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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons, particularly in larger calibres (12.7+mm).

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continuous recoil vs short/long recoil   Small Arms <20mm

Started 15-Aug by graylion; 1510 views.
graylion

From: graylion

15-Aug

I have recently found out about the 'continuous recoil' mechanism as used in the Stoner / Utimax / Knight LMGs. It looks to me like it achieves the same thing as the "short recoil" mechanism of the LWMMG and most of the proposed MGs/ARs of the NGSW programme with less moving parts.

What do people think? And why has this not been more widely adopted? Not least for SMGs?

(I'll admit to watching InRangeTV)

Red7272

From: Red7272

15-Aug

graylion said:

I have recently found out about the 'continuous recoil' mechanism as used in the Stoner / Utimax / Knight LMGs. It looks to me like it achieves the same thing as the "short recoil" mechanism of the LWMMG and most of the proposed MGs/ARs of the NGSW programme with less moving parts.

Well there is obviously something wrong with it if it is not widely adopted. I would guess reliability would suffer with all the slow moving bits and the distance traveled. 

QuintusO

From: QuintusO

15-Aug

Constant recoil definitely works, both as in it functions, and it does reduce felt recoil. However, with weapons that have a very high ammunition power to receiver mass ratio, constant recoil would require an extremely long receiver to absorb all of the recoil energy produced by such a relatively powerful round. The advantage of soft recoil systems like the GDOTS .338 LWMMG is that it is able to use the mass of the entire barrel plus the operating group to slow down the recoil sink, and the spring constants of the action and the recoil sink are decoupled.

graylion

From: graylion

15-Aug

Not necessarily. Military conservatism can play a major role. And it looks like there were reliability issues, not least due to unrealistic test parameters, but I wonder whether anybody knows more?

https://en.wikipedia.org/wiki/Stoner_63#Trials talks a little bit about the reliability issues. The Ultimax 100 OTOH seems to be very reliable.  https://en.wikipedia.org/wiki/Ultimax_100

My gut feeling would be that the Stoner 63 has poisoned the well for constant recoil in the US Armed Forces for the foreseeable future.

graylion

From: graylion

15-Aug

Knight seem to have made it work in 7.62 NATO, which supposedly is similar in power to the new 6.8mm ammo. I can see the law of diminishing returns rear its ugly head though. I wonder how reliability and field maintenance compare?

Also how about SMGs? It's gotta be handier than the Kriss mechanism, I think/hope

Edit: SMGs are probably better with balanced recoil

  • Edited 16 August 2020 0:04  by  graylion
QuintusO

From: QuintusO

16-Aug

The Stoner 63 is not a constant recoil gun. The Stoner 86 is, but that's a completely different design (and much later).

QuintusO

From: QuintusO

16-Aug

The number of people who've shot the 7.62 LAMG could possibly be in the single digits, so "work" is a strong word for what we know about it. We don't know anything about its recoil characteristics, whereas I can tell you what the math says and I can tell you for myself that the Ultimax 100 works.

autogun

From: autogun

16-Aug

QuintusO said:

The advantage of soft recoil systems like the GDOTS .338 LWMMG is that it is able to use the mass of the entire barrel plus the operating group to slow down the recoil sink,

Yes, this system is very common in post-WW2 AA cannon of 20+mm (some pre-WW2 systems had it also). It is clearly very effective. The main problem is that the "ready to fire" position has the gun action and barrel held to the rear, so when the trigger is pressed the action+barrel start to move forwards, accelerating all of the time, while a round is chambered and the breech is locked, and only fires the instant before the mechanism returns to battery. This very long lock time is not conducive to accuracy, especially not in hand-held/shoulder-supported weapons like ARs and LMGs.

gatnerd

From: gatnerd

16-Aug

graylion said:

I have recently found out about the 'continuous recoil' mechanism as used in the Stoner / Utimax / Knight LMGs. It looks to me like it achieves the same thing as the "short recoil" mechanism of the LWMMG and most of the proposed MGs/ARs of the NGSW programme with less moving parts. What do people think? And why has this not been more widely adopted? Not least for SMGs?

There's really no reliability disadvantage - the system is essentially just a lengthened receiver, that allows the bolt to recoil 2-3" beyond where it would normally. This extra distance allows the recoil spring to slow down and then stop the bolt prior to the bolt impacting the rear of receiver, which eliminates the 10-15 bolt impacts per second that makes firing a machine gun so jarring.

If anything, such a system should be more reliable; on the foreward bolt stroke, the spring will be at ~125% power vs where it began when engaged by the sear. In reverse, the extra travel distance allowed by the lengthened receiver can allow the gun to be 'overgassed' (within reason) without adversely effecting recoil or rate of fire. 

As to why we haven't seen this awesome design used more widely:

-There have been relatively few new 5.56 LMG's produced since the M249 and its subsequent dominance of the international market. As such, there has been little market to pursue for a new, ultra low recoil 5.56 LMG.

-The assault rifle market has become completely dominated by the AR15/M16, which cannot use a true constant recoil system, and those that are not AR15 derrivatives are mainly bullpups, whose design would make any lengthening of the receiver problematic, as this would increase both weapon length and exacerbate the already long length of pull. 

Further, the Western World seems to have largely relegated FA use from Assault Rifles to a rarity. As such, it has de-emphasized FA controllability; most don't even use simple muzzle compensators, much less a purpose built weapon optimized for FA control. 

The result is that weapons producers have not focussed on improving FA controllability, as this is not seen to be sufficiently marketable to be worth the R&D.

- Modern SMG's are in decline, and the market for them is dominated by compact /sub compact SMG's. As such, a weapon design that would add 2-3" OAL to a SMG is not seen as worth it for the increased controllability. 

-The weapons most in need of recoil control - 7.62/6.8 etc - are also the ones that pose the biggest challenge for constant recoil. The more powerful the cartridge, the longer the receiver over travel is needed to employ a Constant Recoil system. 

For example, the Knights 6.5 AMG appears to have 6-7" of receiver beyond the pistol grip:

https://soldiersystems.net/wp-content/uploads/2018/10/EA094AFD-7EE6-4254-A569-9BA6B1139CB1.jpeg

Whereas the 6.5 MK48 has ~1.5-2" of receiver beyond the pistol grip:

https://vavqj34csem437aom2bekqda-wpengine.netdna-ssl.com/wp-content/uploads/2019/05/FNA18_022495_FN_MK48_mod2_G7C1_300_SM-1200x382.png

This is not a deal killing problem, but would require a much shorter stock then currently employed on the Knights AMG to reduce length of pull, and also limits overall compactness should a folding stock be desired. I think those tradeoffs are worth it, but others might not agree. 

mpopenker

From: mpopenker

16-Aug

in Russian trials soft  recoul systems (like an Ultimax) for assault rifles were routinely found to be less reliable under harsh conditions (no oil / frozen oil / dirt) than standard "hard impact" systems. They also require longer and thus heavier receivers.

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