The [so called] Robinett 30 BR reamer- exposed.

Discussion in '6BR, 6BR Improved & Wildcats' started by RGRobinett, Aug 30, 2017.

  1. RGRobinett

    RGRobinett

    Joined:
    Sep 13, 2005
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    Attached is a copy (pic) of the original, and only Robinett 30 BR reamer. A reamer featuring a single alteration is not a Robinett reamer, but rather, “something else”. The only reason that my name was attached to the reamer was/is because I ordered it: at the very least, upon any alteration, my name should have been removed.

    While alterations are neither necessarily bad, nor, good, they are different. When I ordered my original reamer - subsequent to, and different than Ronnie Long’s [original] reamer- I did not ask that it be proprietary, nor did I request to have my name attached/associated with copies of my dimensions: only that clones be readily available; no strings attached.

    Regrettably, beyond my control, there are a multitude of reamers bearing my name, many of them, with dimensional changes which, in combination with the short/light thirty caliber bullets, are undesirable. Here are two [common] ‘deal wrecker’ attributes:

    Excessive OAL, thus, too long a chamber neck length - typically, 1.560” (SAAMI Spec. .22 BR OAL). Mechanical neck-up processes reduce neck-length, thus OAL: 1.520” necked-up brass, in a 1.560” chamber will result in 0.040” ‘counterfeit’ free-bore.
    My tooling never produces a necked-up 6mm LAPUA case in excess of 1.515” long - most are 1.512-1.513” before trimming to square the mouths. Thus, the specified maximum OAL of 1.510” on the original reamer - this has worked very well. Note: few expand-up processes/tools produce OAL greater than 1.520” - more on this later; in brief, fire-forming does produce longer necks/OAL. Know the OAL of your reamer/chamber.

    Any amount of free-bore, especially in conjunction with #1(above). Already, #1 will all but preclude seating the short/light bullets against, or even near the lands - actual free-bore, in combination with excessive chamber-neck length [usually] spells poor results. Short 30 caliber BR quality bullets do not require any free-bore.
    Note: my original reamer features a [unusual] 1.75 degree throat angle - the typical 1.5 Deg. angle requires seating the bullet out even further - aproximately 0.035" further! With the 1.75 Deg. throat angle, and brass trimmed only 0.010” short of filling the chamber-neck, the base of a typical short/light thirty caliber bullet, seated to contact the lands, will have only about 0.125” of shank in the case neck. Short case-necks, and free-bore erode bullet grip fast!

    Not quite as bad, is a poorly positioned, or, inadequate cone diameter (variously referred to as ‘throat’, ‘leade’, etc.): the cone should remove every vestige of land material, preferably, at least, skimming (cleaning-up) the bottom of the grooves, affording the bullet free access to the barrel/lands. A zero free-bore reamer does just this, right off of the chamber mouth. This is not to be confused with the typical 45 degree angle at most reamer mouths, which presumably, is a better chamber:barrel transition than a perpendicular wall.

    There are two alterations, which, if ordering a new reamer, I would make to my original:
    Diameter, at the .200” (ahead of bolt-face) DATUM line , I would state, “not less than 0.4715”.
    Neck diameter 0.331”, no taper.

    Note: the hand written .315 above the neck, on this print, is the approximate neck-length of my brass, when trimmed for 0.010” clearance, or, when trimmed to 1.500” OAL.

    I hope that this is understandable and proves useful. Keep ‘em ON the X! RG

    IMG_0511.JPG
     
    Last edited: Aug 31, 2017
  2. WSnyder

    WSnyder

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    Aug 21, 2015
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    Randy can you clarify the throat angle? In your text you say "Note: my original reamer features a [unusual] 1.75 degree throat angle" but the print above shows 1º-45 and your 2005 PS article with a print shows 1º-45 as well. Thanks!
     
  3. sean68

    sean68

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    1.75 is the same as 1 degree 45 minutes.
     
  4. WSnyder

    WSnyder

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    Doh!!! Thanks I should know that :)
     
  5. Link

    Link

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    Jun 5, 2007
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    This might explain why I only have .125 shank in the neck [I often wondered about this. I thought it was to make room for more powder.] with the 118 Bib seated to touch the lands. I have found a lower node that seems to be about as accurate with 2.0 gr less H4198. I also seat my 118 .025 further into the case with this load. The lighter load is a lot easier on cases. This is a informative read for the 30br thanks Link
     
  6. mr.big

    mr.big

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    May 15, 2014
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    is the Model: PTG-000046 reamer sold at Bullets.com your reamer or is it different and just have the Robinett name??
     
    knguyen likes this.
  7. RGRobinett

    RGRobinett

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    Compare the two prints: mine (above) vs the one you mentioned. :eek:RG
     
  8. LCazador

    LCazador Competitive shooter and reloader for 50 years+ Silver $$ Contributor

    Joined:
    Jul 21, 2009
    Messages:
    616
    I bought my reamer from Kiff and I guess I saw through all these changes. Not sure about all the complications that resulted from all this. The bottom line is you need to have enough knowledge to make the right decision and if you're not sure then it should land on a competent gunsmith to make that decision for you. Thank you Randy for letting us know. Maybe this should stand as an eternal sticky!!
     

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