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TM 1 bore demensions ??

Discussion in 'Shooting Related Threads' started by pfofml, Jun 19, 2013.

  1. pfofml

    pfofml Member

    Joined:
    Jan 29, 1998
    Messages:
    130
    I am shooting an used TM1. Looking at the target breaks cause me to suspect that the choke has been opened. What should the factory bore demsions read?
    Peter Falk
     
  2. cubancigar2000

    cubancigar2000 Well-Known Member

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    Location:
    Idaho
    .0724 - ,0727 I believe
     
  3. Dr.Longshot

    Dr.Longshot Banned Banned

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    Choke should be .035 full to .040 extra full, there are 2 bore diameters .724 on early models and .740 on late models. Most early models had .040 chokes

    Gary Bryant
    Dr.longshot
     
  4. Neil Winston

    Neil Winston Well-Known Member

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    Bore 0.727" plus or minus about 0.002", choke 0.038" to 0.045".

    Remember, Peter, there are several possible candidates when you wonder why the breaks are not a good as hoped:

    1. Choke messed with, a disqualifying fault in my book if it is choked 0.023" or less.

    2. Not shooting where guns you are more familiar with do. (See addendum below)

    3. You may be shooting them farther out than you do with your regular gun, maybe trying to get everything just right and so taking more time. "Pretty-rapid" is the preferred tempo for spectacular breaks.

    4. Promotional, reclaimed, or otherwise non-premium ammo doesn't hit them as hard.

    5. You may bit a bit off, as may be the gun fit, or an unfamiliar trigger or your horoscope or . . .

    Neil

    Addendum: Just how close does the POI you expect have to be to get the smoke we are all after? A lot closer than you might think and even then you won't get that perfect result every time, no matter what you do.

    The link above has a video of the results of nine levels of elevation-accuracy. It starts at minus 4, way below the target, through zero, right exactly on, to plus 4, way above. Our numerical rating (the number) is at the lower right of the frame.

    You will see that only zero is what you are after and even then it's not always pure smoke.

    So yes, you can tune in your POI by shooting, but on the other side, if you make a good move and don't the kind of result you think you have earned it does not (necessarily) mean that you did something wrong.

    Note also, of course, that all the shots above and below the targets have the same kind of breaks. They all look about the same: usually small pieces to the left, bigger to the right, mostly up but sometimes the air catches a piece just right and it goes down - or sometimes up. There is nothing about a "shot-cloud below the target" break that distinguishes it from a "shot-cloud above the target" break. You cannot read how the target comes apart for information about where the pellets that did not hit the target were. (Oh come on, how is the bird supposed to know where the pellets which missed it were and so be able to break according to TBR theory?)

    Last, note that _none_ of the shots with the shot-cloud had that "piece driven down" that is such a clear, but misleading tip-off for the coach on the porch to turn to his buddies and diagnose "See, he's over them all. As I've been telling him, he needs a bigger front bead."

    Over on the friendliest site "Coach Super-X" (who they think posts as "Scooterbum" here) is sure Ron and I edit our video and only show breaks that cannot be read. "How else can it be that you can't read any of them?" he reasons. Cross my heart, we don't. This is just plain fact. You can't read target breaks for information about where bulk of the shot-cloud was.

    But you can tell good from bad, Peter, and you are doing the right thing is trying to find out the cause of bad. Because if it really is a choke problem, you don't want it.
     
  5. Hookedonshooting

    Hookedonshooting TS Member

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    If it says 18.4 stamped on the barrel then u have .724.
     
  6. Neil Winston

    Neil Winston Well-Known Member

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    Hos, not really. What you have is "closer to 0.724 than either 0.720 or 0.728." Call 18.4 mm anywhere between 0.722" and 0.726".

    Neil
     
  7. john g.

    john g. TS Supporters TS Supporters

    Joined:
    May 7, 2011
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    I have a Comp4 TM1 that is marked 18.5 and has Perazzi choke tubes that measures .730 bore.

    John G.
     
  8. Hookedonshooting

    Hookedonshooting TS Member

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    Agreed. My 18.4 did measure .724 but perazzi is known to have a .001 + or - in their tolerances
     
  9. Neil Winston

    Neil Winston Well-Known Member

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    It's not really anything to with tolerances, Hos; it's just math and problems of conversion between systems which seem the same but aren't "interchangeable" without some thought about what you are doing, how the systems divide the world.

    The Imperial system we use divides inches into thousandths (when measuring things like this) and so the width of each "smallest chunk" is 0.001 wide - from 0.0005 smaller than the specified value to 0.0005 larger. Metric workers divide things into chunks which are 0.04 in width. The metric specification of 18.4 denotes a chunk of distance starting at 0.722 and ending at 0.726 and every distance in that range is has an equal right to be called 18.4 mm.

    Add to that the reading on your bore mike may or may not be within 0.001 of being right (or worse) and you will accept that any bore diameter you measure should be qualified by "or so."

    Neil
     
  10. seitz10

    seitz10 Member

    Joined:
    May 23, 2008
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    182
    Peter, have a extra tm1 barrel for sale if you need another. 34 inch fixed full with seitz porting pattern. roger check you pm