Firing pin channel

Discussion in 'P-3AT' started by downhill, Jul 6, 2008.

  1. downhill

    downhill New Member

    82
    Jul 2, 2008
    I'm in the process of fluff and buff and things are going real well. I did encounter one problem though. The firing pin bore is an absolute mess. I have a hard time understanding how a guy could drill a hole this screwed up. I suppose you could do it if your drill bit was properly bent and broken, and your feed rate was about 3X higher than it should be. :eek: Bottom line is, no amount of polishing would fix it. The FP was notchy as hell all the way back and forth. To remove all the grooves would require oversizing the bore to the point that the firing pin would be sloppy loose. I'm talking about the larger spring bore. To fix the problem I bought some seamless hard brass tube 3/16" OD X .014 wall. The bore is .1595 and the FP and spring is .1570, for a clearance of .0025. This tube is a nice slip fit on the spring and pin. I cut and trimmed the tube to length, then side drilled and deburred a hole for the lock screw. I used a reamer to enlarge the FP hole to accomodate the tubing with a snug fit. I applied a thin coat of blue loc-tite and pushed the new bore liner into place. Let me tell you, the FP is smooth as butter now!!! The brass is somewhat self lubricating so with a polished spring and pin and proper lubrication, it should outlast the gun. If for some reason I ever need to replace it, I can run a tap into it, then a screw and extract it easily. The tube is available from K&S Engineering, Chicago, IL and the stock number is #129. I found mine at a hobby shop for $1.60 (12" length).

    David
     
  2. pocketgun

    pocketgun New Member

    May 4, 2005
    Innovative solution - well done! :cool:
     

  3. JFB

    JFB New Member

    Jul 25, 2005
    Sounds Like an EXCELLENT improvement
     
  4. Bobo

    Bobo Active Member Supporter

    Jun 13, 2005
    You get five thumbs up for that one![smiley=thumbsup.gif] [smiley=thumbsup.gif] [smiley=thumbsup.gif] [smiley=thumbsup.gif] [smiley=thumbsup.gif]

    Bobo
     
  5. jpaul

    jpaul Member

    233
    Apr 23, 2008
    Have you shot it yet since you did the mods?
    I am by no means expert but the clearance between the hole and the pin may be a shade on the tight side when its being fired.
    If it works it works and good job.
    If it doesn't try opening up the hole just a little.
    I like your thinking either way. [smiley=thumbsup.gif]
     
  6. downhill

    downhill New Member

    82
    Jul 2, 2008
    Jpaul,
    .0025 clearance is fine on a small bore like that, but you bring up a good point. Going too close would not be good because it could produce an air cushion effect. Air needs to be able to escape from the cavity rapidly to avoid creating an airspring. If anyone tries this, I would say .002 to .004 would be close enough for good pin guidance without causing an air cushion. If you use a tube other than what I described, be sure and check that fit. .0005 would probably feel good with your finger, but when it takes a high speed hit it could cause FTF.

    David
     
  7. JFB

    JFB New Member

    Jul 25, 2005
    also remember the spring expands as it compresses and if you should replace the spring, the manufacturing tollerances might have different OD.
     
  8. Very nice solution!

    I have cleaned up all of my 3AT FP Channels, the FP holes,and the Firing pins.

    But I never even considered a sleeve!

    Fantastic!

    Report back on results!
     
  9. JFB

    JFB New Member

    Jul 25, 2005
     
  10. downhill

    downhill New Member

    82
    Jul 2, 2008
    OK Guys,
      Here are some more details for anyone who wants to try this modification.  Here are a list of tools you will need:
    #24 drill (prefer screw length)
    #13 drill (jobber or screw length)
    3/16 precision reamer
    deburring tool
    ultra fine point sharpie (the others are too big)
    1" long #8-32 nylon screw
    Qtips & pipe cleaners
    Lacquer thinner
    Blue loctite
    3/16" brass tube. .014 wall thickness

    [​IMG]

    Step#1: secure the slide in the mill and center the firing pin hole with the boring tools.  I won't elaborate much here since these are basic machinist skills.

    Step #2:  use the #13 drill to remove the extra material from the hole.  You can feel easily when you reach the bottom.

    Step#3:  Follow the drill with the reamer to complete the firing pin channel prep

    Step#4: Clean out the hole and the locking screw hole with qtips and solvent

    Step#5:  Slide the brass tube into the hole till it bottoms, then use the sharpie to mark the hole position for the set screw and also mark the end of the tube for cut off.  Note: be careful to mark the length very carefully. The tube must be just below the lip of the steel hole.  This is critical!

    [​IMG]

    Step#6:  Remove the tube and drill the cross hole with the #25 drill.  The drill will not go all the way through.  Just feed it carefully until the proper size hole is formed. Deburr the hole with the exacto knife.

