Zak Smith Posted January 28, 2005 Share Posted January 28, 2005 I've seen a few comments about how 260Rem isn't always enough to knock steel over at 1000 yards. Is this really a problem? Let's say we're comparing a 175 SMK @ 2700fps with a 140gr VLD @ 2900fps, _BC_ _MV_ 0 200 400 600 800 1000 1200 | YARDS 0.496 2700 > -1.56 -3.90 -31.68 -93.78 -202.90 -377.02 -639.69 | > 308 175gr SMK 2698 2348 2025 1730 1470 1256 1101 | fps, velocity 0.627 2900 > -1.56 -3.01 -25.03 -72.82 -153.17 -275.16 -450.88 | > 260 140 2898 2606 2331 2074 1835 1615 1420 | fps, velocity If we agree that momentum is what knocks steel over and that PF is a measure of momentum (only a constant ratio off real momentum units), then: 1000 yards, 175SMK = 219.8 PF 1000 yards, 140VLD = 226.1 PF If I need to reliably knock steel over at 1000, should I be looking at something more than 260? Comments? Link to comment Share on other sites More sharing options...
benny hill Posted January 28, 2005 Share Posted January 28, 2005 It's like a 22-250 & a 45-70. Both have the same paper energy, but which one knocks over steel better? Link to comment Share on other sites More sharing options...
Zak Smith Posted January 28, 2005 Author Share Posted January 28, 2005 I'm talking about momentum, not energy. Link to comment Share on other sites More sharing options...
EricW Posted January 28, 2005 Share Posted January 28, 2005 Zak, The numbers are good, but remember that its not a perfectly inelastic collision, so there are some unquantifiable things going on - like how long the bullet stays in contact with the plate so momentum transfer can take place. If the bullet simply shatters instead of turning into a lump, that can affect the results. FWIW... Link to comment Share on other sites More sharing options...
Religious Shooter Posted January 28, 2005 Share Posted January 28, 2005 I don't know about the other organizations. But USPSA has a history of calibrating it's poppers. The USPSA membership should contact their area reps and tell them that the calibration issue for MOR needs to be (eventually) addressed. Just like pistol (it has to go down with 9mm). I'm sure something along these lines could be used. I guess that's the problem. It all depends on how the match organizer sets their steel. And since their is no standard... and there are a number of organizations... who knows? Link to comment Share on other sites More sharing options...
Zak Smith Posted January 29, 2005 Author Share Posted January 29, 2005 Well, that's part of the issue. It is unlikely that I will be shooting a real USPSA MOR match soon, but I shoot a variety of other 3gun/tactical matches with long range components. Link to comment Share on other sites More sharing options...
Religious Shooter Posted January 29, 2005 Share Posted January 29, 2005 Looking at the power factors again .260 @ 1000 exceeds the muzzle power factor of 9mm minor, pistol major and any 5.56mm 55 FMJ. And it exceeds .308 at 1000. I say if you hit it solidly and it doesn't go down with .260... screw it. It's unlikely it will go down with .308 (probably what the rest of the field is using) either. So that means a number of people are going to experience the same thing or the stage will be tossed out. I've seen that 2900 fps with 140's figure tossed around for the .260. What powder pushes it that fast? Link to comment Share on other sites More sharing options...
Zak Smith Posted January 29, 2005 Author Share Posted January 29, 2005 Somebody on SnipersParadise said N550. According to QuickLoad, W760, IMR4350, and N550 are the top 3 available candidates, 26" bbl. I might go 28" just for the extra oomph. Link to comment Share on other sites More sharing options...
