Bullet seating depth the easy way

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Aussie, Jul 1, 2004.

  1. Aussie

    Aussie Well-Known Member

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    For those of us who don't own the special Stoney Point tools here's a really quick , easy and quite accurate way that I have discovered to determine a reference point (lands contact) for seating depth of any given projectile in the throat of a rifle .
    1) Seat a bullet well out (to the extent you are sure it will contact the rifling)in an empty , unprimed , resized case .
    2) Remove the rifle bolt , insert the cartridge into the chamber and push it in firmly with your finger .
    3) Carefully insert a cleaning rod into the muzzle and keep feeding it in slowly until you feel it contact the tip of the projectile .
    4) Gently try to push the round out of the chamber .If the bullet is in contact with the lands some resistance will be felt .
    5)Screw your seating die down a little and seat the bullet a little deeper . 1/8th turn changes seating depth around 10 thou. on my dies .
    6)Repeat the test above .
    7)Less resistance means less lands contact so screw the die down in smaller increments as resistance is reduced . Eventually you'll reach the point where the bullet is no longer in contact with lands and no resistance should be felt when pushing the round out of the chamber .
    8) Using a vernier caliper measure the overall length of your loaded round and seating die and record for future reference .
    9) Experiment with different seating depths to see what your rifle shoots best with .
    10)You'll be surprised how easy it is to feel the resistance created when a projectile contacts the lands by only a few thousandths of an inch . Much easier than trying to visually find and measure rifling marks on a projectile .
     
  2. shilen30

    shilen30 Well-Known Member

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    One big problem is though that many bullets change quite a bit from lot to lot. I have a couple boxes of hornady bullets of the same item number but from different lots. Both lots have a different bullet profile(one lot is more "aerodynamic" than the other), and when I use the seating die to seat both, one is .02" farther off the lands than the other, and the seating plug still contacts the ogive far below the tip. You HAVE to adjust your seating plug for different lots, although I haven't had this problem with sierra MKs. Also, overall bullet length changes considerabley from lot to lot as well as from bullet to bullet in the same lot. Your idea does work pretty good overall though if you don't have the stoney point comparator system or the sinclair bullet comparator, but hey, what is $17 compared to hours of fudging around and wondering if your new lot of bullets is different enough that you will see a big change in accuracy without re-doing your test.
     

  3. Harv Peters

    Harv Peters New Member

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    I do it just a little different. When resizing a case just touch the neck in the die so it will hold a bullet but let it slide easily. Than chamber the round and let the rifling push the bullet into the case. Remove the round and measure the OAL. Hope that makes sence.
     
  4. Coyote Hunter

    Coyote Hunter Well-Known Member

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    Hello,
    I am on the same path as Harvey....I just use a pair of pliers and "lightly" squeeze a fired case neck. Just enough so the bullet goes in with resistence.

    Then sliding bolt closed on the casing and checking the "ogive" with a comparator like Shilen30 said. It's fast, accurate and easy.
    Just do the check a couple of times for repeated accuracy.

    Do not mark the bullet with a black marking pen, for the ink on the bullet can make it stick enough to possibly pull the bullet back out of the casing when extacting it.
    -------------
    Zod
     
  5. Aussie

    Aussie Well-Known Member

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    Harvey
    I used to do the same as you but found if I didnt get the neck tension just right the bullet either moved when I extracted it or got jammed in the lands and had to be pushed out with the cleaning rod . You can see how I arrived at the method I use .
    I'm not saying your method can't be done ,just that I had a few problems with it .
    Shilen 30 probably hits the nail on the head . Comparators are cheap at $17 .Probably 50 bucks here in Oz though .
    Must admit I'm too lazy to check seating depths from one box of projectiles to the next . Not shooting competition so the last few thou of accuracy aren't that important to me .
     
  6. shilen30

    shilen30 Well-Known Member

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    Yah Auzzie, I had too many headaches when I did it Harvey's way and my groups wouldn't be quite as good when I went to a different box. HOWEVER, you have found the right starting point for a certain bullet. It is good to start just as yoiu have mentioned, use a bullet comparator to measure the seating depth to the ogive, and record. Then vary seating depth until you hiut the sweat spot. Even if the bullet profile for a certain bullet changes slightly from lot to lot, use the same length measured with the bullet comparator and most every time your groups will be as good as they can, and you don't have to do all the laborious steps that you had mentioned for each lot of bullets. I however am a very big fan of finding one load, confirming it at least a couple times, and then going and buying several boxes of bullets from the same lot and a 5 or 8 lb keg of powder, the powder actually being the biggest deal because powder can change quite a bit from lot to lot. After buying the bulk, you may need to fudge with the powder charge slightly (not seating depth though) if your keg has a different lot number than the one you did your tests with, and you are good to go for many rounds (also, I have seen a big difference in brass from lot to lot so it is always good to buy enough to last at least as long as the number of components you have bought for the load. Ah, just buy 500 pieces to begin with and don't worry about the brass). Many guys say, and a few on this forum, say that when the brass work hardens, or if your brass has been neck sized after the first shot, you don't need as much powder for the load to obtain the same velocity. Well, there is something else that needs to be considered. After the brass has been fired once and neck sized, confirm with your chrony that you are at the same velocity. If not, you may need to lighten the charge a bit to bring it back down to the sweat spot.
     
