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Rimfire As "serious" Cartridge Revisited. Pure Theory And Speculation Galore :)

rimfire LSAT theory

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#1 Blunt Eversmoke

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Posted 22 July 2017 - 0233 AM

Good time of day, y'all!

 

I'd like to hereby open a rant'n'rave topic concerning rimfire cartridges as a weight-saving measure compared to centerfire ammo, as kind of an alternative to the LSAT program with (probably) lower development cost and weapons of more conventional setup.

I estimate the weight difference due to  to be around 30 % due to the thin cartridge base of a rimfire (on a centerfire, it weighs a lot), but I could be wrong.

Feel free to carry together your thoughts as to why such a thing could or could not work, as well as what could be done to make it work.

 

Some things to think about, pro:

 

 

In the past, rimfire ammo was made in calibers up to .50 ballpark, the .44 Henry being a prominent example.

 

.17 HMR is a rimfire cartridge that pushes its pills at a speed of around 3000 fps, so speed which is very important today seems to be doable with a rimfire; if heavy projectiles that seem to excite all the general purpose cartridge proponents are used along with docile powders and long barrels to make full use of these, it would keep the pressure down.

 

For military, lower weight means lower log cost, also, the grunts would be happy.

 

Rimfire tech is well-known, so quicker and cheaper development than for LSAT and little if any development of the weapons firing the rounds.

 

Lead-free priming compounds seem to be possible today.

 

 

 

 

 

Some things to think about, contra:

 

Priming is less reliable on current rimfires compared to centerfires.

Extraction tends to be less reliable. Both things are a liability, but with a bigger cartridge base diameter, may it be you'd profit from positive scaling effect?

 

Rimfire, nomen est omen, necessitates a rim that is a bad thing to have on a mag-fed firearm - although this seems to be the smallest problem, as seen on a galore of mag-fed rimfire weapons, mag capacity ranging from five to hundreds (for the American 180).

 

According to Wiki (yes, I know... But proper info on anything rimfire seems to be so arcane for some reason...), priming compounds for rimfires need some kind of frictionator which consists, mostly of ground glass - not good for barrels, probably also not so good for the shooter if the glass particles exiting the barrel get inhaled.

 

 

 

 

So, what's the state of the art and what's in the making with rimfires?

 

 

EDIT: For clarity, i don't mean existing rimfires such as the .22 LR but rather theoretical cartridges analog to current centerfires.


Edited by Blunt Eversmoke, 22 July 2017 - 0601 AM.


#2 DougRichards

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Posted 22 July 2017 - 0316 AM

Well the 1970s-1980s PPS-50 Bingham Carbine comes to mind: .22 rimfire in a weapon based on the PPS. 

 

Conceptually based on the American 180 M-2

 

https://en.wikipedia...ki/American-180

 

Used by few:

 

The Brazilian Model 02 LAPA Carabina Automatica also used .22 rimfire.

 

All generally considered to be more of use in riot control (but may actually be 'overkill' :unsure: ) rather than as serious military weapons.



#3 Chris Werb

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Posted 22 July 2017 - 0826 AM

In the 1980s the Swedes were looking at something like the .17HMR in a combat rifle.

 

http://modernfirearm...mics-mkr-e.html

 

As to rimfires actually issued (to police and, allegedly, special forces) as combat weapons.

 

https://en.wikipedia...ki/American-180



#4 Olof Larsson

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Posted 22 July 2017 - 1119 AM

In the 1980s the Swedes were looking at something like the .17HMR in a combat rifle.

 

http://modernfirearm...mics-mkr-e.html

 

As to rimfires actually issued (to police and, allegedly, special forces) as combat weapons.

 

https://en.wikipedia...ki/American-180

 

Well. Not the swedes (the Swedish army was busy looking for a 5,56x45 assault rifle during that time), but Georg Kellgren (of later Intratec, Grendel and Kel-Tec fame) at Interdynamic.

The most succesful design that he came up with there, was the Interdynamic MP-9, that he later developed into the Intratec TEC-9 after moving to the US.



#5 Chris Werb

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Posted 22 July 2017 - 1314 PM

 

.17 HMR is a rimfire cartridge that pushes its pills at a speed of around 3000 fps, 

 

About 2550 fps out of a rifle with 17 grainers. Still respectable and mustard on anything rabbit-sized out to about 180 metres IME.



#6 shep854

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Posted 23 July 2017 - 1830 PM

The .22 magnum is considered by some to be close to the 5.7 of the FN P90 PDW.



