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Thread: Abrasives & PP Lapping

  1. #21
    Boolit Buddy

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    Quote Originally Posted by Huvius View Post
    I have no idea how a barrel can be made tight in the middle though...
    I once had a French MAS 36 rifle converted to .308 Win., which had a tight spot somewhere in the middle of the barrel. Don't have the rifle any more, so I can't re-check, but I believe the tight spot was not near any sight cuts or other features, and I think I remember tool marks at the corresponding point on the outside of the barrel. My guess at the time was that the folks who rechambered it (from 7.5 French to .308 Win.) had probably cranked too hard on the lathe chuck, or whatever they used to hold the barrel, and the steel was soft enough that they crushed it a little. (Barrel steel doesn't seem to be especially hard.)

  2. #22
    Boolit Master Good Cheer's Avatar
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    Sweated on barrel attachments can cause tight spots also; bayonet lugs, sling attachments, sights.

    In case this little rascal doesn't resuscitate there are some fun options to consider. Seriously considering ponying up the bucks for a reamer to fit my reloading dies. Alternatively I could go crazy with any .303 geometry cartridge or a .41 Mag for that matter. Meanwhile I need to get some more casting done with the 266469 that was modified to make the lube grooves shallow, patch 'em and load 'em hot enough to see if they'll fly straight in this choke bore X weapon.

  3. #23
    Boolit Master
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    I have a 6.5 Swede 1894 carbine with a similar bore. I tried everything short of paper patching, it still throws keyholes with my 266469. It will shoot inside an inch at 50 yards with 160 jacketed RN's. Mines looking like a rebore candidate. I have lapped at least a dozen firearms with 320 valve compound, and haven't managed to wreck one yet, all showed major improvements. I must be doing it wrong lol..

  4. #24
    Boolit Master Good Cheer's Avatar
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    Is it maybe that the 266469 is "light weight" for it's length due to the relatively big lube volume?
    I just don't know. We'll see how well it works with the depth of the grooves decreased.

  5. #25
    Boolit Master
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    I have no doubt the condition at the muzzle could be improved sufficiently to allow good use of PP boolits. As mentioned by 303 Guy, the idea is to smooth off the edges of the pits and remove their ability to carve off shavings of boolit metal. PP improves the effectiveness of the "repair". I've seen barrels that were hopeless foulers returned to accurate shooting, even if they still needed many patches before clean ones came out due to the pits retaining powder fouling. Just looking at the muzzle photo, I'd start with US Products Crystolon 400 http://http://www.us-products.com/pr.../product61.htm and follow up with some Crystolon 600. Some folks go finer, but these days I let it go after the 600. The 400 is good for initiating the polishing/rounding without materially affecting the throat. The 600 will finish the job. Numerous PP boolits will improve things further.

    By the way, there is no industry standardized way to grade abrasive sizes or type, each company relying on their own system. A container may be labeled "320 Abrasive" but it may not even be close to someone else's 320, hence, if a fellow says "use fine valve grinding compound", his fine VGC may work well, but what your auto parts place carries could be unusable or far too aggressive, as happened to me. As for lapping barrels, I can only speak about the results I've gotten. The US Products mentioned above I have used and know they work.
    Last edited by yeahbub; 09-18-2017 at 09:13 PM.

  6. #26
    Boolit Master

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    While I don't have my old machinists handbook handy right now, It gives the "standard for defining the grit" of lapping compounds. The grinding waste is put in a certain weight type oil and stirred to suspend the grindings. After a certain time it is poured off slowly and gently. what remains is XX grit. the new container is stirred and a longer time period is used this is XXX grit and it continues with different times separating the grits.

  7. #27
    Boolit Master Good Cheer's Avatar
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    Something I've done to get extremely fine grit...

    Set a box fan at one end of a cleaned long and flat surface.
    Turn on the fan.
    Slowly sprinkle fine dry sand in front of the fan.
    Do that a few minutes and harvest the grade of grit that you want to use.

    Where I lived in Texas crawdads in the yard would build chimneys of the finest stuff you could imagine.
    Separating out the fines in a jar of water was easy.

  8. #28
    Boolit Master 303Guy's Avatar
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    I lived near a beach that had real fine sand. I used that as a catch medium in my firing tube. That stuff ended up real fine, like dust. But the idea is to head back there and scoop a few buckets full of that fine sand. Thanks for the tip.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check