ID Barrel specs

This my 1st post so be easy on me.I have a S1K.Pushing a Gamo pellet thru with a dowel rod is easy.to easy!What are my options here? It can`t be sealing at the skirt it seems to get tight half way down for 2-3 inchs then the rest of the barrel the pellet will just drops out.I dont have Chrony I was thinking of somehow swaging or expanding the skirt.So my question is how tight should the pellet be as far as pushing force?and do they make a swag tool for skirt expanding


Joe

[daved]

Far as I know, Joe, pellet sizers only work in the other direction.  Regarding the barrel I.D., maybe Charlie or Peterdragin can give you a definite answer.  Do bear in mind, pellets ain't bullets!  Resistance isn't always a good measure.  Look at the pellet instead.  Are there consistant rifling marks on the pellet?  The other thing to do is try different pellets.  How is the accuracy and consistentcy?  Also remember, when the pellet gets hit by the air blast from the piston, the skirt gets blown out against the rifleing.  At least that's what's supposed to happen.

You got my curiousity up, so I just pushed a couple of pellets throught the S1K I'm using.  The largest pellets I have on hand are JSB Exacts with head diameters rangeing from 4.50 to 4.53.  I just ran a 4.52 and a 4.53 through the barrel.  The .52 barely had any resistance, although it didn't fall through.  The .53 was slightly tighter.  Both had nice, even rifling marks on the skirts.  Interestingly enough, the .52 shoots the best in this rifle, but I've only done one very quick test last night.  Check my post on the Shoot out.

You don't have to have a chrony to get a good idea of velocity.  Look in the Library under Airgun Calculators.  There's a velocity estimator there that uses POI change over different ranges to determine velocity.  I haven't tested it against my (brand new!) Chrony, but will when I get a chance.  Sorry I got so long winded, hope this is some help.

Dave

Dave

I think your right on the air hitting skirt,My caliper lost batteryso i cant mic nothing out,but check is out,i have a ss dowl i push the pellets thru using the weight of the rod about 3/4 of the way the rod pushs the pellet out from the weight of the rod.i took 10 undersized pellets.on the desk i just pushed down on them maybe 5lb of force with my thumb and that did the trick.'Thumb Swaging' This works realy good now i had to reajust my sighs because all the thumb swag pellets hiting higher and tighter now.


Joe Thumb

[Cvan]

I'm wondering what affect the heat of compression has on the pellet skirt. The melting point of lead is very low. The temperatures of the air discharged from the compression chamber can be pretty high.

Chris

[daved]

Interesting thought, Chris.  Combustion temp for dieseling has to be around 500 degrees, melting point of pure lead is 621.5 degrees.  Seems like it might be an issue.  At the very least, it seems likely to soften the pellets, making them conform better to the rifling.  Don't know how you'd test it though.

Dave

I was getting just 1-2 rifling marks before i did the push thing,I would think heat trans from pettet to barrel would keep it from going soft

[Gene_SC]

I think there may be some heat. Not enough to expand the lead. Like Dave said the compression does expand the pellet skirts a bit.

I know you are wondering about barrel choke on a Gamo. I thought Rich said there was no choke on Gamo barrels?

I do know that CDT has mentioned to me several times that on the average Gamo has a good barrel. If you are trying to push a pellet through your S1k, try a RWS Superdome. They fit the tightest. If it is a CFX, Dave has the pellets that fit snug...

CDT or Rich can tell us all about barrels specs and what to expect from them.

Gene

[Cvan]

That is where I was headed Dave. I have the book (trigger to target) which talks about compression chamber temps. It's been years since I read it but I will see if I can find it and get back here with the recorded temps. if they are listed.

    I asked about the barrel choke because I once owned an RWS-34 carbine in .22 caliber. After I detuned it to around 600fps it was one of my favorite guns. I didn't realize how much I liked it until I had sold it. Now they are no longer available. So I was thinking of using a Gamo as a starting point to build another gun like it. It would be nice not to have to deal with the choke. Time will tell I guess.

    You guys take care!
Chris

[CharlieDaTuna]

The majority of the heat is built up in the  compression chamber during compression and is then only for a fraction of a second. Very little of the high temps ever reach the pellet, especially not enough to start working on the pellet. However, the air pressure on the pellet skirt is very high and does expand the skirt of most pellets into the rifling of the barrel. Some, depending on the skirt, expand and seal better than others. The better the pellet seals, the better the accuracy and velocity consistency and the higher the velocity will be as a rule.

But the fastest pellet certainly doesn't make it the best pellet for the gun for sure. Don't be fooled. The fastest pellet is usually not the best pellet for accuracy. Fast doesn't matter, accuracy does. You are much the wiser determining what pellet is most accurate in your gun than investing in a chrony to find out how fast it can shoot.

 A chrony for the most part will tell you your velocity and deviation factors and can help sometimes in diagnosing problems but if the intent of purchasing one is to determine the fastest pellet for your gun or how fast your gun is, save your money. Most people that buy a chrony will use it a couple of times and it just sets and in most cases is a waste of money. Almost anything a chrony tells you other than true velocity and deviation can be determined or diagnosed in other ways though maybe not as quickly.

Gamo barrels for the most part are pretty decent barrels and usually have a good crown but Gamo barrels are not choked.