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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.

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FN SCAR Mk 2 and Evolys   Small Arms <20mm

Started 14/4/22 by Guardsman26; 8330 views.
smg762

From: smg762

16/4/22

with 7.62 SAWs that are as light as an SA80....what would the recoil be like on full auto?

In reply toRe: msg 6
Guardsman26

From: Guardsman26

16/4/22

7.62 mm Evolys has a hydraulic buffer, so recoil is mitigated 

In reply toRe: msg 6
nincomp

From: nincomp

16/4/22

SMG, it depends a lot on the nature of the recoil.  The total force depends solely on the cartridge and firing rate.  When that is smoothed out correctly, the shooter mainly feels a continual push rather than the rapid pulsing of the bolt carrier slamming into the receiver.

In this video, Ian talks about the Knight's 7.62x51 Assault Machinegun which he says weighs about 14 pounds (6.35kg), essentially the same as the Evolys (depending upon who is fibbing more about the weight).

https://youtu.be/6hsOrULshco?t=515

  • Edited 16 April 2022 11:49  by  nincomp
In reply toRe: msg 6
EmericD

From: EmericD

16/4/22

smg762 said:

with 7.62 SAWs that are as light as an SA80....what would the recoil be like on full auto?

I had the opportunity to shoot the Evolys in 5.56 mm and 7.62 mm, and the recoil was very, very smooth (and I'm only 5'7" & 150 lbs).

To the point that one of the senior officer shooting the Evolys told us "the 7.62 mm is so light & easy to shoot, why do we need a 5.56 mm?"

mpopenker

From: mpopenker

16/4/22

So, the soft recoil, basically, means that the forward bolt stroke starts from the zero initial velocity, and thus the power reserve to feed the cartridge under less than ideal conditions (such as increased internal friction due to ingress of dirt, sand, lack of lubrication etc) is minimal. Or am i wrong here?

RovingPedant

From: RovingPedant

16/4/22

mpopenker said...

the soft recoil, basically, means that the forward bolt stroke starts from the zero initial velocity,

I would expect that the forward bolt stroke starts with zero initial velocity on every machine gun ever made. Did you mean zero spring load?

As far as I understand it, the bulk of felt recoil comes from impact with the buffer at the end of bolt travel, which is essentially a very much stiffer spring than the return spring. Using a hydraulic buffer ought to mean that you have put a damper into the system so the resistance from that element is based on velocity rather than position like it would be with a spring. As such you can apply it in parallel to the return spring without running the risk of stopping the bolt short, provided it's tuned right. So the bolt could have a preload from the spring at the point where it is held by the sear and consequently have enough power in the spring to feed cartridges even when fouled.

mpopenker

From: mpopenker

16/4/22

RovingPedant said:

I would expect that the forward bolt stroke starts with zero initial velocity on every machine gun ever made. Did you mean zero spring load?

Not necessarily

When bolt group bottoms up the spring and hits the rear of the receiver, it is usually an elastic impact, and bolt group receives some of its remaining recoil energy back, to start with some initial velocity (imagine a steel ball falling on a steel plate and bouncing back)

Hydraulic or friction buffer (as opposed to the spring buffer) eats up (dissipates) most of its excessive energy, so the return spring starts the bolt group back from the zero, or close to that. Only the power stored in the return spring is available to operate the feed, lock and fire cycle.

For example, in a typical Kalashnikov AK assault rifle bolt group rebounds back from the rear trunnion at the initial velocity of 3-4 m/s under normal conditions, adding some significant surplus KE to the amount of energy stored in the return spring. This is one of the reasons why AKs are so reliable, but also results in an 'excessive' felt recoil. TANSTAAFL.

RovingPedant

From: RovingPedant

16/4/22

mpopenker said...

Not necessarily

When bolt group bottoms up the spring and hits the rear of the receiver, it is usually an elastic impact, and bolt group receives some of its remaining recoil energy back, to start with some initial velocity (imagine a steel ball falling on a steel plate and bouncing back)

 

This is something that would happen under automatic fire only? Otherwise it will be stopped by the sear?

mpopenker said...

Hydraulic or friction buffer (as opposed to the spring buffer) eats up (dissipates) most of its excessive energy, so the return spring starts the bolt group back from the zero, or close to that. Only the power stored in the return spring is available to operate the feed, lock and fire cycle.

Which would be true when the bolt is held by the trigger/sear arrangement, wouldn't it?

 

stancrist

From: stancrist

16/4/22

mpopenker said:

       RovingPedant said: I would expect that the forward bolt stroke starts with zero initial velocity on every machine gun ever made. Did you mean zero spring load?

Not necessarily When bolt group bottoms up the spring and hits the rear of the receiver, it is usually an elastic impact, and bolt group receives some of its remaining recoil energy back, to start with some initial velocity (imagine a steel ball falling on a steel plate and bouncing back)

A steel ball falling on a steel plate reaches a velocity of zero before bouncing back.  The same is true of a machine gun bolt.  Initial velocity is zero.

EmericD

From: EmericD

16/4/22

mpopenker said:

For example, in a typical Kalashnikov AK assault rifle bolt group rebounds back from the rear trunnion at the initial velocity of 3-4 m/s under normal conditions, adding some significant surplus KE to the amount of energy stored in the return spring. This is one of the reasons why AKs are so reliable, but also results in an 'excessive' felt recoil. TANSTAAFL.

The AK is firing from a closed bolt, while nearly all MGs (and the Evolys in particular) are firing from an open bolt (but you already know that). That means that the first round is always fired with zero bolt initial velocity and the return spring should be designed with this point in mind.

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