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Recoil of a bolter
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Old 01 Oct 2006, 04:54   #1 (permalink)
Shas'El
 
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Default Recoil of a bolter

In some pieces of fluff, even a Space Marine has trouble keeping a grip on this weapon of divine wrath.

In others, a Guardsman can easily aim the semi-auto 80 mm RPG launcher.

So... whats the approximate mass/weight of a bolt, a bolt's velocity, and the mass/weight of a bolter? P=MV, and then we can see the recoil of the bolter against the holder.

Mass of Bolter * (Speed of bolter) = Mass of bolt * (Speed of bolt)
p = p
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Old 01 Oct 2006, 05:12   #2 (permalink)
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Default Re: Recoil of a bolter

It's a little bit more complex than that. Even with a normal gun, you have to allow for the momentum not only of the bullet, but also of the exhaust gases that vent from the muzzle. When the projectiles are rocket-propelled, as in this case, it's even more complex, because the projectile continues to accelerate after it has left the barrel.

In fact, a real-world rocket-boosted small arm like the Gyrojet generally has very little recoil. The projectile leaves the muzzle at a fairly low velocity, and then continues to accelerate until the rocket runs out of fuel. In the case of the Gyrojet, this happened at a range of around 70 metres - so the projectile's kinetic energy would actually increase until it reached this distance, after which it would decline as for any other projectile.

A disadvantage of this type of weapon is that, if the target is at very close range, the projectile won't have time to accelerate much before they impact. I could imagine a selector lever on a bolter that would set the bolts to burn more of their propellant while they were actually in the barrel - this would increase the recoil, but make the bolters more powerful at short range. Knowing that he was strong enough to handle it, a space marine might use this option, while an unenhanced human would leave it on the low-recoil long-range setting.
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Old 01 Oct 2006, 06:00   #3 (permalink)
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Default Re: Recoil of a bolter

I'm also open to the idea that bolters have an open vent that shoots the exast out of the bolter. Bazookas have very little recoil (almost none)
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Old 01 Oct 2006, 13:24   #4 (permalink)
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Default Re: Recoil of a bolter

just for cool factor i think it would have a lot of recoil, but SM don't care cuz they got mAcl Sk1Lls
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Old 01 Oct 2006, 14:45   #5 (permalink)
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Default Re: Recoil of a bolter

A lot of general info on the bolter can be found in the third edition rulebook.
Sure the workings of a bolter varies between fluff. But one must also remember that
a bolter is not just a bolter. There are several production patterns (Ultima, Crusade, Heresy, Filienostos, Astartes Umbra etc.), sizes and calibres, between who is being assigned the weapon.

The bolter a Space or Chaos Marine wields are not of the same size or weight as those issued the Imperial guard or Traitors etc. As the bolter weighs too much to be weilded. One can notice in several fluff pieces, different manners of weilding the weapon. Bolters/Stormbolters are fired both one and two-handed. Even some fluff show a Imperial Guard Sargeant firing a Stormbolter one-handed. (Lone Wolves)
Which brings us to the question of recoil.

This is the 41th millenium. Technology has gone a far way from what we have today. The bolter is a "minitaure" missile launcher. It fires self propelled
armour-piercing, mass-reactive missiles, called bolts.
If we look at todays missile-launchers, we would notice that such weapons have little to no recoil, and giving these weapons a few millenia of development, the recoil should net be much trouble.
But again, it could also come down to the ammunition used. As ammunition now, the recoil depends on amount of shell-charge and propellant. And it might have gone on into the far millenia.
For the regular bolter, we have:

The standard bolt: mass-reactive detonator cap, depleted deuterium core (don't ask, please. I know how weird it is) and diamantine tip.

The Inferno Bolt: Deuterium changed with a oxy-phosphur gel.

The Hellfire Bolt: Core and tip replaced with mutagenic acid vials

The Metal Storm Frag Bolt: MR cap replaced with proximity detector. Tip and core replaced with increased charge and fragmentation casing.

The Stalker Silenced Bolt: Propellant base and charge replaced with gas cartiges. D-cap replaced with a solid mercury slug (yes, yes...I know)

Kraken Pattern Penetrator Bolt: Deuterium core replaced with an adamantine core.

