Testing NEW 6.5mm Cerberus 90 Bullet

[BluntForceTrauma]

CC, I'd be hesitant to specify a barrel twist dedicated to one particular bullet. The Cerberus 90 and 85CZ are both 1.25" long, about the same as the A-Max, etc. I fully plan on sticking with 1:8, just so I can shoot these on up to that gorgeous Berger 130 OTM.

The jury is still out on accuracy, although since I hand-seated the tips on the prototypes, it's entirely possible I introduced anomalies. We're going to fix that variable in the upcoming run of C85CZ, which will mechanically seat the tips for better consistency.

1075T, under magnification you can certainly see lathe marks, just as under magnification the surface of a Barnes looks like an orange peel! I can't prove it, either, but I don't think there's any measurable effect on accuracy.

Stay tuned!

[customcutter]

I knew there was a formula for figuring twist rates. I was able to find it tonight. Anyway I plugged in .264" dia, and 1.25" length and it came up with 1/8.36 twist rate based on multiplying by 150. If you get up over 2800fps they said to substitute 180, which give you 1/10 twist rate. The author talks about how over stabilizing the bullet causes the tip to ride high during the flight and it loses velocity quicker, which is detrimental to long range shooters but has little or no effect on hunting ranges. However, to low of a twist rate causes the bullet to yaw during flight and opens up the group at shorter ranges. It's an interesting read for anyone wanting to know more about it, here's the link.

http://www.shootingtimes.com/ammo/ammunition_st_twistrates_200809/

[BluntForceTrauma]

Thanks for the info, CC, it seems that — as with too many things — the "experts" disagree. I could be wrong, but I seem to remember Litz saying there was almost no downside to "over-twisting" or over-stabilizing bullets. I'd have to find it and make sure he actually said that, though, and his rationale for it.

[newb]

In all of my researching reading I have seen the same newer conclusion stated that over-stabilizing (within reason) is not a prob anymore, or not a prob as was once thought.

[JASmith]

The author CC refers to may have been thinking of the tendency of some long range artillery rounds to land in roughly the same attitude they were launched at.

There are more reasons why a slightly off-balance bullet might be less accurate when overspun. BTW all bullets are slightly off balance to at least some degree even though we can't measure that off balance in the best bullets.

Also, Berger has for years advocated that the best accurary is obtained when the bullet is marginally stable as opposed to overstabilized. These statements predate Litz' appearance at Berger.

[customcutter]

The auther CC refers to may have been thinking of the tendency of some long range artillery rounds to land in roughly the same attitude they were launched at.

There are more reasons why a slightly off-balance bullet might be less accurate when overspun. BTW all bullets are slightly off balance to at least some degree even though we can't measure that off balance in the best bullets.

Also, Berger has for years adocated that the best accucarcy is obtained when the bullet is marginally stable as opposed to overstabilized. These statements predate Litz' appearance at Berger.

Do any of the testers have a 1/9 twist barrel to test accuracy, compared to the 1/8 twist barrels? I'm not saying overstabilizing is the accuracy issue, but it can be easily elimanted from the equation, by a few shooters with 1/9 twist rate barrels.

[bwaites]

Over stabilization is a myth in rifles. Per Bryan Litz:


As a bullet arcs on a long range trajectory, it’s axis is torqued (by aerodynamic forces) to constantly align with the oncoming airflow. When a spinning object has its axis torqued, the object reacts by pointing its axis primarily ‘out of plane'; 90 degrees from the applied force. This results in a nose-right orientation (for right twist barrels) known as the yaw of repose. The yaw of repose steers the bullet ever so slightly to the side resulting in gyroscopic (spin) drift.

The bullet nose will point slightly above its velocity vector (pitch), but that pitch is only about 1/10 of the yaw of repose which is not enough to cause a practical vertical drift (less than 1/2″ at 1000 yards). Typical yaw of repose remains below 1/60th of one degree, while pitch is on the order of 1/600th of one degree. This small amount of pitch and yaw is not enough to induce a measurable amount of additional drag, even for highly stabilized bullets.

