Polishing A New Bore

Discussion in 'General Muzzleloading' started by Dixieshedhunter, Nov 20, 2019.

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  1. Nov 21, 2019 #21

    longcruise

    longcruise

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    That was standard procedure in barrel making among at least the builders of the last half of the 19th century. There's more about that in Ned Roberts book on the caplock rifle.

    Some seem to think that shooting in a sharp barrel is fun that stops once the barrel is shot in. I firelap a rough barrel and then enjoy the following 200 to 300 shots even more. :cool:

    Now stand by for the dire warnings against fire lapping from those who have never done it. :)
     
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  2. Nov 21, 2019 #22

    Erwan

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    Normally I have to do this for a "Mountain Rifle" Jukar of the 70's, it' looks like easy but I don't know if I'll do this way. In a other way the barrel is so rusted that I don't see another solution...

    The problem is about the barrel plug if some lead goes inside the bore...

     
    Last edited: Nov 21, 2019
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  3. Nov 21, 2019 #23

    sawyer04

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    The video is interesting, back in 57 I don't remember the breech plug being removed. It all was done from the front. A lot of busy work on the video method. Sure is a funny looking muzzle loader.
     
  4. Nov 21, 2019 #24

    Erwan

    Erwan

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    Yep, in this video it is a Withworth profile an not a eight grooves like this I have to do. So after firing if the bore doesn't tear the patches, it has good speed and accuracy I'll perhaps let it how it is now.
    I'll see that next week at the range with the Chrony, bullets .440", patches thikness .014" and a target at 50 yards.

    If doesn't works I'll do the job... :(
     
  5. Nov 22, 2019 #25

    springfield art

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    Does lead indeed shrink? How can bullet moulds be accurate? Anyone else have an opinion on this? Just wondering, not to question your statement. Thanks.
     
  6. Nov 22, 2019 #26

    springfield art

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    I have an un-fired Uberti plains rifle from mfg. date of 1989. This .54 cal. has a bore so sharp you could shave with it if turned inside out! I'm going to mellow it out a bit with the valve grinding paste. Did that with a .54 Lyman GPR, and the difference is readily
    "feelable" with the pinky finger...
     
  7. Nov 22, 2019 #27

    Britsmoothy

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    Pretty much anything in a heated state will shrink when cooled.
    Elements such as pure lead will give consistent constant results and hence predictable.
     
  8. Nov 22, 2019 #28

    hanshi

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    Be forewarned that in the area where the groove edge meets the lands that a small demon lives there. This demon relishes the job of messing with patches and resultant accuracy. Sometimes sacrificing a chicken helps.
     
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  9. Nov 22, 2019 #29

    Zonie

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    Unless your a geek or just curious, you can skip my answer.

    All materials have certain properties that are known and the value of the change in size of a material due to temperature is called its Coefficient of Thermal Expansion (COTE). This value is multiplied by the degrees of temperature change and the answer is in either inches or millimeters.

    The Coefficient of Thermal Expansion for pure lead for temperature changes in Fahrenheit and the answer in inches is 16.3 millionths of an inch per degree temperature change per inch of length or size.

    The standard temperature for distance measurement is 20 degrees C. or 68 degrees F. so that number has to be subtracted from the temperature you want to know the answer for.
    Say you want to know how much lead will expand at its melting point of 618°F. Subtracting 68° from 618°, the temperature change value is 550°F. 550 times 16.3 millionths of an inch = .0090 inches per inch of length.

    If you are talking about a ball or bullet that is 1/2" in diameter, you would multiply the .0090 expansion value by 0.500 which gives a growth size of .0045 inches so, the cavity in the mold needs to be .5045 in diameter when it is heated to 618°F .

    Now, you can't just use this value to get a .500 diameter bullet because the mold is also going to expand when it gets hot. Due to this, the Coefficient of Thermal Expansion value for the mold material must also be known and taken into account.

    If the mold is steel, it's COTE is 8.4 millionths of an inch per degree F per inch of thickness.

