Vanir Posted January 7, 2001 Share Posted January 7, 2001 It's my understanding that how well a round retains its energy is a function of its mass (inertia) and its ballistic properties (how aerodynamic its shape is). I don't have access to the actual energy ratings for these guns so I tried to approximate them by comparing their penetration values at 2000m at 0 degrees with 100m meters at 0 degrees. Allied guns 75L38: 64.9% 76L54: 73.2% 90L50: 67.8% 17 pdr: 70.6% German guns 50L60: 36.6% 75L48: 64.5% 75L70: 65.9% 88L56: 66.9% 88L71: 71.4% 128L58: 77.0% It makes sense that the 50mm retains the least percentage of its energy and the 128mm the most, but what seems strange to me is the 76 is second best behind the 128. It retains a greater percent of its energy even though the 88L71 and 90L50 must have fired heavier rounds. Is the 76 shell shaped especially aerodynamically or is my methodology all wrong? ------------------ You've never heard music until you've heard the bleating of a gut-shot cesspooler. -Mark IV Link to comment Share on other sites More sharing options...
Guest Michael emrys Posted January 7, 2001 Share Posted January 7, 2001 If the 76 was firing tungsten cored shot, that might explain it as tungsten has a higher specific gravity than steel, unless I am completely mistaken. Thus it would retain its velocity better, given anything like equivalence in aerodynamics. You'll notice the 17 lbr. is pretty high as well. In any event, trying to derive velocities from relative penetration is fraught with all sorts of difficulties and complications. Would be best to try to track down the actual data before proceeding further on this line. Rex? Michael Link to comment Share on other sites More sharing options...
Vanir Posted January 7, 2001 Author Share Posted January 7, 2001 <BLOCKQUOTE>quote:</font><HR>Originally posted by Michael emrys: If the 76 was firing tungsten cored shot, that might explain it as tungsten has a higher specific gravity than steel, unless I am completely mistaken. Thus it would retain its velocity better, given anything like equivalence in aerodynamics.<HR></BLOCKQUOTE> Actually, the exact opposite is true. I didn't post any tungsten values but 76mm tungsten rounds only retain about 50% of their energy (as I calculated it here). Charles explained this in another thread. The faster a round starts out the faster it loses velocity, so super speedy tungsten rounds bleed energy faster. <BLOCKQUOTE>quote:</font><HR>In any event, trying to derive velocities from relative penetration is fraught with all sorts of difficulties and complications. Would be best to try to track down the actual data before proceeding further on this line.<HR></BLOCKQUOTE> Yeah, I know. I happened to notice how the 76 kept so much of its penetration ability and it got me curious, and that's all I have to go on at the moment. ------------------ You've never heard music until you've heard the bleating of a gut-shot cesspooler. -Mark IV Link to comment Share on other sites More sharing options...
illo Posted January 7, 2001 Share Posted January 7, 2001 In other thread by rexford it was said that 88L56 retains energy clearly better than 76L54. CM just seems to model the opposite. So is there any realism behind this? Link to comment Share on other sites More sharing options...
Vanir Posted January 8, 2001 Author Share Posted January 8, 2001 Slightly self-serving anti-spam bump Link to comment Share on other sites More sharing options...
Guest Germanboy Posted January 8, 2001 Share Posted January 8, 2001 What would the figure be for the UK 77mm (Comet) and did you take muzzle velocity into account? I think you did, but it does not say clearly. ------------------ Andreas Der Kessel Home of „Die Sturmgruppe“; Scenario Design Group for Combat Mission. Link to comment Share on other sites More sharing options...
Vanir Posted January 8, 2001 Author Share Posted January 8, 2001 <BLOCKQUOTE>quote:</font><HR>Originally posted by Germanboy: What would the figure be for the UK 77mm (Comet) and did you take muzzle velocity into account? I think you did, but it does not say clearly.<HR></BLOCKQUOTE> Comet 77: 66.9% Note that these figures are arrived at by simply dividing the gun's penetration at 2000m by it's penetration at 100m. About velocity: Velocity would perhaps explain the 76s numbers vs. 90L50 and 88L71 since they are much faster and therefore bleed their energy faster, but it does not explain 88L56 which is slightly slower than the 76 APBC (773 mps vs. 793 mps) and is also larger. A more massive round traveling at equal or slower speed than a lighter round should bleed energy more slowly, all else being equal. The Comet gun is a similar case. IIRC the Comet 77 is actually 76.2mm. Its velocity is also nearly identical (792 mps). Yet it has significantly better penetration than the 76, both with APBC and HVAP (tungsten) so I assume it must fire a longer, heavier round. This would suggest better energy retention than the 76, but once again, this does not appear to be the case. ------------------ You've never heard music until you've heard the bleating of a gut-shot cesspooler. -Mark IV Link to comment Share on other sites More sharing options...
stevetherat Posted January 8, 2001 Share Posted January 8, 2001 The British 17pdr (which I'm sure is 77mm cal.) fired APDS shot - Arour Piercing, Discarding Sabot. This type of ammunition discarded all but a very hard, and small, projectile after firing, which increased muzzle velocity, and therefore penetrative power. But there again I might be wrong... Steve Link to comment Share on other sites More sharing options...
Guest Germanboy Posted January 8, 2001 Share Posted January 8, 2001 The 17pdr is 76.2mm IIRC, and the 77mm is indeed 77mm. They are different guns, with the 77mm packing less punch according to vet accounts from 11th Armoured I read. They still liked the Comet better, better armour and lower silhouette than the Firefly. Flotation apparently not as good. Hmm, Vanir I don't have the foggiest notion about how you have to calculate this stuff, but I am sure that to meaningfully compare energy retention, you have to look at muzzle velocity. One of the experts might want to comment on this. ------------------ Andreas Der Kessel Home of „Die Sturmgruppe“; Scenario Design Group for Combat Mission. Link to comment Share on other sites More sharing options...
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