Air Gun Home :: View topic - New 9mm/.357 JSB Exacts & Upsizing .30 cal Exact to .308

rsterne · Moderator

I received my .35 cal JSB pellets from AirGunSource today.... and while the .30 cal are too small for a Lothar Walther barrel, these appear to be PERFECT....

The head measures 0.357", the skirt 0.366", and they are 0.423" long.... I weighed out 10 at 776 grains, so they avergage 77.6 gr. virtually exactly what it says on the tin.... They are covered with a black substance, possibly graphite, which rubs off on your fingers, making them a bit messy to handle.... but they are typical JSB quality.... I pushed one through my LW barrel, and once the skirt is fully engaged in the rifling, it slides through with just a nice resistance.... Upon examining the pellet (lower one in the pic), the head has some very slight scuff marks between the rifling grooves, indicating it is barely rubbing on the groove diameter of the barrel, with the rifling fully engaged.... The skirt was slightly collapsed from being pushed through with a rod (which pushes on the middle only), just as you would find with any pellet when pushed by hand.... IMO, they are a perfect fit in a 9mm (0.357") LW barrel.... I can't wait to test them when I get the .357 barrel on my Hayabusa....

Bob

radar · Silver Status Member

I'm on it.
Thanks for the heads up! I was never super impressed with the Eun Jins in this caliber, and have better results with Air Venturi, 115 grain, cast airgun bullets.

I would like to try these diabolos...Who sells them, if you don't mind?
cheers
Rob

rsterne · Moderator

I bought these from AirGunSource in Ontario.... I had them on order since December from Pyramyd Air but they keep pushing the due date out 2 weeks so I cancelled them....

By now, most people will have heard that the JSB .30 cal pellets are a true 0.300" head diameter, and loose in a Lothar Walther barrel.... I made an upsizing die today for them to increase the head to 0.308" diameter and swell the skirt to match.... Here is the die (poor photo, sorry)

I made a shouldered punch that can only go together a set distance.... The tapered pin the pellet sits on is 22* with a 0.120" end.... It swells the skirt to about 0.316" when the end is seated far enough to allow the head to be sized to 0.308".... The inside of the punch has a 1/2" clearance hole, and the a 5/16" guide hole to keep the pellet centered is made with a mill so that it has a flat end.... I wanted to leave a meplat on the pellet to see how it works that way.... The tapered pin is adjustable for height.... raising it increases the head diameter.... Once I had the height set, I turned off the end of the pin flush with the bottom of the die so they can sit on a steel block and it will have no tendency to move.... To use it, you balance a pellet on the tapered pin, slide the punch over the top and into the hole, where it stops, resting on the pellet, about 1/16" above the shoulder.... A couple of taps with a hammer upsized the pellet.... You remove the top punch, and pull off the pellet.... Here are the pellets, one is sitting on the pin in the die....

On the bottom right is a stock pellet that was pushed through my Lothar Walther barrel.... there are virtually no rifling marks on the head, and only light ones on the skirt.... To the left of it is one of the upsized pellets pushed through the same barrel.... You can see the difference, the head now lightly touches the groove diameter, and the rifling is fully engraved.... I won't know how the accuracy is until I can get outside when the weather warms up.... but I'm hoping to see a significant difference....

Bob

radar · Silver Status Member

Beautiful! Thanks, Bob Mr. Green

rsterne · Moderator

I still haven't had a chance to try them outside, but I tried a comparison indoors at 7 yards between the stock pellets and the upsized ones in a .308" PB barrel on my .30 cal Disco Double prlject.... Here are the results with the stock pellets (0.300" head size) on the left and the ones I upsized to 0.308" head size on the right....

The C-T-C groups size on these 5 shot groups went from 0.3" stock to 0.1" with the proper head size for the bore.... I would be surprised if results outside are any different.... I know that Voltar1 found a huge difference in a 0.308" barrel with the pellets he swaged larger as well.... Incidently, I can upsize a tin of 150 in 15 minutes....

I'm encouraged by the way the upsized JSBs shoot in the PB barrel.... It bodes well for how the stock pellets will work in our new 0.300" barrel....

Bob