Just got my Airmarksman Ace slugs

[Ballisticboy]

I know the math says the 40.1gr Ace slugs shouldn't shoot the best from a 1:16 twist liner but, I just shot all of the slugs I shot the other evening.

The Ace shot the best of all of the slugs I have.

I shot 8 shots of each slug, 3 to confirm zero and then a 5 shot group.

Each of the slugs shot MOA or slightly over MOA. Any one of them capable of being a fine slug for shooting varmints.

Ace 3 shot group to confirm zero.
View attachment 586834

5 shot group that followed
View attachment 586835
I consider #2 shoot shooter error.

Now if they make it a hollow point boat tail of the same design and 34, 35 or 36 grain !

I didn't say it couldn't be shot from a 16-inch twist, I said it will start off being unstable, but the level of instability is small so it will soon gain stability as it slows down. Also, if the slug is a good fit in your gun and leaves the barrel with very little yaw or very small yaw rates, then it will still fly well, and you may well get away with it. Minimal stability will give smaller groups for a well-matched slug and barrel, the problems occur when the slug and barrel are not well-matched as any yaw will not damp out and may reduce BC as well as giving increased group sizes. That is when you need more, but not too much, stability.

 

[drumie]

I don't remember in any of the videos of them saying they had a higher BC than the Altaros but they did say you can push them faster and get the same accuracy with them. That I have noticed with my little testing so far. Also with a 1-16 twist marginal that might be why they get the best accuracy shooting them fast. It would be nice if FX does put out a 1-14 liner for us to buy. I have a 600 Dynamic that shoots the Altaros great at 900fps. I just set up a 600 Panthera to shoot the Ace so I can compare. Gonna push them over 1050fps and see how they do.

 

[Impact701]

Neither Strelok nor the Element ballistic app have the capability to accurately calculate the gyroscopic stability factor. To do it properly, you have to have the moments of inertia, and the aerodynamic pitching moment coefficients at all Mach numbers. Software like McGyro and the Kolbe calculator can be used for supersonic bullets, but they make sweeping assumptions and fall apart between Mach 0.9 and 1.1, which is OK for bullets from firearms, but is not good for airguns, neither can they cope with large meplat projectiles.

The software I used is not exact, but it was good enough to be used for initial estimates for bullets, shells and anything else fired from guns at high spin rates. A very early version can be found on the JBM website called Intlift which was based on RARDLIFT, the original spinning projectile aerodynamic program developed here in the UK and sent over to Bob McCoy under a software exchange program.

I dug a little deeper into the Applied Ballistics App.

Airmarksman/Corbin has designed a very accurate slug.

 

[Impact701]

This is where I got the BC

Could it really have a BC close to a 223 Remington 55gr V-Max ? ?

 

[Centercut]

This is where I got the BC

View attachment 586955

Could it really have a BC close to a 223 Remington 55gr V-Max ? ?

View attachment 586956

In Dub-dubs video, he got a believable 0.195 G1. Like I said in my previous post, mine was about 0.160 G1 from similar 1:16 twist 700mm barrel.
So 0.245? I do have a bridge to sell in Manhattan if anyone is interested

 

[drumie]

I wonder what the BC would be if shot out of a 1:14 barrel? Might be better since they might not be fully stable in a 1:16 barrel? Just a thought. But I don't think it would go from .195 in Matts video up to the .245 claim.

 

[Centercut]

I wonder what the BC would be if shot out of a 1:14 barrel? Might be better since they might not be fully stable in a 1:16 barrel? Just a thought. But I don't think it would go from .195 in Matts video up to the .245 claim.

The BC in Dub’s video in the Impact with 800mm 1:14 was about 5% better than the 1:16 twist 700mm guns. But nothing to write home about.

 

[drumie]

The BC in Dub’s video in the Impact with 800mm 1:14 was about 5% better than the 1:16 twist 700mm guns. But nothing to write home about.

Ok, I guess I missed that part. I figured it would be just a little better. But they seem to shoot as well as the Altaros or better in the guns I have tried them in.

 

[Centercut]

Ok, I guess I missed that part. I figured it would be just a little better. But they seem to shoot as well as the Altaros or better in the guns I have tried them in.

Agree. They are very similar to the Altaros King 40 grain. Both are very accurate. IMHO, the Altaros have a slightly better BC, about 5-10%, and are slightly more accurate, especially past 100Y. At the Utah WFAL 150Y BR weekend before last, the Altaros took 1st and 2nd over ACE and ZAN.

PS, when comparing make sure you compare apples to apples. Manufacturer recommended speeds for Altaros are 880-910 fps, and ACE are recommended much faster at 970 ish fps. No one has compared them at manufacturer recommended speeds, and most have tested them at the same 960-980 speed, like Dubber did. Had he tested the @Altaros at manufacturer recommended speeds, the results would have been much different.

 

[drumie]

I have only tired the ACE out to 100 yards and they just stack. Also they seem not as picky about a tune as the Altaros. I set a speed in 3 different guns and at every speed they just stacked. Better groups than a long of slugs even after finding a good tune. I am sure I will have to tune once I start to shoot farther out. The Altaros seemed like they did the same but between 850-910fps. As long as you were in that speed they shot great. Get too fast and not so much with most guns.

 

[Ballisticboy]

I tried something different for the stability factor. I modelled the projectile with a cylindrical base, i.e. no boat tail. The results are below.

M​	Sg​	Sd​	State​	sd*(2-sd)*sg​
0.3​	1.65​	0.825​	Stable​	1.6​
0.5​	1.452​	0.705​	Stable​	1.326​
0.6​	1.445​	0.576​	Stable​	1.185​
0.7​	1.388​	0.435​	Unstable​	0.944​
0.8​	1.327​	0.341​	Unstable​	0.751​
0.9​	1.264​	0.305​	Unstable​	0.654​
0.925​	1.248​	0.284​	Unstable​	0.609​
0.95​	1.232​	0.332​	Unstable​	0.683​
0.975​	1.217​	0.366​	Unstable​	0.728​
1​	1.203​	0.406​	Unstable​	0.779​

While I do not know exactly where they have got their figures from, it looks to me as if an approximate method has been used which does not take into account the destabilizing effect of all boat tails. By their very nature, boat tails produce destabilizing moments about the CG, it is a basic property of boat tails. Empirical methods which may work for cylindrical base slugs will not work when a boat tail is added. The stability prediction software must take into account the boat tail effects to give an accurate estimate. The comment on the tin regarding the boat tail is not correct for this reason. The boat tail used may be less destabilizing than many others, but it is not a stabilizing tail geometry, it would need to be a flare to do that, not a boat tail.

The projectile is still predicted to be unstable, even though it is predicted to be gyroscopically stable due to the dynamic stability factors. The equation above the final column needs to have a value greater than 1 for complete stability. Many small arms rounds are dynamically unstable, but it is not a major problem at the relatively short ranges in small arms fire.

 

[Impact701]

That's a lot of math !

 

[Ballisticboy]

That's a lot of math !

Not with the right program.

 

[drumie]

I got a chance to shoot these in almost no wind out to 400 yards. Out of my 700mm Panthera at 997fps groups at 400 yards looked to be right at MOA. I didn't walk out to measure but it was fresh painted steel. Very good groups for a liner that has less than 100 rounds thru it. My FX chrono had a BC average for these slugs at 0.244. I punched in my numbers into Hornadys Ballistic app and it also comes up with .24 as a BC using my dope. So I think they are very close to the Altaros slugs. But this is just my findings with one gun at one speed. But the more I shoot these slugs the more I like them.