What prevents a cocker bolt from getting blown back?

[nicad]

Tom- old member here on AO? very possibly.. been aound for quite some time.. I think I used to have an account on here long ago as well. dont remember for sure. :)
so what your saying the answer might be is that the mass of the bolt takes too long to react to the burst of air (inertia wins!).. ? so that if i were to have a bolt (and backblock) that weighed close to nothing, it would prolly get blown back on each shot.

Vegeta- yes the momentum(spl?) of air traveling down the barrel does create a vaccume.. and if the bolt is opened at the right time, will actually suck the next ball in. kinda like how a 2-stroke engine's tuned exhaust system works.. on resonance(spl?).

xatle- sorry buddy.. one has nothing to do with the other. :) for one, id like to see your 700 lb car. :) lets say an average car weighs 2800lbs.. if your tires have 30psi in them, thats 30lbs of pressure per square inch. lets say each tire is 6" wide and its footprint on the ground is like 4" long. thats 4*6 = 26 square inch footprint. 24*30psi = 720lbs for each tire. 720*4 tires = 2880lbs, and thus your car dosent fall to the ground. :) now make sence?

thanks for the thoughts yall.. but for some reason im still not 100% satisfied.. something still dosent quite add up. im gunna have to do some testing pretty soon to ease my mind. :)

[nippinout]

From my understanding...

Once the hammer is released, it slams into the valve.

This gas goes out the bolt normally. You are questioning how the bolt doesn't move when this occurs.

When the air is being expelled, the bolt does want to move but it cannot. Why ask? If the bolt wanted to move back, it would now need to push the hammer back also (due to the back block).

From my understanding of the cocker, that is why it will not move back when such a low cocking pressure is used.

I hope this helps!

[Vegeta]

OK so we know hte cocker can be timed to cuase ball suck. That is a really good thing, if you achive it. But can this be applied to other guns? Lets take to mag. Lets say we tune it to where the air is released when hte bolt reaches it's apex, in the barrel. Then we would need to spring to push the bolt back fast enough to where the resonace of the air in hte barrel creates a vaccum leaving e barrel, cuasing ball suck. Now the question is- can we have a spring that is powerful enough to throw the bolt back fast enough to achive this yet still be weak enough to allow for the bolt to seal the barrel and travel fully forwards? We can't have our spring be stronger than the pressure of the air behind the bolt now can we? This is where the mag is a bit limited. But what happens if we replace the spring with something else? Possibly a ram to push the bolt backwards. This could push the bolt back faster than the spring could right? I say what we should do is have almost constant pressure on this ram, with some sort of reg that, when the ram is pushed against (when hte bolt is moved forward by hte air) it opens, allowing the ram to move back, but then immediately springs back sending a surge of pressure to the ram, springing it forward, like a spring would. Now, when the bolt is moved forward by hte air pushing against the bolt, the ram gives a little, but as the air is released, and hte barrel is sealed, the ram surges backwards into it's position, pushing the bolt back into it's cocked position. Weather this would cuase a vacuum or not I cannot tell. Would it wold allow for some neat tinkering.


Did you all understand that? Or should I illustrate?
Tom any comments?

[nicad]

nippinout- VERY good theory.. and I thought it did that for a good while.. but, well, not all cockers are setup the same, and i dont belive any of them that iv seen (quite a few! :) ) allow the hammer recocking knob to come within touching distance to the backblock. most will have anywhere from 1/4" - 1/2".. some even more, some even less, gap. easy way to tell is to degass the marker, push the hammer all the way in compressing and bottoming out the valve, and see how much gap is left to the backblock.. it still has some good room to move back.. atleast enough to unseal the breach and/or cutoff the flow of air up through the bold from the hole in the body.

So far I like Tom's suggestion the best, but still not 100% satisfied. easy way to prove/disprove his idea is to disconnect the 4-way timing rod (need to keep pressure on the LP system), and lightly set your finger on the backblock. ill bet it does not move at all when firing out a ball. :)

out!

[314159]

one of my guns is a pgp with a palmer bolt (no bearings to hold the bolt in place when you fire it). when i do not hold the pump arm, the bolt and pump arm will blow back, bounce of the force of the hammer spring, and come most of the way closed. this points out that there is more than just the weight of the bolt kepping it closed.

measured over a chronograph, firing the pgp holding the pump arm forward, and not holding the pump arm yeld almost the same velocity, signifing that the gas pushing the ball, does it's work fast, and is most of the way done before the ball is out of the barrel.

let's say that you are operating your front pneumatics on your autococker at 30psi. if you were to cycle the backblock manualy, with out moving the 4 way valve to vent the gass in the ram, you will need to compress the gass in the back block to move it back, thus the foce needed to move the back block back is not a linear relationship.

out of all the bolts i have seen for the autococker, most of the bolt tips hang past the feed tube for about an eight of an inch.

to make an autococker misfunction, the back block would have to be pushed back more than 1/8 th of an inch, while the gas burst firing the paintball is going on.

the force pushing back on the bolt should be equal to the force on the paintball which i have heard is just under 3 joules (havent calculated myself). from the pgp example above, the time that this is acting on should be around the time it takes a paintball to leave the barrel.

this force is not great enough to move the bolt, backblock, pump arm, and ram pistion, against the pressure in the ram more than 1/8th of an inch in a couple milliseconds.

[the electrician]

excellent description!

there it is. that sums it up pretty good.
I've noticed that straight thru, single tube design pump guns are more apt to push the bolt back than the stack tube guns. I wonder if the air making a 90 degree turn helps in the matter at all.seems like it would also have an affect but I'm not for certain.

[314159]

just a hunch, as far as the stacked tube pumps go(with the exception of most PGPs). maby the air flowing through the hole in the bottom of the bolt in effect helps hold it in place.

it seems to me that if the hole in the bolt was not lined up perfectly over the hole in the body where the gas vents out. so if the bolt moved back a little, maby the gas going through the hold in the body, would hit the area right in front of the hole, (even more so if it was tapered) and would push this forward.

[tat2dhillbilly]

bolt blowback on a cocker

The bolt does not move because what little force acts on it is not enough to overcome the pressure on the ram holding the bolt forward. As you pull the trigger you cycle the four way to move the bolt back and then forward to load a ball. The pneumatics are not vented until you release the trigger fully. This will keep the bolt pneumatics a closed system and the blowback forces on the bolt face which are minimal at best due to the fact that the bolt is hollow and the forces can only act on the lip around the face of the bolt.

Path of least resistance and all that too..........

[nerobro]

though the thread was dead a long time ago...


You're incorrect in your asertion that the outer edge of the bolt is all that revieves force. The entire aera of the bolt recieves force. The shape of a surface does not change the force applied when it comes to gasses.

On snipers, the bolt is blown back signifigantly unless you hold it forward. If your'e looking for proof that the force is there.

314159's suggestion that there might be uneven force on the bolt from the air coming from below has some weight. In spyder type blowbacks there is a long standing issue with wear on the top of the bolt, something is shoving it into the top of the gun. That could provide some locking force on the bolt.

As far as I can tell, the ram is what keeps the bolt shut. Becasue there is pressurized air in the ram and a relitively small outlet, it will provide some signifigant dampening force to the bolt movement.

[Killaman]

NO..... a cocker isnt blown back because you need the RAM's power to blow it back and evenw hen u cock it back manually u need about and extra 5 lbs of pull to let a PB in the chamber