I assume this tool gives me distance to lands?

Discussion in 'Reloading' started by The Oregonian, Jun 4, 2015.

  1. The Oregonian

    The Oregonian Well-Known Member

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    This came with my custom rifle and looks like a seating depth gauge...so if I measure from cartridge base to end of tool (where the lands start) it will give me distance to the lands?

    Assuming so, I would then measure CBTO and that should be my max length, or where the bullet is touching the lands?

    Thx in advance.
     

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  2. Stob

    Stob Member

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    It is made from a drop off of the barrel, and the reamer is run into it up to the shoulder. The tool will give you a couple things. First, it is a good way to measure how much the shoulder of the case is being bumped back during resizing. You usually don't need to bump a shoulder back more than a thousands or two, assuming the sizing die matches the chamber fairly well. Then it can give you a measurement where the bullets contact the lands. The easy way to tell is seat a bullet, insert it and twist the case.If the bullet is contacting the lands it will be obvious with marks on the bullet, or keep seating them out further until you see the marks. If you are feeding from a magazine, you may be limited in ow far out you can seat a bullet and still work in the mag. This will only work until the throat wears from firing, then you would have to adjust seating depth accordingly. It;s mostly used for shoulder setback.
     
  3. Mikecr

    Mikecr Well-Known Member

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    Useful for comparative shoulder/bump measure.
    I don't see it helping for seating.
     
  4. The Oregonian

    The Oregonian Well-Known Member

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    On the end it is cut where the rifling starts so it looks like it would allow me to put a round in this tool and see if it touches the lands.
     
  5. Mikecr

    Mikecr Well-Known Member

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    Your actual chamber has length beyond shoulder contact, and the actual barrel throat breaks in and erodes.
    New brass also varies in shoulder dimensions/angles, it doesn't match your chamber shoulder yet, and then won't again with bumping.
    So there may be a window where your tool is relatively good or even perfect, but fleeting.

    IMO, best measure of touching COAL/CBTO is from the boltface.
    Search around a bit for all the Hornady OAL issues everyone seems to be having. They have these problems because they're trying to take datum off shoulders. This, as you're considering with that gizzy.
    On the other hand, those of us measuring to boltface with the old cleaning rod approach -no problems there.

    Your tool is very useful, I have a few myself, for comparative shoulder bump measure.
     
  6. Stob

    Stob Member

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    As I said before, when the throat erodes, you will have to adjust your seating depth. But for now, new barrel, it can certainly give you a very good starting point where the lands are in relation to the loaded round, without having to actually load the gun.

    If by chance you had a custom chamber cut, with a minimum spec, you can use the same tool to check and ensure you have neck clearance with different brands of brass.

    They are very useful, but you'll probably find the shoulder bump function the most used. Glad your gunsmith did it for you.
     
  7. Mikecr

    Mikecr Well-Known Member

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    See, the thing is: who really cares if they're off the lands .xxxOTL, or in the lands .yyyITL?
    Don't get hung up on this, I'm trying to help you.
    The relationship 15thou OTL, or 7thou ITL, etc., is only for description of your seating to others.
    There is no actual benefit or affect with measure of it beyond that.

    Review Berger's seating testing procedure pinned at this forum. You do the test and find best seating cartridge base to ogive z.zzCBTO. This is a huge factor in your end results, and wherever it is, you log it & reproduce it until your barrel quits. You won't have to mess with it again, unless you change bullets. Then you test again.

    In other words, you don't log '.045"off' for your best seating. You log '3.575"CBTO'.
    CBTO is to boltface, it don't change.
    If this important term was to shoulders, it would be called shoulder datum to ogive SDTO.
    And the reason we don't do that; every case shoulder in the box is different.
    Even fireformed, and even after bumping, they're all a bit different, because they sprung back to where they are to case bodies stretched and sprung back to where they are. That's why the Hornady/stoneypoint tool folks have to 'average' their readings.
    Same holds for trimmers. If you trim based off shoulders, then your cases are being trimmed to an average OAL..

    A great little gizzy for CBTO, believe it or not, is Sinclair's 'NUT'. It works great.
    http://www.sinclairintl.com/reloadi...r-hex-style-bullet-comparators-prod34262.aspx
    For me it works better than caliper attachments and indicator sorting stands, I guess because it's floating.
    I've used them all, and went back to the nut.

    You pull out YOUR gizzy during sizing to verify every shoulder bump.
    You pull out the Sinclair gizzy during seating to verify every CBTO.
    2 tools, great results.
     
  8. FEENIX

    FEENIX Well-Known Member

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    You've been provided excellent advice by previous posters!

    Mikecr, I think you might have coined a new acronym/word. :D

    I use ...

     
    Last edited by a moderator: Sep 8, 2018
  9. The Oregonian

    The Oregonian Well-Known Member

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    Yes, good info. That gizmo is what I use for CBTO...works well.
     
  10. Stob

    Stob Member

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    Never change seating depth until the barrel is shot out? Really? Seriously? I guess accuracy means nothing to you. Seating depth and powder charge are the two biggest factors in accuracy to any rifle. Magazine restrictions aside, a rifle can benefit greatly by finding the seating depth it likes, and more often or not, the closer the bullet is to the lands, the better it will shoot. In a hunting situation, you wouldn't want the bullet jammed in the lands to the point the bullet pulls if you unload the rifle. But close may very well be more accurate. And there can be a significant change in accuracy with as little as .005" of seating depth. Accuracy beats velocity every time.

    Common sense will tell you if you change a bullet, you need to retest. One thing Mike has said is true, the bullet ogive tool that Sinclair sells (measuring nut), is the way to measure seating depth, not by the tip of a bullet. By the way, this nut tool is made to BORE diameter of the caliber, which is in essence the lands, like the tool you have! Imagine that.

    But you have to check the magazine fit and feeding if you seat bullets out. Some factory chambers have long throats and you may never reach the lands with lighter bullets. Factory chambers are made to swallow every factory loaded round out there.
     
  11. FEENIX

    FEENIX Well-Known Member

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    :rolleyes:This is about to get interesting, ..................................................wait for it! :rolleyes:
     
  12. The Oregonian

    The Oregonian Well-Known Member

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    Or, maybe I am not as experienced as some, and was looking for help rather than a smart --- answer.
     
  13. Stob

    Stob Member

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    Smart ---? Where? By questioning the opinion of another poster? IMO his advise was wrong.

    I come from an accuracy background and profession. If having an accurate rifle doesn't appeal to you, then sorry. If you want to over work your brass by not adjusting the sizing, then sorry.

    The mere fact that your gunsmith made that tool for you tells me he is also is interested in someone getting the most out of a rifle.
     
  14. Mikecr

    Mikecr Well-Known Member

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    Oregonian, I was just passing on my views about it, and not knocking your tool. It's a good tool, custom for you. I too have a gizzy cut for each chamber, and I also get dies cut with my reamers at the same time(barrel finishing).

    I'm hoping you'll consider ALL inputs here at LRH.
    Some subjects don't really lead to yes or no, right or wrong, etc. They bring out contrast in experience and discussion.
    It's a good thing. Otherwise, we'd all being do the same things, and it's likely some of what we're all doing would be wrong.

    An example; 20yrs ago, 10yrs ago, it was widely assumed that Berger VLDs needed to be in the lands(ITL) for best performance. There were a lot of heated discussions about it, but in the end the crowd apparently won.
    No, the crowd lost..
    Turned out they were wrong..