GTA
All Springer/NP/PCP Air Gun Discussion General => Projectiles => Boolit and Pellet Casting => Topic started by: WobblyHand on October 19, 2024, 06:49:36 PM
-
Just trying to understand this. I have the above mold. It's supposed to have a 0.219 drive band, but I'm measuring 0.001" over, sometimes 0.0015" over. (0.2200"-0.2205") I measured the slug using my dad's old Starrett micrometer. Casting with Rotometals 99.9% lead. This is pretty much normal?
If I were to add tin, (not going to, just a hypothetical question) it would get bigger? Kind of new to this.
Actually it is good that the slug runs slightly over, as it is a good fit in my GK1.
OT, I measured a 22LR standard velocity bullet, it measured 0.2250". (Very old Remington ammo.)
Maybe the GK1 guys with loose bores could use 22LR bullets? Or molds for the same? Think there are still some .223 BBT molds left at NOE. As for the 217, there are only 2 molds left. Will more ever be made? I only have a 2 cavity mold, might be nice to get a 3 or 4 cavity one.
-
What do they measure after you push a pellet through the bore?
Hunter
-
I just size mine to.218 for my impact. I assume you have a aluminum mold? Aluminum expands .0034" per inch at 350f. Which means a 1inch square will be 1.0034" at 350f. That's why a brass mold will be much more consistent in slug diameter. You know, Noe sells sizing kits very cheap for what you get.
-
What do they measure after you push a pellet through the bore?
Hunter
Not very easy to push a slug through a GK1 bore, easier to fire it. Basically have to disassemble the whole gun to access the bore.
-
I just size mine to.218 for my impact. I assume you have a aluminum mold? Aluminum expands .0034" per inch at 350f. Which means a 1inch square will be 1.0034" at 350f. That's why a brass mold will be much more consistent in slug diameter. You know, Noe sells sizing kits very cheap for what you get.
Brass thermal expansion coefficient is about 10% less than aluminum. So the difference is not that great. But you are right, a brass mold would make a slightly smaller projectile under the same conditions. My mold is aluminum. In my case, I'm happy it's aluminum and running slightly large, since it seems that GK1'S run large. I guess I'll fire into some mulch to see what the diameter really is.
-
The tec is almost the same but the brass doesn't loose heat as quick so will stay more stable in slug/pellet weight.
-
I have the same mold too in five cavity, but what you are experiencing is by design. The real question for me is what diameter are you sizing the slug, or at all?
-
I have the same mold too in five cavity, but what you are experiencing is by design. The real question for me is what diameter are you sizing the slug, or at all?
NOE is only showing 2 brass 2 cavity molds left in this design. Not much to choose from lately. Wonder when NOE will make some more, as I'd like to buy a mold with more cavities.
I'm not sizing the slug at all, as the un-sized slugs fit my GK1 well. I dug out a slug from my mulch target and it seems to measure 0.2195" across the widest point of the drive band rifling. Don't think that sizing would help, and it might make the slug too small for a GK1.
However, the slugs are tight in my PP700SA. The bore is about 0.2175" for that gun. Guessing I could use a sizer for the PP700SA. Right now, I need to use a slug starter to seat the slugs for the PP. I printed one, and it works good enough.
Wasn't really having an issue, just was trying to understand as cast dimensions. At least for the GK1, which runs a little large, it is good that the drive band is around 0.220.