Why should i use Semi-automatic Burst on a weapon the can also fire Full-auto burst ?

The action are both the same except you gain +20 and one exra hit per DoS on full-auto opposed to +10 and one extra hit per 2 DoS.

I m thinking to change the he Semi-auto to a half action from a full

The comparative benefit of using semi-auto is the difference in ammo usage.

The Boy Named Crow said:

And semi-auto is more accurate if you want to be moving while shooting.

If you want to move up to your AB in meters while firing on semi auto, the test is at +0. But if you do the same with full auto fire, the BS test is at -10. But extra hits still land as normal, so semi-auto might not be so useful here.

The Boy Named Crow said:

Always have shot selectors. *G* Three times the ammo!

JacobKlunder said:

The comparative hindrance of using shot selectors is the difference in weapon weight.

Bilateralrope said:

Where are you pulling these rules from? I don't think I've ever seen them...

The Boy Named Crow said:

Read the bottom few lines about full auto bursts (pg 239) and semi-auto bursts (pg 242) in the Rogue Trader rulebook. Easy to miss, especially for people who are so used to the Dark Heresy rules (which don't allow moving and shooting) that they skim over large parts because they are mostly identical.

Which was exactly the case for me. Huh, that adds a lot of value to semi-auto bursts as a combat tactic...

I've been thinking of semi-bursts. This might sound like deliberate complication on my part (and I guess it is to a degree), but from what I know of real world military procedures, the more accurate way of placing several shots on a single target is by using semi-auto fire (or a "three round burst") rather than spitting away 10 rounds at a time.

Im starting to feel inclined to change the rules so that you get +10 to hit with full auto and +20 to hit with semi auto instead of the regular setting, but not change the DoS needed to place several shots at the target. (while full auto might be harder to hit with, it usually tend to have a more numerous interval of shots landed on the target when semi-auto misses are usually just a miss).

Im gonna have to think this through a bit though...

Varnias Tybalt said:

Do those military procedures care about what happens to the bullets that don't hit the target ?

I can easily see how a semi-auto burst would get a higher proportion of the bullets to hit the target.

But how does putting more bullets into the general area of the target result in less hits ?

Sure, each bullet would have a lower chance to hit. But that it made up for by the number of bullets sent that way.

Bilateralrope said:

Depends on the military organisation in question.

But if you consider most historical warfare scenarios, where tank and artillery companies have little issue with simply crushing and destroying entire buildings, villages and small cities where they "suspect" that the enemy is located... Well I think you get my meaning.

Bilateralrope said:

Recoil and muzzle climb, both extremely influential factors as to whether you hit your target or not when firing on full auto.

If we speak on purely realistic viewpoint then short bursts should be more accurate. As anyone who has ever actually fired a weapon on automatic can tell the actual problem is that the recoil tends to move the barrel away from the point of aim and the longer burst you fire the more hard it will be to control the burst. However, this depends a whole lot on the weapon in use.

Typical modern-day assault rifle will have quite extensive recoil and no matter what you do you simply cannot control the burst on longer range beyond the initial two to four shots. In this case using full-auto beyond ranges of maybe 30 meters or so is just wasting bullets. The semi-auto, however, is usefull even in long range since the "climbing" of the burst is actually quite handy in compensating for the difficulty of judging the range. You can aim deliberately low and stand a good chance of hitting the target even though you blundered in judging the distance of the shot.

A submachinegun type of weapon is whole other deal. If the weapon is heavy enough and the cartridge realtively unpowered you can keep the gun in very good control. Many WWII submachineguns as well as current day things like H&K MP5 are items like this. You can actually "walk the burst" to target as long as you can see where the bullets are hitting.

Machineguns (bipod, tripod and pintel-mounted ones) are also usually heavy enough to compensate for the recoil and you can "walk the burst", adjusting your aim by looking at where the bullets hit. Tracers help in this a lot. Some of the ehaviest machineguns (like Russian PSV anti-air machineguns) are actually too accurate for their intended purpose and are deliberately built such a way that when fired full-auto they spread the fire more than the actuall weight-recoil ratio and the inherent accuracy of the gun allows.

If you are aiming for full realism then you should really have different set of auto-fire rules for different weapons. Stuff like autoguns and autopistols would be inaccurate on full-auto while heavy stubbers would be accurate.

Lasguns would be superaccurate on auto-fire since there is no recoil and adjusting the aim by looking at the laser bursts is easy as hell.

Bolters would also fall in with the accurate auto-fire guns since they are rocket propelled and thus the recoil is small in contrast to the weapon weight.

I'd say the easiest thing would probably just say that autoguns and autopistols firing full-auto will have their range increments halved. This would eat away the benefit of full-auto away on longer ranges quite fast.

Polaria said:

Yes, on would think that about lasguns and lasweapons in general. But some fluff sources describe the lasguns as suffering from recoil for some reason (don't ask me why, but something in the mechanism seems to kick backwards when the lasgun is fired). Also, considering the mass produced nature of lasguns, I believe that the focusing prism used in their operation isn't really built for the necessary exact standards that would be required of a laser weapon. The prism used is most likely of "acceptable" quality (hence why las weapons have a limit to their range in the profiles, a real lasergun wouldn't have much in the way of range limits since the beam moves at the speed of light and in a perfect straight line).

Quite simply, las weapons don't usually have high quality parts, they have okay parts but with a really hefty but portable sci-fi powersource. But the power used seems to have focusing issues on longer ranges.

