Bolters w/ Felling

By ddunkelmeister, in Deathwatch House Rules

First off, my apologies if this idea has already been discussed to death. happy.gif

So, as we all know, the bolter is one of the most controversial aspects of DW. Some like the idea that SM weapons are more powerful than the versions used by the rest of the Imperium, others dislike it. It also raises balance issues.

As I recall, one of the reasons given for the high damage output was the need to overcome the intrinsic damage-soaking ability of other SMs. As such, bolters can currently hurt SM, while (in the eyes of many) providing total overkill for most other targets, and rendering several of the other weapon choices largely irrelevant.

So, here's a possibility: why not give bolters the Felling attribute? That way, you could lower the damage stats w/o rendering SM completely invulnerable to it.

While this could be seen as removing the applicability of Vengeance rounds, I would suggest that Vr could simply raise Pen to 9 and retain their risk of overheating.

Of course, this provides somewhat of a domino effect, as this change would in turn infringe on the purpose of Kraken rounds. I would suggest dropping the Pen of Kraken rounds to 6; this would preserve their purpose of "longer range with a bit more punch," as well as giving them an effective 'AP' of 4 (ignoring carapace armor), which better mirrors their tabletop counterparts (for anyone who takes such things into consideration).

So, what are your thoughts? What balance concerns would this address, and what issues would it exacerbate?

ddunkelmeister said:

First off, my apologies if this idea has already been discussed to death. happy.gif

So, as we all know, the bolter is one of the most controversial aspects of DW. Some like the idea that SM weapons are more powerful than the versions used by the rest of the Imperium, others dislike it. It also raises balance issues.

As I recall, one of the reasons given for the high damage output was the need to overcome the intrinsic damage-soaking ability of other SMs. As such, bolters can currently hurt SM, while (in the eyes of many) providing total overkill for most other targets, and rendering several of the other weapon choices largely irrelevant.

So, here's a possibility: why not give bolters the Felling attribute? That way, you could lower the damage stats w/o rendering SM completely invulnerable to it.

While this could be seen as removing the applicability of Vengeance rounds, I would suggest that Vr could simply raise Pen to 9 and retain their risk of overheating.

Of course, this provides somewhat of a domino effect, as this change would in turn infringe on the purpose of Kraken rounds. I would suggest dropping the Pen of Kraken rounds to 6; this would preserve their purpose of "longer range with a bit more punch," as well as giving them an effective 'AP' of 4 (ignoring carapace armor), which better mirrors their tabletop counterparts (for anyone who takes such things into consideration).

So, what are your thoughts? What balance concerns would this address, and what issues would it exacerbate?

It has been, but then again that's what forums are for.

My gut says this isn't a bad way to do it, but I guess after playing with some of the house rules (esp. those proposed by AK) things seemed to have blanced out. The RF Rules combined with the DW training combined with the high damage seems to have been the culprit. You end up with the same ridiculous damage issues with something like a lascannon (6d10, gives you something like a 45-50% chance of getting a 10, which would mean you get to roll all of those dice again, and again, and again) if you leave those rules in place. Outside of the heavy bolter's rate of fire, the bolt guns don't feel too out of control- you can still one shot your average human but with a cap on RF etc. you can't do the same to a hive tyrant anymore.

That said, the remaining dominos from your idea off the top of my head seem to be other weapons (meltas, plasma guns) still feel out of sync, and modifying the Pen of the bolter ammo could ripple into the pen and damage of other weapons and their costs. You'll also impact encounter design, as some enemies rely on toughness bonus over amor, and others armor over toughness- this is done (I assume, otherwise it's simply how I use them) to present the players with some tactical choices. If you modify the characteristics of the weapon profiles too much, you could alter the design of these enemies. Not that it would neccesarily break it, it just means you'd have to be aware of the changes and take them into consideration when plotting out your bad guys.

