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Thread: mold suggestion for firelapping boolits

  1. #1
    Boolit Buddy
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    mold suggestion for firelapping boolits

    Hi everyone. I am new to the forum. I have some previous casting experience and am getting back into it because Ohio now allows straight-walled pistol cartridges for deer hunting. I got a Ruger 77/357 which has worked out fine. I am planning to order an LBT 160 grain FN mold for it pretty soon.

    I had purchased firelapping supplies from LBT and Beartooth Bullets and recently ordered more lapping bullets from Beartooth (apparently Ruger stainless barrels can require hundreds of lapping rounds), but I read somewhere that the Stantons are busy taking care of a family member. Since I'm also doing that too, I completely understand why they might not be able to ship orders quickly.

    I apologize for the long introduction but felt it necessary to give context to my question: Can anyone suggest a factory/non-custom mold that will drop sufficiently oversized bullets (sorry, boolits) from COWW (or other alloy so that I can get the desired 12-14 BHN) so that I can keep lapping the barrel? Bore slugging suggests that groove diameter is 0.358", but I measured that with a dial caliper, not a micrometer. Part of the reason (I think) that I've needed so many lapping rounds is that I squeezed the boolits too hard to get them embedded with the (LBT) lapping compound and reduced their diameter somewhat, possibly too much to be effective. I realize that I could just use the LBT mold when I get it, but wonder if I need a larger diameter for lapping rounds than regular shooting ones? If so, I'd prefer to buy a second, less expensive mold since I expect to be done with lapping in maybe another hundred (lapping) rounds and then hopefully get to shooting cloverleaf groups with the LBT mold boolits. Thank you. I've found a lot of valuable advice and information here before I registered.

  2. #2
    Boolit Master

    Kraschenbirn's Avatar
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    I've never had to lap any of my handgun-caliber barrels...just shot 'em 'til they smoothed out...but I've had good results cleaning up old milsurp rifle bores using the Lee 'tumble-lube' designs. For a .357, I'd recommend the TL358-158-SWC as your best candidate for a 'lapper'.

    Bill
    "I'm not often right but I've never been wrong."

    Jimmy Buffett
    "Scarlet Begonias"

  3. #3
    Boolit Grand Master

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    I would go with the lee tumble lube desighn one with the longest bearing surface and shortest nose. The bearing surface is what is impregnated with lapping compound not the nose. Depending on what you want to do. the grit you start with is important and will affect the number of rounds needed. a bullet with more surface area will work quicker also. Maybe one of the new desighns with out grease grooves for PC coating? You can set a press up to bump cast bullets up a few thousandths in dia also. Its a little touchy on the set up but not hard to do. The big thing is getting it set right to give the bump up you want. Or bump big and size back down. A bolt 7/8" 14 with a 3/16" hole drilled and reamed thru on center then a bored section on the end depth of bullet Plus .100-.200 length and at the desired dia or slightly bigger and a relief for the nose above that. A solid pusher to drive the bullet and a dowel for an ejector. Set press to just touch and adjust die down from there until base is expanded to what you want. The bearing surface is shortened and swelled out in size doing this. But you can fairly easily bump up .001-.003 in dia.

  4. #4
    Boolit Master


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    I would look at a dewc mold. Size, lube and impregnate with lapping compound and load into cases fired in the rifle. Prime, charge and single load by hand to preclude set back. With that many rounds, yiu might wear out the lead before you accomplish your goal.

  5. #5
    Boolit Master
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    Midway has a fireman kit that can be used with jacketed bullets. Come with 3 different grits of lapping compound and 2 steel plates to coat the bullets with compound.

  6. #6
    Boolit Master
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    It doesn't sound like a mold is what you need - maybe. May I ask what the problem with the barrel is which suggests pressure-lapping is the solution? New factory barrels from reputable makers (of which I would count Ruger as one) rarely need more that a dozen or so 600 grit to smooth the sharp edges on left-over reamer marks on the lands, if present, 400 grit if they tend to copper up. Does it have reverse bore taper, tight at the breech end, loose at the muzzle? This may well take more effort to correct, but not "hundreds" of them. I'm unfamiliar with the commercial lapping kits by LBT and others. Maybe you could fill me in on the grades of abrasive they use. Wonderful work can be done with pressure lapping, but taken to excess may leave one in need of a new barrel. By the way, how are you gaging progress? What is your criteria for knowing when the job is finished?

    I've lapped a number of barrels, but only those with serious restrictions have needed more than 40 rounds or so, and that was a lot. That one had a rear sight dovetail restriction that felt like a bore obstruction when the slug I was driving through hit it. It explained why I couldn't keep them on a paper plate at 50 yards. If your barrel doesn't have a show-stopper of a problem, there's no way it would need "hundreds" of lapping rounds. If boolits from your mold shoot well, they're big enough for lapping. If your lapping boolits are less than groove diameter, you may be lapping the lands only and the rifling is getting more and more shallow as bore diameter increases. Measure the O.D. of the grit-embedded boolits and you'll find them to be pretty big. The actual working diameter is a bit less, because the abrasive isn't yet pressed in as fully as it will be when it goes down the bore.

