NOE .25 cal Pellet Moulds

[K.O.]

Cutting the sprue is going to throw the nose balance off no mater what you do IMO. I'm trying to figure out a way to shave the nose some without deforming the rest of the pellet, kinda hard with soft lead but I'll keep at it.

I think we might be able to overcome that problem (could someone measure size the sprue hole) because looking at the marks Bobs pic(knowing the meplat is .160) it looks to have about a .140 sprue hole( I think .125-130 would be best)... hard to tell from a pic tho... also check to make sure of a nice sharp edge for cutting the sprue...

Wanye if you are getting smearing it needs to cool a touch more... I blew up the pic of your pellet an you can see some at the edge of the head...that is part of the nose getting distorted...

I was running into the same distortion with the boat tails on the BBT 30g .22 and 40g .25 at first... till I got opening timing down and it got  better...  Blew up and cropped a pic of Bobs pellet that shows about perfect timing, attached below...might be able to do even better... I will be trying cooling the sprue and maybe the sprue plate with a wet rag next...

I actually am surprised at the accuracy I get with the BBT with my  barrel, molds and casting procedure not quite up to snuff yet...

I think that aluminum is the right mold material for these small rounds but that means that the mold is heating up and cooling down much faster than the sprue plate... so the hottest part of the mold is the part we need cool  to not distort the nose...

so yeah trying a wet rag just might help  minimize nose/base distortion... and I think it is the biggest problem we face with getting accuracy...Mountain molds had the  base distortion on his flat base .30 pellet mold he was developing... wrong mold material, to thick of a sprue plate and to big a sprue hole...IMO... In below thread you can see the pulling away at the far side of the mold... might as well toss any like that back in the melt and change procedures or mold cause they will not shoot well...

https://www.mountainmolds.com/phpBB3/viewtopic.php?f=3&t=195

 attention to detail is needed to develop these  ...  I know I need to better my attention to detail casting the BBT...

For consistency sake and to help re heat the cooled/cold sprue plate that needs to be hot for good fill out I am going to make a small mold oven...  out of something like an old metal electrical box upside down with a BBQ/oven thermometer and a hole to get the mold in... will sit on top of the hotplate...probably will set the mold sprue side down... will help to have consistent mold temp to get more consistent  size and weight  which of course is important to accuracy...

I think it is way to early to call it the designs fault...I do think being a small caliber it will be more of a challenge to get right... I  suggest the modded versions mostly because of the non standard barrels we send them out with may like different pellets... because it would also be designs that are heavier and different from what we can get  at P.A. etc and I now know a stock  Mrod .25 can spit 40g at 700-750 fps so that makes a 35g-40g pellet useful if you can get things right...

The next detail is one that may effect the accuracy of my BBTs more than the 33g pellet I bet... and it is one I should have recognized first but was concentrating on getting as little base distortion as possible and did not notice...

I was for a while a mold/core maker on the sand side of an aluminum foundry and working with damp sand the importance of venting to fill out stared me in the face every day....

yet I did not see the slight rounding of the base of my boat tails till thinking about how I would work to get this mold working... the faces of the mold are vented but not the top and the sprue plate seals to well... IMO... bet it is the same with this mold...thinking of breaking the edges of the mating surfaces very slightly with fine wet dry on a stick..and I mean very slightly... this is not a iron mold making big rounds it will not take much... Probably should talk to Swede about it and see what he says first...  not as important to have the nice crisp corner on the nose but I have always heard it is very important on the base...

http://www.artfulbullet.com/index.php?threads/base-fill-out.27/

so that is what I think so far...can't call it a design prob before I  know I am not the prob in how I am doing the casting...

I go by my gut some, and my gut is saying the design will fly well if we get it all worked out... me I just want more designs also..

I do bet the old timers at casting would say this is a challenging design to pour right...probably quite a bit easier as a .30...

[K.O.]

I do want to thank you guys for sharing your experiences with the mold/pellet also Bob and Swede... I think it does help move casting for air forwards just a bit more... I am hoping Swede is willing/can to mod a mold for me am really wanting the challenge  of  it and do feel they would be maybe a touch less sensitive to get right...

[K.O.]

a coupl other things to try

Offsetting the  sprue holes can even try partially blocked in near hole...or just to the far side a bit away from the side that gets pulled...

need some about (2% is oft quoted) tin for flow in most folk opinion... in fact I might long term even add enough to see just how hard a mix the barrel can tolerate.... pretty sure the NPXL barrel can handle 8-10 BHN (4%-5% tin) might even like it... the Mrod while only choked mildly  might lead up with a harder mix..?

