Spudtech Forum

Originaly posted by spudlover,
Does anyone know how much a coaxial barrel would effect velocity, I used the chrono on my "semi coaxial" gun today and it wasn't shooting very fast. The barrel(1.5"by59" long rifled) extends 7 inches into my 10 inch chamber. This was done so I could lower the ratio for the small barrel, but have the big chamber for my TB barrel. I also did 40 shots to verify the fastest fuel mix. The fastest shot was 328fp, average out of 5 shots at the fastest fuel mix was 301fps. BTW the ratio is 1.2:1 with a 2300 cc chamber. This pissed me off because Latke was getting 400fps at the same ratio, but he didn't have a coaxial design... Any input would be greatly appreciated.

Originaly posted by _latke,

get a barrel that sticks way into the chamber but push the slug all the way up to the normal breech loading position at the chamber opening. Fire and record a few or more shots. Then cut the coax part of the barrel off and load slug in same position as before. Compare results. The volume of the chamber will be bigger after the inner barrel is cut off. leave the scraps on the bottom of the chamber to keep the volume the same. I've been meaning to do this test for a looooong time.

How far do you put your first chrony sensor from the muzzle? I'm at two feet.

Originaly posted by spudlover,
Right after I posted my first message I cut down the barrel so only 3.5" was sticking in the chamber. This yielded an average increase of 30fps in velocity over 8 shots! I wonder what effects of having a long barrel in the chamber are. Do they disrupt the "funneling" of the air? Here are a few pics of my test setup.

My L3, brand new and not finished. Note the aluminum box containing the stun gun and fan controls. Latke, have you had problems with fan drain. I started out with 18volts, at the end of the day it was 15! Working on an AC/DC adapter.




My dad getting ready to shoot. Note the wood box, we set the end of the barrel on it. The first chrono sensor is approximately 1ft from the muzzle. Only problem was small potato bits flying on it.



This was the the "penetration" layer, over 5 layers of heavy duty carboard easily pierced every shot. The tennis balls and more powerful shots penetrated all 5 layers, went through 3 feet of paper wadding and came out the back hard enough to split the plywood on our garage door. This photo was taken after several shots.



The launcher with a 4ft long TB barrel. Tennis Balls fell so much more powerful than spuds, and they are much louder.



Pic of my "CCU," the wiring has since been cleaned up. I have also removed the stun gun circuit board.



And finally a pic of my cut down pass through barrel. One of my most highly reccomended upgrades. The ease of loading a spud compared to muzzle loading is unbelieveable.



That was a lot. My test conclusions. Don't have your barrel extend more than 3" into the chamber, or you are asking for trouble. BTW, how did the 2.5" CB test go Latke?

Originaly posted by _latke,

It would appear the the coaxial design may have an effect on velocity. Nice job. I haven't had inadvertent battery drain since adding the relays to the circuit. As far as normal drain, haven't measured but should last at least one busy day. I use rechargeable NiMh batteries. Order online for $25 or so. They have a nice constant voltage over their life but die without warning. Spare alkalines are suggested. I got my ACDC transformer at goodwill for 50 cents. It's 15v DC. I've got a dozen or so now.

Try a 5 gallon bucket filled with soft stuff like plastic wrap to catch the spud guts. It works super. No mess. I remember the chrony directions said when using subsonic ammo, it may be required to move the sensor further from muzzle to avoid misreadings caused by faster sonic boom. I've never seen this problem though.
Your launcher looks smooth. I always wondered what an "outie" 4" endcap would look like. Looks cool, finished. Do you have a 3" male to 2" female adapter? This item lets you use cheap 2" male fitting on 1.5" barrels.


Hows that CH regulator working? Do you have to readjust pressure each shot to get it exact? I do.

Originaly posted by spudlover,
I had a nice post, timed out though. Current project is an AC/DC adapter so I can have the fan running the whole time. I used a 5 gallon bucket with newspaper before, spuds broke the weld seam on the back! This may be of interest to you Latke, some of the first slugs in the 200fps range were in perfect condition! Could see the rifling grooves in the slug, very cool. Never had a problem with the muzzle blast either. When I look at slow mo shots the muzzle blast is very small, not like a .308 Winchester. Yes the endcap is cool. Very solid, it weighs around half a pound and is Spears. I would have used a hex head end plug, but the plumbing store didn't carry them. Special order next time.

Link to pics, notice the spud bits and burn ring.

BTW I am ordering a 3" to 2" adapter, 3" fittings are soooo expensive. Latke, both of us have big ideas, we should talk. If you want a cheap camlock fitting go to http://www.kthsales.com/website/vendors/Banjo/cam_lock_fittings.htm I'm sick of screwing and unscrewing my barrels. And yes, I have problems with my regulator. After I open the first valve it will usually raise a couple of psi, which is very annoying. I am ordering a guage for my meter soon.

Originaly posted by spudlover,