I'm surprised that there's been discussion on the fact that SM bolters are 'better'. I seem to recall canon dictating that they are .75 compared to the .50 calibre bolts used by mere mortals. It simply makes sense that the upscaled Marines are capable of using upscaled bolters. In fact, DH specifically mentions a sniper-rifle bolter that fires the much more powerful Astartes bolt rounds.

I certainly don't have a problem with using them as listed. Although Felling kind of makes sense, I'm not too sure that bolters need changing. And any change would require a re-write of every other weapon, in probability.

Bolters -specifically Astartes ones- are the weapon of choice for Mankind's finest troops. It seems to follow that they SHOULD be good.

According to the 4th edition Space Marine codex Space Marine bolters are .75 inch. According to Dark Heresy "normal" bolters are also .75 inch. Yet Space Marine ones are bigger (consequently they must be longer... which is not a solution I like.

Really? Coulda sworn they [DH ones] were .50.

How do they explain the greater power of the SM-bolt-using sniper rifle in the text, then?

The .50.75 comparison just makes so much sense that it's what we've adapted to.

The .50 inch "normal" bolters was never mentioned anywhere in any Games Workshop product (nor the 1 inch Heavy bolter), just one suggested by some people when it was clarified that Space Marine bolters were .75 inch (I think that was the first time a specific calibre was mentioned). I personally preferred the idea that Space Marine bolters are not that special, its just noteworthy that they get as standard a weapon that is usually considered rare and relatively prestigious. It may have extra features (I prerred the idea that most bolters are semi-automatic, but Space Marine ones were capable of burst and automatic fire) and was obviously sized for someone of a Space Marine in power armour's stature. Then Dark Heresy explicitly stated somewhere that even non-Space Marine bolters were .75 inch, but said for certain that Space Marine bolts were larger than normal ones and Purge the Unclean and The Inquisitor's Handbook gave them more potential for more damage (by making them 2d10, exactly the same as a "normal" Heavy Bolter).Then Fantasy Flight went and made the damage even higher.

Apparently all bolters were 2d10 damage at one point during play testing, and I am presuming at some point they decided this didn't work for whatever reason, and changed the damage. However, I am guessing they thought the new stats were too anaemic for the Space Marines' weapon, so introduced some guff about larger rounds to justify them having more powerful weapons. However, they still used the established size for bolt rounds, maybe muddling things up due to the change in damage. My guess all bolts were going to be described as .75 inch when they were the same damage. However, they then changed the damage, but forgoting Space Marine rounds were already established as .75 so they stated SM rounds were bigger rather than reducing the size of "normal rounds".

To answer your question: Basically they don't ever clarify why they get more damage aside from the general statement of larger rounds. As I said, the only way to marry the two statements about bolt rounds together is to conclude that Space Marine ones are longer rather than wider, which just seems silly to me. You could also justify it partly by saying Space Marine rounds are better made and have superior explosives and propellant, meaning they hit harder on impact and they have a ****** bang afterwards.

I presume you mean "bigger" bang? gui%C3%B1o.gif

Dark Heresy simply states: "It would be a mistake to confuse these 'civilian' issue weapons with those of the Adeptus Astartes. <snip> The standard bolter round is .75 calibre..." DW simply states they're larger and higher quality than the ones found in the IG or other organizations.

Calibre doesn't necesarily denote weapon size, capability, or power. Look at the difference between a .22 Long Rifle and an M16. The .22LR is essentially a 5.59mm, and the M16 is a 5.56mm weapon. You'll need a very special 22 rifle to try and compete with the M16. Or look at magnum rounds- the calibre may be the same, but the lethality of those bullets will be different.

Different sized shells, different propellant, different bolt core, different explosive contents of the bolt, different internal components, longer barrel, better recoil suppression, better internal parts could all lend to the Astartes having a significantly better weapon.

The one thing I never got was the idea that a 'normal human' couldn't use one without being eaten by the machine spirit, so I nixed that but left the 'larger size category rule' in place, but that's a different, if similar, thread.

