HPT and MPI testing. Why?

[1168]

I bet it would still run LOL.

it does.

[lysander]

Energy the spring can store

Es=0.5*1.53*((10.7-3.2)^2-(10.7-6.8)^2)=31.4 lbf-inch

Work done on the bcg by the gas
Eb=300*0.325=97.5 lbf-inch

You have three times the amount of energy from the gas than the spring can absorb, in order to have thee "buffer just touch the tube end," you would need a spring with a spring rate of 4.75 lb/in. If you had a pre-load on the spring of 4 pounds (a little light), the force to cock the bolt back would be around 21 pounds. An MG-42 doesn't require that much force to lock the bolt back . . .

You get to bleed off about 1.0 to 1.1 fps bolt velocity with the spring. The buffer is going to hit the back of the extension with about 80% of its initial velocity. And if you want enough energy to extract, cock and cycle, you will need an initial bolt velocity of about 6.5 fps

[tangolima]

You have three times the amount of energy from the gas than the spring can absorb, in order to have thee "buffer just touch the tube end," you would need a spring with a spring rate of 4.75 lb/in. If you had a pre-load on the spring of 4 pounds (a little light), the force to cock the bolt back would be around 21 pounds. An MG-42 doesn't require that much force to lock the bolt back . . .

You get to bleed off about 1.0 to 1.1 fps bolt velocity with the spring. The buffer is going to hit the back of the extension with about 80% of its initial velocity. And if you want enough energy to extract, cock and cycle, you will need an initial bolt velocity of about 6.5 fps

I don't plan to do that with stiff spring, but an adjustable gas block.

When come to think about it more, the primary extraction process would take up a bit more energy than I have thought. Say full 300lbf for 1/16" traveling would take out about 20 lbf-inch.

Also the gas impulse can't instantly pressurize the "gas cylinder". The pressure takes time to ramp up from zero to port pressure of 2000psi. It takes a big chunk out of the work done on the bcg+buffer.

Not sure about the exact figure, the weight in the buffer is lossy. It helps to some extend.

-TL

Sent from my SM-N960U using Tapatalk

[lysander]

I don't plan to do that with stiff spring, but an adjustable gas block.

When come to think about it more, the primary extraction process would take up a bit more energy than I have thought. Say full 300lbf for 1/16" traveling would take out about 20 lbf-inch.

Also the gas impulse can't instantly pressurize the "gas cylinder". The pressure takes time to ramp up from zero to port pressure of 2000psi. It takes a big chunk out of the work done on the bcg+buffer.

Not sure about the exact figure, the weight in the buffer is lossy. It helps to some extend.

-TL

Sent from my SM-N960U using Tapatalk

First, extraction takes place much faster than 1/16. Empirical data from tests shows the time for extraction is only about 1.5 ms, the energy loss is only about 1 lb-in.

Second, the fact that the pressure ramps up over a period of time does not change the total amount of energy delivered, only how fast the maximum is reached.

[tangolima]

I don't have data on extraction. 1/16" is just a guess. Here I meant primary extraction. The fired brass to be pryed off the chamber wall, which requires quite a bit of effort. Looking at the primary extraction cam on a bolt action rifle, 1/16" travel doesn't seem too far off. 1 lbf-inch sounds low. Assuming 300lbf, the travel is only 0.003".

Gas pressure ramping up means the force on the bcg is not a constant 300lbf from beginning to end of the 0.325" travel. But rather it start from 0 and end up with 300lbf before the 0.325" runs out. It definitely bites a big chunk off the work done on the bcg.

-TL

Sent from my SM-N960U using Tapatalk

[lysander]

I don't have data on extraction. 1/16" is just a guess. Here I meant primary extraction. The fired brass to be pryed off the chamber wall, which requires quite a bit of effort. Looking at the primary extraction cam on a bolt action rifle, 1/16" travel doesn't seem too far off. 1 lbf-inch sounds low. Assuming 300lbf, the travel is only 0.003".

Gas pressure ramping up means the force on the bcg is not a constant 300lbf from beginning to end of the 0.325" travel. But rather it start from 0 and end up with 300lbf before the 0.325" runs out. It definitely bites a big chunk off the work done on the bcg.

-TL

Sent from my SM-N960U using Tapatalk

Yes, the work is different, but the energy is the same . . .

1 lb-in may be a bit high for a brass case . . .

[tangolima]

Work done is amount of energy transferred.

The x-axis is time. We need distance traveled to calculate work done (energy). For brass it looks like 20lbf? Assuming 1/16" travel still, it would be 1.3 lbf-inch. Steel is 15x of that? No wonder they always overgas the gun.

Interesting. Thanks for sharing the info.

-TL

Sent from my SM-N960U using Tapatalk

[lysander]

Work done is amount of energy transferred.

The x-axis is time. We need distance traveled to calculate work done (energy). For brass it looks like 20lbf? Assuming 1/16" travel still, it would be 1.3 lbf-inch. Steel is 15x of that? No wonder they always overgas the gun.

Interesting. Thanks for sharing the info.

-TL

Sent from my SM-N960U using Tapatalk

Bolt velocity at time of extraction is about 20-25 fps.

[tangolima]

Bolt velocity at time of extraction is about 20-25 fps.

Wow. I haven't seen information this detailed. Thanks.

I would say primary extraction happens when unlocking completes at about 2.3ms mark. End of piston motion means primary extraction completed and the bolt travels with the bcg at the same speed. That happens at 2.5ms mark. The displacement difference is about 0.8mm, or 0.031", or 1/32". Energy needed is 20*0.031=0.6 lbf-inch for brass and 9.3 lbf-inch for steel. You are right. My estimate was off by factor of 2.

Energy loss to extraction is indeed insignificant except for steel cased ammo. Looks like adjustable gas block is way to go.

-TL



Sent from my SM-N960U using Tapatalk

[Dutch110]

1) [/B]

Now, if you want to play with spring rates, and pre-loads, and C-S is the only offering available, that's fine, they will work just as well as anything else and last a long time if you take care of them. They might even be better because you can get the spring rate you want, but don't try and convince everyone they are better springs because they are C-S. They aren't.

_________________________
* Careful, there are two popular types of stainless steel for springs, 17-7 and 302/304. The 300 series stainless steels work harden only and not nearly as good as 17-7 stainless.

Was about to post exactly this. My entire use case for using Sprinco is that they are a known quantity when trying to tune a rifle to run suppressed. I keep a selection of them in sealed bags with a light coating of oil on them for just this purpose. And, when it comes to running an A5 setup, the Sprinco green seems to be the baseline when talking set ups.