[Wayne52]

I'll try a 30 second delay cutting the sprue the next time molding these and see how they turn out that way
 I'm so darn use to casting for the muzzle loaders it is no issue at all being larger caliber like they are

[K.O.]

I shot mine again today and had no problem grouping UNTIL I turned up the power and it shot like a shot gun. I was shooting them really slow at 600fps but once I cranked it up it really started wandering. Is this a sign of too heavy a head or too long a pellet etc. Curious.

Edit at bottom



Rich_B
"RPMs will bring out the worst. Like inconsistent spots in the nose get really bad the faster you spin them"

yep is probably part of the Problem... I think that pellets have a lot more in common with foster slugs than they do with a regular slug... I think they do actual require very little twist to work well...Pellets have less gyroscopic stability because the waist moves the weight inwards...   smooth twist is one and  shotguns sending a weight forward heavy pellet/ slugs is another... then there are the differences in the drag profile

the below link has a velocity plot of a foster slug at 450 fps notice that the body is flying in a low pressure zone already it will get bigger as velocity goes up towards 600-800 fps and the bigger the meplat/nose shape etc....but the pic is a good aid to visualize what a pellet does just  imagine a waist... and remember that a wad-cutter nose will have supersonic flow at the edges  starting at about 600fps... my point is that the pellets tail is providing less drag stabilization because of it...the rule is double the speed quadruple the drag... and we have a slightly out of balance nose that now matters more...

http://mcb-homis.com/slugcfd/slugcfd.html


I have head edit* heard from a neighbor confirms what I have read... gets clover leafs a lot at 75 yards 2"-4" at 100 with 12 Gage K.O. Slugs... and it is just a big weight forward pellet

http://www.brennekeusa.com/hunting-ammunition/kotm/


150 or so yards offhand open sight torso shots with a foster slug...


Foster rpm thru one shotgun skip to about 1:30



so now thinking of pellets well the hemi nose is best for long distance... why..? I think it is partially due to the drag profile changing the least over the range of velocity... the low pressure bubble is smaller at higher velocity than semi dome, wad, and semi wad noses... so there is less shift away from drag stabilization to gyroscopic stabilization...

and when it comes to gyroscopic stabilization well the pellet can handle to much spin the best... why would that be...it is because of where the weight is...less on the outer diameter means less stabilization... the foster slug is more spin stabilized and then the solid slug is most...

So with the design of this pellet with the necessary meplat to be able to nose pour we have a pellet that as velocity increases wants more spin stabilization so just may handle the fact that we over spin it by comparison a bunch...

so now go to the drag function form and put in these numbers... link below...

http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=inches&weight_unit=grains&bullet_name=dewc&re_calculate=yes&diameter=.250&length=.375&nose=.142&meplat=.162&drive_band=.250&base_diameter=.250&angle=0&boat_tail=0&secant_radius=&weight=29&density=8

Bullet diameter (inches) 
.250
Bullet length (inches) 
.375
Nose length (inches) 
.142
Meplat diameter (inches) 
.162
Drive-band diameter (inches) 
.250
Base diameter (inches)
.250
Boat-tail angle (degrees) 
0
Boat-tail length (inches) 
0
 
Bullet density
11.4 gms/cc  (soft lead non-jacketed)

and you  get the figures for a bullet of the same nose and length as our pellet that weighs 40g... and about a 1:25 twist at 500fps...

now it is time to jigger things a bit

 our pellet is about 32g... so 40 x .8 =32 so now change the density to 8 grms/cc and watch the twist rate needed rise for the same bullet at our 32g weight...

so is this a crude representation of our pellet at velocity..? it does sort of represent max twist we could possibly need to me...

so now enter those figs in the twist rate calc...

http://www.geoffrey-kolbe.com/barrel_twist.htm

I used  7gms/cc for a lighter pellet  cause I did this first as an estimate just to see the if I was close... what I got is below...shows my 1:19 twist XL 725 barrel looks good... the twist I used was L.W. 17.7

More to say about the mold and procedures but need a break... but I do think we can improve on the performance  and these can work as drawn...  so yep maybe a hint of some of the why of the 600 fps speed limit..?

 
EDIT*

the  Labradar measurements in the below thread seem to lean towards confirming my theory...  that the skirt drag and drag stabilization  decrease with velocity, reply # 26...

https://www.gatewaytoairguns.org/GTA/index.php?topic=124298.20

[Petetheairgunner]

Norm, NOE can easily cut a larger diameter, using the same tool (they just interpolate the circle larger in the mill to increase the diam.), but unless they make larger RG pins for the hollow base, the skirt thickness would increase.... Also, you would have to get this done while a production run is happening, or there might be an extra charge for a one-of.... Since the head of the existing pellets is large enough to bore-ride the lands in a .257, and the skirt large enough to engage the grooves, I would try some of the current diameter before going the custom route.... Tom at AAA found that .30 cal JSBs work fine in a .308 barrel, so stranger things have happened....

