Gear Rifles - design assistance requested

[Varyon]

Originally Posted by Anthony

If it's expressed in units of force it's almost certainly in error, the peak instantaneous force for a .223 rifle is in excess of 2,000 lb and that's a relatively low recoil rifle. I suspect the sources you were looking at were actually giving foot-pounds, which is a unit of energy.

I think I may have jumbled some of the sources I was checking together; the less-reliable ones talked about pounds, but the one I was remembering with the note of most service rifles being around 15 was indeed talking about foot-pounds, which simplifies matters. Rereading that one, I'm considering that perhaps the maximum recoil before you start suffering penalties* is more around 3/4*BL in ft-lb for a rifle (so 15 ft-lb for a character with ST 10 and thus BL 20). I'm fairly confident this is going to mean the weight of the weapon will be the limiting factor for most gear rifles - I think I worked out my reference weapon would be roughly 5 lbs (assuming twice the weight of a comparable firearm), so 251 J - 185 ft-lb - in a 0.1 lb bullet corresponds to a mere 3.7 ft-lb recoil for a 5 lb rifle.
(EDIT: Actually, now that I look at it, if I use BL for weight and 3/4*BL for recoil, those two call for the same ST - ST 5 gives BL 5, and 3/4 of that is 3.75)

It seems like the gear rifle would have an odd recoil profile, although I could be mistaken, but I don't think this would really have a detrimental effect (should just be part of Familiarity). Basically, you get traditional rearward recoil from the piston being pushed forward and the bullet being propelled, but you'd also have some forward recoil when the piston gets arrested upon striking. For most rifles, I think the piston slamming into its base is probably the noisiest part of "firing" the weapon - although my spreadsheets do indicate that pi- (5 mm) rifles break the sound barrier at around ST 17, pi (10 mm) rifles do so around ST 27, pi+ (15 mm) rifles do so around ST 37, and pi++ (20 mm) rifles do so around ST 47. This would technically require the compressed air to get rather hot, so that the speed of sound in the air increases... but this is a modified fire piston, so I'm alright with that, even if it isn't strictly realistic.

*Realistically, above a certain threshold, I think it's more that you can manage some number of shots before the soreness starts damaging your accuracy, but for GURPS purposes, a set cut-off works best.

[Anaraxes]

Originally Posted by Varyon

would it be feasible that a vibrating gear rifle - say, because the gears aren't quite properly well-aligned - could impart spin to the projectile?

One option I forgot to list in the gauss rifle thread that seems steampunky would be the method famously used in the Whitworth rifles (both small arms and cannon) in the late 19th century (American Civil War era, though Whitworth was English). Hexagonal barrel with a hexagonal projectile to match. (The small arms had hexagonal cross sections; the cannons had projectiles that were also twisted, so they look spiral-shaped.) The orientation of the hexagon rotates down the barrel. So, no grooved rifling that bites into the bullet; instead, the has flat surfaces that match the barrel all the way around, rotating as it moves down the barrel because the barrel itself twists. Your plan started with an elongated bore to have room for the chains; rotate that all the way down the barrel.

The Whitworth small rifles would also fire cylindrical bullets if they were made of soft lead. Polygonal rifling without the fancy ammo has been used in a lot of weapons, including fairly modern ones.

Anecdotes say that the Whitworth cannon projectiles made a distinctive and peculiar screech as they flew through the air, which also might be an appealing detail just for color.

[Varyon]

Originally Posted by Anaraxes

One option I forgot to list in the gauss rifle thread that seems steampunky would be the method famously used in the Whitworth rifles (both small arms and cannon) in the late 19th century (American Civil War era, though Whitworth was English). Hexagonal barrel with a hexagonal projectile to match. (The small arms had hexagonal cross sections; the cannons had projectiles that were also twisted, so they look spiral-shaped.) The orientation of the hexagon rotates down the barrel. So, no grooved rifling that bites into the bullet; instead, the has flat surfaces that match the barrel all the way around, rotating as it moves down the barrel because the barrel itself twists. Your plan started with an elongated bore to have room for the chains; rotate that all the way down the barrel.

