Does the SCAR16 have any advantages over the AR15 when it comes to using larger diameter, more powerful cartridges like the 6mm ACR or are the limitations posed by the dimensions of the magazine well and strength of the bolt/barrel extension about the same?  I vaguely recall a multi-caliber SCAR, but I think it was based on the larger SCAR17.  Is that correct?

These questions are related to an earlier discussion about the potential development of something along the lines of a "NGSW-lite" cartridge somewhere between the existing 5.56x45 and the proposed 6.8mm ones.

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

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

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

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?"

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?

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.

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.

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?

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.