nose shape varies between your two examples.

That's why I don't use COL (cartridge overall length) at all except for magazine length restrictions.

The important dimension is from the case head to the datum line on the bullet where the ogive reaches bore diameter. That's the circumferential line on the bullet that will touch the lands.

I call it the bore line, and once you find the place that gives good accuracy, if you measure the case head to bore line and record that number, you can repeat the same Headto BoreLine (HBL) length with any bullet. Simply scribe a ring on the bullet at bore diameter and adjust the seater until you match your recorded HBL.

BTW, that ring on the bullet is at bore diameter NOT groove diameter. In a 30-cal rifle, it'd be where the bullet is .300", not .308"