All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"
How much jump before pellet hits the grooves?
Greg_E:
Down in my velocity after valve thread, I discovered something that I'm not sure about.
When I chamber a round in my Bulldog, it embossed the rifling pretty far back. Should the projectile be able to travel a short distance before encountering the rifling?
Or do we want the projectile engaged in the rifling to help seal the barrel for optimum performance?
With firearms you normally want at least a small jump distance, or else chamber pressures can get high. Not sure if the same is true for airguns, just without the pressure spike since the pressure is the pressure with air.
rsterne:
I cut my chamber so that the bullet is slightly engaged into the tapered leade portion.... I position the taper so that the longest bullet is nearly fully engaged in the taper, while the shortest one just touches it.... I don't want any "jump", nor do I want to have to force the bullet into the full depth of the rifling.... Here is a selection of .257 bullets....
I have a very shallow taper on the leade, just 1 degree per side.... If you look carefully, you can see marks on all of those bullets....
Bob
oldpro:
If you add 1/8 of and inch of jump you will see pretty big velocity gains BUT it can cause some degree of accuracy concerns but not always. I use jump in most of my bullet shooters but none in my pellet shooters. JMHO
Greg_E:
I'm pretty sure the taper is much steeper than Bob's.
Since I'm probably never going to shoot pellets in this rifle, I'll have to think about about cutting the leade deeper for a little jump, or at least get them to be on the taper. If I can get a shallower angle reamer, I might be able to get what I want by simply changing the angle.
Anyone know a place in NY that can do this work for me? After that any place I can send it in the US?
I can buy a teamed for around $60 plus shipping from the Ukraine, but you know how some of those things go. I don't have a lathe to make my own or I'd try it.
rsterne:
You can modify tapered pin reamers into leade reamers.... They are just about ideal for the job, the taper is very shallow, just 1/4" per foot (1.2 deg.)... You just grind away the big end of the reamer behind the chamber diameter you want....
Bob
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