    Knowing the temperature of the mold when it is up to casting temperature will be fairly close to the temperature of the solidifying lead, we can use the 550°F, value to figure out how much the mold will grow. 550°F X 8.4 millionths = .0046 per inch growth per inch times the .500 bullet diameter = .0023 inches.
    Because the steel mold expands less than the lead expands, we have to make the mold at room temperature, larger than the finished bullet size. The difference in size between the two materials is .0045 (lead) - .0023 (steel) = .0022 so, if we make the bullet mold .5022 in diameter at 68°F it should produce a lead bullet that is .500 in diameter.

    By the way, the COTE for aluminum is about 13.2 millionths of an inch per inch so it is very close to the COTE of lead. This means a aluminum mold will grow just about the same as the lead so, an aluminum mold can be almost exactly the same size at room temperature as the bullet will be at the same room temperature.

    Now, aren't you sorry you asked the question? I know some of our members are. :D
     
  10. Nov 23, 2019 #30

    Griz44Mag

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    Dang it Zonie, that's exactly what I was going to say, you beat me to it.....:D
     
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  11. Nov 23, 2019 #31

    springfield art

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    Sheesh! Sorry I asked! Seriously, though, thanks!
     
  12. Nov 24, 2019 #32

    akaMOTU

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    I guess I qualify as an engineer geek. I used to design/build high wattage CO2 lasers years ago and COTE was very important - we used round bars made of invar (for it's low thermal expansion rate) to build our laser optic resonators.
     
  13. Dec 3, 2019 #33

    FlinterNick

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    It depends on the shape of the bore.

    I purchased a bicentennial Miruko Brown Bess a few years back, the bore had some spots I didn’t like.

    i jagged the end of a wooden down and wrapped some Emory paper on the end and just worked it by hand down the barrel, I started with 600, 800, 1000, 2000 and then 3000 and the bore was super bright and never rusted.

    Some people will take a bore mop and use polishing compound then use a drill to lap the inside of the bore, this works very well.

    For rifled guns I use a slightly smaller jag than the bore and wrap with Emory and work it through the groves.

    I’ve done this on a few guns but only on used guns that were not cared for.
     
  14. Dec 3, 2019 #34

    M. De Land

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    Lead slug lapping is the only correct way to polish a bore that will not change the shape of the lands and to a lessor degree grooves.
    Almost any bore can be improved by proper lapping as it uniforms both dimension and gets rid of tool marks left by any of the reaming and rifling processes used currently.
    Steel wool is not a good way to get the job done correctly but will not harm much in a patch shooting gun. It will never remove any pitting or tight dimensions but it will round off land corners of whisker and such. It is more or less a burnishing process and will some times stop a bore from ripping up patches.
    Proper hand lapping with a poured lead slug will maintain the cut profile , smooth and level all surfaces and can be used to employ taper and choke into a barrel.
     
  15. Dec 4, 2019 #35

    springfield art

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    Good tip. Thanks.
     
  16. Dec 4, 2019 #36

    springfield art

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    I would never use a drill...too fast & powerful. Patient hand polishing helps avoid "hot spots" or over-worn areas. Just my opinion.
     
  17. Dec 4, 2019 #37

    Woodnbow

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    Probably why my grandson has such difficulty with iron sights. On the other hand, my granddaughters are fine markswomen...
     
  18. Dec 4, 2019 #38

    FlinterNick

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    You’d want to use a low setting, and if you’re using a high grit like say 1500 or 2000 its not likely you’ll have any hot spots, I mean you’d need to really run the drill at max capacity for that to happen.

    However, all of this can be avoided by taking care of the barrel, cleaning it and lubricating it.
     
  19. Dec 4, 2019 #39

    springfield art

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    There's a couple of repro BB's coming up at an auction later in the month. I have a Pedersoli "kit" that I just finished, plus a nice quality India BB that I fully re-finished. Can never have too many Besses!?
     
  20. Dec 5, 2019 #40

    FlinterNick

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    Certainly not, I’m working on my third Brown Bess.
     

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