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Thread: Another OAL and off the lands question

  1. #1
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    Default Another OAL and off the lands question

    So I have been learning about C.O.A.L., off the land measurements, etc. I do not have a stoneypoint gauge (yet) so I made up a dummy round using resized trimmed once fired brass that chambers easily. I reamed out the neck a little so a bullet will fit snugly but still be able to slide. I drilled and tapped the primer pocket so I can screw a bolt up the case and push the bullet out. I chambered this dummy round thus pushing the bullet into the case theoretically giving me my "jam length" for my Kimber 325 with 220gr gk's.

    Now, after doing this a few times with different bullets (all 220gr gk's) I have come up with the OAL of this jammed round to be 2.860 - 2.863 depending on the lead bullet tip. In fact the first couple times it was 2.872. I think it may have jammed to tight and then slightly pulled the bullet out of the case durring extraction. After several more jammings I never got that long of a measurement. Anyway, the SAAMI OAL is 2.860, the magazine in the Kimber will take longer.

    Before all this I tried the smoking the bullet thing and can't seem to determine anything very accurate as far as OAL. In fact if I seat the bullet to where I get no rifling marks the OAL is like 2.810. Much less than the min OAL's the recipes dictate. The factory loaded 200gr accubonds are 2.821 OAL.

    The load recipes I have show a min OAL of either 2.845 or 2.850. If my dummy jam round is 2.860 what OAL should I set my die to seat the bullet at? 2.845 or 2.850... 2.855?

    Until I can get up to see Murphy for a lesson I figured I'd post this.
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  2. #2
    New member George's Avatar
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    Default OAL

    Well, sure enough sounds like you've mastered the theory of "Off the lands", "Jam length" and OAL. Also, sounds like your technique is good enough to safely say the jam length of YOUR RIFLE WITH THAT BULLET is 2.860. What is recommended by any other source is only a best "questimate" based on averages, minimums, maximums, standards and the like. Those numbers are usually conservative to account for most chambers, ammo and magazine lengths. So what OAL to load for that bullet in your rifle? Preferences vary but most serious target shooters don't look at any off-the-lands lengths greater than .010". Some hunters/reloaders like about +/- .050" off-the-lands". I usually start at about .020"-.025" off-the-lands. Anything approaching .010" may not be as reliable. Measurement errors coupled with variances in bullet ogive can put a bullet into the lands at the wrong time as you approach jam length. That can stick a bullet in the throat or cause pressure spikes- neither a good thing when hunting.

    One thing you noticed while measuring OAL.... bullet tip variances cause measured length variances. One way I eliminated that was to dedicate a caliper to OAL measurements only. I permanently attached a small bullet seating stem to one jaw of a caliper. That yields an "index" length. By measuring each round from base to bullet ogive (not base to bullet tip) it gives a more reliable comparison number. So when measuring the Jam Length for a particular rifle and bullet I end up with a "Jam Length Index". I then set the bullet seater die to yield a loaded round with an "OAL Index" of about .025" less.... using the same dedicated caliper. Seems to be a more accurate and consistent way to do those length measurements involving a bullet.

    Bottom line. If you're confident in your length measurements I'd start around .020-.025" off the lands. Seems to be a pretty good in-between area for best accuracy vs best reliablility. I woudn't go closer than .010" for hunting ammo. Also, about 1 caliber seating depth is a ballpark minimum for enough bullet neck tension to keep most jacketed bullets seated without crimping for bolt guns. It also seems to be enough to help maintain good bullet alignment with case axis. But, thoughtful and rational experimenting is half the fun of reloading. Lots of experience here on the forum for things I've missed or otherwise fouled up Good Luck!

  3. #3

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    Snyd

    Hornady is now making the Stony Point OAL gauges and bullet comparators. For a little more than the price of a box of premium bullets you can get the OAL gauge and basic comparator set and a modified case. Like George, I start experimenting with OAL at .020. I usually start with the OAL listed in the manual for that manufacturer and after working up an accurate load make the OAL adjustment the last thing I do. If you have a really good barrel that is properly bedded OAL sometimes doesn't make a practical difference in hunting accuracy. Sometimes you get a gun or bullet style that is hypercritical about seating depth. It sure is fun trying to sort it all out. Good luck.