As for bolters, they aren't only rocket propelled (like the real world gyrojet gun was), a bolt shell works more like a two stage rocket, where the shell is ejected from the barrel by the force of some explosive (like gunpowder) and the rocket engine kick's in during mid-flight. It has to be that way because otherwise the bolter would be useless in close quarters (rockets need momentum to actually be able to penetrate materials, and what good would a bolt shell be if it couldn't even pierce the skin of a target five to ten metres away?), and also for the reason why all pictures of bolters in action see them spitting out oversized shell casings when fired.

But the bottom line is that there is some sort of conventional explosive involved in a bolters firing operation, and this explosive stage cause the infamous recoil associated with them.

Just some tidbits worth mentioning.

Varnias Tybalt said:

Superheated air from the shot being fired. Assume that it pushes the rifle around enough to knock the firer's aim off.

Errant said:

Makes sense... Sort of (hard to make sense of certain sci-fi inventions).

Here's a plausible theory: the focusing lens of a lasgun is probably located way "inside" of a long gun barrel in order to protect it from dirt and wearing. Which means that the beam has to travel through a long and airtight "tube" before leaving the gun, meaning that there's plenty of air and ambient moisture to flash heat inside the tube, and this might just give a "knock back" effect.

How does that sound?

Varnias Tybalt said:

http://en.wikipedia.org/wiki/Diffraction#Propagation_of_a_laser_beam

No matter how good the laser is, its beams will widen over distances even in a vacuum, thus reducing their killing power. Then you have the energy lost to heat the air the beam goes through.

Varnias Tybalt said:

Varnias Tybalt said:

Sounds like your searching for an excuse for something written by someone who didn't know what they were talking about.

If the tube was airtight they couldn't be recoil because there is nothing escaping from the tube. If the tube isn't airtight, then that will mean that when dirt gets in there it is very difficult to get out. Especially when your in a muddy trench.

Imagine the long-las variant uses a tighter set of focusing rings (magnets, charged particles, convex mirrors, crystal matrices', prayer beads etc) which happen to be along the barrel, improving its aim compared to a stub barreled version. This also explains why the barrels need frequent replacement (as they're highly calibrated, and shift out of true over repeated use) and why they're used by be specialist snipers, rather than grunts without needing constant Mechanicus maintenance (beyond the increased cost).

Bilateralrope said:

Uh, yes?

You pretty much have to when trying to determine the exac function of inventions that doesn't exist at the moment. Most of my estimates about how a bolter functions is based on guesswork and excuses.

Though for me it's enough when a theory makes sense for fictional settings. It doesn't always have to be realistic as long as the intended audience can see some degree of sense to it.

Forget about Full Auto for a second...

Also, forget about "Three Round Burst".

Most of the weapons in RT that have a Semi setting, it's "2". Meaning with the bonus to-hit, I'm still mathematically more likely to score by squeezing off two single shots.

If "Semi" meant "pull the trigger and 3 bullets come out" then I would understand...as it relates to real-life 3-round-burst, but like I said most DH/RT Semi rates are "2" which is...(sigh) ridiculous. The only way I'd ever use it is if I had to have the +10 bonus to have any chance to hit at all (in which case I'd probably need to flee or change my tactics in some way).

I still can't figure out why I would EVER want to use Semi unless the Semi rating was "3" or higher.

Someone please explain to me (because I'm a dullard apparently) why I shouldn't make "Semi" a half-action.

Because you can take a semi-auto/full-auto action whilst walking, and the full-auto in fact gets a negative to hit whilst doing so, where as the semi-auto doesn't.

Therefore, on the move, the semi-auto option is the best.

Also, take into account you can only make one combat action a round. You can't fire off 2 single shots in a single round.

It seems like whoever wrote the rule didn't understand what semi auto fire really is. Semi-auto fire means one trigger pull fires and cycles (ejects the spent cartridge case and loads another) the gun once.

Danger said:

This.

Also, the -10 difference between the Semi and Full-Auto when using them on the move probably isn't worth it at above average or better Ballistics Skill, given that a successful Full-Auto attack is much more likely to incur additional hits. Consider the following:

Semi-Auto: Average Damage * (1 + ROUNDDOWN(Ballistic Skill / 20)) / 2 * (Ballistic Skill/100) = Net Damage

Full-Auto: Average Damage * (1 + (ROUNDDOWN((Ballistic Skill - 10) / 10) ) / 2 * ((Ballistic Skill-10)/100) = Net Damage

Let's assume the Average Damage is 8.5 (1d10+3), which is the case for most longarms. Let's also assume a BS of 40. This is the break even point:

Semi-Auto: 8.5 * (1 + ROUNDDOWN(40 / 20)) / 2 * (40/100) = Net Damage

8.5 * 1.5 * 0.4 = 5.1

Full-Auto: Average Damage * (1 + (ROUNDDOWN((40 - 10) / 10) ) / 2 * ((40-10)/100) = Net Damage

8.5 * 2 * 0.3 = 5.1

Beyond this, Full-Auto is flat out better.

Beyond this, Full-Auto is flat out better.

So much better that it compensates for the additional ammo used up and the round(-s) of reloading?

Usually, given things like Ammo Backpacks and Fire Selectors that increase munitions capacity, and talents/upgrades that reduce reload times. Further, weapons with longer reload times tend to have larger clip sizes. Finally, the difference in ammo consumption between Full and Semi-Auto can be as little as 2 rounds.