Aiming Past 3000 FPS With Cast In .300 Weatherby Magnum
Haven't been on here much for several years, in fact I haven't been doing much casting, loading or shooting other than a bit of play with the muzzle loaders and making some BP round ball loads in 12 gauge brass cases. (That's fun!) I've gotten the bug to try something I've read about often in the past on this board, going for full jacketed bullet velocities with cast. I've just taken my first shot (s) at doing this with my .300 Weatherby Magnum. I used the Lee CTL-312-160-2R bullets, cast out of random nondescript cast lead of unknown composition and hardness but much softer than typical wheelweights, water dropped from the mould and sized .314" for my 7.62 X 54R Russian Mosins. They were tumble lubed in LLA. I figure a key factor for success with cast bullets is getting a tight seal in the chamber throat to prevent gas blowby that melts lead from the bullet surface, as often does frictional heating towards the far end of the barrel. After I'd decided on this bullet, largely because of its shape that just looks more like a supersonic rifle bullet than most cast ones do and because I knew it would tightly fill the leade, I found SAAMI's chamber drawing and thought I might have overdone the sealing. http://www.saami.org/PubResources/CC_Dr ... Magnum.pdf If you study the chamber drawing at the bottom, the much discussed Weatherby "freebore" is a cylindrical leade of .3084" nominal diameter .36" long. That's why it's capable of good accuracy with jacketed bullets seated far away from the rifling, it doesn't give them much room to rattle around or tip, and the long case neck offers support. At the beginning of the leade, there is an abrupt taper from .340" to .3084" over .0153", quite a squeeze for the .314" body of this bullet and in fact too tight to accept most of the nose of it, too. When seated to the level of the crimp groove, the bullet is about .312" diameter at the end of the chamber, and it tapers down quickly to about .309", then gradually, only reaching .308" right before the beginning of the radiused ogive. That means that in a .308" groove diameter bore, much of the length of this bullet is full groove diameter or greater with no lube grooves. Not ideal. (Or Ideal. HA!) But I went ahead and loaded 10 of them in old Remington cases. The .314" bodies were a very tight squeeze into the unsized fired cases. I used the Lee Factory Crimp Die to just remove the light mouth flare I'd given them, no crimp. Load was 93 grains of pulldown WC860 I got from Hi-Tech back in 1998. Actually I weighed each charge, and they varied between a low of 92.5 and a high of 92.8, mostly right at 92.7 grains. Close enough, I thought. Primers were CCI #34 military surplus, which have very hard cups and relatively insensitive mix to resist inertial fire by firing pins in autoloading weapons and are said to be magnum strength. This load will push 180 grain Hornady SP bullets out of my snub nosed Vanguard (24" barrel) at about 3050 FPS, with an extreme spread of only 20 FPS and groups between .5-1" off of the bench. These bullets, cast of my soft alloy, checked and lubed, come in right at 174 grains. I crimp those jacketed bullets tightly with the FCD, but for these I thought not only that the crimps might produce bullet damage, but knew that the starting pressure would already be high from jamming the bullets into the leade. The front part of the bullet will be swaging into the rifling while the base of it is still swaging into the leade, producing a lot of resistance. WC860 is way on the slow side in the .300 Weatherby, and with 200 grain Speer Hot-Core bullets I'm not able to compress enough in the case to produce any pressure signs, it seems to be very mild and won't quite reach the velocities of other powders in the load books, let alone Weatherby advertised velocities. So I was unconcerned about hazardous pressure. The main concern is whether the pressure will cause asymmetrical slumping of the unsupported bullet nose as it undergoes axial compression from the acceleration down the bore. The shape of this bullet actually makes for a very short unsupported ogive in front of the tightly supported bullet body as I mentioned. Compressive pressure on the bullet metal is divided along the length of the bullet, greatest at the base and much less at the nose. I am hypothesizing that the peak pressure of this load will be in the low to mid 40K range, not much more than magnum handgun cartridges. Pressure rise is nice and slow, peaking after the bullet is fully engaged in the rifling and several inches down the bore. Getting it off to a nice straight start is critical, and the tight fit pretty much assures that, with fireformed neck sized cases keeping them concentric to the bore to start. Trial chambering of one of these rounds required stiff pounding with the heel of my hand to ram the bolt home and to close the handle. It was also tight to eject unfired. The bullet had the Alox removed and the lead scrubbed bright for half the length of the exposed nose, It was neither pushed in nor pulled out of the case. The case necks were doubtless a tight squeeze into the chamber, but the brass was unmarked. Lubricated cast bullets cannot "cold weld" to case necks as jacketed ones can, and require no case obturation to let them go. They simply slide out as the pressure rises high enough to overcome the static clamping friction of the case neck. The main resistance is the swaging into the leade and into the rifling. I got out to the range late this afternoon, put up a single target and fired these slow fire with plenty of barrel cooling time in between. My main interest was in seeing whether the bullets would remain intact with the centrifugal force of going ~3000+ FPS in a 10" twist bore BEFORE trying to shoot them over a Chrony, and also to see how badly they'd lead the bore. I'd last set the sights for 200 yards with the custom 200 grain ".30 VLD" driven at 2200 FPS by a charge of IMR 7383. So it was shooting quite high at 100 yards, and most of the group was off of the paper on the backing board. The Mark I calibrated eyeball says it was about a 3" group, not too bad really. That VLD at 2200 FPS cast of oven heat treated, quenched and aged wheelweights gives 2 1/2-3" 200 yard groups. The bore has a uniform gray color with no streaking, pretty much what I'm used to seeing with cast bullets. So while this is nothing to write home about in terms of accuracy, it has potential. I know it won't blow anything up, and the bullet holds together. Sadly, I believe I'll let the CTL-312-160-2R go, because of the tight fit issues. Sizing it down to near the leade size will heavily reduce the grooves between the microbands, I think. I have one of those custom 6 hole Lee moulds for the Ideal #311291 design that was a group buy deal on Cast Boolits a few years ago. I have a bunch sized to .311" for general .30 caliber use, and I think I've sized some to .308" for my K-31 carbine. (If I haven't, I will.) I think I'll try those, lubed heavily with the liquid Alox. They're not as pretty or aerodynamic, but I'll bet they can be made to shoot!
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Originally Posted by Charlie Sometimes
