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Thread: Micro Grove and fire lapping

  1. #1
    Boolit Master MGySgt's Avatar
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    Micro Grove and fire lapping

    Anyone ver firelap a Marlin MicroGrove rifle? What were your results?????

    Drew
    Big Bore = 45+

  2. #2
    Boolit Master


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    Yep. Friend's 45-70 just would lead, no matter what we did. Finally decided to firelap it. Cured the leading completely.


    Cat
    Cogito, ergo armatum sum.

    (I think, therefore I'm armed.)

  3. #3
    Boolit Master MGySgt's Avatar
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    Do you remember how many rouunds it took?
    Big Bore = 45+

  4. #4
    Boolit Master

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    I didn't fire lap but lapped by hand.

    I have a Marlin 1894 in .44 mag. that had a few quirks. I worked my way through and found out the hard way that the SAAMI spec for rifle barrels is larger than handgun barrels. DOH! I probably should have known that but didn't and available moulds cast at 0.429"/0.430" where I needed 0.432" minimum. So fatter boolits helped there but I still got leading. Then I read on the Marlin Owners Forum that some Marlin barrels have constrictions in them under dovetails and roll stamped lettering so I slugged the bore and ran the slug from one end to the other. Sure enough there were several tight spots!

    So, I made up a couple lapping slugs and worked the tight spots until the lapping slug slid through easily then lapped from breech to muzzle working more strokes towards the breech than muzzle to try to make a slightly choked bore. I was a little concerned with lapping a microgroove barrel because there just isn't much rifling depth there but it worked for me. Accuracy improved and leading disappeared.

    Not sure about fire lapping but I have to say that hand lapping really was not that difficult and did what I wanted.

    Longbow

  5. #5
    Boolit Master
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    Done a few, I know I did about 25-30 rounds on a 336 in 30-30, using 320 grit. Bore shines like a mirror, doesn't lead, and it shoots very well now. I believe I used a similar number in my 35 Rem with the same results. I probably have done others, but most have been conventionally rifled barrels.

  6. #6
    Boolit Master MGySgt's Avatar
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    As noted by longbow -- I too am concerned about the shallow Micro Grove and really don't want to barf this up. I really need to slug the barrel, I am already using .432 boolits as that is what my SBH likes after firelapping it.
    Big Bore = 45+

  7. #7
    Boolit Master
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    Firelapping works REALLY slowly, not much to fret over.

  8. #8
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    Quote Originally Posted by dubber123 View Post
    Firelapping works REALLY slowly, not much to fret over.
    Any info out on the net i should read on this "fire lapping"? Never heard of it before and can see same issue on my new marlin 1895...

    Sent from my SM-G920V using Tapatalk

  9. #9
    Boolit Master
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    I just hand lapped my 336 because of the really poor accuracy.
    Will find out tomorrow if it helped.
    If not, it will get a new barrel.
    Failure is not an Option

  10. #10
    Boolit Master MGySgt's Avatar
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    Quote Originally Posted by Lakehouse2012 View Post
    Any info out on the net i should read on this "fire lapping"? Never heard of it before and can see same issue on my new marlin 1895...
    Do a search here - I am sure there are many threads here that deal in Fire Lapping. Midway sells the Wheeler Fire Lap kit, and Veral Smith has his own at LBT. I have both and used both on Ruger 44 mag and 45 Colt. It does smooth out the barrel, reduces leading, improves accuracy and makes cleaning easier.

    But you can do too much annd greatly increase the dore diameter.
    Big Bore = 45+

  11. #11
    This is on my to do list for my 1894 44 mag. There was a lot of info on Marlin owners.com.

  12. #12
    Boolit Master
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    I've pressure-lapped a number of barrels, some of them micro-groove and there are some differences, but not enough to materially change the lapping regimen. I don't use very coarse grit on micro-groove rifling, generally starting with 320 silicon carbide and finishing with 400 or 600. The results are mostly considerably better accuracy, since Marlin barrels seem to have the tight-at-the-breech and loose-at-the-muzzle characteristic with some regularity, but not all of them. They almost all shoot better now and clean more easily. Only one .44 mag I lapped didn't do better on target with cast, but was better with jacketed, and precisely why couldn't be determined before time ran out and the owner had it custom re-barreled. Another, more recent one does very well with cast and particularly well with paper patched. Generally, they'll take at least 20-50 lapping rounds, sometimes more depending on the degree and length of constriction, if that's the problem, or how loose it is at the muzzle. Some barrels have both problems, but it's still a lapping job. It's good to slug them more than once before you begin in order to be sure you're familiar with what that barrel feels like, since repeated slugging informs you of your progress will tell you when you're finished with the job. It's a whole 'nother experience when they slug smooth and consistent from end to end. You'll wonder if it's the same one you started with. Once consistent, a lot of the accuracy mysteries go away.

