TL bore rider boolit design with TL grooves on the bore rider section too?

[turbo1889]

Well now that we potentially have a new custom mold cutter that is willing to do TL boolit designs I have been gearing up to put in an order with him, about two or three more pay-checks and I will have the financing to order two custom molds from him (two brass three cavity molds is what I'm a thinking).

I already know I want the first design to be an experimental heavy weight 38-spl boolit; a hybrid design with both regular and tumble lube grooves. I did a discussion thread on that design concept a while ago:

http://castboolits.gunloads.com/showthread.php?t=85317

For the second mold I'm thinking of doing a plain base TL bore rider design proportioned to provide smooth feeding in my SKS and potentially other actions chambered for the 7.62x39-Soviet. The boolit may pull double duty for 7.62x54R and 303-brit. as well but would be primarily for mass production plinker loads in the 7.62x39-Soviet.

http://forums.handloads.com/uploads/turbo1889/2010-08-28_220725_762x39_Soviet_TL_BR_SR_Boolit.GIF

Tumble lubed, loaded, and shot as cast no sizing. I'll slug the bore on my SKS and specify the Major bore diameter as what my gun is plus 0.001 with the mold cutter in questions tolerances being +0.0015/-0.000 and then specify the minor bore diameter as what my gun is minus 0.001 to offset the stated tolerances on the bore rider section to ensure smooth chambering when shooting as cast.

I also put in a conservatively small sized tapered stop ring directly above the crimp groove sized at 0.01 over major diameter. I know the throat on my SKS and the other guns I have in the mentioned cartridges have enough slack in them to accommodate it and it should easily squash back into the crimp groove below on firing or if I do have to size it in a Lee push through reloading press type sizer die.

So comments, $0.02 worth, etc. on both the idea of putting TL grooves on the bore riding section of a bore riding boolit as well as the main body in general and specifically my proposed boolit design so far? :coffeecom

[HORNET]

Looks kinda like a tumble-lube plain-based version of the 311407. A straight taper with standard lube grooves would be similar to the Pope 311403(?) without the oversized base band. It should work OK if you can get all the details to fill out consistently. What weight range were you trying for? I can't read any of the dimensions on the drawing.

[turbo1889]

Usually when I design a custom boolit mold I have specific dimensions and design details in mind and let the chips fall where they may as far as weight; in other words I haven’t calculated the weight from the volume and really don't care all that much. Although if I were to hazard a guess as I would say it is probably about 160 grains or so from WW/range-scrap + 3% tin alloy.

It don't surprise me that you can't read the dimensions; that is just a quick low res .gif screen shot.

~ Bottom drive band is 0.05" thick.
~ From the base to bottom of stop ring (inside case neck dimension) is 0.31"
~ from the bottom of stop ring to the base of the nose taper (bore riding length) is 0.44" for a total bearing length of 0.75"
~ Total boolit length is 0.90"
~ Meplat is 0.18" diameter
~ For my gun (slugged it) the major diameter specified would be 0.314" and the minor diameter specified would be 0.303" which also puts the stop ring diameter at 0.324"

I have been loading the Lyman 314299 boolit as cast, un-sized, tumble lubed with no gas check ultra deep seated in the case to match the COAL on mil. spec. loads and that works okay just want a lighter shorter boolit that doesn't eat up a whole bunch of powder space in the case due to being ultra deep seated. Tried the Lee molds made specifically for the 7.62x39 but never could get the accuracy I demand out of my gun which I believe is due to their long unsupported nose with a short bearing length. At least that is what conventional wisdom concerning cast boolits says and since I can't get any better then about 4-5" groups at 100 yards with those boolits and I can get 2" or better with the 314299 or jacketed hand loads it seems to be well supported by my real world experience; thus leading to my design where I'm attempting to maximize bearing length without resorting to a deep seating an extra long boolit for the cartridge size.

[Bass Ackward]

One thing that many people don't consider is not the throat size, but the transition angle. The smaller the case capacity, (and faster the powder)(and the more bullet weight as well) the more gentle it needs to be. In fact, even larger case capacities can benefit, just that a larger case volume mitigates the ignition wave that can tip all but the hardest, best fitting slug. (which is what you appear to be trying to over come)

My .02: If this fails, ( I have no idea that it will or won't) I would recommend a reamer with good dimensions (no more than 1.5 degree with your case volume) and put a more slug friendly throat in the gun that allows for more bearing length that can be supported by steel and less bore ride. Cause even jacketed can be seated out some. Let that slug move out faster, and it doesn't have to fit as well.

[HORNET]

You might want to bump the diameter up a tad on the first or second band back from the nose to provide a light interference fit (ala: the DD band that NEI used to offer). That should still engrave with little effort but will provide support for the nose section against slumping and allow for minor diameter variations due to allow and process variations. You only need .001/.002 over minor bore diameter and a .040 wide bearing surface if it's near the front. I'd also go wider on the rear band (.093") and use the modified TL groove design that Ranch Dog and 45_2.1 used on some of the Ranch dog molds to allow pan lubing or a lubrisizer, but that's just my preference.