Decking a mold

[Spacebus]

I have two molds that shoot accurately in my Eagle Claw, the NOE .249-39 and .250-41, but I would like the slugs to be moving a bit faster. My 'Claw is sending the .249-39 down range at 940-950 FPS at full power and the 250-41 around 900 FPS. I've read a few posts here and there were folks have gotten a machinist to deck the mold to reduce the length of the cast projectiles. Will I lose accuracy or precision if I get one or both of these molds decked?

Using the NSA FPE calculator a 30 grain slug should be moving at 1000-1100 FPS at full power, and my .249's drop at 36.5 grain with a hollow point. My .250 mold does not have pins, so I'm not expecting it get those up to 1000 FPS without a big power bump.


Currently I researching what is more feasible, finding a tuner to get my gun up to 100-ish FPE or getting the molds decked.

[Pellethuntr]

I am definitely not an "expert" but I have decked a few of my own molds. Quick glance at the blue print and I'm thinking that taking 6.5 grains off shouldn't be to big of a deal. I would have to 3D model the bullet and run some numbers to know how much you would need taken off but rough guess 0.050-0.060?

I wonder if it wouldn't be easier to have a bigger or different shape hollow point pin made?

[Spacebus]

I am definitely not an "expert" but I have decked a few of my own molds. Quick glance at the blue print and I'm thinking that taking 6.5 grains off shouldn't be to big of a deal. I would have to 3D model the bullet and run some numbers to know how much you would need taken off but rough guess 0.050-0.060?

I wonder if it wouldn't be easier to have a bigger or different shape hollow point pin made?

Different pins would be a good option. I think NOE is sending me some that are also a bit different compared to the originals. I sent an email after I couldn't get the original pins to stop sticking really bad and they called me and said they are sending replacements. It was a few days ago and not a long conversation but the gentleman may have mentioned they were longer.

Perhaps I could ask a friend with a lathe to help me out with this. Would a machine shop be interested in such a small job like decking a mold or making pins?

I wouldn't mind getting pins for my .250-41 if there is an affordable way to add them. It may be easier to just buy the HP mold, but it would still be a bit heavier than I want and also there is the general lack of availability. I felt lucky to get my pinless mold, which is a joy to cast with.

Looking at the drawings for the .250-41 the boat tail and rebate are .062" long and removing that would make it .271" long overall with a flat base. Knowing an estimate of that weight would be nice. They fly pretty accurate even at "just" 900 FPS, but I only get six good shots per fill at max power before falling off the "Korean cliff".


My favorite option is of course more power, but I don't know if there are any airgun smiths specializing in the Korean guns remaining. The only other shop I know of that does Korean guns is in South Africa, and I don't know if they offer anything for the Eagle Claw and I don't feel comfortable shipping it that far.

If either mold can get down to 30-ish grains that would allow me to send them at 900+ FPS at a one power setting lower on the poppet. This increases shots per fill up to 18-24 before dropping off, which is much better. Then I can still send them at 1000+ FPS if I want to.

[Pellethuntr]

Perhaps I could ask a friend with a lathe to help me out with this. Would a machine shop be interested in such a small job like decking a mold or making pins?

Most of the ones around here will take on small jobs but they generally charge $80-100 an hour with a minimum number of hours. I don't know that I would feel comfortable decking an expensive mold for someone else but I could certainly make you some pins to try.

I wouldn't mind getting pins for my .250-41 if there is an affordable way to add them. It may be easier to just buy the HP mold, but it would still be a bit heavier than I want and also there is the general lack of availability. I felt lucky to get my pinless mold, which is a joy to cast with.

It would almost certainly be more cost effective to buy the mold that's already set up for pins. I have added that feature to a couple of my molds in the past. If I was charging hourly rate to do the job it would certainly cost more than a new mold. I don't even charge half of what the "real" shops do.

[Spacebus]

Perhaps I could ask a friend with a lathe to help me out with this. Would a machine shop be interested in such a small job like decking a mold or making pins?

Most of the ones around here will take on small jobs but they generally charge $80-100 an hour with a minimum number of hours. I don't know that I would feel comfortable decking an expensive mold for someone else but I could certainly make you some pins to try.

I wouldn't mind getting pins for my .250-41 if there is an affordable way to add them. It may be easier to just buy the HP mold, but it would still be a bit heavier than I want and also there is the general lack of availability. I felt lucky to get my pinless mold, which is a joy to cast with.

It would almost certainly be more cost effective to buy the mold that's already set up for pins. I have added that feature to a couple of my molds in the past. If I was charging hourly rate to do the job it would certainly cost more than a new mold. I don't even charge half of what the "real" shops do.

I wish I had known about the lack of tuning support for the Korean guns before we bought the 'Claw. At the time there were few air guns available with comparable power output. Everything was out of stock and we were concerned about predators coming that winter. I've still not had to deal with any predators since buying the gun, but I've got other air guns better suited for that now.

Do you need a sample pin to make more? Once the NOE replacements get here I can mail the originals to you. 

[rsterne]

DJ, removing the boattail and rebate (a total of 0.062") from the 250-41 BBT will lighten it by about 7 grains....

Bob

[Spacebus]

DJ, removing the boattail and rebate (a total of 0.062") from the 250-41 BBT will lighten it by about 7 grains....

Bob

How does removing the boat tail and rebate affect accuracy?

[rsterne]

Knife had good luck with shortening slugs, I have no personal experience with it....

Bob

[Pellethuntr]

Do you need a sample pin to make more? Once the NOE replacements get here I can mail the originals to you.

Yup I will need something to measure for fitment.

Send me a PM when you're ready!

[Pellethuntr]

DJ, removing the boattail and rebate (a total of 0.062") from the 250-41 BBT will lighten it by about 7 grains....

Bob

Thanks for running the actual numbers Bob, looks like I was spot on with eye ball guesstimating huh?

[Back_Roads]

 I had this mold decked, and polished out to .178, I had it shortened to the lube grove and left a hint of boat tail. turned a keyhole @ 10 m slug into 1" straight on 1" or under @ 50 slug out of my Outlaw, and Marauder.


 
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