HPT and MPI testing. Why?

[Tiribulus]

It would be interesting to see one of you guys take one of THESE for a whirl.

[lysander]

Here's why I don't mess with springs, and generally control things with the gas flow and buffer mass.

The initial bolt velocity is governed by the first 0.325 inch of carrier movement, the travel of the cam pin. The pressure in the cavity maxes out around 2,000 psi, with a 1/2" diameter piston, that generates a force of about 300 pounds. The spring is pushing forward with 6 pounds, that force is negligible, as the variation in pressure from round to round makes more difference than that. So, the bolt velocity is independent of the spring. The deceleration of the bolt carrier is governed by the mass of the bolt, carrier and buffer, as well as the force generated by the spring. The energy absorbed by the spring does not change that much, for example, the ones in the link above will absorb the same energy as a standard spring. These means changing the mass of the bolt/buffer assembly has more impact on final velocity. And the final velocity will always be positive when the buffer hits the back of the extension.

Since the buffer impacts the back of the extension, its velocity drops to zero, and all the forward velocity will come from the spring (and a small amount from the rubber tip rebounding). The spring cannot deliver more energy than it absorbed, and the rebound energy from the rubber tip on the buffer is the same, the forward velocity is also mostly governed by the mass.

(Although, I do concede that changing spring might allow finer adjustments, but I have never found that level of control necessary.)

[Disciple]

“Just put oil on it” is silly, because the action spring is not a place where lubrication would be required if we could just stop tinkering. Saying that it’s the solution, is admission that there’s a problem, and I’m saying that problem doesn’t need to exist, because CS springs don’t solve any problem.

I don't use any CS action springs but I lubricate all of them, even stainless ones. Is there a good reason not to?

[1168]

I don't use any CS action springs but I lubricate all of them, even stainless ones. Is there a good reason not to?

Not that I’m aware of unless you’re in a high sand/dust environment.

[Uncas47]

I don't use any CS action springs but I lubricate all of them, even stainless ones. Is there a good reason not to?

Every so often check the end of the RE for any accumulation and clean it out. If you stand the gun on its butt CLP can migrate off the carrier etc and gravity never ceases, so a peek now and then never hurts. The carrier going back in there brings shit with it over time anyway.

[1168]

Every so often check the end of the RE for any accumulation and clean it out. If you stand the gun on its butt CLP can migrate off the carrier etc and gravity never ceases, so a peek now and then never hurts. The carrier going back in there brings shit with it over time anyway.

I actually took apart my 605 not-clone today and found that the spring and buffer were slathered in black CLP. It spends most of its time sitting in the safe exactly as you describe, and I think lube migrates off the chromed carrier more than my phosphate carriers, which will migrate also. Ironically, I lube my guns minimally.

[Uncas47]

I actually took apart my 605 not-clone today and found that the spring and buffer were slathered in black CLP. It spends most of its time sitting in the safe exactly as you describe, and I think lube migrates off the chromed carrier more than my phosphate carriers, which will migrate also. Ironically, I lube my guns minimally.

I bet it would still run LOL.

[tangolima]

Here's why I don't mess with springs, and generally control things with the gas flow and buffer mass.

The initial bolt velocity is governed by the first 0.325 inch of carrier movement, the travel of the cam pin. The pressure in the cavity maxes out around 2,000 psi, with a 1/2" diameter piston, that generates a force of about 300 pounds. The spring is pushing forward with 6 pounds, that force is negligible, as the variation in pressure from round to round makes more difference than that. So, the bolt velocity is independent of the spring. The deceleration of the bolt carrier is governed by the mass of the bolt, carrier and buffer, as well as the force generated by the spring. The energy absorbed by the spring does not change that much, for example, the ones in the link above will absorb the same energy as a standard spring. These means changing the mass of the bolt/buffer assembly has more impact on final velocity. And the final velocity will always be positive when the buffer hits the back of the extension.

Since the buffer impacts the back of the extension, its velocity drops to zero, and all the forward velocity will come from the spring (and a small amount from the rubber tip rebounding). The spring cannot deliver more energy than it absorbed, and the rebound energy from the rubber tip on the buffer is the same, the forward velocity is also mostly governed by the mass.

(Although, I do concede that changing spring might allow finer adjustments, but I have never found that level of control necessary.)

I concur. Very good analysis on the system. One thing to add is the vent holes in the bcg. That limits the active period gas impulse. Beyond that longer dwell time is not going to make any difference. That corresponds to the 0.325" bcg travel that determines the bcg speed.

The carbine spring in the other thread on action spring, K=1.53 lbf/inch", L0=10.7",L1=6.8",L2=3.2".

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

The spring is going to bottom out and the buffer is going to slam on the buffer tube end. I like setting up my gas to have the buffer just touch the tube end. That requires cutting the gas pressure by about half, with 25% margin to account for loss and energy required for extraction/feeding.

-TL

Sent from my SM-N960U using Tapatalk

[Tiribulus]

Here's why I don't mess with springs, and generally control things with the gas flow and buffer mass.

The initial bolt velocity is governed by the first 0.325 inch of carrier movement, the travel of the cam pin. The pressure in the cavity maxes out around 2,000 psi, with a 1/2" diameter piston, that generates a force of about 300 pounds. The spring is pushing forward with 6 pounds, that force is negligible, as the variation in pressure from round to round makes more difference than that. So, the bolt velocity is independent of the spring. The deceleration of the bolt carrier is governed by the mass of the bolt, carrier and buffer, as well as the force generated by the spring. The energy absorbed by the spring does not change that much, for example, the ones in the link above will absorb the same energy as a standard spring. These means changing the mass of the bolt/buffer assembly has more impact on final velocity. And the final velocity will always be positive when the buffer hits the back of the extension.

Since the buffer impacts the back of the extension, its velocity drops to zero, and all the forward velocity will come from the spring (and a small amount from the rubber tip rebounding). The spring cannot deliver more energy than it absorbed, and the rebound energy from the rubber tip on the buffer is the same, the forward velocity is also mostly governed by the mass.

(Although, I do concede that changing spring might allow finer adjustments, but I have never found that level of control necessary.)

I appreciate the detailed response. I love tech stuff.
Honestly, I just like the way the Bexar springs "feel."

Not only do they function perfectly, but they give the rifle a highER end feel when working the action.

I also throw a bit of OO grease in the tube.

My main AR (Aero receivers, BCG and tube) feels like the action is on roller bearings, though I know that's not just the spring. Also, instead of a"THWANG" sound and sensation, it drops with a really smooth, quiet and satisfying... "thunk."

It might sound dopey, but I really like it this way

[Tiribulus]

The spring is going to bottom out and the buffer is going to slam on the buffer tube end. I like setting up my gas to have the buffer just touch the tube end.

I shoot for that too.