DD 16” midlength gassing

[georgeib]

Kinetic energy is certainly lower for a heavier BCG/Buffer because velocity affects the calculation far more than mass and a heavier BCG/Buffer must travel slower. Momentum should be the same (or very close).

The main take-away for me personally is that the BCG and buffer mass have less effect on the system than I believed.

Andy

We know that the amount of energy/force doesn't change appreciably, but as you said, the velocity must indeed be slowed in order for the force to remain the same (or essentially the same). Doesn't this mean that carrier velocity is then noticeably reduced, increasing lock time?

[Curlew]

Kinetic energy is certainly lower for a heavier BCG/Buffer because velocity affects the calculation far more than mass and a heavier BCG/Buffer must travel slower. Momentum should be the same (or very close).

If it weren’t for the vents, I’d agree. For a given profile of pressure (and hence force) vs time, the acceleration and velocity are decreased in inverse proportion to the mass. Momentum is unchanged but kinetic energy is reduced.

But the vents change the picture because they cut off the pressure curve after the carrier has moved a fixed distance, not a fixed time. With a heavier, slower carrier/buffer, it takes longer for the vents to open, and that means the force acts over a longer interval of time. To some extent that makes up for the reduced acceleration.

With the simplest model, in which you apply a constant force over a fixed distance, it turns out that it’s the energy (rather than momentum) that’s unchanged when the mass is varied.

ETA: It’s _energy_ that matters when trying to compress a spring. So if MistWolf is correct in claiming that lock-back is independent of buffer mass, that suggests the initial kinetic energy of the carrier/buffer must also be independent of mass. If the kinetic energy were reduced by use of a heavier buffer, you’d expect to need more gas to obtain lock-back.

[win&legend]

According to Daniels tech line, most of their 14 and 16" barrels are gassed to produce a 3 o'clock ejection on full powered ammo with an H1 buffer. (standard mass carrier's run 11ish oz). Depending on your application, that may be over gassed for reliability purposes.

I have found that NiB carriers / bolts with Wilson Combat's one piece 4 coil gas rings really create 1. good gas seal to fully utilize the available gas pressure 2. significantly reduce the amount of friction buildup with fouling, so less mass and drive is actually needed to achieve the same reliability as a phosphate carrier with more mass.

I run a hybrid setup with an 8.5oz low mass carrier (NiB) and JP SCS set for H1 weight and their 85% black spring with the gassing tuned for 3 o'clock ejection. Very light and short recoil impulse, but also has been 100% reliable even when heavily fouled without cleaning. I ran 1,500 rounds before cleaning. Doing it again but only at 500 rounds on this interval.

Slightly more buffer mass gives a little extra dead blow over carbine buffer obviously. The JP SCS is another key element, because you reduce the spring friction against the buffer tube which is probably more than most people realize. This also has a small benefit on muzzle velocity as the less gas you need to run the system, the less pressure drop you get as the bullet travels down the remaining length of barrel until it exits. Not huge, but 10 to 20 FPS is still 10 to 20 FPS. Also others note far less fouling than heavily gassed systems, so in general, it stays notably cleaner for longer and is far less prone to changes in friction over that interval.

Some times more is not better for reliability. It's about efficiency. And reducing recoil is entirely about gas port pressure and reducing friction to minimize the required energy. Gas pressure is the energy transfer. Buffer masses and springs do not change recoil impulse energy, they only affect carrier speed, BCG energy storage potential when going back into battery and ultimately the shape of the recoil impulse wave form. Slower speed, you get more of a rainbow wave form, faster speed and you get more of a mountain top wave form over a shorter time interval.

If you want to actually reduce recoil, you need to reduce the source of the energy, which is at the gas pressure. Then balance the system around that energy level. I've found a short recoil impulse (2 to 3 o'clock ejection) with a lower mass / low friction system to really be the ideal balance for a fighting gun. Not sure if it would remain reliable in a sandy environment, but given I'm a civilian in the US around the Great Lakes region, not really a concern so I can reap the benefits of this system.

However I suspect it most likely would still remain reliable even in dusty conditions due to the significant reduction in friction over more common BCG configurations. Also you can always douse it with SLIP2000 or other high performance oils. Even with external fouling (dust, dirt etc.), the US Military found that more oil was still better than light or no oil, at least with phosphate carriers.

[mpom]

Interesting discussion. Also running an adjustable gas block, 100% reliability and lockback on empty even w PMC/American eagle 223. Full weight BCG but substituted aluminum weights in the A5 buffer so is it a minus something buffer?
Thinking of trying a Wolff reduced power rifle length action spring to reduce dot movement during rapid fire. $20 experiment.

Mark

[Disciple]

I run a hybrid setup with an 8.5oz low mass carrier (NiB) and JP SCS set for H1 weight and their 85% black spring with the gassing tuned for 3 o'clock ejection. Very light and short recoil impulse, but also has been 100% reliable even when heavily fouled without cleaning. I ran 1,500 rounds before cleaning. Doing it again but only at 500 rounds on this interval.

Why the reduced power spring? Any failures to strip the first round from dirty magazines?

[MistWolf]

if MistWolf is correct in claiming that lock-back is independent of buffer mass, that suggests the initial kinetic energy of the carrier/buffer must also be independent of mass. If the kinetic energy were reduced by use of a heavier buffer, you’d expect to need more gas to obtain lock-back.

Let's keep in mind that we're talking buffers that work within the span of operation. Go too light or too heavy and function will be affected. There are three legs to AR function and all three must be in balance-
- Gas drive
- Reciprocating mass
- Spring rate

Change one of those legs too much and it throws the system out of balance. It changes the timing. However, there is room for small variations while maintaining the span of operation. For example, buffers weights ranging from about 3.0 oz to 5.4 are within that span of operation using 5.56 spec ammo. Venture too far outside that range and you start having problems. (While ARs will function reliably with 3.0 oz buffers, a 3.0 oz buffer is too light. It gives sharper recoil and it's affects on the shooter accumulate with each shot. It also adds time needed to get the AR back on target.)

Timing is very important to reliable feeding. If the carrier is moving too slow or with too little momentum, the round being stripped from the magazine will bobble. It will nose up and jam in the action. The round has to be stripped with enough speed and authority it doesn't have time to bobble. If the carrier speed is too high or there's too much momentum, the carrier will bounce. While carrier bounce may not have an impact on function in semi-auto, it adds to the time required for the AR to get back on target.

While I found the buffers tested didn't require different gas settings, it's important to understand my testing was confined to buffers falling between Carbine and Rifle/A5H2 in weight.

[ta0117]

My last 3 have gauged out at 0.076"

A friend pin gauged his DDM4 16" barrel and it was between 0.072" and 0.073", which checks out with what DD told me in an email. Curious about the 0.076" you gauged, are they 16" midlength government profile in 5.56? Wonder if their S2W or LW barrels would have different gas port diameters, or perhaps you had a different caliber. According to DD their 14.5" midlength is 0.076", and it would baffle me if DD drills their gas port size wrong by mistake.