All of the above applies to stable projectiles in supersonic flight on ‘flat fire’ trajectories. For projectiles fired at high angles (above ~10-20 degrees above the line of sight), it is possible for the bullet to not track, or trace with the trajectory. This is a common design challenge for artillery shells that are often fired on high angle trajectories. The axis of the spinning shell may be too rigid to bend with the exaggerated trajectory. In that case the shell can ‘belly flop’, or fall base first. However for small arms projectiles on flat-fire trajectories, this isn’t a problem.

Another consideration with spinning a bullet too fast is related to bullet failure. This discussion assumes the bullet remains structurally in tact.



It certainly will not affect Grendel velocity bullets. MAYBE if we got these up in the 3500+ FPS range there would be a measurable effect, but I sincerely doubt it.

In fact, most of the serious long range shooters prefer a slightly tighter twist to what might be the "ideal" for their bullet.

[kmon]

How consistent are the heals of the bullets and the rifling marks on the bands at the back of the recovered bullets? You can file a tip a little to one side and it will still be pretty dang accurate but a little off on the base of the bullet where gasses act upon it at exit of the barrel will cause a lot more adverse effect on accuracy of the bullet much like a damaged crown will.

[Joseph5]

I read an article in Sniper magazine that Todd Hodnett wrote and if I am remembering correctly he had a barrel made for a 308 that was a 1 in 4 twist that he was using for testing and found no negative effects from the fast twist. He said that it allowed bullets to stay stable when they transitioned from supersonic to subsonic at extended ranges making for more predictable trajectories.

[customcutter]

Well it's almost 2 in the morning. I read the post several days ago in the Howa bolt thread, and it looks to me like the Cerebus is stringing horizontally (call me CRAZY). I've thought about this for several days now, but if the tip is even slightly out of concentricity, I think it's going to cause it to string to the right because it's a right hand twist. Put it a little further out of concentricity and it's going to string a little further to the right. Maybe we'll find more info when the next batch comes in and some are tested with out the tips mounted....

I keep reading the first paragraph of bwaites reply, especially the last section of it and thinking about a tip that exacerbating that phenomenon....

I certainly want these bullets to work. I'd love a high BC bullet, with higher velocities. Just trying to help figure out the accuracy issue.

[BluntForceTrauma]

Changed the tip design slightly to promote earlier opening, and it is now in the hands of the machinist, but I don't have an ETA. Concentricity of both body and tip, and concentric seating of tip are all givens. Gonna test 'em when we get 'em.

And accuracy-wise, I'm perfectly willing to blame a new prototype bullet first — it's only fair, after all — but there really are a LOT of little things that can go wrong with accuracy in a gun-cartridge combination, even with a proven weapon and proven bullets. So, it's a step-by-step process of isolating variables.

[customcutter]

I looked back through the thread for accuracy group pics and didn't see any. Just wondering guys, did you see shots all over or notice what I say more of a horizontal stringing?

One other variable comes to mind. I'm wondering who is shooting button rifled barrels vs cut rifled barrels and if that is showing any difference in accuracy?

I agree it's a matter of eliminating/isolating the variables changing one at a time, noting the result then change another. If you change 2 or 3 at once it's just guess work as too what is doing what. We will figure it out, it's in everyone interest for this to succeed.

[rickOshay]

Comparing tip vs. not tip

Here are my results, comparing the 90 Cerberus with and without the tips at 100 yards indoors with my 17.5" Lilja.

I started out shooting 95 VMAX over 30.5 gr H335 to get warmed up and sighted in. Then a 3-shot group as a control. On these targets, the grey square is 1"



So far so good. Then a 5-shot group of C90s over the same load of H335.



Then a 5-shot group of C90s w/o tip using same load, but manually fed because these won't feed from magazine.



You could argue that those w/o tips shot better, but neither was very good. Interesting that the C90s shot low left compared to the VMAX.

Rick.

[customcutter]

Rick, any idea if the top left shot in the middle group with tips was first or last shot of that group possibly? I'm guessing/thinking first, for one of two or possibly both reasons. Cold barrel or copper fouling from copper bullet versus guilding metal jacket.

Everyone might want to try shooting an accuracy control group before and after testing with the C90's. Just to see if anything has changed or eroded the accuracy potential.

[rickOshay]

Not 100% sure, but I think it was 1st. I remember thinking "WTF".