
Here are the bullets. 36gr looks as heavy as the 55gr
The reason the 4th bullet tripped people up was they assume they are all made of the same material Just looking at them the far right bullets has to be at least 50-55grs not 36grs right?
But if one were told just the weights and caliber a 36gr might be assumed to be good for 1/14 twist. I think maybe listing bullet lenghts or at least recommended twist rates would be more helpful than the standard velocity from a 24" barre spec.
It does seem that bullet length and not weight is what people should be talking about when trying to match twist rates to ammo/bullets.
What was it, the 62gr but super long tracer round that prompted the changes to 1/7 twist? So its not new information but manuafactures don't seem to want to list a simple bullet length on boxes (yes some do for just the bullets but not ammo)
Curious if any of you had issues with these alloy bullets in 1/12 twist 223s or 22-250s. Wondering how many people have issues with these long for weight bullets. I've seen some people saying the VG don't shoot good at all from their guns but they often don't mention what twist rate or velocity they shot them at.
I found it interesting just how much longer some of the bullets were in relation to their weight. Most articles (not all) never mention bullet lengths or stability or why a bullet wont shoot well. I would guess many reloaders have spent time trying to get instable for twist bullet to shoot using various powders only to give up saying the bullet is no good but not really knowing all the possible reasons why.
I Looked at some common bullets to see a trend using Berger and JBM(corrects for plastic tips) twist rate calculators looking for trends. Anything over SG of 1.0 can shoot well but the BC is comprimised. Looks like anyting over 1.3 should shoot well and not have too badly comprimised BC. SG of 1.5 seems to be the point where any additional spin won't help the BC of the bullet.
Temp 59, Atl 0 (Sea level)
(under 1 UNSTABLE 1-1.49 marginal, 1.5 and up = stable)
It seems that Flat based bullets get some "Free" stability just from being flat. So a flat based bullet with SG of 1.2 might be like a boatail with a SG of 1.5 BC and stability wise. They had a separate chart for flat base and omitted all bullets under like 70 grs.
3000 fps spin rates for 1/12 and 1/9 twist = 180,000/240,000 rpm
Things to increase SG
Alt - .048 per 1000 ft
temp - .025 per 10d increase
lower twist - .2 to .6 per twist increment (depends on bullet)
Velocity - .01 per 100 fps increase
The Miller stability value. It should be between 1.3 and 2.0 to ensure stabilty (the military uses 1.5) Barnes uses 1.5 and JBM uses 1.3 for lowest number for stability.
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Example: A 53 gr vmax which is not stable at sea level 59F in a 1/12 Could be made to shoot well without modifying the gun.
Sea Level SG = .927 and bullets are keyholing all over. Then takes a drive to a buddies house who lives at 6,000 feet and its a hot spell. Now the gun is shooting the same stuff lights out!
Change to 6000 feet + 100 temp = SG goes unstable SG=0.927 to 1.25! Issue solved just have to move to new house in the mountains.
Increase the velocity from 3000 to 4000 and SG is 1.37 which lowers the BC some.
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All the numbers I used were default settings of 59F and Sea level. Anything faster, higher altitude or higher temps will be more stable. Any bullet with a plastic tip should use the JBM Ballistics program. So unstable might be stable when the plastic tip is taken into account. It looks like a plastic tipped bullet they take about 2/3 of the tip off for a new OAL bullet length. So a 1" platic tip bullet (Tip is .141") is treated like a shorter bullet 1" - 2/3 the tip lenth. Not exact but a trend I saw.
35 Vmax .517" BC G1 (.109) Berger Stability 3000 fps 1/12- 2.28 (stable) 1/9 4.06 (stable)
35gr NTX .767 BC G1 (.177) Berger Stability 3000 fps 1/12- .841 (UNSTABLE) 1/9 1.50 (stable)
36 VG - .697" BC G1 (.149) Berger Stability 3000 fps 1/12- 1.03 (marginal) 1/9 1.83 (stable)
40 Vmax .689" BC G1 (.200) Berger Stability 3000 fps 1/12- 1.18 (marginal) 1/9 2.10 (stable)
50 Vmax .800" BC G1 (.242) Berger Stability 3000 fps 1/12- .969 (UNSTABLE) 1/9 1.72 (stable)
50 VG - .858" BC G1 (.183) Berger Stability 3000 fps 1/12- .793 (UNSTABLE) 1/9 1.41 (marginal)
53 Vmax - .829" BC G1 (.290) Berger Stability 3000 fps 1/12- 0.927 (UNSTABLE) 1/9 1.65 (stable) (JBM 1/12 plastic tip 1.306)
55 MPG .935" BC G1 (.225) Berger Stability 3000 fps 1/12- 0.681 (UNSTABLE) 1/9 1.21 (marginal)(Manf 1/9 twist or faster)
55 FMJ - .735" BC G1 (.243) Berger Stability 3000 fps 1/12- 1.36 (marginal) 1/9 2.41 (stable)
55 Vmax .813" BC G1 (.255)
60 Vmax - .870" BC G1 (.265)
60grHornSP.700" BC G1 (.264)
69gr SMK .898" BC G1 (.301) Berger Stability 3000 fps 1/12- 0.960 (UNSTABLE) 1/9 1.71 (stable)
Based on weight a 1/12 should stabilize any bullet 58gr and lighter. But based on length of bullet roughly .7" and shorter will stabilize.
Barnes recommends 1/9 twist or faster with the 55gr alloy MPG bullet. When plugging in the numbers it comes up as marginal for 1/9 twist SG=1.21. Maybe look at SGs of 1.21 and higher in terms of will it stabilize from your rifle. Maybe of the bullets that say "Unstable" are probably stable enough to shoot well except maybe ones near SGs of 1.0 like the 36gr VG in a 1/12 twist.
No good way to calculate the true SG of the VG because it has a flat base and the Berger is only good for boat tail bullets. So a bullet with a SG of say .90 (Unstable) but is also a flat base might be stable. .9 + (Flat Base) modifier = SG for flat base. Just don't know what that modifier is. I would guess at least .1 added to SG.
Velocity seems to trump all when it comes to marking boxes of ammo for the public. I don't think I've seen ammo with twist rate and bullet length listed. You sort of need to know bullet lengths when reloading yet sometimes I have to wait to get the actual bullet and measure it to find out. Wonder why they opt to not list that specification so often?