Super Bolt and Low pressure upgrades

[bjjb99]

Woo hoo! Some measurements!

I couldn't locate my calipers, so I had to make do with rulers and various other measuring aids. The mag I measured is an older one (serial no. CF10xxx), a powerfeed left mag body with a standard A.I.R. valve.

The first thing I measured is the depth from the rear of the Mag body to the retaining ring inside the which the main spring rests against. Using my precision calibrated plastic chopstick as a depth gauge, I measured 2 -13/16" from the rear of the Mag body to the retaining ring.

I then measured the thickness of the fully compressed main spring. This worked out to be darn close to 3/8".

I next measured the thickness of the bolt flange which engages the sear. It's pretty close to 5/32".

Using my chopstick again, I measured the depth of the bolt plunger inside the bolt. It's recessed about 3/16" from the rear face of the bolt. This puts it about 1/32" ahead of the front face of the bolt flange.

We now have enough information to calculate the position of the bolt plunger relative to the rear of the Mag body when the main spring is fully compressed. First we subtract the compressed main spring length from the Mag body depth; this gives us the position of the front face of the bolt flange relative to the rear of the Mag body. 2-13/16" - 3/8" = 2-7/16". Since the plunger is about 1/32" ahead of the bolt flange, we add 1/32" to our previous result. The position of the bolt plunger relative to the back of the Mag body is right around 2-15/32".

Now we need to determine the location of the powertube tip relative to the back of the Mag body. I first measured the length of the portion of the A.I.R. valve that rests inside the Mag body (from the step right behind the on/off body to the face on which the bumper rests). It's right around 1-7/16" on my Mag. I then measured the length of the powertube, which is rignt around 1-1/4". Adding these two values together gives us 2-11/16", which is the position of the end of the powertube relative to the back of the Mag body.

If we compare the plunger and powertube tip locations, we see that the back end of the plunger is about 7/32" down inside the powertube tip.

Looking at the inside of the powertube, we see a taper. I tried to measure the location of the taper's beginning; this was the least accurate measurement I made. It begins right around 3/16", give or take 1/32". So the tip of the plunger sits darn close to the beginning of the powertube tip's taper.

My bolt plunger has a tiny step on it. As best as I can tell, this step is about 1/64" high (eyeball estimate), and it's about 3/32" from the plunger tip. I could not measure it with the tools on hand.

After reassembling the Mag and firing it a few times, I noticed that the valve body does not rest up against the back of the Mag body; there's a tiny gap there measuring right around 1/32". This extra gap puts the back end of the plunger around 3/16" down inside the powertube (instead of 7/32").

From what I can tell, there isn't much distance between the beginning of the taper inside the powertube and the bolt plunger tip, even when the main spring is totally compressed. What this says to me is that a tiny change in the relative positioning of the bolt plunger and the powertube tip will result in significant changes in airflow through the powertube. Of course as you stated above, if your main spring is a bit on the strong side and thus your airflow is a bit on the low side, you'd crank up the valve pressure to compensate for the decreased airflow (which would also change the relative position of the plunger/powertube due to the increased pressure in the dump chamber).

It's a fascinating little balance going on in there. I think I'm going to have to chalk this one up to the elves.

BJJB

[FatMan]

Cool!

Wow.

So, the plunger is right at the transition point. Interesting! I would have expected another 1/32 or so of clearance.

Did you measure clearance between the inside of the power tube and the outside of the plunger?

That's a really interesting setup. I'm going to have to think about that for a bit.

Thanks for posting the data!

FatMan

[bjjb99]

FatMan wrote:
>
> So, the plunger is right at the
> transition point. Interesting! I would
> have expected another 1/32 or so of
> clearance.

Yeah, I was surprised to learn how close the plunger and taper are to each other. I had figured on a little more clearance as well.

> Did you measure clearance between the
> inside of the power tube and the
> outside of the plunger?

I wish I had been able to measure the plunger OD and the powertube ID, but I just didn't have the right tools handy. I eyeballed the plunger at around 1/4" in diameter; the powertube should be a few thousandths (perhaps up to a couple of hundredths?) of an inch larger inside for a slip fit.

BJJB

[Cristobal]

That's really great work bjjb99!

As an additional observation, if Tom said a bit back that the spring rarely is compressed all the way unless the marker is dry fired, then I would think that the plunger would sit just a little further inside the pt tip than assuming complete spring compression.

[Cristobal]

Wait a minute...

The flange on the bolt which engages the sear is angled inwards, such that the inside width will be slightly less than the outside width -- which one did you measure bjjb99? I'm going to guess it was the outside width because the inner width would be more difficult to measure without "real" tools. If so then the bolt will sit a bit further forward with the spring at maximum compression.

Of course, given that the spring isn't fully compressed during normal firing, this may not be a big deal. Also given the relative error of the above measurements due to the precision of the chopstick method this may not be a big enough difference to worry about.

