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rickyburkhalter
I have been at the range twice with the new bullets. First outing was so so. I’m still working on getting my rifle accurate. I just built it about a year ago. The second range time was a lot better. I cast these using 5lbs of lead and 2oz of tin. My rifle has a 1:20 TJ barrel and the bullets are designed for 1:14.
Shot string from first test.5 shot groups 2900psi fill untethered
809
805
801
809
798
AVG 804
ES 11
SD 4
FPE 193.82Bullets
Target @ 100 yards from second test. Just under 7/8″.
rickyburkhalter
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Replies
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tomkerrigan
rsterne
Tom, in general terms, the worst stability is right at the speed of sound, and as the bullet slows down the stability increases…. The calculations for that bullet show a 14″ twist as being optimum for high Subsonic, so I’m a little bit surprised they are stable in a 20″ twist, even at 800 fps…. Shooting them faster, in a 20″ twist, would likely cause problems….
The only caveat here is that bullets didn’t go to school, and can’t read or do math…. The use of boattails in airguns is so new, and we have so little hard data, that we are basically in a “try it and see” situation….
Bob
kirbyolsen
I am not aware of any method to cast a bullet that is both hollow point and hollow base, as you need one end flat to allow the sprue plat to cut off the sprue…. It is possible to make a hollow base bullet by making a mould that is a nose-pour design, but whether or not NOEs manufacturing method suits that you would have to PM Al (SwedeNelson) to find out….
If is, however, entirely possible to change he HP pins to vary the weight removed…. and the larger the cavity the further back the CG moves…. This increases the distance from the CG to the CP, which is ahead of the CG…. This particular bullet has too small a Meplat to suit the RG2/RG4 style HP moulds, so all that is available is the Lyman style HP pin in one cavity only…. You would have to ask Al if he can supply different pins to allow you to experiment….
I do not know if NOE can supply plastic tips, again something you would have to ask Al….
Bob
Bob
I was thinking to try milling the hollow base post casting and also the hollow point in order to be able to test and prototype… then the pin/pins…
was also thinking of making the tips myself… But I think Carl had Eric make some for Als 80 gr .257 ?
the corbin tips are $$$… 500 for 95$ and so are the cutting edge (if they sell the .308 tips they do make a .308 bullet)… tips are bout 13$ for just 25…
me I picked the 40gr .250 to see if it makes it thru the choke on the Marauder better and for fpe reasons… but then maybe the 51gr .250 will be easier to get thru the choke with a deep hollowpiont and try and balance the round with a hollow base… get it down to 44gr or whatever is possible..? size just under groove and knurl drive band to help get past the choke..?
just brainstorming on how to adapt the .25 to 50-60 fpe and a choke besides just shortening the boat tail…
teemu
I had change to test those BBT .30cal bullets. Gun was Dutch made Warrior and bullets was sized to .309. This was first time when I shot this rifle and I could not get good position my sandbag was not that tight what it should be.So results could be better if there was someone who is familiar this rifle and had better sandbag and blaa blaa
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7 shot was 38mm but those 3 flyers…Could be wind or my fault.. This was 10 shot @ 109 yard
Ricky ran some downrange velocity tests today, so that I could calculate the Ballistics Coefficient…. He shot 10 shots, in two 5 shot strings, with the Chrony at 1 yard, refilling between strings, and then moved the Chrony to 51 yards and repeated (50 yard separation)…. The 10 shot averages were 803.5 fps (2.6% ES) and 773.2 fps (1.7% ES)…. The average temperature was 82*F, altitude 269 ft., barometric pressure 30.03″, and humidity 89%…. I ran these numbers through my own Spreadsheet, the JBM BC Calculator, and ChairGun, and using the G1 Model got BCs of 0.163, 0.164, and 0.165, so the average BC (G1) at 50 yards, at an average velocity of 788 fps is 0.164, corrected to ICAO conditions….
Thanks for your help, Ricky, much appreciated….
Bob
rsterne
tomkerrigan
kirbyolsen
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