  7. Brent

    Brent Well-Known Member

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    Any of you guys ever try the "split neck" method? It's one kind of like Harvey and Zod describe, only using a sized case that the neck has been split lengthwise with a dremmel or hacksaw down into the shoulder.

    I get repeatable results to the thou, year in, year out with the same case and it's very quick, beats the Stoney Point OAL tool that attempts to accomplish the same thing. Stoney Point's Comparator works well though, it's a Highly recommended tool.

    Here's a pic of some cases I use to check the land contact distance.

    [​IMG]
     
  8. shilen30

    shilen30 Well-Known Member

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    Never tried the split case method, but it aught to allign the bullet better and give you more repeatable accuracy. I agree completely about the stoney point OAL gauge. Don't think it is necessary, but the comparator on the other hand is a must IMO.
     
  9. dbhostler

    dbhostler Well-Known Member

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    I've tried several methods over the years but now use the Sinclair Bullet Seating Depth Tool. Works best for me.
    db
     
  10. Brent

    Brent Well-Known Member

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    While checking the 210 JLK VLD design, it sometimes sticks in the lands just enough that the bullet will pull from the case as the bolt is withdrawn. When I check them now I will just push the case into the chamber fully with my index finger and push the bullet and case back out with a cleaning rod so it does not seat the bullet deeper of allow it to be pulled out farther. Pushing it out with a cleaning rod will not work if your fired case is sticky in the chamber, so select one that is not.
     
  11. kidcoltoutlaw

    kidcoltoutlaw Well-Known Member

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    i set up my redding dies the other day for seating the .338 sierra bthpm .then went to a different lot and its now .008 to .010 longer but still not touching the lands.im going to shoot them any way.have you seen it make a big difference.i myself have not.if your touching the lands and it then jams the lands i could see the difference im sure.right now im shooting 3 shot groups of .208 at 117 yards in a 338 RUM,thanks,keith
     
  12. kidcoltoutlaw

    kidcoltoutlaw Well-Known Member

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    i forgot to say im checking with a davis sds tool that measures off of the ojive {sp}got it from sinclair international,thanks,keith
     
  13. Lightvarmint

    Lightvarmint Guest

    Take the extractor out of the bolt. Seat a bullet long into a case to engage the lands. Seat the bullet with the bolt and then remove said bolt. Push the dummy round out of the chamber (from the muzzle) with a cleaning rod that has the brush/jag removed. This is the most repeatable and accurate method I have ever seen since it uses the bolt force to seat the round vice finger pressure. Remember we are only talking several thousanths of an inch between success and failure. [​IMG]

    James
     
  14. shilen30

    shilen30 Well-Known Member

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    Kieth, yes, I was in a store that carried the stoney point comparator instead, but the one you mention is great too. Remember (those of you who don't do so already), finding oal to the lands is only a starting position! You have to vary seating depth after this. Personally, I find my OAL by the methods you mention. I then seat a bullet in a sized case to this OAL and chamber the round. If I see marks from the lands, I seat a tad deeper until I am barely off the lands, and I use this as my starting point. Then, find the best powder/charge/bullet combo FIRST before varying seating depth. When you have found the most accurate powder/charge/bullet combination, THEN vary seating depth to squeeze those groups down! To find the correct seating depth I load 6 shots with OAL to the lands (enough to get some real data (and remember plenty of cooling time between shots)), and then 6 more with an oal (again, measured with the bullet comparator) .005" less than this, and continue to do this until you have several sets of 6 rounds that span from just off the lands to around .03" off the lands. Once you found the best OAL out of these, you can vary seating depth .002" from this if you desire. After testing oal and finding the most accurate one, write down the "sweat spot" oal after finding it, and use it for the differnt bullets and lots of the same bullet you use. Very important: the bullet profile changes from lot to lot, and certainly from bullet to bullet, but use the same OAL MEASURED BY THE BULLET COMPARATOR for each. this means you will have to adjust your seating stem of your seater dieevery time you change lots or brand of bullets, but the oal measured by the bullet comparator stays the same.

    [ 07-15-2004: Message edited by: shilen30 ]