GTA
All Springer/NP/PCP Air Gun Discussion General => Projectiles => Boolit and Pellet Casting => Topic started by: scion19801 on September 19, 2022, 08:45:53 PM
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I realize there has been a thread or two on this. but I like to have my own. lol
so, I cast a bunch of these and just did a quick and dirty test without changing the tune on my impact. did a barrel swap from .22 cal. then turned power wheel to max. chrono seen an average of 790 fps for 23 shots. 77 fpe. 127 bar on regulator. 66-yard groups of 2 inches square. this was shot as cast. no sizing yet, no lube. no barrel stiffeners or support. using the superior liner. no heavy liner yet. sizing dies on order and awaiting arrival.
I cast pure lead and seen a .2 gr difference in the two cavities. I get a 56.1 average weight. NOE you guys' rock at making molds. Always been impressed with NOE molds. I got the 2-cavity brass mold. At this power and against a steel target this slug just compresses to a pancake. the hollow point is massive. can't wait to see damage done on game and if slug can be recovered after a hit.
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Nice basic review! What twist rate on your impact?
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std. superior has 1:22 if I'm not mistaken
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std. superior has 1:22 if I'm not mistaken
Gotcha!
BTW- What did you use to polish the pins?
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500 grit sandpaper. chucked the pins gently in a drill a hit them quick. I used magnifying glass as I did and watch for turning marks to smooth out.
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I prefer the cup point pins in the .22 cal mold.
(https://i.imgur.com/sX8fCK6.png)
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Had a chance to work on a tune. 140 bar on regulator. valve almost wide open at 9.62mm. hammer at 19mm. power wheel on max. seeing an 888 fps average. Now these so far are being shot as cast, stacking at 30-66 yards. stable. I dropped a few into 100 yards but starting to see stability loss and corkscrewing. Remember this is a 1:22 superior. I think the Heavy superior liner may clear that up. Sizing and lube may get a speed jump as well.
Thought I'd post some findings as I dial this slug in and give some ideas of what this slug is doing.
Edit:
I also printed a barrel band and tensioner spacer to firm up the barrel. Still has Orings supporting the liner
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Sounding really good, Dan!
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Heavy liner in route. just found one in stock and ready to ship. Thus far the tune is holding, and things still look good when used through the superior liner. Got my sizing dies yesterday and tried the .299". groups are still holding, and speed seems to be up just a touch. I also just got strelok pro and playing with dialing in the weather and speed figures. BC listed seems to be very close to what I'm seeing at .0751.
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I just ran the .30 cal 55 gr. slug through the Kolbe twist calculator with a 22" twist, and it has about twice the stability needed.... Certainly no need to go with a faster twist.... In fact, a 32" twist is fast enough.... The 26"twist TJ's would be plenty fast enough....
Bob
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Bit stuck on twist rates with the impact. 1:22 in the superior. 1:18 in the heavy superior. then there is the super slow 1:37 superior that has been mentioned before out there in the wild some place.
if this has twice the twist rate needed in the 1:22, then why would I start seeing corkscrewing and stability loss at 100 plus yards? Is it due to the twist being way too much?
Maybe i need to mount up my camera and get some video and slow it down to see what the slug is really doing at closer range. It may be cork screwing but it sure is consistent if it is doing so. consistent to the point of stacking at 33 yards.
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That's good info, Bob. I'll have two barrels to try, my slug A with a 1:21 twist and an STX with a 1:40 twist. It sounds like the STX maybe too slow though.
I just finished seasoning the mold and casting a few up. Spot checking a few for weight they look to be right at 56gr using pure lead. I ran a few through a 0.300" body bushing and had about 3/4 markings around them. I then dropped down to 0.299" and had full markings aroud them. I'll have to finish sorting to know more.
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Yes, if the twist rate is too fast, you are more likely to see spiralling/corkscrewing at longer ranges.... The reason is that the slug slows down faster than it loses RPM, so at 100 yards, it acts like it was shot from a faster twist barrel than it does at the muzzle.... When projectiles are "overspun", they can become Dynamically Unstable, which can lead to wobble and spiralling.... It is very common for pellets, less so for slugs, but it can happen....