Religious Shooter Posted January 29, 2005 Share Posted January 29, 2005 The numbers are good, but remember that its not a perfectly inelastic collision, so there are some unquantifiable things going on - like how long the bullet stays in contact with the plate so momentum transfer can take place. If the bullet simply shatters instead of turning into a lump, that can affect the results.FWIW... I read someplace that in the olden days, instead of chronos they used ballistic pendulums to determine power factor. Some bright guys casted some bullets harder than normal. The bullets didn't deform and splatter like the normal (softer) bullets. As a result the pendulums moved more when shot with the harder bullets. I guess that's a lesson. Use "solids" if you want to move the steel. If you use varmint-type bullets (that "explode" or readily disentigrate) expect problems. It kind of throws a monkey wrench in reloading for MOR. Aspects of the bullets construction in relation to it's terminal performance actually come into play. Another thing that's different between the disciplines. Link to comment Share on other sites More sharing options...
John Dunn Posted January 29, 2005 Share Posted January 29, 2005 At the ITRC last year I was shooting a 6.5-284 with relatively wimpy loads, because they were super accurate in my rifle. I was getting about 2860 fps using a 142 SMK. This worked great on steel targets hanging from rubber straps (heck, a .223 hit would probably be easy to call at 1000 with those targets), was good at moving the 10" MGM flash target out to 600 (never shot at that target from a longer range). My biggest concern would be Larues, unfortunately I don't have access to any to shoot at 1000 to see if my load would take them down. My gut feeling is that the .260 will be plenty. You might give Matt Burkett a call and ask him, he has always been super helpful, and I know he's a proponent of the .260. Link to comment Share on other sites More sharing options...
titandriver Posted January 29, 2005 Share Posted January 29, 2005 I'm using H414 in my 260 with a 24 inch Krieger barrel and 140 MK's, average velocity is 2884, loaded to fit the short action magazine. I believe H414 & WW760 are either the same or nearly so. Link to comment Share on other sites More sharing options...
Religious Shooter Posted January 30, 2005 Share Posted January 30, 2005 I might go 28" just for the extra oomph. If you haven't already check out this article http://www.tacticaloperations.com/swatdec2000/index.html I know the calibers are different. Maybe longer is better... but maybe it isn't? During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each increment. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps). ... Tac Ops took a 26-inch barreled .300 Win. Mag. and chopped the barrel down in one-inch increments as they previously did with the .308 Winchester. Ten rounds of Federal Match 190-grain BTHP Gold Medal were fired from each increment. No velocity was lost from 26 inches to 22 inches. Velocity loss started to occur only after they went below 22 inches. If I ever attach a comp to my .308 I'm probably going to ask the smith to also chop it down to 20". When you shoot out that .260 barrel do us all a favor and please take a hacksaw to the barrel and see what the velocity does. That'd be cool. Link to comment Share on other sites More sharing options...
Zak Smith Posted January 30, 2005 Author Share Posted January 30, 2005 Surprise, they're selling 18 & 20" rifles. And they provide no data. My friend's PSS shoots BH 175gr much faster than it goes in my 20" AR10. But yes, they are different barrels. FGMM 168 is a lighter load than the BH 168, however. I can believe that it gets done burning faster. Link to comment Share on other sites More sharing options...
George Posted January 30, 2005 Share Posted January 30, 2005 The trick to bbl length is to find a powder/bullet combo that reaches and holds it's pressure peak duration long enough and late enough for the bullet to exit the bore without beginning to decelerate, or coast appreciably. The test where the 26 was chopped inch at a time shows that it wasn't accelerating after the 22 inch point and was probably dropping pressure very early. Keep it accelerating until it exits the muzzle and you can get all sorts of V on a projectile. You just have to load for that characteristic. -- Regards. Link to comment Share on other sites More sharing options...
Religious Shooter Posted January 31, 2005 Share Posted January 31, 2005 My friend's PSS shoots BH 175gr much faster than it goes in my 20" AR10. But yes, they are different barrels. What was the velocity difference? Link to comment Share on other sites More sharing options...
Zak Smith Posted January 31, 2005 Author Share Posted January 31, 2005 In my AR10, BH175 shot about 2570fps. I thought it was closer to 2650 in his PSS, but I don't remember for certain. Link to comment Share on other sites More sharing options...
