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Well, while I'm at work I have a tendency to mull over different number based issues to keep my mind busy as my body flies along on auto-pilot. That being said, the main task I've set myself up to do for the past couple of days is develop a d10 based version of 40k and come up with a couple of unit and weapon profiles to test it's accuracy compared to the current version of 40k. So.. here goes:
First off I decided that all tests should be rolled "leadership style", by trying to roll equal to or less than the desired number. Leadership tests are taken with 2d10 as a "percentile" test. You'll notice my revised strength values are MUCH higher, this is because I think it's simpler to determine the value needed to wound a target by subtracting an attack's strength from the target's toughness. Anyways, enough general blabbering, here's the conversions:

Leadership Conversion
2----3----4------5------6-----7------8-----9------10
3%-8%-17%-28%-42%-58%-72%-83%-92%

BS Conversion
1-2-3-4-5-6-7-8---9----10
2-3-5-7-8-9-9-9-(9/5)-(9/7)
parenthesis denote re-rolls as per speculated 5th ed. rules.

WS Conversion
Attacker's WS > Defender's --------> 7
Attacker's WS =< Defender's ------> 5
Attacker's WS < 1/2 Defender's --> 3

Strength Conversion
1-2--3---4---5--6---7--8--9---10
6-8-10-12-13-15-17-18-20-22

Toughness Conversion
1-2-3-4-5-6----7--8---9--10
1-3-5-7-8-10-12-13-15-17

To-Wound Conversion
Subtract the target's toughness from the attack's strength, you must roll 1 d10 at or below this value. (I'm lazy and didn't feel like typing up a 17x17 grid)

Armor Save Conversion
6+ 5+ 4+ 3+ 2+
2---3---5--7---8

AP Conversion chart
1--2-3-4-5-6
10-8-7-5-3-2

AV conversion
10-11-12-13-14
21-22-24-26-27

Vehicle damage conversion
D6 result : --1-----2-------3----4---5------6
D10 result:(1-2)-(3-4)-(5-6)-7-(8-9)-10

As for a couple of quick d6-d10 conversions and mathhammer comparisons:
Space Marine: St: 12 To:7 I:4 WS:4 BS:7 SV:7 Ld: 72%
Imperial Guard: St:10 To:5 I:3 WS:3 BS:5 Sv:3 Ld: 58%
Lasgun: Rng: 24" St:10 AP:-
Bolter: Rng:24" St:12 AP:3
Heavy Bolter: Rng:36" St:13 AP:4

10 IG Lasguns firing on Imperial Guard:
d6 result: 1.666 casualties vs d10 result: 1.75 casualties
10 IG Lasguns firing on Space Marine:
d6 result: .555 casualties vs d10 result: .45 casualties
10 SM Bolters firing on Imperial Guard:
d6 result: 4.444 casualties vs d10 result: 4.9 casualties
10 SM Bolters firing on Space Marine:
d6 result: 1.111 casualties vs d10 result: 1.05 casualties
10 IG Heavy Bolters firing on Imperial Guard:
d6 result: 12.5 casualties vs d10 result: 12 casualties
10 IG Heavy Bolters firing on Space Marine:
d6 result: 3.333 casualties vs d10 result: 2.7 casualties

As you can see, for the most part, things stay pretty close after the conversion. My next project is to start converting over each army's stats for use with d10s, then we can go about re-balancing them between their fluff and game play without worrying about 1 point of any stat throwing a unit way off balance in any regard. Still, I'm beginning to think that even a d10 won't allow enough "wiggle room" to afford proper game balance, but outside of going to d12 or d20 I really don't see any answers forthcoming.. Unfortunately, the heavy bolter's d10 conversion loses some bite(almost 20% of it's effectiveness against MEQ's), after some play testing I may decide to bump it up to strength 14 to overcome this
Comments and criticism is welcome, and if anyone gets a chance to properly play test this set up, let me know..

Looks like a good starting point. The thing that I like about the prospect of a d10 (or d12) system is that it allows more differentation between units and equipment. Currently the difference between BS3 and BS4 is huge, but the difference between those stats in a d10 system would be significantly less and would allow for more variation of units.

I don't see the point... why fix something that's not broken?

Maybe he's in the pocket of the d10 manufacturer's cabal?

DeathGod wrote:I don't see the point... why fix something that's not broken?

