4thGordons Posted 25 July , 2012 Share Posted 25 July , 2012 Could someone identify this rather concealed British gun please, I'm struggling. TIA Chris Link to comment Share on other sites More sharing options...
MikB Posted 25 July , 2012 Share Posted 25 July , 2012 I think it's a Breech Loading (Converted) 15 pdr . Mk.I. This was a 15 pounder of an older design converted to quick-firing after about 1905. It's on p.128 et seq. of Len Trawin's 'Early British Quick Firing Artillery'. A major, if not the major feature of the conversion, was the addition of a recoil system in place of the previous rigid trunnion mounting. Oh, and a bulletproof shield, better sights, some redesign of the trail.... Regards, MikB Link to comment Share on other sites More sharing options...
centurion Posted 25 July , 2012 Share Posted 25 July , 2012 Yes a a 15 pounder BLC. A cheapo short cut to giving the Terriers a modern gun without having to spend too much money. . AFAIK here was no shield but seats for the gunlayers were added. It still used bagged charges even though the breech was modified (and the old friction tube vent plugged) so it wasn't so much a quick firer as a less slow firer. Introduced in 1908 and issued to he Territorial Force. Some went to France in 1914 but proved hopelessly out ranged by the German artillery So replaced with 18 pdrs ASAP and used for training until declared obsolete in 1919 Link to comment Share on other sites More sharing options...
4thGordons Posted 25 July , 2012 Author Share Posted 25 July , 2012 Thanks very much. The older type makes sense. This picture is annotated in some detail and indicates that it is indeed a TF unit and the photo was taken in Sept 1914. Thanks again. Chris Link to comment Share on other sites More sharing options...
centurion Posted 25 July , 2012 Share Posted 25 July , 2012 Just to add a little detail - it fired the same 14 lb shrapnel shell as the real 15 pdr QF(which was also issued to the TF) with a range of 5,750 yards. Link to comment Share on other sites More sharing options...
MikB Posted 25 July , 2012 Share Posted 25 July , 2012 Also these guns employed three different gain-twist rifling patterns (whereby the twist rate increases toward the muzzle). These add significantly to the difficulty and cost of manufacture, and AFAIK have no practical merit whatever - anybody have a different view? Regards, MikB Link to comment Share on other sites More sharing options...
centurion Posted 25 July , 2012 Share Posted 25 July , 2012 Also these guns employed three different gain-twist rifling patterns (whereby the twist rate increases toward the muzzle). These add significantly to the difficulty and cost of manufacture, and AFAIK have no practical merit whatever - anybody have a different view? Regards, MikB Don't forget that the 15 Pdr BLC guns were a double conversion having originally started out life as RML before being converted to breech loaders and then into the BLC with a recoil mechanism and a different breech. I suspect that originally it was thought rightly or wrongly it would make them easier to load. Link to comment Share on other sites More sharing options...
MikB Posted 25 July , 2012 Share Posted 25 July , 2012 There could be some value in reducing the severity of angular acceleration if - for example - driving band attachment was weak. But I'm not sure delaying full rotation until the round is travelling faster in the bore would actually do that - it might make it worse. The action also tends to mash the engraving of the rifling grooves, potentially increasing blow-by, gas-cutting and the risk of stripping, though the first two are perhaps trivial. I can't see any advantage in loading as the band would normally be at most just 'rung into' the rifling lead, and may even be in clearance of it, until firing. Beats me why they did it. Regards, MikB Link to comment Share on other sites More sharing options...
centurion Posted 25 July , 2012 Share Posted 25 July , 2012 As I said if the tube was originally made for a rifled muzzle loader it would make ramming the round down the barrel easier Link to comment Share on other sites More sharing options...
smleenfield Posted 25 July , 2012 Share Posted 25 July , 2012 This type of rifling is used to reduce stress on the barrel at the point where the driving band is first engraved by the lands ahead of the chamber. Gain-twist rifling begins with very little change in the projectile's angular momentum during the first few inches of travel after ignition during the transition from chamber to throat. This enables the projectile to remain essentially undisturbed and trued to the chamber or case mouth. After engaging the rifling, the projectile is progressively subjected to accelerated angular momentum as burning powder propels it down the barrel. By only gradually increasing the spin rate, torque is spread along a much longer section of barrel, rather than only at the throat where rifling is eroded through repeated rifling engagement. Link to comment Share on other sites More sharing options...
CharlieBris Posted 25 July , 2012 Share Posted 25 July , 2012 There might be a couple of reasons gain-twist rifling would be an advantage. I expect to get shot down in flames from my views but at least we may get to some understanding of why this form of rifling would be used. 1. To even out the erosive effect of reactive torque on the barrel. A round has to accelerate on firing, the effect of the rifling is to increase the angular momentum of the round but this is at the cost of eroding the rifling from the reactive torque of the round acting on the barrel. By increasing the twist of the rifling the effect of this erosion is reduced at the throat of the barrel and increases towards the muzzle. The rifling at the throat will experience erosion from the engagement of the round as its rammed in. The gain-twist rifling should even out the erosion of these two effects. 2. To slightly increase the residence time of the round in the barrel. Once engaged in the rifling a round will accelerate along the barrel on firing. The time the round is accelerated will depend on the pressure in the breech and the length of the rifling. The gain-twist rifling will be longer than straight rifling which for a given breech pressure will give a slightly longer residence time in the barrel. The effect of this is that more energy can be extracted from the driving gas. This could be exploited by using higher peak breech pressures which will give higher muzzle velocities and hence longer range. The additional cost of machining may not be very large - the rifling machine for a 25 Pounder gun simply had different profile plates for straight and gain-twist rifling. Regards, Charlie Link to comment Share on other sites More sharing options...
MikB Posted 26 July , 2012 Share Posted 26 July , 2012 Thanks for the reasoning on gain-twist rifling, those who answered. Smleenfield's point makes sense. Charlie, your first point is similar and I can see that easily enough, but No. 2 is very hard to buy - increased barrel-time could only lead to increased MV by making acceleration a lot more non-linear than it already is. Most of the efforts of propellant developers have concentrated on trying to flatten the curve, reduce early peak pressure and maintain residual as high as possible as far as possible up the bore, and your theory seems to encourage the opposite - so I don't understand how that could work at present. Regards, MikB Link to comment Share on other sites More sharing options...
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