9x45 Posted February 10, 2005 Share Posted February 10, 2005 The ballistic pendulum works on the assumption of a completely inelastic collision and that all the useable energy is used to displace (do work on) the pendulum. Energy from heat is ignored. Even though a soft bullet would experience an inelastic collision, more energy would be lost in deforming a soft bullet (work is done to the bullet). The same would be true for a pendulum made of soft material. Link to comment Share on other sites More sharing options...
rhino Posted February 10, 2005 Share Posted February 10, 2005 My friend's PSS shoots BH 175gr much faster than it goes in my 20" AR10. But yes, they are different barrels. Does your AR10 have a 7.62x51NATO chamber, or a .308 chamber? Link to comment Share on other sites More sharing options...
AikiDale Posted February 11, 2005 Share Posted February 11, 2005 Does your AR10 have a 7.62x51NATO chamber, or a .308 chamber? and I thought these were the same. What is the difference? Does one tend to have more energy than the other? curiouser and curiouser.... Link to comment Share on other sites More sharing options...
EricW Posted February 11, 2005 Share Posted February 11, 2005 The ballistic pendulum works on the assumption of a completely inelastic collision and that all the useable energy is used to displace (do work on) the pendulum. Energy from heat is ignored. Even though a soft bullet would experience an inelastic collision, more energy would be lost in deforming a soft bullet (work is done to the bullet). The same would be true for a pendulum made of soft material. You are confusing momentum and kinetic energy. Heat is included with KE, not momentum. P = mv <- not energy, therefore no heat is included KE = 1/2 mv^2 <- energy, this is where you put the heat Momentum is conserved. Kinetic Energy is conserved. Each gets its own separate equation. N'eer the twain shall meet. Link to comment Share on other sites More sharing options...
Zak Smith Posted February 11, 2005 Author Share Posted February 11, 2005 re: chamber. I don't know. It's a JP barrel. Link to comment Share on other sites More sharing options...
rhino Posted February 11, 2005 Share Posted February 11, 2005 Does your AR10 have a 7.62x51NATO chamber, or a .308 chamber? and I thought these were the same. What is the difference? Does one tend to have more energy than the other? curiouser and curiouser.... Someone correct me if I am wrong ... I think the 7.62NATO vs. .308 is analgous to 5.56NATO vs. .223. There is no difference in the external dimensions of the cartridges, but pressure specs are different. The NATO/military spec ammo is loaded to higher pressures than the .308/.223, which are loaded to SAAMI specs. The chambers are different, though. I know you can see the differences between the 5.56 vs. .223 on ar15.com somewhere. I would expect the 7.62 vs. .308 to be similar. In general, the military chambers are looser for reliability, have longer ledes to tolerate the higher pressures, etc. Link to comment Share on other sites More sharing options...
tightloop Posted February 11, 2005 Share Posted February 11, 2005 Get a bigger gun Link to comment Share on other sites More sharing options...
Zak Smith Posted February 11, 2005 Author Share Posted February 11, 2005 7.62 NATO vs. 308 links http://www.fulton-armory.com/308.htm http://www.thegunzone.com/30cal.html http://www.armalite.com/library/techNotes/tnote45.htm http://www.cruffler.com/trivia-June01.html Summary: 7.62 NATO headspace is longer 308 SAAMI max pressure is 62,000 psi while NATO is 50,000psi "They are the same, 'cause nobody makes 7.62mm (NATO) ammo that isn't to the 308 "headspace" dimension spec. So 7.62mm ammo fits nicely into .308 chambers, as a rule." For practical purposes they are the same because of headspace interchangability, except commercial ammo may be loaded to higher pressure. Link to comment Share on other sites More sharing options...
rhino Posted February 12, 2005 Share Posted February 12, 2005 For practical purposes they are the same because of headspace interchangability, except commercial ammo may be loaded to higher pressure. Thanks, Zak! That means the ammo is loade the opposite of mil-spec 5.56 vs. commercial .223 (the military is higher pressure). I wonder why? Link to comment Share on other sites More sharing options...
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