My two cents of the Bolter.
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Old 03 Oct 2006, 21:41   #6 (permalink)
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Default Re: Recoil of a bolter

If I fired a bolter... I'd lose my arms and fly a mile backwards.
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Old 03 Oct 2006, 22:52   #7 (permalink)
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Default Re: Recoil of a bolter

I think the problem is not how 1 bolt is fired. But the rapid firing of MANY bolts. A single pull of a tripper sends 3-4 bolts according to the fluff and probably most SMurfs would try to fire as fast as possible (think Paintball). Since, high-school physics dictate that when you fire more the recoil gets more.

So if we use the (extremely) simple formula: R= x + (y(x)(0.01)) where "x" is the initial recoil and "y" is the number of shots fired then we can (very inaccurately) figure out an approxiamate value of recoil. If each shot fired increased the recoil by 1%

Ex. If "x" was 2N and "y" is 100. If we plug the numbers in:

R= x + (y(x)(0.01))
R= (2N) + (100)(2)(0.01))
R= 2N + 2N
R= 4N

Therefore, after 100 shots the recoil has doubled to 4N.

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Old 04 Oct 2006, 00:15   #8 (permalink)
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Default Re: Recoil of a bolter

Remember that recoil does not stack for each shot.
And since the Bolter is a burst weapon (4 round bursts), the recoil is not much of a problem. And there is a restriction in ammunition as well. The largest clip, the "drum" contains up to 60 bolts. But it tends to jam.
You mathpiece would be: (if I'm not too much mistaken)
R= x + (y(x)(0.01))
R= (2N) + (4)(2)(0.01))
R= 2N + 0,08N
R= 2,08N
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Old 04 Oct 2006, 00:51   #9 (permalink)
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Default Re: Recoil of a bolter

hmmm.....everytime I think of a Genestealer Cult, I think of a hybrid with four arms, a Bolter in each hand, charging....scary. Then again, the 'stealer would probably just bonk the Imperials on the head with it instead.
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Old 04 Oct 2006, 08:22   #10 (permalink)
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Default Re: Recoil of a bolter

Quote:
Originally Posted by Stargazer Zero
So if we use the (extremely) simple formula: R= x + (y(x)(0.01)) where "x" is the initial recoil and "y" is the number of shots fired then we can (very inaccurately) figure out an approxiamate value of recoil. If each shot fired increased the recoil by 1%

Ex. If "x" was 2N and "y" is 100. If we plug the numbers in:

R= x + (y(x)(0.01))
R= (2N) + (100)(2)(0.01))
R= 2N + 2N
R= 4N
Aargh. This makes my brain hurt. Let me see, where should I start...

Let's start with the smallest error. A Newton is a measure of force. If a gun is firing continuously, at a constant rate of fire, you can say that its recoil is so-and-so-many Newtons, because that's the average force that it's applying to the firer. If you're talking about the recoil due to a particular number of shots, you're talking about impulse, not force, so you shouldn't be using Newtons. The SI unit for this would be kilogram-metres-per-second-squared, or second-Newtons. This is the sort of subtlety that you might not get taught until year 10, so I guess you might not have learned it yet.

Next, your formula: R= x + (y(x)(0.01)). I don't know where you got it, but either it's wrong, or it doesn't mean what you think it does. The total recoil is equal to the recoil of a single round, multiplied by the number of rounds - using your definitions, that's: R = x * y. For a sanity check, try inserting y = 0 into both equations - yours will give a non-zero recoil of x, even though there were exactly 0 rounds fired.

Apart from that, your working is at least self-consistent. If you'd had the correct assumptions in the first place, you could have worked it through just fine. The only advice I've got to give you here is not to use expressions like 'y(x)' - to anyone who's worked with functions, that will appear as 'y as a function of x' instead of what you meant, which is 'y multiplied by x'.

Quote:
Originally Posted by MechTau
I'm also open to the idea that bolters have an open vent that shoots the exast out of the bolter.
This makes sense. As you say, bazookas and similar weapons already work this way. We can even weave this in with my idea by saying that the vent can be closed off to increase the bolter's firepower at short range, at the cost of increasing the recoil.
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