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Barrel Porting - Deburring

l-girll-girl Member Posts: 131 ✭✭✭
edited March 2004 in Ask the Experts
I have acquired a porting jig that allows one to drill 1/8th inch holes in any desired pattern (above, below, or along the side) on the barrel.

I read an older post that said all factory porting is now done with EDM (Electronic Discharge Machining) which utilizes an electrode and requires no drilling (and leaves no burrs).

I have an old shotgun and a sporterized Enfield (no collector value) that I wanted to experiment with using the jig and a drill. Do I need a reamer or would polishing work to clean the burrs from the inside of the barrel?

Also, are there any patterns of holes that work better than others. I've read one source that says and 8 to 1 ratio of holes on the bottom half of the barrel (vs. top half) reduces muzzle jump the best. Any opinions?

Thanks,

Best regards,Rich

Comments

  • nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    I-girl,

    Just as a suggestion, I would practice first on some tubing in order to get a feel for the set up. Start with a combination drill to spot the position then finish with the drill. That way the drill won't walk. For de-burring the shotgun tube, you can use a brake hone with fine stones powdered by a drill. Go slow.

    For rifles, remove the barrel first, drill your hole pattern then go to the lathe and set the barrel up with muzzle end in a steady rest. Grind a tool to make relief cuts inside the barrel for at least the length of the holes. This is supposed to act like an expansion chamber. The depth will in part be determined by the contour of the barrel at the ports. The crown should be opened up about 0.020" over the diameter of the groove depth. That's if everything was done in line with the centerline of the bore.

    From one of the sites below:

    Drilled Holes

    To drill Holes into the Barrel will damage its internal Surface. One Way to work around this Mess, would be to afterwards attach the Flashsuppressor concentrically on a given Barrrel. Another Way would be to ream the Barrel slightly, to cut the Drillrelicts off.

    Expansion room

    The Expansion room must be as big as possible.

    Exit

    The Exit from the Expansionroom must no just be a plain Hole, to allow turbulences, but a Tube with an expanding Funnel. So from the Suppressormuzzle reaches a lon concentric Tube till the internal Muzzlebrake. The may in Fact be Made from the same raw Steelpiece. The inner Diameter must be slightly above the Bulletdiameter and very concentrically to the Bore axis. If Concentricity cannot be guarenteed, then increase the Bore, to dampen the Concentricity error.
    The moderated but still speedy Powder gasses expand in the, say 15? Funnel, thereby further lowering their Speed.
    http://home.snafu.de/l.moeller/Flashsuppressor.html

    I've attached some sites for you to look at regarding porting and it's effect. Look at the drawings also.

    http://home.snafu.de/l.moeller/Bremse/Muendungswolke/Muendungswolke.html

    Website translator: http://world.altavista.com/

    http://www.kurzzeit.com/index_e.htm (available in English)

    http://home.snafu.de/l.moeller/English_Rifle_Articles.htm

    Be sure to open some of the other links in the first site as there is a bunch more information. The second site has videos.

    Hope that this helps!

    Best.
  • AlpineAlpine Member Posts: 15,092 ✭✭✭✭
    edited November -1
    The reason why EDM is used for porting is that there is no burrs. I would not recomend drilling any barrel. However there are machinist tools to deburr a hole from the outside.

    All porting on shotguns that I have ever seen has been on the top half of the barrel before the shot goes through the choke portion of at the end of the barrel. Two reasons for this: The vented gases helps limit "barrel jump", and the shot column has gotten all the push from the powder that it is going to get.

    "If you ain't got pictures, I wasn't there."
    ?The problem with socialism is that you eventually run out of other people's money.?
    Margaret Thatcher

    "There are three kinds of lies: lies, damned lies and statistics."
    Mark Twain
  • rsnyder55rsnyder55 Member Posts: 2,526 ✭✭✭
    edited November -1
    Wouldn't drilling also produce heat that could affect the material surrounding the area being drilled?
  • BallisticBallistic Member Posts: 160 ✭✭✭
    edited November -1
    Here is a method to help "reduce" the burr on the I.D. of the barrel.
    Measure the I.D. of the barrel, produce a length of soft brass or copper rod to that exact dimension +.0001 -.0000 dimension, this will provide for a push fit, insert rod in barrel end by holding the barrel in a soft jaw lathe chuck and then use the lathe tail stock (locked) to push the rod in the barrel.
    Now when you drill the ports, the drill end will enter and end in the rod thus greatly reducing or in some cases eliminating the burr on the I.D. of the barrel. Light honing is all that is required, no deburring tools should ever touch the lands or I.D. of the barrel.
    Sounds like a lot but it is easy and it works. This is a typical machinist procedure.
    Good luck.
  • AlpineAlpine Member Posts: 15,092 ✭✭✭✭
    edited November -1
    To measure the "true ID bore" requires that you measure the bore after the forcing cones and before the choke. This could present a problem unless you have a bore dial.

    A deburring tool is a lot cheaper.

    "If you ain't got pictures, I wasn't there."
    ?The problem with socialism is that you eventually run out of other people's money.?
    Margaret Thatcher

    "There are three kinds of lies: lies, damned lies and statistics."
    Mark Twain
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