Tuning Surprise! same slugs bad group at close range but good group at long range ?

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mubhaur

mubhaur

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Nov 8, 2015
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Karachi, Pakistan
Hi
A friend told me that he uses slugs exclusively. JSB Knockout are his favourite slugs in .22.

He further advised that he shoots these slugs at 1000fps and above and he achieves 1" to one quarter inch group at 100 yards.

Further he has done good shooting at beyond 200 yards.

He left his Impact with me alongwith slugs.

I chronied it and it was shooting 1010fps.

I tested the gun at my home range that is only 24 yards. But no good group couldbeachieved. A bit of shotgun pattern.

I called my friend on phone and discussed it with him that how he achieves accuracy.

He advised that at 24 yards, slugs are not accurate hence I should go out to at least 50 yards for testing.

I went out and shot a few groups at 60 yards and the same slugs were shooting around 1/2".

I am not a slug shooter but I witnessed myself this all.

I am unable to understand it.

Please discuss it and guide me that how a bad group at 24 yards becomes good group at longer distances with slugs.

Is it just a one of incident or its a regular behaviour of slugs?

Regards,

Bhaur
 
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Just shot this 24 yards group with same slugs. To me it looks like at least 1" group while the 60 yards group was either similar or most probably a bit better.

I just want to understand as I didn't found this phenomenon and discussion on it.

It never happens with pellets to me.

Regards,

Bhaur
 
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muhaur!
You should take a look at some of ballistic boy's threads. He is an expert in this field.
Here is a typical thread with his input....

Velocity vs. Barrel Twist Rates

Hey Folks, I curious if a faster twist rate of a barrel , while shooting slugs, will reduce the velocity verses shooting a slower twist rate barrel, all settings remaining the same? If so, how much velocity might be lost? Thanks, Mike
www.airgunnation.com www.airgunnation.com
 
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When any projectile leaves a barrel, it will have an initial yawing rate, i.e. it will be swinging from side to side. As Bob Sterne says, if it is dynamically stable, the amount of swing will decrease as it moves down range. It does not mean that the projectile is unstable when it leaves the barrel, it is just the normal behaviour of a spinning, stable projectile. When a projectile is yawing to any significant degree, we get what is called heave and swerve. The diagram below shows how a trajectory is usually shown from a trajectory program.

177traj4.jpg


In reality, the projectile is not following a smooth path, but one like this with heave and swerve.

177traj2.jpg


The above diagram is exaggerated to show the effect. If the yaw is decreasing to a significant degree, the heave and swerve will decrease until we get a smooth trajectory, not a wobbly one. This may give a small decrease in group size.

The only problem with this idea is that normally a high yaw rate close to the barrel gives an angular change to the line of the trajectory which will increase the group size with increasing range, as the yaw rate will be in random directions. The effect of the angular change will need to be less than the effect of the heave and swerve. It may be that it will not give increased group size with range is if the initial yaw rate is consistently in one direction, which suggests there is some interaction between the gun and the slug. Even then, any reduction in group size should be small.

Can we have simple questions next please? :(
 
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Angular convergence is probably mostly myth, though there are a few circumstances under which it can occur for real, though not due to bullets spiraling. And there are various optical and psychological explanations for apparent angular convergence. See Brian Litz' Modern Advancements in Long Range Shooting Vol. II, chapter two, for a serious exploration of angular convergence. With firearms, but the same principles apply here.

Reading that changed my shooting... I use smaller aimpoints, and work up loads at 100 yards only before moving further out (firearms). And I'm really careful about parallax adjustment with my scopes.
 
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It’s an Impact. That first group you fired at 24 yards was just getting the gun warmed up. When you shot at 60 the gun was up to operating normally. I’m being a bit of a wise guy with that statement but there is truth in it. Some slug tunes walk a very fine line. If either of my slug M3’s act a little crazy out the gate at 30 yards when I’m doing a POI check, I don’t jump the gun. I just keep shooting and 90% of the time they go to shooting all the bullets in the same hole. I’ve had 22lr rifles do this so for right now I’m taking a break from always wondering why. Now I just say why not. Too many things happen in slug land that send us off on wild goose chases. We search powder burner data looking for answers. They are not necessarily there. Yes our guns shoot projectiles. Problem is we don’t fire them. More things at play here. It’s good to discuss though. I just don’t jump to conclusions and run with it anymore. I could sit here and fill three pages with stories or data but I won’t. But I’ll leave you with this one. My M3 Compact .22 slugger for the longest time does this. First shot out to quite far is dead on. Animal left laying there, soul leaving the body. But the next 2-4 shots can wonder around a little. Not enough to miss anything bigger than a mouse but on paper, some slugs can be a half inch from each other. Then it’s spot on. Velocity is not jumping either. It is what it is. I’m too picky.
 
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