[einhander619]

wow, this is all a little much for 19 year old brain to handle. Who needs physics and material science classes when I can just hop on 'mags.org! I hope you guys get paid to think like this!:)

[than205]

It seems to me that what you would end up with is a dual pressure system. Meaning "x" pressure moving the bolt at a acceptable speed and force. (this would have to be balanced out)
And "y" pressure needed to send the ball down the barrel at the desired speed and have the ball get to that speed within certain distance. (perhaps avoiding breakage down the barrel?)
It's been mentioned that the mags peak behind the ball pressure takes a longer amount of time than other markers. What if that is the key? What if the air got to the ball faster? Couldn't the pressure behind the bolt be lowered and thereby lowering bolt speed and bolt force.
I have no doubt that someone knows exactly what pressure is needed to get a paintball to 300 fps with in 8(?) inches. Couldn't you back your way into the appropriate power tube configuration this way? Perhaps this would restrict the systems flexibility for paint variation.

Is there really a taper on the inside of the power tube?
Would it be better to have some sort channels milled running a certain depth and length along the inside of the power tube?
You would maintain the slip fit of power tube and plunger, but when the bolt moved out to a certain point the dump chamber would be expended as quick as possible.

[athomas]

To allow the paintball to be accelerated to 300fps in the required distance takes a certain pressure behind the ball. The mag has about 60 psi behind the ball even though the chamber pressure is at ~400psi. This is due to restrictions in the flow path such as the size of the power tube and the bolt stem being in the way. The ball could be accelerated to 300fps in the same distance using a lower chamber pressure if the air could be delivered with less restriction. Ultimately we would require the same 60 psi behind the ball pressure starting out.

All that being said, the mag's biggest problem is not the actual operating pressure but the rate of acceleration on the bolt. This causes the bolt to strike the ball with a lot of force and could cause breakage if using bad or brittle paint. We need a two stage pressure system. First stage gently accelerates the bolt to strike the ball and the second stage releases the full force of the chamber pressure (we still want about 60 psi behind the ball).

Now looking at what bjjb99 said, it appears that there isn't much of an opening for the air to pass out by the bolt stem from the power tube. If we are restricting the air flow anyway, why not do it in two stages. Start the power tube at a smaller diameter at the back, sealed with an o-ring, and then open it up to the wider opening near the front. This would cause the force on the bolt to be lessened (the total force on the bolt is directly related to the cross sectional area of the object and the psi behind it) for the initial push. When the bolt reached a forward point it would open up to the larger tube diameter and by now the smaller part of the tube would be free of any obstruction and the pressure would be released to the ball much like it is now at about 60 psi. We wouldn't have to restrict the back of the power tube very much either. If we reduced the total cross sectional area by half it would effectively reduce the force on the bolt by half as well. The power tube would still be fairly large so the majority of the restriction would still be at the front where it is now.

I have to think about this some more. Keep the ideas flowing guys.

[FatMan]

Experimental mod

This sounds like a mod that could be easily tested. We would need:

1) a lighter bolt spring.

2) a modified power tube tip that opens up more agressively than the existing one.

3) reduced pressure (should be easy, just turn it down, maybe different spring pack).

Of course, I think Tom has done this kind of thing and eventually settled on the exsting configuration. The problem may be that it is hard to experimentally find other workable configurations. That's where I'd like to try to model it on a computer and see if we can find potential configurations before we hack up the metal.

In the mean time, who wants to try?

I wonder if AGD would give cphillip and I some springs, power tube tips, and spring packs to experiment with (in the name of science, of course).

FatMan

[AGD]

Before anyone thinks we are ripping off their ideas we are already all over this in reducing bolt speed. We have a two stage acceleration system in debug and its looking quite promising. I would prefer to keep this quiet until we get finished with it so I am not getting plagued with questions.

Thanks

AGD

[than205]

nuff said tom
thanks

[athomas]

Excellent, I can hardly wait for the results of the testing on a two stage bolt system.

Just when you come up with a good idea, AGD is already working on it. Thats just a good R&D dept.

Keep up the good work.

[FatMan]

Originally posted by AGD
Before anyone thinks we are ripping off their ideas we are already all over this in reducing bolt speed.

No way dude! You totally took that from us! I think we deserve a cut of the business!


Well, at least we should get to hear about it.

FatMan

[orangejulius]

yeah like beta testing release to like a 1000 people and get them to test them :)

[FactsOfLife]

Originally posted by orangejulius
tom you can get 2500 shots off a impulse with 68/45 what you talken about

baloney, I HAVE an Impy that I generally run with a 20oz Co2. With that tank I get about 900 shots. I have the angled full flow solenoid isolator, a delrin bolt and titanium pin. I can run my input pressure at 150psi with these mods. For an Impy it's fairly efficient.

To see how much of an improvement I would get with HPA, I borrowed my cousins 68/4500 MaxFlow and played with it. Same paint, same everything, got 1400 shots out of it before it went flat.

I'd PAY cash money to see somebody get 2500 shots out of anything smaller than a 114/4500.

You might be able to do it with a 5000psi system but that ain't the boast now is it?