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Thread: Finding Custom Cartridge OALength?

  1. #1
    Member kodiakrain's Avatar
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    Default Finding Custom Cartridge OALength?

    Another question: I tried to find out the ideal bullet seating OAL for my specific rifle and following instruct in Speer book - First, barely seated a round, chambered it in rifle after marking bullet up with a sharpie magic marker to see if it was touching the rifling in the barrel, and I can't tell at all. Possibly it isn't touching the rifling (?) as I had to press it in a bit more from barely seated to fit the magazine. I chambered it slowly feeling for contact with anything and it went easily as if no contact bullet to chamber.

    Do you guys have this factored in for your rifles or do you just use the OAL from the book? Better ways to find the rifling or even get this measurement from a book somewhere or factory?

    Speer describes it as "Often, best accuracy is obtained when the bullet almost touches the rifling in the chamber throat" then spends two pages describing how to find this, a guy in a store in Anch also went into this as a fairly big deal. Now I can't see the rifling marked on the bullet, am at max magazine length at 2.936", adjusting the seating die in one full turn got me to 2.904 and progressively six more full turns down to get to the "book listed" Oal of 2.70 for the Speer Spitz BTSP bullet I was seating.

    Seems like a lot of depth away from the max possible?

    I checked the length of Factory rounds and the longest I have is a Federal 130gr Vital Shock 2.827 OAL

    What do you think?

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    Default

    I don't know about your caliber so can't tell you what OAL it may like. Some guns and some calibers just have a very long chamber and you can't find the lands with a led bullet and must make due with a long free bore. That could be the case with your WSM so it will work with copper solids that are long for weight.

    To find the land I make a dummy round with the bullet tail just in the case and loose enough it will move under pressure from my hand but not move on its own. It will be too long to fit in the magazine so lay it on the feed rails and gently close the bolt. Sometimes it’s best to hook them behind the extractor before you shut the bolt. Gently open the bolt and don’t let it chuck the round to the floor. Measure the OAL of the dummy and jot it down. Repeat this a couple times to be sure of the number. You have found the max OAL for that bullet or know you don’t have one with that bullet. Because the shape of bullets is not the same each new type of bullet will have its own max OAL.
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  3. #3

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    On some factory chamberings you cannot seat the bullet far enough out to touch the lands and still fit in the magazine box. The WSM family of cartridges is an example. This is why custom WSM rifles have an extended magazine box, so you can seat the bullet out further.
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    Smoke the bullet with a candle. The Magic Marker might be too tough to skuff up to see.

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    I think what Speer is describing, when you seat the bullet slightly then chamber, is to allow you to push the bullet down in to "max" length as it is chambered in the chamber and the bullet comes in contact with the lands at the end of the throat. Don't put the round in the magazine to do this, if possible.

    What is this caliber? You say custom, is it a known wildcat? The best source for all custom and wildcats for dimensions of brass is Ken Howell's book of Custom Cartridges but it won't give COAL that is set by the designer.

    If it is based on a commercial cartridge the OAL of the parent cartridge is usually used. Also you may have a throat length in your rifle to allow very long bullets or just a free bored rifle and touching the rifling may not be obtainable.

    I just read back through some of your post. Are you using a 270 WSM? That isn't a custom and the length of the magazine is the limiting factory unless you want to hunt with a single shot. Most new loaders get way to hung up on this touching the rifling. Probably isn't going to happen with any WSM cartridge unless the chamber is custom made.
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  6. #6
    Member kodiakrain's Avatar
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    Default not custom

    No, it is a 270WSM in a Sako 85, Not Custom, so maybe I won't be able to reach the land, don't really see using something I can't load in the mag as practical so that length I found as Magazine max may be it?

    I may try smoking the bullet and using a hand seated one just to see if I can find the land.

    I'm brand new, so bear with this thought, should I try to maximize the OAL to magazine length if the bullet is long enough to be well seated for the sake of being closer to the land for sake of accuracy or just not mess with it and stay with book numbers for OAL for that bullet from that company?

    For example the Federal Vital Shock round is a 150 gr bullet that could be set longer (Factory loaded it is 2.827 OAL and my magazine could fit a 2.936" round) Hand loading a similar 150 gr bullet could I seat it out to magazine max (or closer to say 2.900")

    It just sounds like makes a lot of sense to seat as close out to the land as possible?

    Probably getting too fancy for my britches at this point, eh??

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    Default My Two Cents

    There are all kinds of ways to determine the OAL length to the lands of your particular rifle. There are special tools you can use, to find it, too, but they arenít needed. And, certainly not for a Hunting Rifle. Thatís IMO.

    Some of them donít work so well, either, at least for me. When people tell me they are seating .002 from the lands, for example, I think the likelihood is, theyíre kiddin themselves. Measuring that close, and even not that close is fraught with error.

    Iíve tried most methods I think. A SIMPLE way, Iíve been using of late is to put a bullet in the chamber, and hold it there. (With a Pencil, if you have a Bolt Action rifle.

    Put a wooden dowel down the barrel to touch the bullet, and mark the dowel at the end of the barrel with a knife. Then take the bullet out, and close the bolt and push the dowel against the bolt, and mark it again.

    The Max OAL for (a cartridge with) this bullet is the distance between the marks. You can measure that with a Dial Caliper. If you seat a bullet to that length, and then .030 deeper, but not much less, you should be fine.

    Your seating die will be adjusted for that bullet, and there should be little difference with other bullets of the same brand, type, and lot. Even if they have slightly different Ogives, they will be safely off the lands.

    Iím just suggesting, not getting all hung up on things that are a lot more IFFY, and harder to accomplish than they sound like.

    As long as you understand that a bullet touches the lands at different places on different bullets, because the Ogives (curvature of the nose) are different with different bullets, BUT the distance from the bolt to the lands doesn't change except due to throat erosion, and it is the length to the bullet tips that varies, you will have something to work with.

    Itís already been mentioned that your cartridge OAL may be limited to one that is short enough to feed through your magazine,

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    Quote Originally Posted by kodiakrain View Post
    I can't load in the mag as practical so that length I found as Magazine max may be it?
    Correct, if you can't feed it you may as well have a single shot. Like Smitty said .030" off the lands is the usual starting point and about optimal in most rifles. However it sure is not the end of the world if you have a long free bore most rifles will shoot quite well that way, well under minute of moose. Every 30-06 M1 I have played with has had way deeper lands than magazine and some of them have been a lot more accurate than I am.

    In working up a load you need to tune one thing at a time so you can credit the result to it. If you change two things (powder & OAL, powder & primer, primer & crimp) you learn nothing because you don’t know what thing is responsible. I work in what I unscientifically think is order of importance, powder, primer, crimp, then OAL all assuming matched brass. So one of the last thing I play with is OAL if the load even shows enough potential to get that far. You can usually get sub MOA from a good gun just from the first two or three and MOA is a tack driving hunting rifle.
    Andy
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