GTA
All Springer/NP/PCP Air Gun Discussion General => Projectiles => Boolit and Pellet Casting => Topic started by: Mr.P on December 23, 2020, 10:42:15 PM
-
Did some casting with a new mold which got here from NOE in record time. I can't recall the product code but it's for 50 grain .25 boat tail with drive bands. I believe these are what you all call "Bob's Boat Tails"...
It was very cold out and i haven't sorted through these. First handful had light wrinkled texture until the mold heated up but like all my molds casting is really easy and works without much messing around at all.
I smoked the mold first as per directions. Overfilled one 350 count jsb tin in about 35 minutes of casting. Hollow points are about 48 grains, solids are about 51 grains.
It's funny because I expected casting to be difficult based on what I read online... almost didnt give it a try at all after reading some of those posts. I wonder why this ends up being so difficult sometimes? Was I just lucky and got some particularly well-made molds or something, or maybe by reusing old slugs and pellets I am avoiding using the wrong alloy? Or do I just not realize how bad my slugs are!?
-
I have that mold I use with my M11 Artemis .25 my experience with the NOE BBT molds is they are pretty easy to cast, pellets are a it trickier for sure, not for beginners IMO, but worth a try if you have some skills.
Nice BBTs BTW ;D
-
Those look good to me. It's all about temperature when you're casting. I tend to run my pot a little hotter when I'm casting smaller bullets and hollow-points. Smoking the mold keeps you bullets from sticking and helps them drop out easily. I coat my hollow-point pins with a little graphite before I start too.
-
Thanks - I imagine diablos would be challenging with the waist and skirt - that's probably what the difficult experience folks were casting I suppose
I had a little sticking to the pins and will try smoking them again.
I am used to the MP 8 cavity mold so it really feels like slow going with the four cavity mold at first. I decided to do 1/2 deeper hollow point and 1/2 solid. Will try the shallow cup pin some
other time.
This probably is to be expected but surprised me - the hollow points are easier to seat deeper into the barrel. Guess even with that pin you end up with a smaller diameter.
The seems to shoot well but what can I tell with my indoor 11m range? Was getting 46-63 fpe out of these with the power wheel between 1 and 6 on my .25 12" barrel airforce mashup gun.
My other gun will shoot these much faster - high 900's to 1000fps at least. Don't know much about these slugs and what is needed to stabilize them honestly.
-
On the FN slugs, you have the pins set too low in the mould.... They should be straight across, with no lip....
Bob
-
I noticed that thanks for pointing it out. Guess I have to bend the little metal tabs on the mold. I was looking at those not sure I can improve on it unless there is a trick...
-
Are you signed up on the N.O.E. forum... day gots destructions.. ;)
Tis a bit fiddly but not hard... and critical for the pellet molds to get just rit..
-
Or do I just not realize how bad my slugs are!?
What?? ya want us to list defects to watch for...
Fine... Mooning of the base
rounding of the base
and heavy smearing of the base.. ;)
there are others but they are obvious...
pick out the best sharpest bases and send them together... then if some have more rounding then send them...
may want to try weighing also...
some days I have more culls than others... the lee 50g Bators did not like being poured at 750* had to try just to see...
when I first go my 40g .25 BBT mold I kept getting rounded bases ladle pouring 4% tin @790*... was watching the sprue puddle go concave and realized my problem was shrink(have been a mold/core maker; aluminum foundry)... asked Swede for a .22 sprue plate(smaller sprue hole) and prob fixxed for my style of casting with a ladle...
-
Thanks for that detailed post. I've occasionally seen the smear or sunken base but I have the ladle with a pour spout that lets me put a little pressure on there and fill the sprue what seems like the right amount. Also had one time where there were little flanges on the base of some of the slugs.
I haven't looked at the range of weights, I just threw a couple on there. Will eventually look at that just out of curiosity.
It is satisfying to be able to make these and reuse my old pellets
I don't have any way to measure the temperature I just set the pot's dial at about 85% the first time and have it down to about 75% and still casting fine. I should check the temperature one of these days for sure.
-
I've been running some of these through the chronograph. They come out about 20 to 30 FPS slower than my MP molds .25 round nose slugs of similar weight. The MP slugs are around 47.5 grains and the BBT HP are around 48 grains so the mass is close. The MP slugs seem PERFECT for the barrel. Seat well, come out with high energy for their weight, very accurate.
These NOE slugs seem to shoot very well but are hard to seat in the Airforce barrels. A push to get the tip in and then a harder push to get the drive band in there. The boat tail always sticks out the back, drive band recessed maybe .2mm in the breech. thumb is sore from pushing hard... this tight fit plus the much thicker drive band hitting the choke is the reason for the lower speed I guess.
This is the smaller mold - .250 was the spec.
What do I need to do here? Polish the breech end of the barrel? Would tumbling these make them just a hair narrower? Is there a cheap resizing device I can push these through without investing another $150? Obviously I'm planning to get a slug barrel for these bullets eventually... just haven't made that happen yet but any day now. :)
Thanks as always for the guidance.
-
If you don't want to change the chamber, then get a sizing die and some bushings from NOE.... You will, however, need an inexpensive press (I use a Lee).... Once you have the basic setup, different size or caliber bushings are only $10 each....
https://noebulletmolds.com/site/product-category/sizing-tools/
Air Force chambers are notoriously tight, not a problem with pellets, a PITA with slugs....
Bob
-
I know I really have to experiment with this myself but is there any ballpark for a minimal low end speed for slugs like this to be stable / accurate? I have a gun that will shoot these at 1000 FPS but I'm just wondering if they will also be expected to work at lower velocities from my 12" barrel (650 - 770 FPS). The Huben guy who was involved in the MP mold said they were stable at low speed as well as high (this is the only other .25 slug I cast which is why I keep mentioning it).
I keep reading about slugs needing high twist rates and velocities but I think that's for powder burner bullets? Can these NOE air gun bullets be stable at lower velocity as well?
Thank you I have a lot to learn.
-
In the subsonic range, where airguns operate, stability increases at lower velocities.... The worst stability occurs just below Mach 1.... Don't be afraid to try slugs in the 500-700 fps range....
(https://hosting.photobucket.com/albums/oo221/rsterne/Ballistics/.highres/Lyman%20257420_zpsxaoknzqd.png) (https://app.photobucket.com/u/rsterne/a/ad32680a-7969-443d-ab0e-5a65c7b8979e/p/776bdd88-8e5e-4916-9073-6a97d487a26c)
The above is for a 257420, note how the stability increases as you drop further below Mach 1.... the left hand edge of that chart is 500 fps....
Bob
-
That's great, thank you.
-
I'm with Mr. Sterne. Thankfully my BSA barreled Gamo Urban loves the 217-30-FN BBT as cast. I'm launching them at 630 fps and they group well at 60 yards. I've done some slow motion scope came video and they are definitely stable all the way out to the target.
https://youtu.be/YY21dWGpcao
-
Hey Eddie
You need to tie a nylon string to that hog's leg and to the post, would save you walking ALL over your wood lot,
you could do MORE shooting than chasing that critter down ........LOL.......... ;)
It does look like a flying pig to me........ ;D
Tia,
Don