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    Thanks guys. It looks like this weekend I'll sling my first rifle handloads down the range.
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    Snyd: what will help doing the jam to off lands is to use a case with the neck only partially sized using a bushing die. and a black magic marker. You can then determine the engagement of the bullet to the lands. The vary best way is with a false chamber cut from a piece of barrel that is cut off from your new barrel blank, with the same reamer used to cut your chamber . About 2" long, you then using a mic or calipers measure the amount of setback on the shoulder also. This is the best way to get shoulder bump back.

    I shot bench rest for years and only used the magic marker and the part sized neck method to set die and chase the filling for throat erosion.

    Just remember, some like it jammed in the throat and some like it .0001 (or more)off.

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    Snyd:

    I found the SP OAL tool to be too inconsistent to get a measurement I could trust. I donít use it anymore.

    I've gone back to my previous method that is simpler, and has proven to be safe and reliable for me.

    Size the neck of a fired case just enough to hold the bullet snugly,

    seat a bullet long,

    chamber it,

    remove it carefully, (hold it straight if for a plunger type ejector rifle)

    measure the OAL,

    adjust the seating die to a dummy round, using that (Same bullet) seated to the same length you just measured.

    Then adjust to however much less you like. I use at least .030 myself so I have some leeway in not contacting the lands.

    Use that adjustment for that batch of handloads. When you load another batch of that load, you can always adjust the seating punch to one of the previously loaded rounds. You could also make a dummy round and save it for the same purpose.

    There must be 10 jillion variations of the above method in the naked city, but I only toltchew mine.

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    SNYD,

    I second Smitty of the Norths method - Same method I use. I too found the Stoney Point OAL gauge to be iffy at best, but I do use their bullet comparator. Their bullet comparator takes the bullet tip variance out of the equation, it rests on the ogive of the bullet, not the tip and is repeatable. It looks like Hornady may have picked up Stoney Points comoarator.

    Where I vary from the conventional wisdom is the distance off the lands. After I have settled on a load I like (starting with .010" - .015") then I load 4-5 rounds each at .005", .010", .015" off the lands (depending on magazine length) and test to see if there is any differance in accuracy. On a couple rifles it makes quite a difference, some not. I have two Browning A-Bolts that like the bullet as close as I can get it to the lands. For hunting rounds I don't like to go any closer than .005", but I test chamber all my rounds prior to use in the field.

    http://www.midwayusa.com/eproductpag...904&t=11082005

    Woody

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    Thanks guys. I used my home made dummy round and double checked my jam length a few more times. I then seated the bullet an additional .023. Then loaded up my rounds.

    This put my OAL at 2.845-2.860 for all my rounds depending on the length of the lead tip. My magazine can take much longer. They all chamber very nicely. I must say I am surprised at the difference in the length of the bullets.

    Now to see how they group. I loaded 10 at min load of 58gr, 10 at 60gr and 8 at 61.7 which is max load. Now I just have to find time to get to the range.
    A gun is like a parachute. If you need one, and donít have one, youíll probably never need one again

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    Quote Originally Posted by Snyd View Post
    Thanks guys. I used my home made dummy round and double checked my jam length a few more times. I then seated the bullet an additional .023. Then loaded up my rounds.

    This put my OAL at 2.845-2.860 for all my rounds depending on the length of the lead tip. My magazine can take much longer. They all chamber very nicely. I must say I am surprised at the difference in the length of the bullets.

    Now to see how they group. I loaded 10 at min load of 58gr, 10 at 60gr and 8 at 61.7 which is max load. Now I just have to find time to get to the range.
    Perry,

    Your OAL does seem to vary a lot, .015" is extreme. Do the loaded rounds vary from the dummy rounds in length? Is there any chance the load is compressed? I haven't loaded any Sierra bullets lately but don't recall them varying that much at the nose.
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    Quote Originally Posted by Murphy View Post
    Perry,

    Your OAL does seem to vary a lot, .015" is extreme. Do the loaded rounds vary from the dummy rounds in length? Is there any chance the load is compressed? I haven't loaded any Sierra bullets lately but don't recall them varying that much at the nose.
    Thanks Murphy.
    I remeasured my loads. I must have made a mistake when I typed my post about my OAL's. They all come in between 2.850 - 2.855 with one at 2.849 and one at 2.857. Does this sound more reasonable?
    A gun is like a parachute. If you need one, and donít have one, youíll probably never need one again

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