Infinity Legend bolt speed questions

I know, I know...it's an incredibly simple design. But I love the Infinity Legend due to its simplicity and reliability. I'd like to get some insight on the following items from you guys:

Ram design--it's not a flat-back ram, but instead has a cone-shaped rear profile. This should aid in a gradual ram/bolt acceleration, correct? Is anything done to restrict the flow to the ram aside from limiting the size of the port?

Return spring--the stock spring is stiffer than the Rhino spring. I'd like to make the gun as gentle on paint as possible. The stiffer spring provides more resistance (slower ram speed) but requires higher pressure to overcome the added resistance to achieve the same velocity, given the same dwell time. Does either spring provide a paint handling advantage over the other?

With the lack of a LPR, there are only two variables--dwell time and pressure. I've noticed that it takes about 250 psi to reach ~290 fps with the dwell set to 10ms. I'd like to lower this pressure a bit in order to reduce the impact on the ball, but without sacrificing reliable cycling or killing efficiency (increasing dwell). Any ideas? The valve seems to be quite large with some decent flow.

The bolt (soft face)--oringless. I haven't taken calipers to the bolt and breach (to determine size difference), but I'm wondering if adding orings to it would reduce blowback or provide any other advantages. And is there any real advantage to the breach oring? I've replaced it so it's in good shape (buna 70) but I can't help but to wonder if it's contributing to splitting balls down the seam at times.

The whole point of this thread is that I'd like to be able to use the Legend out in the woods in the cold. It's a good 'beater' gun in those situations but I just can't get it to completely stop breaking paint. I don't underbore in the winter. Any help is appreciated.

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Originally Posted by imped4now

I know, I know...it's an incredibly simple design. But I love the Infinity Legend due to its simplicity and reliability. I'd like to get some insight on the following items from you guys:

Ram design--it's not a flat-back ram, but instead has a cone-shaped rear profile. This should aid in a gradual ram/bolt acceleration, correct?

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Nope, this won't have any effect.

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Originally Posted by imped4now

Return spring--the stock spring is stiffer than the Rhino spring. I'd like to make the gun as gentle on paint as possible. The stiffer spring provides more resistance (slower ram speed) but requires higher pressure to overcome the added resistance to achieve the same velocity, given the same dwell time. Does either spring provide a paint handling advantage over the other?

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There's a lot going on in a system like this, but my first-order thoughts would be that you need a certain amount of momentum to open the valve well, so it doesn't really matter. If you account for the lower opening force due to running at a lower pressure, you probably get away with slightly less momentum to open the valve - which means lower bolt speed and gentler on paint...

Guess I'd start with the Rhino spring for gentler paint handling, but this is really an empirical thing. Isolate the variable and see which one works better.

Quote:

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Originally Posted by imped4now

With the lack of a LPR, there are only two variables--dwell time and pressure. I've noticed that it takes about 250 psi to reach ~290 fps with the dwell set to 10ms. I'd like to lower this pressure a bit in order to reduce the impact on the ball, but without sacrificing reliable cycling or killing efficiency (increasing dwell). Any ideas? The valve seems to be quite large with some decent flow.

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I don't see an easy way around this, and I'm not sure it's your problem.

Quote:

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Originally Posted by imped4now

The bolt (soft face)--oringless. I haven't taken calipers to the bolt and breach (to determine size difference), but I'm wondering if adding orings to it would reduce blowback or provide any other advantages. And is there any real advantage to the breach oring? I've replaced it so it's in good shape (buna 70) but I can't help but to wonder if it's contributing to splitting balls down the seam at times.

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The SFT ring on Smart Parts guns is a very well-known paint breaking point, especially in cold weather which causes the ring to shrink slightly. My first recommendation would pull the breech o-ring completely for cold weather use. If you want to add a ring to your bolt for a permanent switch I don't think it's a terrible idea, the SFT style rings suck.

Another suggestion is to go to a Metric o-ring for cold weather. 1.5mm CS, 18mm ID.

Thanks for the info, Steve. I'm going to run the weaker spring and pull the breach oring for a little testing. I'm going to test for blowback up the feedneck and if it's there, I'll look more into adding orings. It's plenty cold out to do a cold weather/brittle paint test so that won't be a problem. ;) If I break paint with that setup, I'll change out one variable (spring first) and focus on that solely.

Any other thoughts are appreciated.

Well, no blowback issues with the breach oring pulled. Should be able to get some cold weather testing in soon.

You could design a 2-stage ram and back cap, reduce the valve force requirement and/or go for a very linear loaded spring.

One thing that stands out when I look at that gun is that if you can add volume to the firing chamber it should reduce operating pressure. Maybe a CP stubby reg with some type of hollow extender will allow you to add volume without modifying the gun permanently. Then you can work with a lighter valve spring and main spring.