Because it allows a larger set of random numbers to be generated, therefore allowing for more variety in units. Imagine for a second if 40k was played with a flipped coin ( a d2 if you will). Your only options for success or failure would be never succeeds ( 3 or more on a d2, or neither heads nor tails succeed), succeeds half the time ( a 2 or higher on a d2 or heads wins tails loses ), or always succeeds ( a 1 or higher on a d2 or heads/tails both win ). At that point there would only be three units in the game: 1. weak units that can only destroy each other or medium units upon applying modifiers 2. Medium units ( Guard, marines, tau fire warriors, etc.) 3. Strong units ( daemons and the like).

Not fun to me.

One reason I like the GURPS RPG system is that it uses a 3d6 roll. That means that you can have lots of small differences in skills ( more depth and more options ), and you end up with non linear results ( I don't know if I'm using the correct word there, basically I mean a 7+ would be better than a 10+, but a 4+ would be many times better than a 7+)

Given that we don't use the full range of d6, going to a similarly restricted range of d10 won't solve anything. That is, most 40k rolls are 3+, 4+, or 5+ out of d6. That's a +/- 15% range equivalent to a 4+ to 7+ on a d10. Gaining one extra step in the usable range isn't worth the hassle.

The main feature of 40k is to roll lots of dice in succession. This produces a nice normal probability curve that allows for a wide variation in net results. Going to d10 won't fix that.

For all intents and purposes, we would do just as well to move to a d2 (with integrated re-rolls), making things even simpler:
0 - automatic fail
1 - poor = re-roll pass
2 - normal = no re-roll
3 - good = re-roll fail
4 - automatic pass

The real reasons I'm doing it are for "sh!ts and giggles" and to give my noodle something to work on instead of having to focus on how monotonous my job really is. There are good arguments both for and against going to a die system that offers a less segmented spectrum.
Right now, the d10 idea is more or less a stepping stone. I'd like to use whatever I learn from this experiment to try and develop a system with near to the same results as current 40k but with only one roll per attack being needed. This one roll would ideally include to-hit, to-wound and armor/cover/invulnerability saves. The likelihood of that is pretty slim in my opinion though..

Anyways, first up on the chopping block, chosen purely by their popularity are the ever present Space Marines:

Unit Stats:
Space Marine Scouts:
St:12 To:7 I:4 WS: 4 BS:7 Sv: 5 Ld: 72%
Space Marine:
St:12 To:7 I:4 WS: 4 BS:7 Sv: 7 Ld: 72% (Veteran Ld: 83%)
Terminator:
St:12 To:7 I:4 WS: 4 BS:7 Sv: 8 Ld: 83%
Bikers:
St:12 To:8 I:4 WS: 4 BS:7 Sv: 7 Ld: 72% (Veteran Ld: 83%)
HQ's have WS: 5 and those who normally have Ld: 10 have Ld: 92%

Weapons:
Shotgun: St: 10 AP: - St: 12 AP: - for manstoppers
Storm Bolter/Bolter/Bolt Pistol: St: 12 AP: 3
Flamer: St: 12 AP: 3
Heavy Bolter: St:13 AP: 5 (sidenote: playtesting may reveal St: 14 would better represent St:13 weapons)
Heavy Flamer: St:13 AP: 5
Deathwind: St: 13 AP: 2
Typhoon: St: 13 AP: 3
Whirlwind missiles: St:13 AP: 5
Assault Cannon: St: 15 AP: 5 (sidenote: playtesting may reveal that once d6 St: 5 weapons are converted to St: 14, assault cannon may need adjustment in some form)
Auto Cannon: St: 17 AP: 5
Plasmagun/Pistol/Cannon: St: 17 AP: 8
Missile Launcher: (frag) St: 12 AP: 2
Missile Launcher: (krak) St: 18 AP:7
Multi-melta/Meltagun: St: 18 AP: 10
Lascannon: St: 20 AP: 8
Demolisher: St: 22 AP: 8

Powerfists increase Space Marine Strength to 18.

Vehicle Armor:
Dreadnought: 24/24/21
Land Raider: 27/27/27
Land Speeder: 21/21/21
Predator: 26/22/21
Razorback: 22/22/21
Rhino: 22/22/21
Vindicator: 26/22/21
Whirlwind: 22/22/21

Anyone who likes the idea of this gameplay system please playtest these modified rules and let me know either on this thread or in a PM how accurately this system still represents the normal d6 version of 40k. Then, after I get a few playtests myself I'll post a slightly modified fluffier version.