The Whitworth small rifles would also fire cylindrical bullets if they were made of soft lead. Polygonal rifling without the fancy ammo has been used in a lot of weapons, including fairly modern ones.

Anecdotes say that the Whitworth cannon projectiles made a distinctive and peculiar screech as they flew through the air, which also might be an appealing detail just for color.

ACW-era is a bit late for what I have in mind, but those do sound pretty awesome. I was considering smoothbore longarms (powder or piston driven) to have Acc 2 (pistols would have Acc 1), while rifled ones would have Acc 3 (pistols would have Acc 2), with double barrel cost (I separate the cost of the barrel, the breach, and the stock for firearms; for gear rifles, the piston mechanism and battery would also have separate costs). The Wikipedia entry on the Whitworth notes it had increased accuracy but was around 4x the cost of a Lee-Enfield. I'm thinking such hexagonal barrels may well be available; they'd increase Acc by a further +2 for longarms, or +1 for pistols, with the option in either case to get another +1 by using special expanding ammunition (like the soft lead bullets of the Whitworth, which had a Minie-style expansion when fired); barrel cost would be x10 compared to smoothbore (x5 compared to rifled), and the special ammunition would be +2 CF. This is in addition to the options to make the weapon Fine (Accurate) for +0.75 CF and +1 Acc, or make the ammunition Balanced for +4 CF and +1 Acc (a dedicated marksman's rifle would have a hexagonal barrel, be Fine (Accurate), and use Minie-style, Balanced bullets, for a grand total of Acc 8 - on par with a modern sniper rifle firing match-grade ammo, which is pretty ridiculous but... whatever, it works).

[johndallman]

Originally Posted by Varyon

The Wikipedia entry on the Whitworth notes it had increased accuracy but was around 4x the cost of a Lee-Enfield.

The comparison is with an Enfield, formally a Pattern 1853 Enfield. The Lee-Enfield didn't come along until 1895.

[Varyon]

Originally Posted by johndallman

The comparison is with an Enfield, formally a Pattern 1853 Enfield. The Lee-Enfield didn't come along until 1895.

Ah, thanks. It seemed too early for the Lee-Enfield, but I thought maybe it was just that there were a lot of rifles that were given that name; guess my mind just threw the "Lee-" onto it.

[sir_pudding]

I used something similar, specifically orichalcum spring gun, in Desolation Road. Rather than rifling I assumed finned bolts.

I also had advanced Wheelock revolvers called "clocklocks" and resonating crystal alchemical "blasting rods".

[Varyon]

My current inclination, with regards to MinST, is to say that rifles and the like use BL/2 (so a 15 ft-lb rifle actually calls for someone with BL 30, or around ST 12... which is honestly probably appropriate for modern infantry), while pistols and the like use BL/4; using a pistol two-handed, or firing a rifle without the stock, would probably use BL/3, while firing a rifle with a bipod or similar would use BL. That's for sustained use - you can fire a much heavier weapon, up to twice the above (BL, BL/2, 2/3*BL, and 2*BL, respectively), but you must pay 1 FP per shot to do so. Does this sound feasible? Again, you'd use the higher MinST between weapon weight (up to BL lb for rifles, up to BL/2 lb for pistols; weapons using bipods and the like probably 2*BL) and recoil energy. I feel the former would use Lifting ST, while the latter would use Striking ST, but I could be mistaken (if the character has different Lifting ST and Striking ST, his/her Lifting ST must meet the weight requirement, while his/her Striking ST must meet the recoil energy requirement).

[Rupert]

Originally Posted by Varyon

I'd rather have independent shots than something that just flings metal downrange for a bit after pulling the trigger (also, I don't think my cup idea would be compatible, here). A magazine could well be an option for the default version of the weapon, although given the way it would generally need to be set up, it would interfere with aiming (although a bottom-mounted magazine, using springs or a manually-operated lever to push bullets up into the cup like a modern firearm rather than gravity to drop them down like a repeating crossbow, might be doable; it would absolutely require a dedicated weapon, or at least modifying a normal gear rifle).

A top-mounted magazine need not interfere with the sights - both the Bren Gun and the Owen Submachinegun had top-mounted magazines and sights (the sights are off-set to one side). What it does do is stop you aiming the weapon 'wrong handed'.