Erm... yes. That's an embarrassing typo.

Oh, yes I certainly have no problem Space Marine weapons being better quality, and having features lacking on normal bolters. And yes, better quality /more advanced ammunition could also explain some increase in damage, range, penetration or other performance indicators, but the Deathwatch decision was not one I terribly like (not only are they better than normal bolters, they are better than normal heavy bolters) or terribly logical except maybe from a game design perspective.

I have considered returning all bolters to 2d10 damage, including Space Marine ones (who instead would receive Good or Best Quality bolters, maybe with slightly different characteristics but even then they wouldn't really get much if any increased damage) and then producing a quality system for bolt shells (and with their complicated nature I can see them justifying having quality levels even if other ammunition generally doesn't). Common would be as normal, Poor would possibly have reduce weapon stats and maybe some danger of exploding in the weapon (due to using inferior materials and being slightly unstable) while Good and Best quality would receive some bonuses over standard shells (and again Space Marines would always have the better ones as standard). I prefer that kind of idea to what has resulted where Space Marine bolters just have base stats that are miles better than standard.

Of course doing that would make the need to re-examine the damage for things like plasma and melta guns essential (rather than just probably need doing), which is one of the reasons I haven't bothered yet.

Good informative post, Borithan. I sprayed tea on my keyboard at the typo, though!

I think though that we'll probably stick with the 'fluff' of SM bolters being a much heavier shell than 'mortal' bolters and HBs. Be it from a combination of calibre, warhead components, amount of explosive, or simply angrier machine spirits thanks to being carefully and individually blessed and announted when manufactured (this is 40k, where a tech-priest can unjam a firearm at ten paces... it doesn't have to make sense).

Simply: They're better because they're bigger and better. That keeps them out of the hands of DH characters, too, as they'd be too powerful for normal humans to use safely.

I'm not keen on downstatting and then giving out better quality weapons. This takes away a possible route of advancement for players, as they can no longer upgrade their standard issue firearms. By all means, I'll assume that SM weapons are already of excellent quality having been made to the highest standards and carefully blessed, cherished, and maintained for thousands of years, but not of 'book' higher quality standards: You want it, you buy it.

If I have a problem with the bolters, it's reliability. No elite soldier is going to be equipped as standard with a firearm that fails to function 5% of the time. Reliability in the field is utterly essential. For me, jamming only happens on a '00' when fired on full auto. I don't believe that jams should occur at all in semi and single shot modes.

If bolters are too effective, I'll simply throw more goons at the characters. However, I'm not overly happy with the performance of plasma and melta weapons in comparison.

Sorry to make this my first my first post, been lurking a wile though....

borithan, actually, the Heavy Bolter is listed as a 1" shell, it's in the current Dark Angel's codex, under war-gear. And I think it was the 3rd, well 3.5edition IG codex, that listed their bolters (when sargents / officers could buy them) were .50 cal.

Also in Dark Heresy, the only bolt weapon that's close to the DW bolters, is the Angelis pattern bolter, at a wapping 2D10, and it is mentioned that the reason for that, is beacuse it uses the larger SM round, but owning one, and getting caught with it, carries a heavy punshiment.

Siranui said:

Good informative post, Borithan. I sprayed tea on my keyboard at the typo, though!

I think though that we'll probably stick with the 'fluff' of SM bolters being a much heavier shell than 'mortal' bolters and HBs. Be it from a combination of calibre, warhead components, amount of explosive, or simply angrier machine spirits thanks to being carefully and individually blessed and announted when manufactured (this is 40k, where a tech-priest can unjam a firearm at ten paces... it doesn't have to make sense).

Not to mention that impresses the hell out of the players. I mentioned it before - some of my players got a glint in their eye when they heard that the Oblivion's Edge chimera had a Heavy Bolter. Only to find out that their Bolt Pistol rounds do more damage than the non-Astartes (DH-level) HB.

