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Thread: Measuring across the lands and proper sizing for PP bullets?

  1. #1
    Boolit Mold
    Join Date
    May 2024

    Measuring across the lands and proper sizing for PP bullets?

    I’d like to try out paper patching for a 38-55 (using black powder). I’d like to PP to the lands, not the bore. There seems to be a lot of conflicting opinions and I have a few questions:

    1. What is the best way to determine your diameter across the lands? Dropping pin gauges down the barrel?

    2. Is there a rule of thumb to selecting the bullet diameter and final patched diameter? Like #-thousandth under lands for the bullet and #-thousands over land diameter once patched? I’m assuming I’ll have to buy a custom PP bullet mould and want to order a diameter that may lead to the best chance of success.

    3. Best PP mould for a 38-55?


  2. #2
    Boolit Grand Master

    Join Date
    Mar 2013
    Northwest Ohio
    Most barrels have a small amount of taper from breech to muzzle, thats why the breech end is normally marked on a blank.
    Using a gage pin will get you very close. Once you have this groove dia - ( paper thickness X 4) = a good place to start with bullet dia. I always start .001-.002 small on bullet dia as the mould can be lapped up much easier than new paper found or making the mould smaller.
    How you wrap will have an effect here to dry or wet/damp wet the paper will stretch more and thin some. resulting in a smaller bullet dia.

    Think of pp to bore dia as breech seating with out the tool. You want the bullet as far into the bore as possible. I only have about an .125-.187 of the base in the caseAnd its a very light tension. to allow the bullet to align in the bore.

    Making your template to cut patches: Take a strip of the paper your going to use but 3 wraps around the bullet and a small cut thru all 3 on one edge. use 2 cuts and from the first cut your angled end then subtract .030-.045 from the second and your second angled end. There will be a small gap between ends when wrapped and this will allow for the radius were the second wrap lays over the first end. I normally use a 45* angled end. Glue this paper to a piece of brass steel aluminum or plastic shim stock and you can now cut and file in your template to cut the patches. I make my templates wider so if I want to change patch width I can with out making a new template.
    I wrap so the patch fold under leaves a small circle of the base showing (about the size of a pencil lead.) no tail.
    When testing watch for patches in front of the muzzle they can tell you a lot. the first wrap will be confetti and you should recover the second with the base fold under attached. You will see the rifling in this wrap also when recovered.

  3. #3
    Boolit Grand Master Nobade's Avatar
    Join Date
    May 2005
    SE WV
    The top of the lands is the bore diameter. As opposed to the groove diameter. Pin gauges work the best for that.

  4. #4
    Boolit Buddy
    Join Date
    May 2006
    1st, bore = land diameter, so that´s clear. Next determine barrel twist and chamber configuration of your rifle. The twist will determine max. bullet length. And if your chamber has freebore, chances are that it won't work well with the bore diameter bullet, you might need a dual diameter bullet: groove diameter in the case and the freebore bit, bore diameter for the front bit in the barrel.
    Start with selecting the paper you want to use, do a double wrap around a bullet and measure the diameter. The difference wrapped-unwrapped will tell you the bullet diameter required for your mould. That's the fundamentals required for a good start. Usually thinner paper is better.

  5. #5
    Boolit Master
    Bent Ramrod's Avatar
    Join Date
    Apr 2005
    Southern Arizona
    Pin gauges in the bore (or leade) are the most convenient way of measuring bore diameter, although some people are pretty good at measuring the grooves between between the lands of their lead barrel slug with calipers or micrometer.

    I would say the first order of business would be to go to the paper store with your micrometer and find some hard, crinkly, tracing paper of about 0.0012”- 0.0015” thickness that looks like it will always be in stock. Four times the thickness of this paper, subtracted from your bore or leade diameter is the diameter of the boolit you want to use.

    If your barrel was set up for grease groove boolits, it is likely that a patched-to-bore (or even leade) boolit will be loose in the mouth of a fired, or even resized, case. I’ve made “shell mouth reducing” dies that press the very end of the case against the boolit so it doesn’t fall out with handling, although it can certainly be shaken or pulled out, and turned in the case. This is not a crimp die, which would tear the paper.

    Others use a dual diameter mould where the base of the patched boolit is a push fit in the fired case but the rest of the boolit fits into the leade. I’ve never gone this route myself, but dual-diameter boolits have their advocates and success stories.

    The .38-55 is one of those calibers where the bore/groove can be anywhere between 0.367”/0.375” and 0.373”/0.381” and some even beyond these. I ordered an Accurate mould for a ~300gr boolit that casts (IIRC) around 0.367” but can be pushed through a Lee-type sizer to bring it down to 0.359”. I can patch the unsized boolit to fit the bores of the old barrels or run them through the sizer to fit those of the modern 0.375” barrels. Ordinarily, this much sizing in one pass would mangle a grease-groove boolit badly, but the straight sided slug (lubed slightly) goes through with no problems. I have to remove the lube afterwards, of course.

    My boolits are for the old time twist rate (16”, IIRC) so the boolit weights that work are in the low 300gr. If you have one of the modern quick-twist silhouette rifles, you can go longer and heavier.

    The “best” mould is the one that shoots best in your rifle. For me, the “best” mould has always been the next one I see on a gun show table.

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