#7 Simon Tan

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Posted 24 July 2017 - 0150 AM

No.



#8 EvanDP

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Posted 24 July 2017 - 1655 PM

I would put .17 WSM as the closest rimfire to PDW rounds.

 

https://en.wikipedia...er_Super_Magnum



#9 Blunt Eversmoke

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Posted 25 July 2017 - 0158 AM

...And those modern little scorpion-pepper fast rounds, WSM and HMR, are the reason for my question if one could just, y'know, kinda scale them up :)



#10 Simon Tan

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Posted 25 July 2017 - 0246 AM

MP7 ammo. Erosion blablabla. No.



#11 Blunt Eversmoke

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Posted 25 July 2017 - 0651 AM

MP7 ammo. Erosion blablabla. No.

Erosion - why exactly? Due to small caliber, due to too high pressure? (Just to clarify again, I am not advocating use of really small calibres, scaling up would mean scaling up the caliber as well, to something like 6 mm or so...)



#12 toysoldier

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Posted 25 July 2017 - 0859 AM

If they can bother to try and make rim-fire work, IMHO they could go the whole mile and try caseless ammo.



#13 GregShaw

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Posted 25 July 2017 - 1106 AM

In addition to feed complications due to the rims, rimfires can't handle rifle pressures. The .17 WSM is the highest pressure rimfire I know of, at about 33,000 psi a bit less than high pressure handgun cartridges, and about 30,000 psi less than 5.56. The high velocity .17 WSM is also about 500-600 fps less than the mild .17 Hornet, 1000 fps less than the .17 Remington Fireball and 1500 fps below the .17 Remington. Scaled up to 6 or 6.5 mm and velocity will drop below 2000 fps, go with a bigger case for capacity and you lose any advantage in cost/materials over centerfire, and the pressure difference means it will never be as efficient as a centerfire.



#14 Blunt Eversmoke

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Posted 25 July 2017 - 1225 PM

Well, that's pretty much a diagnose. Thanks to all participating! :)



#15 TTK Ciar

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Posted 25 July 2017 - 1514 PM

What about pinfire?

It came up last year as a (only half-serious) dodge around California's SB880 ban, which specifies centerfires.

The main problem I see with it is feeding, since the orientation of the pin must be precise.

Since you're drilling a hole through the side of the cartridge, it should permit use of arbitrarily thick case walls.

#16 bojan

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Posted 25 July 2017 - 1637 PM

What about pinfire?
 

They were known for leaking gasses along pin even with 19th century BP generated pressures.



#17 TTK Ciar

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Posted 25 July 2017 - 1824 PM

Perhaps you could seal the pinhole around the pin and detonate the primer electrically instead of mechanically?

This fellow did something similar with a caseless powder approach, but since the electrode was exposed to the chamber it broke after moderate use (first the alumina collar, then the electrode itself):

http://www.ctmuzzlel...electricml.html

http://www.ctmuzzlel...plink_king.html

If the combustion gasses were instead contained in the case, and the electrode detonated a primer (instead of the propellant) via an intermediate pin, it might require less power and inflict less wear on the electrode.

#18 GregShaw

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Posted 25 July 2017 - 1907 PM

Why bother with the pin at all if you're going to electrically ignite it? I like the idea of electrically primed, 0 lock time, when the front site is wandering from 7 ring to 7 ring in offhand I want it to go off right now when I see it in the middle of the black. That's my excuse for those wide 7s and I'm sticking to it.



#19 TTK Ciar

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Posted 25 July 2017 - 2012 PM

Why bother with the pin at all if you're going to electrically ignite it?


To isolate the electrode from the combustion gasses, and avoid the electrode wear problem that guy had with his "Plink King".

I suppose there's no reason the pin couldn't be very short and coming out the back of the cartridge instead of the side, though, as long as it wasn't centered. A wide enough electrode would make the exact orientation of the cartridge irrelevant.

I like the idea of electrically primed, 0 lock time


That could be an advantage, yeah. Hadn't thought of it.

#20 GregShaw

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Posted 25 July 2017 - 2057 PM

Just go with a conventional primer pocket, electrically ignited primer and electrode just contacts it, trigger completes the circuit and bang. No worry about gas erosion, I remember seeing a commercial varmint rifle with that sort of system in a gun rag sometimes in the 80s. A quick google search found a Remington 700 from the 2000s as well;

 

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