Siranui said:

Simply: They're better because they're bigger and better. That keeps them out of the hands of DH characters, too, as they'd be too powerful for normal humans to use safely.

Errrrr.... no. I've come to the conclusion that my DH Scum PC wants one of those. I don't want to shoot with the thing at all (couldn't afford the ammo). I just want it for 'show off'. And to underline that my PC isn't too picky about ethics - even though he's a faithful follower of the Emperor, he won't mind that someone picked the gun out of the cold, dead hands of one of the Emperor's finest possibly.

Siranui said:

If I have a problem with the bolters, it's reliability. No elite soldier is going to be equipped as standard with a firearm that fails to function 5% of the time. Reliability in the field is utterly essential. For me, jamming only happens on a '00' when fired on full auto. I don't believe that jams should occur at all in semi and single shot modes.

It doesn't fail to function 5% of the time. Only 5% of the time during a game. gran_risa.gif What I am trying to say by this is: DW isn't a game of simulationism. Just like every good Hollywood script it dramatizes the action and part of that is the increased chance for jamming.

Alex

mangled Post and inability to fully delete it.

WingKia said:

Sorry to make this my first my first post, been lurking a wile though....

borithan, actually, the Heavy Bolter is listed as a 1" shell, it's in the current Dark Angel's codex, under war-gear. And I think it was the 3rd, well 3.5edition IG codex, that listed their bolters (when sargents / officers could buy them) were .50 cal.

The .50 IG bolter I don't remember, but then it has been a long time since I saw the 3rd edition codex. Of course then that is totally at odds with Dark Heresy itself.

.50 caliber for an IG round makes sense... If you think a human can fire anything larger with a handgun just go onto youtube and search for .75 handgun, its quite amusing.

My issue with the standard Astartes bolter statline as it stands right now is two fold.

1. The weapons damage output outshines almost all other variant weaponry to the point that no one would spend their requisition on anything other than different ammo, at least in the ranged weapon department.

2. If you fix the other ranged weapons to make them viable along the same lines as the Astartes bolter then the possibility of running a game with anything other than a Space Marine is just laughable. This issue cannot even be fixed by giving the weapons to non Astartes because a space marine would kill them for it....

This is kind of why I am trying to work out House Rules that will fix the issue. cool.gif

To quote my self from a similar thread in the Deathwatch Rules Questions sub forum.

  • "I liken the difference between "civilian" and Astartes bolt rounds to the differences between a regular round and a magnum round of identical calibers. Best real life example would probably be the difference between a standard 12-gauge (.729 caliber by 2.75) shell and the bigger 12-gauge magnum (.729 by 3.5) shells. My two pence. "

The specific thread being titled Machine Spirits Love Space Marines . I don't know why it seems so hard for people to grasp that not all weapons which fire the same caliber rounds will be created equal; nor the ammunition, for that matter.

On topic, I don't much see a reason to include Felling to the bolters. They've always seemed fine to me. But then, as a house rule, if you feel it makes sense, do it.

-=Brother Praetus=-

Hadriel said:

1. The weapons damage output outshines almost all other variant weaponry to the point that no one would spend their requisition on anything other than different ammo, at least in the ranged weapon department.

2. If you fix the other ranged weapons to make them viable along the same lines as the Astartes bolter then the possibility of running a game with anything other than a Space Marine is just laughable. This issue cannot even be fixed by giving the weapons to non Astartes because a space marine would kill them for it....

I've had a lot of luck so far with AK's weapon stats. But then again I'm running a game with space marines so 'crossing the streams' isn't much of an issue for me. And I've nixed the angry machine spirit rule but kept the one size category bigger, which means most non marines won't be using much more than the pistol versions of guns anyhow.

And the enemies in my game still strike fear into the characters, because as much as they wish it were the case, the bigger gun doesn't always equate to victory.