BTW, when I said the stability was about double what it needed, that does not mean you can use twice as long a twist rate.... Stability varies with the square of twist rate, so changing from a 22" twist to a 32" twist would reduce the stability by (22 / 32) ^2 = 0.47 of what it was with a 22" twist.... It was roughly Sg = 3.0 at 1000 fps, so that would drop to an ideal 1.5 in a 32" twist.... The only way to find out if it works in a 36 or 40" twist would be to try it.... It may work fine, depending on the MV, as slower speeds need less spin (when Subsonic)....
I just ran a 36" twist and a 40" through Kolbe, and I got Sg = 1.4 at 1000 fps for the 36" and 1.3 at 850 fps for the 40".... The 36" should be fine, the 40" may be marginal, but might well work if you don't push it too fast....
Bob
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Bob,
thanks for the insight. your knowledge is respected. So, it seems my next liner to try and find with be the slower 1:37 slow twist 30 cal 700mm liner. right now, my tune is hanging around the 900 Fps with this slug.
I did manage to get some 33- and 66-yard shots on my scope cam and slowed them down in post video editing. they are flying straight and true. due to light conditions and angles I was not able to get good 100-yard shots on video just yet, so they could be checked to see what is going on.
Triggertreat,
I just tried a magazine worth of this slug sized to .298, the pattern opened up and terrible accuracy. the .299 seems to be the ticket. seeing about the same weight consistency you are at a 56.1 gr with pure lead.
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My fist cast yielded a 206 count with a 0.58gr spread. I did have a number of culls with the HP tips not being fully filled out or being slightly catawampus. I have them sorted per the base grain weight and will shoot them in those groupings.
These do have some deep sockets and like to stick to the pins. I was able finally get them to drop using one hand while opening the mold up. Some did need a slight tap of the handle screw though. I was able to get to this point by putting a drop of 2-cycle lube in one of the HP sockets and dipping the pins in it. I cast these at 735°F.
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i cast at 800 on my pid. i also polished my pins. was having the same sticky hp as you did.
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i cast at 800 on my pid. i also polished my pins. was having the same sticky hp as you did.
I'll try bumping up the PID temp next. These are a little more critical in getting the tips perfect it seems than the pellets are and is why I decided to go brass for these to help hold the heat more. I got 206 that look good but am tossing quite a few others back into the pot. Looking forward to seeing how your heavy liner does before ordering one.
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based off Bob's input, I think we need to get ahold of the new super slow liners. the 1:37 twist ones. so far, my search hasn't located one.
But my heavy liner is one its way as well as a removable barrel tuner as well. Made an adapter for the lee hand press. listed in the 3d print gate. helps a ton when sizing.
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new 1:18 twist liner arrived today as well as fx harmonic barrel tuner. Props to SPAW for the 2-day early arrival. No chance to try them out yet. so more to come. I did get my mag that I 3d printed sorted out and working for 30 cal now.
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new 1:18 twist liner arrived today as well as fx harmonic barrel tuner. Props to SPAW for the 2-day early arrival. No chance to try them out yet. so more to come. I did get my mag that I 3d printed sorted out and working for 30 cal now.
Nice!
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Interesting results so far. the 1:18 twist heavy superior has this slug hitting higher than the 1:22. the only change was the liner. I had to decrease my turret setting by half a rotation to come back to the 1:22 twist zero mark. Also, hitting way right at 100 yards, and only slightly right at zero point of 33 yards. Need to test more. this was just a quick observation shooting almost a mag worth to see where things were at. grouping has also opened up some as well. Need to air up and throw on the camera to get slow motion on some shots to see if the slug is spiraling and that could be accounting for the way right at 100.
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Could also be barrel harmonics....
Bob
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need to get more lead stock. this 30 cal mold eats it up in a hurry. LOL. scored 29 lbs at my local scrap yard *.84 cents a pound) but I want at least another 75 lbs. yet.
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I wished I could play but am in the middle of packing and moving out of state. I'll be taking a good 80 pounds of pure sheet lead with me though.