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Post by subunit on Nov 8, 2016 1:25:05 GMT
OK, so I went to make some common small arms calibers in the designer and got stopped dead at my first attempt to make an AR-15:  I am here representing a typical 20" AR-15 barrel firing a 62 grain 5.56mm NATO round. I have calibrated the propellant grain size to achieve the normal muzzle velocity of 5.56 from a barrel of this type. Bizarrely, neither lead nor copper projectiles survive the propellant combusting, and the barrel doesn't stand up to the force. I am willing to admit that if you ran an AR-15 at 18000 rounds per minute or whatever, you would damage the barrel. I therefore set about finding the optimum barrel for this system to engage at proper spacecraft ranges and settled on a length of.... 100m:  Well, I don't think you can put a 5.56 NATO round in a 100m barrel and achieve 1.35 km/s muzzle velocity.. can you? That just seems silly. Am I doing something stupid here? |
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Post by RA2lover on Nov 8, 2016 1:32:16 GMT
You don't have to deal with atmospheric pressure pushing the bullet back in after a sufficient amount of expansion.
That said, barrel friction appears to be missing indeed.
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Post by Dhan on Nov 8, 2016 1:48:09 GMT
You are also firing caseless ammunition in your AR-15. Although I'm not sure what impact that has on performance.
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Post by subunit on Nov 8, 2016 2:21:07 GMT
You don't have to deal with atmospheric pressure pushing the bullet back in after a sufficient amount of expansion. That said, barrel friction appears to be missing indeed. Yeah, I think it's a missing barrel friction term. That volume of nitrocellulose should be completely combusted after a couple of meters, beyond that barrel length shouldn't help much and should eventually stop the round dead. Shouldn't have much. H&K's G11 fired a round with broadly similar characteristics and without needing any kind of crazy barrel reinforcement or shattering its slugs. One thing that might help is being able to jacket slugs. |
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Post by bdcarrillo on Nov 8, 2016 4:06:23 GMT
You don't have to deal with atmospheric pressure pushing the bullet back in after a sufficient amount of expansion. That said, barrel friction appears to be missing indeed. If barrel friction is missing, heat from that friction is also likely missing. Kinda leads me back to one of my theories on the ludicrous cyclic rates |
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Post by subunit on Nov 8, 2016 4:44:20 GMT
You don't have to deal with atmospheric pressure pushing the bullet back in after a sufficient amount of expansion. That said, barrel friction appears to be missing indeed. If barrel friction is missing, heat from that friction is also likely missing. Kinda leads me back to one of my theories on the ludicrous cyclic rates Likewise barrel wear isn't going to be simulated properly. Some stainless or cromoly barrel isn't going to feed 50k rounds without destroying the rifling and losing accuracy, requiring a change. |
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Post by n2maniac on Nov 8, 2016 8:06:44 GMT
Bullets deform in the barrel to some extent. Pressure behind them exceeding their yield strength on soft metals shouldn't be an issue, though it could shatter brittle materials. That being said, I don't know if it would impact the game (why would you shoot soft bullets against armored targets?)
Barrel yield strength seems really weird that it is off by a factor of 6. That sort of compression on a tube should normally be a buckling failure mode, based entirely on stiffness. I am now somewhat curious the game calculates it. On overall impact, that one does lead to oversized barrels...
Lack of projectile friction against the barrel is an interesting one, but I would be tempted to ask how tightly the barrel should squeeze the projectile? On conventional guns it needs to be tight enough to seal and guide. Do you have a better idea?
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Post by subunit on Nov 8, 2016 9:22:46 GMT
Bullets deform in the barrel to some extent. Pressure behind them exceeding their yield strength on soft metals shouldn't be an issue, though it could shatter brittle materials. That being said, I don't know if it would impact the game (why would you shoot soft bullets against armored targets?) 5.56 NATO has special effects on both commies and greys, common foes in outer space. I.. have no doubt these special properties will fall out of the simulation... as its vital fluids are purified. Barrel yield strength seems really weird that it is off by a factor of 6. That sort of compression on a tube should normally be a buckling failure mode, based entirely on stiffness. I am now somewhat curious the game calculates it. On overall impact, that one does lead to oversized barrels... Lack of projectile friction against the barrel is an interesting one, but I would be tempted to ask how tightly the barrel should squeeze the projectile? On conventional guns it needs to be tight enough to seal and guide. Do you have a better idea? No that sounds about right. The guns in game look to be smoothbore so the friction need not be large, but it should have enough of an effect to show up in the module editor I think. |
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hal
New Member
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Post by hal on Nov 8, 2016 14:26:16 GMT
If barrel friction is missing, heat from that friction is also likely missing. Kinda leads me back to one of my theories on the ludicrous cyclic rates Likewise barrel wear isn't going to be simulated properly. Some stainless or cromoly barrel isn't going to feed 50k rounds without destroying the rifling and losing accuracy, requiring a change. Is rifling necessary in space? Doesn't rifling only make the bullet more aerodynamic, something that doesn't matter in space? |
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Post by RA2lover on Nov 8, 2016 15:06:09 GMT
not really, it only makes the bullet less likely to tumble.
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Post by bdcarrillo on Nov 8, 2016 16:14:52 GMT
Good point on rifling... Not technically necessary in space.
However, barrel friction still needs to be significant enough to promote increased pressures to get decent velocity.
Ie, a smoothbore mortar uses a very low projectile friction, but a high-speed (brisance?) explosive impulse to generate a relatively low muzzle velocity.
A typical gun requires the "backpressure" of the tight projectile fit (or high mass) to support complete combustion. This mass aspect appears to be partially modelled in game, but I rarely bump into incomplete combustion with sensible weapon builds.
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Post by subunit on Nov 8, 2016 17:39:13 GMT
Likewise barrel wear isn't going to be simulated properly. Some stainless or cromoly barrel isn't going to feed 50k rounds without destroying the rifling and losing accuracy, requiring a change. Is rifling necessary in space? Doesn't rifling only make the bullet more aerodynamic, something that doesn't matter in space? Rifling stabilises the projectile. If barrel wear was simulated, rifling would have a purpose, I think- to stabilise the projectile after your barrel crown has been melted by a 20000 rpm magdump  |
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