Brother Praetus said:


The specific thread being titled Machine Spirits Love Space Marines. I don't know why it seems so hard for people to grasp that not all weapons which fire the same caliber rounds will be created equal; nor the ammunition, for that matter.

On topic, I don't much see a reason to include Felling to the bolters. They've always seemed fine to me. But then, as a house rule, if you feel it makes sense, do it.

-=Brother Praetus=-

A) Because not everyone understands firearms all that well? There is a lot of misinformation out there, and 40k doesn't always follow logical rules either.

B) I think the reason to add felling was so that you could reduce the base damage, but still give it the potential to kill a space marine (you'd cut 4 or 5 off of their damage soak)

@Siranui - I thought the lack of the reliable quality odd at first blush too, but as Alex put's it, it only fails during a game. And half the time my group has enough fate points that they can spend them to avert said jam. And in practice we see a lot fewer jams than we do RFs, not sure how that works out...

I give in trying to quote anything on this forum /grumble.

DH Scum wanting a bolter for the wall:

I meant in the functional sense. Of course there is nothing 'against' just nailing it to the wall of your quarters. Y'know... apart from heresy...

5% Jam rate:

I see what you mean. It's just that I find it to be a dreadful rule, and very frustrating as a player. If I spend the points on something, I don't want it to statistically inevitable that it turns into a brick within the first 4 firefights. It breaks the forth wall for me in quite a bad way.

Bolters are grim, nothing else really is:

I'm not running a cross-over game, so the thought of compatibility doesn't weigh on me. I don't think that a cross-over game would particularly 'work' well as regards DH; as having a SM along for the ride immediately jumps up and down on a wide variety of covert scenarios, investigations and the like, which are the bread and butter of DH. If I wanted to just run DH as a kill-fest, I'd run DW.

If DH characters want to step up and fight next to SMs in a DW game, then I'm very much of the opinion that they should indeed feel completely outgunned and underpowered while fighting alongside men who were born into warrior societies, survived, rose to the top to become one of perhaps the twenty finest warriors of their entire generation, who then passed tough trials before being injected with gene-seed from the Emperor himself, bio-engineered to the extreme, were given the finest arms and armour available, and who are now immortal warriors who do nothing much each day other than training to become better at it, or actually fighting. Let's face it: Few DH characters should even come close in 'killyness'.

Additionally, I don't like nerfing too much. I'd rather beef up the unusual weapons than nerf the standard issue ones. Plasma and Melta don't look great, but are probably easily tuned, when the occasion arises.

Praetus:

Yes, I understand how firearms work. I don't struggle to grasp it. We're just talking fluff around the stats.

Charmander:

It would be easier had we not set precident for more reliable bolters in DH, where FPs were refreshed daily, and so scarcer perhaps. Still: IT does grate on us all that weapons jam so much, so we unanimously change it. It makes it easier for the GM, too - one less thing to generally remember and deal with. It also prevents gritty fights turning into an episode of the Keystone Cops, where a bunch of bad guys hilariously [sic] suffer multiple jams per turn. This isn't helped by the idiotic critical tables that would have every human capable of pumping out a dozen gallons of blood, thus ensuing the combat zone becomes an ice rink for more slapstick moments. I don't want comedy fights scattered liberally with ineptness.

Siranui said:

If DH characters want to step up and fight next to SMs in a DW game, then I'm very much of the opinion that they should indeed feel completely outgunned and underpowered while fighting alongside men who were born into warrior societies, survived, rose to the top to become one of perhaps the twenty finest warriors of their entire generation, who then passed tough trials before being injected with gene-seed from the Emperor himself, bio-engineered to the extreme, were given the finest arms and armour available, and who are now immortal warriors who do nothing much each day other than training to become better at it, or actually fighting. Let's face it: Few DH characters should even come close in 'killyness'.