Something I'd suggest is heading over to Warseer and checking out their Rules Development Forum. Someone posts a d10 40k project their every other month or so, essentially whenever the last attempt dies of apathy and sinks out of sight on the first page.

Everyone seems to be missing the obvious next logical step, D8's. D10's are far too unwieldy for 40k. D8's are the future!

I'm all for D12's for deviation instead of those poxy scatter dice.

Actually, in a sheer stroke of genius, I found an amazing way to combine both the to-wound and the to-hit rolls into one D20 roll using my current modified stat system. It just takes a player's willingness to do a wee bit of math before hand. Although, if I get bored enough I could probably come up with a cheater chart..
Simply multiply the chance to hit by the chance to wound, round that number to the nearest .05 then multiply it by 20. That's the number you need to meet or come under on 1 D20. For example: BS:7 St:14 shot against To: 7 target. That's 7/10= (.7) chance to-hit times (14-7)/10=7/10=.7.
.7*.7=.49
.49~.5
.5*20= 10
Now, the only problem is that, unless you have a lot of D&D fans for friends, where are you going to find a large supply of D20's to play this way with?

The main issue I've run into with this project is that the more you try to simplify the number of rolls the more complicated everything outside of the dice becomes and the more you try to slim down the outside stuff the more rolls you end up with

themandudeperson wrote: Actually, in a sheer stroke of genius, I found an amazing way to combine both the to-wound and the to-hit rolls into one D20 roll using my current modified stat system. It just takes a player's willingness to do a wee bit of math before hand. Although, if I get bored enough I could probably come up with a cheater chart..
Simply multiply the chance to hit by the chance to wound, round that number to the nearest .05 then multiply it by 20. That's the number you need to meet or come under on 1 D20. For example: BS:7 St:14 shot against To: 7 target. That's 7/10= (.7) chance to-hit times (14-7)/10=7/10=.7.
.7*.7=.49
.49~.5
.5*20= 10
Now, the only problem is that, unless you have a lot of D&D fans for friends, where are you going to find a large supply of D20's to play this way with?

The main issue I've run into with this project is that the more you try to simplify the number of rolls the more complicated everything outside of the dice becomes and the more you try to slim down the outside stuff the more rolls you end up with

Apparently GW believes the averge 40k player can't do simple math or will lose patience with it so nix that one, at least officially

The very small gaming group i am in have started to hash about with the dark heresy rules for the table top, it does make things alot more drawn out but the D10 % system in allows for much cooler distinction between units and stats.

Suppose i will post it on here when we have hashed things out a little better

Anyways, I've finally got off my arse and got to number crunching. To use the D20 1 roll with my D10 idea, use the first chart. Otherwise, use the second one. Remember, the Strength column is the difference between the attack's strength and the target's toughness
D10:
BS------1--2--3--4--5--6--7--8----9-9/5-9/7
ST+1 | 1--1--1--1--1--1--1--2---2---2---2
ST+2 | 1--1--1--2--2--2--3--3---4---4---4
ST+3 | 1--1--2--2--3--4--4--5---5---6---6
ST+4 | 1--2--2--3--4--5--6--6---7---8---8
ST+5 | 1--2--3--4--5--6--7--8---9--10--10
ST+6 | 1--2--4--5--6--7--8--10-11-12-12
ST+7 | 1--3--4--6--7--8--10-11-13-14-14
ST+8 | 2--3--5--6--8--10-11-13-14-16-16
ST+9 | 2--4--5--7--9--11-13-14-16-17-18

D6:
BS----1--2--3--4--5---6---7---8----9-10
ST-3|-1--1--2--2--3---3--3---3----3--3
ST-2|-1--1--2--2--3---3--3---3----3--3
ST-1|-1--2--3--4--6---6--6---6----6--6
ST-0|-2--3--5--7--8---9--9---9---10-10
ST+1|-2--4--7--9-11-12-12-12-13-13
ST+2|-3--6--8-11-14-14-15-15-16-16

Warlord is based on a D10 system, and it was one of the things I liked the most about it.