    [​IMG]

    Step#7  I used my mini lathe to part off the tube at the correct marked length.  The forward end should have a slight chamfer, and the back should be square with no burrs anywhere

    [​IMG]

    Step#8  Now you are ready to test fit the sleeve.  Thread the nylon screw into the sleeve from the back about 1/4" and use it to insert the tube into the hole.  Check the setscrew hole alignment and also check the back to be sure that the sleeve is below the hole edge.  If it is left proud, the hammer will peen it over and jam the firing pin.

    [​IMG]

    Step#9  Remove the sleeve and make any final adjustments.  Roughen the outside with 320 sand paper and clean the tube thoroughly.  Clean the hole and setscrew hole again with qtips and solvent.  I use lacquer thinner.  Brake cleaner in an aerosol can works good too!

    Step#10:  Coat the sleeve and the hole with blue loctite and push the sleeve into the hole, making sure that the setscrew hole is aligned.  If the setscrew hole is a tad off you can rotate the tube using a punch.  Clean all the excess loctite from the hole, setscrew hole, and the minor firing pin bore.  Qtips and pipe cleaners work well with a little lacquer thinner.  Test fit the setscrew to be sure the screw goes in cleanly.

     Let it dry overnight and reassemble with good lubrication.  Now you have the slickest firing pin to ever grace a P3AT!

    [​IMG]

    If you ever need to remove it, screw a #8-32 self tapping screw into the back and extract it.

    David
     
  11. Forge

    Forge New Member

    26
    Jul 15, 2008
  12. wyo-man

    wyo-man New Member

    726
    Nov 27, 2006
    Nice job...........

    wyo-man
     
  13. downhill

    downhill New Member

    82
    Jul 2, 2008
    Well,
     After firing it I can say that it was worth the trouble  The FP action is smooth as butter and the strike marks on the casings prove it.  They are robust!  I was so jacked up to get working on the gun that I didn't collect any "before" casings to compare.  When I pick up my new P3AT, I'll fire it right out of the box and see what I get.  I'll try and take a close-up of the two to show you.  I have a light trigger mod coming from 2PP, and I figure this will only enhance the way it works.

      My next project is a press-in barrel bushing.  Right now, the barrel play in the slide at lock-up is about .014".  I have the tooling to ream the hole in the slide slightly and then press in an oil impregnated bronze bearing that is custom fitted to the barrel to produce a .002 clearance.  That should cut my groups in half, and the bronze bearing may even improve function by presenting a slick passage for the barrel.  Truth is, after all my prep work I have yet to have any malfunction.  Anyway, I'll start another thread when I get to that.
     
  14. JFB

    JFB New Member

    Jul 25, 2005
    I would be interested to hear how the barrel neck down, the effect of the barrel tilt and the "length" of the bushing fit.

    I think there was a period when KT wanted to reduce the clearance of the recoil rod hole in the slide by making the bushing length less (drilling the hole deeper). resulting in the thin metal around the hole working out. One of the traits of the nylon washer used for that hole was it had less clearance but would deform as the rod tilted.
     
  15. downhill

    downhill New Member

    82
    Jul 2, 2008
    JFB,
    You are right. It wouldn't work if the barrel were a cylinder, but that funky ball at the end is what makes it possible I believe, LOL. As soon as I saw that my gears started turning :)Before I start carving on the 3AT though, I'll make a mock-up to test the function through the range the barrel has to move. The barrel aft of the ball is much smaller diameter so once the slide moves back a small amount, it is that portion that comes into play. The guide rod really gets exercised during recoil and there isn't much to gain by cramping it anyway
     
  16. JFB

    JFB New Member

    Jul 25, 2005
    How about a ferrule collar pressed on the barrel.  I think the concern is provide precission placement in the barrel to slide (sights) during bullet discharge, but there is no need once the barrel unlocks from the slide. :-?

    However, I'll back out to my position the primary concern is relaiblity not precession
     
  17. downhill

    downhill New Member

    82
    Jul 2, 2008
    JfB,
    LOL, we seem to think alike. I looked at that too, and I'm sure it would work, the problem is, I can't figure a way to do it securely without building some elaborate crimper. The other problem for me at least would be creating the ferrule since it would have to have a wall thickness of about .006"

    Today I created the bushing for the slide. I used progressivley larger drills to prevent swelling the bearing and then finished it with a .4600 straight reamer. The sleeve has a wall of .018. I also built a .4600 drive mandrel to press the bearing into the slide. The slide nose will get reamed out .0395 x 1/4" deep and then while the slide is aligned in the mill, I'll put the mandrel in the chuck and press it in.

    The object of course is to align the barrel in the slide the same way everytime. If my math is right, this should cut my group size in half.
     
  18. JFB

    JFB New Member

    Jul 25, 2005
    TWO points define a line