Let me tell you from Rifts RPG experience that PCs don't need to have nearly the same combat level. Challenges can be designed so that either enemies focus their attention on the main threat (the marine) or you in an Elite class enemy (or two to keep the marine busy) and a bunch of (non-horde) mooks. If the marine dispatches his enemies quickly, he'll be able to kill the rest quickly, hopefully before they harm any of the DH PCs. If the other PCs can kill their enemies first one or two of them might help the marine overcome his enemies.

Alex

I'm aware that DH characters have other strengths that they would bring to a Kill Team. It's just that in the realms of battlefield combat abilities, any DH character SHOULD be pretty underwhelming next to an Astartes of the Deathwatch, IMHO.

If I may,

I belive it was in Inquisitor or Necromunda that it was made clear that Bolt Pistols are 50 cal, Boltguns are 75 cal, and heavy bolters 100 cal. It was also stated that these were all nominal values, with a great deal of variation between patterns (how the hell does the Ordo Munitorum do it?).

I have to do a tonne of digging to find the source material, but Adeptus bolters fire self-propelled shells out of a standard cartridge. Simply put, their is a boom in the gun, and then the rocket lights off after the round clears the barrel. Thinking about a 75 caliber shell, you are talking about something akin to firing a solid slug out of a 10 gage shotgun, with a one handed pistol grip.

Non-astartes bolters have similarly been described as caseless, so the round is a pure gyro-jet with no casing to eject. This makes the individual round lighter, and cuts recoil to almost 0. The down side of this is the same is real gyro-jets, they take a certain amount of time after clearing the barrell to reach lethal velocity. Depending on the design 5'-30' for the real thing.

The best illustration of the difference would be putting your hand over the end of the barrell. For a non-adeptus, the round has aceclerated from stop for about 8", and would hit your hand. The rocket would have enough power to push your hand away, and would eventually foul the barrell, and possibly detonate the rest of the rounds sympathetically. Doing the same thing to an adeptus bolter would result in you hoping you have enough requisition for a cyber hand, because your's would be gone, and probably not even trigger the mass reactive detonator.

Also of interest, way back in 2e, bolt rounds were listed as having a fail safe that limited their effective range. It would disable the mass reactive charge so missed shots didn't turn into a mine field the marines would have to advance through.

^Which is all well and good. And thanks for the source: I knew I'd read calibres somewhere.

Although bolt shells do not need to reach a 'lethal' velocity. They require a decent velocity only to give a decent range. Bolt shell warheads are explosive, and it doesn't matter how fast an explosive or shaped charge warhead strikes.

Only partially true. The rounds won't detonate on impact, they detonate after penetration to cause maximum damage. No penetration, no detonation.

Siranui said:

Charmander:

It would be easier had we not set precident for more reliable bolters in DH, where FPs were refreshed daily, and so scarcer perhaps. Still: IT does grate on us all that weapons jam so much, so we unanimously change it. It makes it easier for the GM, too - one less thing to generally remember and deal with. It also prevents gritty fights turning into an episode of the Keystone Cops, where a bunch of bad guys hilariously [sic] suffer multiple jams per turn. This isn't helped by the idiotic critical tables that would have every human capable of pumping out a dozen gallons of blood, thus ensuing the combat zone becomes an ice rink for more slapstick moments. I don't want comedy fights scattered liberally with ineptness.

My [relatively limited] experience with DH bolters was that you had to get special bolters from the supplements in order to find a bolter that had the reliable quality- the base bolters just have tearing iirc.

Don't get me wrong, if you and your group rolls high a lot, then weapon jams become the cornerstone of the fight, which is not all that cool. I've made more house rules over the years around how crap my players luck is than I care to count. My group has just never had that much problem with jams, maybe once every couple of sessions someone will jam. I will say I don't understand how you lose the whole clip due to a jam (so do you lose all 250 rounds from the hb on one unlucky roll? how lame is that?), so we axed that, especially given that it takes the full reload time of the gun to clear the jam.

