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burldude · New Member

Oh no!!! I have ruined this Quest. Oh please.

I can see that you have an abundance of knowledge on Spring guns. Have you applied any equations to determine the optimum air nozzle size (transfer port) and piston weight for beeman silver arrow pellets in .177 ? What is the equation to find optimum chamber, piston stroke, pellet weight, and spring tension? With my limited knowledge on this topic I guess I must get lucky with my outcomes. To think that the piston does not slap the front of the compression chamber would be foolish, I am sure it does. I have however noticed that with lighter target pellets the pellet does in fact leave the barrel with less twang or slap. With the heavier pellets I am sure that I am getting piston bounce. In order to make this gun shoot faster with heavier pellets I have to increase spring pressure and add piston weight or decrease piston weight and enlarge the transfer port to alleviate the bounce. Whatever the case I will tweak and adjust. I honestly could not ruin a thing on this gun other than the barrel which I lack the equipment to manufacture. All other internal components are trivial. I am going to open up the transfer port even more and chamfer the barrel. I have noticed a smoother shooting gun with pellets inserted an 1/8 of an inch deep into the barrel. Yes I am sure there could be numerous reasons for this.
Using the initial inertia from the stored energy of the spring is the reason for the heavier piston. But it comes to reason that is not the fastest time in the stroke, the piston is just starting to accelerate. I am going to experiment and learn more. Will keep everyone updated. No need for slow lock time.

Starfish · Member

I just bought a phantom and I'm reading some intresting stuff here Very Happy

I think I was lucky with mine because I only had some accuracy issues the first 200 shots... from then on it was very pleasant to shoot with Smile

I'm planning on doing some serious tuning on it like replacing the trigger and installing a gas ram instead of the spring mechanism... I'll keep you posted Mr. Green

AirGunEric · Site Admin

I would be very curious about that gas-ram idea. Have you got a particular unit to use for it in mind?

broommaster2000 · Moderator

I recon that's gonna cost so much that you'll end up with an over powered gun.

Starfish · Member

cw · Banned

I have to agree with Bob on this one. I have done transfer
port work before. I have a Patriot that I put an adjustable
trasfer port orifice in. Not very many airguns at all respond
favorably to transfer port tuning. The longer the transfer port,
the less effect it will have. The .22 caliber Patriot resonds
quite well and the .25 caliber even more so because their
transfer port was designed as a compromise for three different
calibers. Also, when you tune the transfer port it has to be
tuned to a specific pellet weight. Mine is tuned to 21 grn and
above kodiaks. Anything lighter and it makes a horrible
noise. Shooting 18 grn Cro Mags sounds kind of like a
ball peen hammer striking an anvil when the piston hits the
end of the chamber.

If you want to tune the tranfer port in a spring piston gun
without making an adjustable port you can't guess at the
port diameter and stand a very good chance at being
successful. You will need to first get an averaged base chrony
reading.
Then drill out the transfer port in very slight increments,
average chronying after each time. If each enlargement
produces an increase in velocity you are on your way to a
tuned port. You keep drilling slightly larger each time and
chronographing after each enlargement untill there is no
gain in velocity. That is your stopping point. If you go too
large, you will have to TIG the hole shut and re-drill.
This can be a very long process as the gun has to
be completely disassembled, drilled cleaned lubed and
reassembled and average chronied each time. It's really
a lot of time and work for such a marginal gain in
perforance (up from 32 fpe to 34 fpe in the gas Patriot)

I have had very good results doing this to
a Patriot, Vulcan, C1, R9 and several others.

I have also heard of some guns responding well to having
the port welded shut and redrilled to a smaller size
producing an increase in velocity. You have to be careful
going this route too as narrowing the trasfer port has
the same effect as shooting heavy pellets and could stress
the spring. So it is all a balancing and a chronograph is a must.
Otherwise it's a crap shoot.

As far as lightening the piston that's gun dependent.
Usually though, with a coil spring, you want the piston
to weigh more and with a gas spring you want less weight.
Like when you put a gas spring in a Patriot you remove
the 98 gram OEM piston weight (top hat). This produces a
way shorter lock time. It produces a shorter lock time in
a coil spring gun also but causes a lose in power.
I talked to Dave Slade a couple of years ago and he flat
out told me that the reason that the piston weight is in "is
to produce power" He ought to know as he gunsmithed for
Webley and Beeman for years.

Good luck in your experimenting. These thing sure are fun
to try different things on. Have fun and be safe.

CW