Bob

Hi Bob, the link I found to purchase the .25 mold does not work any more. Can you provide a new link?

[K.O.]

Here is the page for some of the .250 rounds used in air rifles... Most if not all are currently sold out I think... I have the .250 34g pellet and the .250/.252 40g slug... I have read Swede is working on getting some back in stock and with RG pins..

https://noebulletmolds.com/site/product-category/251

[K.O.]

oops looks like there are some of the 27g pellet molds...

[Insanity]

You can find it in the .25 cal section on the new sight.

[rsterne]

The original NOE pellet moulds have been discontinued.... It turned out the nose was too long, and the design was changed a couple of years ago.... Here are the two new designs....

https://noebulletmolds.com/site/product-category/251/250-27-rf-cc3-hunter-pellet

https://noebulletmolds.com/site/product-category/251/250-34-rf-br3-magnum-pellet

There is actually a wadcutter as well....

https://noebulletmolds.com/site/product-category/251/250-22-wc-cd1-target-pellet

but don't expect them to be accurate at 900 fps.... Keep them below 700....

Bob

[Madd Hatter]

Any idea when Al is going to make a run of the 34 grain .25 pellet molds? Been waiting and waiting but no joy yet.

[rsterne]

All I have heard is "soon"....

Bob

[Wayne52]

Well I bought my second ever break barrel and my first ever Hatsan 1000X.  I seen a deal in the bargain gate I couldn't turn down after Avator. . . .  Bill brought it to my attention when he had seen that I was thinking about ordering an XS46U from FDAR, well for $99 I couldn't turn it down and ordered one from Midway and got it yesterday.  The first thing I did was go out in my back yard and took three shots at a coke can and all three connected at 15 yards using the open sights.  I immediately went back insided, broke out the 250-22-WC mold and started casting after I chiseled of a good hunk of lead from the pig ingot, heated up the pot and mold.



Not only does that Hatsan break barrel look nice it's light as He$$ !!! . . . very cool

[K.O.]

If I had this original pellet mold am thinking that hollow pointing by hand would be an interesting endeavor...just might help it's balance problem...

If not...well...

 am thinking to deck it to a 75% meplat to help the balance issue... can even hollow point by hand a bit for further balance adjustment... Do not think it would make a good long distance pellet but at 25- 40 maybe even 50 yards just might make one heck of a hard hitting semi-waddcutter med range Hunter pellet...  Maybe  could talk Wayne into modding His.? could not afford to buy one unless it was about half price(fixxed income and some recent big expense)...and Knife was willing to do the decking and play with it for a while... A lot more practical than trying to turn it into a cylindrical pellet or changing waist/skirt angle...

used the .30 drawing to show about what it would look like... and honestly it brings to mind a heavy H&N  Baracuda Hunter X-treme with a bigger meplat... Really do think it could work... wonder if extra base pins to make custom base pins are an option(could help fine tune balance that way)... Below is a pic of some hand made hollow base/hollow point 40g .250 I plan on experimenting with... will even try sending the hollow base backwards for a salute to the Pamela mold..    

http://castboolits.gunloads.com/showthread.php?59198-Ever-See-A-17-Caliber-Mould   

https://www.airgundepot.com/h-n-baracuda-hunter-extreme-pellets-25-cal-hollowpoint-200ct.html#gallery-1

[rsterne]

You could probably get some of the long pins from Al, and then just shorten them yourself to end up in between.... That would be a good idea for anyone who wants to play with the balance of any NOE pellet.... If you are not aware, shortening the nose of the "Hunter" designs to increase the Meplat is exactly what I did to create the "Target" pellet, in fact the are cut with the same Cherry, just not as deep in the mould block.... From the feedback I have seen on the wadcutters, they aren't great at higher velocities, but perform well below about 700 fps....

If you want to make a jig to drill your own HP's, might I suggest using a center drill from a lathe.... They are short and rigid, with a 60 deg. taper on the main body.... The only thing you would have to watch it make sure that the pilot section doesn't go too deep and hit the base cavity.... Alternately, you could use a stub drill and grind the point angle to 60 deg. instead of 118 deg.... or maybe even use a 60 deg. pointed end mill....

I have the original .25 cal mould, and I might just try decking it someday....

Bob