    Measuring outside diameter with a dial caliper is not a problem. A properly zeroed quality caliper will be sufficient for this kind of work.
    Last edited by yeahbub; 01-19-2018 at 08:32 PM.

  7. #7
    Boolit Buddy
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    Thank you for the replies. In the process of getting the Ruger, I found out that there was considerable evidence that the .357 Magnum was completely adequate for deer at close ranges. I found out about LBT, bought Veral Smith's book and have read and re-read it since. Then I bought Marshall Stanton's book and read it more than once. I had shot a couple of hundred mild reloads with Rainier plated bullets and Titegroup at around 1,000 fps and the groups I got would be more precisely called "patterns" - 8" - 10" at 100 yards. By contrast, factory ammunition (Blazer Brass) delivered 3" - 4" groups at a hundred yards at around 1750 fps (measured with a basic Chrony).

    I cleaned the barrel (including copper removal) and slugged it with some LBT push-through slugs. Bump. Bump. Bump, Bump... maybe six or seven bumps total; I didn't write down how many, so, not the world's smoothest bore. LBT doesn't say what the grit size is for their bore lapping compound. Mr. Smith seems to enjoy a very good reputation from what I can find, so I took it on faith that it would be appropriate. Both Veral's and Marshall's books state that Ruger stainless barrels are of an extremely wear-resistant alloy and may require many more lapping rounds than chrome-moly barrels (both books specify around 30 lapping shots tops for chrome-moly). More push through slugs; bumps are still there. About then it was getting to be deer season, so I switched back to factory ammunition and got a nice deer with the Federal American Eagle 158 grain JSP. So it's time to clean the barrel and slug it again. I've shot about 100 rounds of jacketed ammunition all told. Because of its light weight, the rifle is difficult for me to hold consistently on the bags, so it very likely shoot better than I can hold, at least for now. I occasionally get a couple of shots touching.

    I think Stanton's lapping compound is Clover 320 grit, but don't have his book handy to make sure.

  8. #8
    Boolit Master
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    SCORE!! The freezer is full. Excellent. . . I got skunked this year - job interference.

    It seems to me that you have a sound sense of gaging barrel condition and I agree that it will benefit from judicious lapping - most do, even if accuracy is not markedly improved, cleaning will be, at the very least. The tight spots you mention are on the order of .0001" or so and are one of the differences between "factory" barrels and the $600 benchrest variety. If Ruger button-rifles their barrels, the groove diameter will be consistent, but generally, buttons don't also form the land tops in anything but soft .22 rimfire barrels. Broached barrels are the same way - generally the variation involves land height more than groove depth. My experience with stainless is that it is wear resistant, but lapping is a cutting/stock removal process, which leads me to wonder if there are abrasives which are more effective for use on stainless. I get my abrasives from http://www.us-products.com/category-s/1876.htm, and they have sample jars available for jobs like this. There is also great information on their site about what types are best for which material. The Crystolon 320 Silicon Carbide is the coarsest I will generally use on barrels which are in near-factory condition and can be slugged with the heel of my hand tapping the rod, more often Crystolon 400 SC to start, but YMMV. I have used diamond paste with no ill effect, but it's imperative to prevent getting any anywhere you don't want it, so lapping boolits should be entirely inside the case before chambering to avoid inadvertent contact. It's aggressive, so a finer grade can do the job, but it's hardness means it never wears out and it will embed in anything softer than itself, like chamber walls if it gets between brass and steel. I get the job done with conventional types, so I don't use it anymore. Merrill Martin wrote for Precision Shooting Magazine in the late 1980's about a number of things lapping related and came up with using diamond grit to lap with jacketed bullets and getting the job done in sometimes a half-dozen rounds at full velocity. If you can find his articles, I recommend them to anyone who would like to glean details about the process.
    Last edited by yeahbub; 01-19-2018 at 08:33 PM.

  9. #9
    Boolit Buddy
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    Quote Originally Posted by yeahbub View Post
    SCORE!! The freezer is full. Excellent. . . I got skunked this year - job interference.
    Sorry you missed out because of work. Generally I think jobs are good things, but not when they interfere with hunting.


    Well...full disclosure is in order. I got last year's deer with the Ruger. This year's was with the crossbow. So I've got till November to get the Ruger sorted out.

  10. #10
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    Steven66, welcome to the forum! Some of the nicest, most helpful folks that you will ever meet, post here.
    I have fire lapped several handgun barrels but never done a rifle...yet. IME, Ruger revolvers seem to benefit the greatest from firelapping. I would suggest choosing a full wadcutter boolit for your lapper, because:
    1) Their long bearing length will hold more compound.
    2) They can be seated entirely in the case, reducing the possibility of grit getting in your chamber.
    Hope this helps, Treetop
    "Treetop"
    Sgt. USMC
    1968-71

    "Accuracy has a suppressive power all by itself."
    Lt. Gen. George Flynn, USMC

    “The Second Amendment was not written to protect your right to shoot deer.
    It was written to protect your right to shoot tyrants…”
    Judge Andrew Napolitano

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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
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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
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