Idiotic criticals? I personally love the critical tables, it fits with the explosive feel of the setting to me. When you kill someone, they don't just die, they effing explode. I have seen some 'critical fumbles' that have nearly taken out a weakend party when you start detonating the explosives or weapons they're carrying that seem...out of place, but overall I like 'em. One note though, I don't use critical tables on anyone except for PCs or 'important' NPCs. Hordes and even higher level fodder I simply just kill and don't waste time turning the battle field into a goey, slippery mess- so the criticals are usually used for 'dramatic moments.'

Dragonmann said:

If I may,

I belive it was in Inquisitor or Necromunda that it was made clear that Bolt Pistols are 50 cal, Boltguns are 75 cal, and heavy bolters 100 cal. It was also stated that these were all nominal values, with a great deal of variation between patterns (how the hell does the Ordo Munitorum do it?).

I have to do a tonne of digging to find the source material, but Adeptus bolters fire self-propelled shells out of a standard cartridge. Simply put, their is a boom in the gun, and then the rocket lights off after the round clears the barrel. Thinking about a 75 caliber shell, you are talking about something akin to firing a solid slug out of a 10 gage shotgun, with a one handed pistol grip.

Non-astartes bolters have similarly been described as caseless, so the round is a pure gyro-jet with no casing to eject. This makes the individual round lighter, and cuts recoil to almost 0. The down side of this is the same is real gyro-jets, they take a certain amount of time after clearing the barrell to reach lethal velocity. Depending on the design 5'-30' for the real thing.

Erm... just checked Inquisitor and there is nothing there (in fact, there is no distinction made between normal bolters and Space Marine bolters in that). And I know Necromunda very well, and it certainly has nothing about different calibres of boltgun. Still to find a copy of the 3rd edition Imperial Guard Codex though.

And the caseless bolter is a myth as well. Much discussion on Warseer has never revealed an actual GW source which mentions bolters being caseless.

Just checked the Dark Angel's Codex. No reference to 1 inch Heavy Bolters there either. Instead it talks about "fist sized" bolts. The Bolt Pistol fires the exact same shells as the standard Bolter (and curiously, and contradicting previous GW statements, the bolter is given a 6-10 round sickle magazine... I am guessing someone mixed up the labels with the bolt pistol's ones).

Yes, there is no evidence for 100 cal heavy bolters in any GW fluff I've ever read. The only concrete number given is that bolters are 0.75 calibre, this is true regardless of what bolter is being used.

The 'astartes' appelation is silly imo. Astartes promethium? Really? An astartes flame thrower uses identical but more burny fuel? It's just silly.

THe OP's suggestion is pretty good as it prevents the bolter's scale from pushing everything else up to ridiculous levels as well. The Felling rule though is a bit....awkward imo. It's like they realised the problem with Unnatural Toughness and rather than fix that problem they added a rule to get around it instead.

If you are using UT though, then adding Felling to weapons is a simple cheat to avoid the inherent problems it causes.

Don't forget that it means the bolter will hurt orks and tyranid warriors equally easily, but then the ork was one of the major opponents marines were originally designed to fight so it makes sense.

EDIT: Personally I would have preferred unnatural toughness to grant additional pts to TB without doubling/tripling TB. ie an ork has Unnatural Toughness (3) which means it gains an additional 3 TB. This would have produced a far nicer gradient rather than the step system where the jump is higher and would also allow a rule like Felling to fit better. In this case Felling would have a number in parentheses that is how much damage to Unnatural Toughness it does - so a Felling (3) weapon would ignore all the extra pts of TB the aforementioned Ork received.

This too would allow felling to follow a nicer progression, rather than the current rule where it can ignore anywhere from 2pts of TB (a gretchin has UT) to 6pts (a carnosaur).

This method of Unnatural toughness would also allow creatures to differ, rather than an ork having an identical level of UT to a space marine.

Hellebore