    Abused/neglected rusted barrels also take more work, but they can be surprisingly good, though I never had a micro-groove barrel in that condition, so I can't say whether a rusty/pitted mg can come back.
    Last edited by yeahbub; 02-02-2018 at 09:50 PM.

  13. #13
    Boolit Master Big Mak's Avatar
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    I have a 2008 Marlin standard rifling (JM marked barrel) that absolutely hates .429 copper jacketed but plug a Missouri Bullet Co powder coated .430 lead bullet in the chamber and it hold 1.5" moa with iron sights at 50 yds.

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    Boolit Bub
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    Good post,can you tell me where I can learn about how to hand lap.Thank you

  15. #15
    Boolit Master
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    It has been talked alot here on this forum and the search mode should give you info. I did a few and all improved. I used the valve grinding mixture from napa or any car parts store. Usually a course and a fine tube.
    Look twice, shoot once.

  16. #16
    Boolit Master

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    Lapping is not inherently hard but you do have to be careful or you can ruin your barrel. In my case (like hylander) I figured if it didn't help my barrel I would get a new one so why not try?

    You need some lapping slugs which can be cast in the bore or bullets that have been driven through the bore to impress the rifling on them, some valve lapping (grinding) compound, a brass or steel rod that will fit through a drill hole in the lapping slugs and a bore guide of some sort. Boolits driven through the bore will be pretty tight to start with so might be better to put lapping compound in the bore then run the lapping slug over it.

    Here is a basic description of the process. Oddly I can't find a good detailed description:

    http://www.shootingtimes.com/gunsmit...barrel_200805/

    Here is something else that might help:

    http://bisonarmory.com/content/RifleBoreLapping.pdf

    Also, a point... don't push the lapping slug out of the bore! Once it is started, stroke until you feel smooth all the way pushing the lapping slug to the ends of the rifling at the breech and muzzle, so protruding but not right out. If you replace that lapping slug to use a finer compound or to use another repeat with the finer compound until you are happy with the results. Go Slow!

    And... do not let the long rod touch the bore! Use a bore guide to keep it centered and not touching the bore.

    Longbow

  17. #17
    Boolit Master MGySgt's Avatar
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    Shot the 1894 Marlin yesterday to see the velocity, I hadn't run that load over the Chrono when I worked that load up in late 90's. I was surprised, first it holds 3 in at 100 for 5 rounds.
    The Chrono results - Average MV = 1658 with an extreme spread of 8. 265 grain. picture attached.
    I was pleased, but I wanted to clean it down to bare metal so I could slug the bore to see if I really wanted to firelap it. If it is over .431 - I won't firelap it.
    Still cleaning - it is taking me forever to bring it down to bare metal. Everytime I think I am done I run a NEW bore brush through it and the next patch is black with carbon and a few tiny flecks of lead, real small fleck's but they are still there. I will work on it again tomorrow.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Big Bore = 45+

  18. #18
    Boolit Master
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    Was thinking of doing just to brighten the bore a bit. Have a model 36 closed receiver model. Changed my mind at the last minute. Just couldn't chance ruining a decent shooting old 30-30 having no problems. We both know that Micro Groove rifling isn't all that pronounced and might not handle a accidental too aggressive lap.
    "JUST A OLD DEPLORABLE THAT'S IRREDEEMABLE."

  19. #19
    Boolit Master MGySgt's Avatar
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    The firelapping kit I use is Veral Smiths from LBT. I have firelapped a number of 44 mag's and 45 colts, just not a rifle - Yet.

    BTW I am still cleaning it. I may be getting near the end as I am getting some copper out now. This is a new to me rifle, I don't know what the original owner put through it, but I am prettyu sure it was jacketed. I haven't fired any jacketed ammo out of it.
    Big Bore = 45+

  20. #20
    Boolit Master
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    Quote Originally Posted by OverMax View Post
    Was thinking of doing just to brighten the bore a bit. Have a model 36 closed receiver model. Changed my mind at the last minute. Just couldn't chance ruining a decent shooting old 30-30 having no problems. We both know that Micro Groove rifling isn't all that pronounced and might not handle a accidental too aggressive lap.
    You'll die of old age before you "accidentally over lap" one. People seem to think a lot happens in a few shots, or 10, or 20. Nope, nope, and nope. You should be cleaning and inspecting the bore every 5 shots or so anyways. When you fire your first 5 and see NOTHING, you will relax a little

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BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
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