Cast Loads

Posted by on November 24, 2005

I’ve probably fired more cast bullets from my 308 Sako than jacketed. I am also interested in cast bullet performance in rifles but haven’t explored it in any depth beyond shooting them in my own rifle. It has crossed my mind that in certain possible scenarios that I won’t explore here, cast bullets might have some use for hunting for the pot, for example. While small calibres are not without value, for medium game and bigger, low velocity would need to be compensated by calibre and bullet weight for velocity retention.The other day I picked up a magazine that contained an account of the celebrated long shot by Billy Dixon at the battle of Adobe Walls, Texas, in 1874. He knocked an Indian from his horse at a range later measured at 1538 yards ( 1400 metres ) with a Big 50 Sharps. The writer of the article carried out some interesting tests with a replica rifle at the actual site of the battle, where Dixon’s position and that of his victim can still be identified.With a 425 Grain bullet, MV is 1475 FPS. That drops to 1000 FPS at 300 yards ( 270m ). At 1000 yards it is only 640 FPS, and at the range of Dixon’s shot, remaining velocity is less than 500 FPS, and energy a bit more than 200 foot pounds. Maximum height of trajectory would have been 168 feet ( 51m ). Time of flight was given as 2.50 seconds, but can’t be right, must be four seconds at least.A 425 Grain 50 cal bullet is pretty much the same shape as a handgun bullet, and a similarly poor ballistic coefficient. Lyman’s 425 grain 50 cal bullet has a BC of 0.25. Lyman’s 45 cal 490 grain bullet, being longer and slimmer, has a BC of 0.384, and not surprisingly, retains it’s velocity better than the 50 cal bullet. Fired at 1475 FPS, the 50 cal bullet retains 800 FPS at 600 yards. That’s 54% of MV. The 45 cal 490 grain bullet fired at 1500 FPS retains 940 FPS at 600 yards. That’s 63% of MV.By comparison the 30 cal 168 grain BTHP fired at 2600 FPS retains 1660 FPS at 600 yards. That’s 64% of MV, the same as the 45 cal cast bullet. The loss of velocity is a constant accross all weights and MVs of 30 cal bullets. They all retain about 64% of MV at 600 yards and 47% at 1000 yards. I don’t have figures for the cast bullets at 1000 yards, except for the 50 Sharps. But the data I have suggests the same 47%. That would be almost 750 FPS for the 45 cal 490 grain, fired at 1500 FPS.That’s a lot of performance for a cast bullet of RN or FP shape. And don’t forget that a 500 grain cast bullet can be fired at 2000 from a 458 Winmag. That would translate into 1000 FPS at 1000 yards and a hell of a lot of energy. I suspect that could be improved with a blunt pointed nose like my Lyman 311334 bullet, which, by the way, delivers sub MOA accuracy on a good day.The 30 cal Lyman 311334 gas check bullet ( 185 grains ) retains 50% of MV at 600 yards. That is consistent with it’s blunter profile compared with a jacketed spitzer. But note, that despite it’s superior ballistic shape, it retains less of it’s MV at 600 yards than the 45 cal 490 grain bullet ( 63% ). That demonstrates what we all know, that a heavy bullet will retain it’s velocity better all other things being equal.There are two other factors. The first is the greater velocity loss from high MVs. The 30 cal BTHP fired at 2600 reduces to 1200 FPS at 1000 yards. The 45 cal 490 grain fired at 1500 FPS reduces to a bit under 750FPS at that range. The velocity difference at 1000 yards is therefore much less than the difference in MV. The longer the range, the less the difference becomes. That is of course obvious, as all bullets would eventually decelerate to zero if they didn’t fall to earth first. What matters is the relationship between calibres and bullet types.The second factor is that velocity decay is greatest in the early part of the flight. The 30 cal BTHP, fired at 2600, loses 800FPS in the first 500 yards, and 600FPS from 500 to 1000 yards. Looked at in more detail, it loses 350FPS in the first 200 yards, but only 200FPS from 800 to 1000 yards. The Lyman 45 cal 490 grain bullet fired at 1500FPS loses 280FPS in the first 200 yards, but only about 100FPS from 800 to 1000 yards. Not only is the velocity loss less, but the loss in the last 200 yards compared with the first 200 yards, is proportionately less than the 30 cal BTHP. In other words, the decay is less in both absolute and proportional terms, and gets less as the range increases.Both are because air resistance and drag increase exponentially with velocity, with the result that velocity decay is greater at higher velocity, and also greatest at the first part of the flight when the velocity is highest. Therefore, comparison of muzzle velocities does not necessarily provide a reliable guide to long range performance, and the longer the range, the less reliable it is.This is of course all well known, and it could reasonably be argued that it is not important for most purposes. I just find it interesting, and it might possibly have some application in the unfolding scenario in SA. Consider light loads for example. I have mentioned BP loads in brass cases before. But similar or almost similar performance can be achieved with handgun powder. My 308 Win cast loads chrono 1600FPS with only 11 grains of MP200. The Lyman manual lists 1300FPS for a 480 grain bullet in the 458 Winmag with 21 grains of Unique, and a 385 grain bullet at 1500FPS with 23 grains. Unique is quite similar to MP200.I’m sure that higher velocities could be achieved with slightly slower powder like 2400, but still with economical powder charges. A 500 grain bullet at 1500FPS is not all that far behind factory ballistics in the 458 Winmag, and more than ample for medium game at any range at which game should be taken. Why would that matter ? Ordinarily, it wouldn’t. But in an increasingly restrictive scenario, powder might become hard to get, and should therefore be economically used. It will then also be useful for various calibres to be loaded with the same powder. That is, don’t stock lots of slow burning rifle powder that’s good for nothing but big charges in magnum calibres. Thin skinned game ( or human miscreants ) can easily be taken with light loads at short to moderateranges, with three or four times as many shots per can of powder.In case anyone thinks that the need to conserve powder in that way is unlikely, we all surely remember the seizing of NGA’s consignment of ammo at Durban docks. The ammo was seized on an invented excuse, and took NGA two years and a lot of money to sort out in court. Now, PMP is out of production, at least it’s 9mm ammo line is, on the say so of SAPS. It is astonishing that a big company with billions at stake and a substantial export market to serve, can be closed at the whim of a cop. But that’s what is happening. If you want 9mm ammo you have to load it, and for that you need components.And now that government is having such difficulty enforcing the FCA, what’s betting that the next line of attack will be stopping or limiting local production of ammo and components, and preventing import.I have no advice as to how to get around such a scenario. I’m just making the point that methods of conserving what one has might not be so wild, and that cast bullets, light loads and the like, might have a place.[Originally posted to SATalkGuns -- Admin]

Comments

Respond | Trackback

Comments

Comments: