Changing My Thinking About Slugs

[ballisticboy]

Unfortunately, Ted's results are seem to be due to a series of his own mistakes. First, as said, he is using the wrong reference drag law, secondly he is using the least accurate method of finding BC by looking at drop, and thirdly, if you look carefully at his input data he is using the wrong atmospheric input data, unless he really is wearing shorts and a tee shirt when it is 0 degrees Fahrenheit. The trees have all their leaves on as well, which does not seem likely at that temperature.

So all three of the above taken together, it is not surprising he got an exceptional result.

[subscriber]

So, Ted was doing a snow-job on himself; unintentionally.  Prestidigitation, while pressing the wrong keys, as it were. 

Rather than argue about the BC numbers Ted calculated then, I wonder if his field experience since has him still shooting at 1100 FPS as a cure-all; or if he has reset back to 1000 to 1050.

[splitbeing]

Because Ted is using the G1 drag model, I’d expect the BC to read higher at velocities over 1000fps, but not as much as he reported. I would not even report that “BC” that I got from drop measurements without first confirming it with a check on velocity degradation. Besides muzzle velocity, He needs a chronograph reading at some distance down range. Without that, there are just too many things that can produce significant errors in a BC that was calculated from a 50yd to 100yd drop difference.

That tracks. Thanks for the clarification on the Ted mystery.

[splitbeing]

So, Ted was doing a snow-job on himself; unintentionally.  Prestidigitation, while pressing the wrong keys, as it were. 

Rather than argue about the BC numbers Ted calculated then, I wonder if his field experience since has him still shooting at 1100 FPS as a cure-all; or if he has reset back to 1000 to 1050.

Yes!  The experience he documented seems consistent with other experiences referenced in this thread. He's been quiet for a while and so we no longer have his experience as food for our thinking here, unfortunately.

[MJP]

So you finally figured the science out why we have said that shooting faster than your charts tell you we get smaller groups at distance aka less wind drift.

This is why I always stick to the tested facts and not on theory alone. Theory is a good starting point but when pushing the envelope a little you might find something that was not as the theory suggests.

Not here to say told you so, just to remind to ask why do they have this point and could the chart be faulty. Always question the theory if there are some that get different results that they should.

Edit: oh yeah forgot, the sweet spot should be around 1000fps, but consider the distance and how long you stay in that sweet spot?
The muzzle velocity can be significantly higher.

Marko

[rsterne]

Marco, my mantra has always been, when reality doesn't match the theory, it's time for a new theory.... In this case, the drag model everybody has been using for many years does not match the drag curve of the slugs we are using.... This is not surprising, considering the G1 model is for a spitzer, whereas our slugs have a blunt nose.... What IS surprising is that the drag for our blunt projectiles is less than what we thought, from 800-1100 fps....

While the "sweet spot" is around 1000 fps, the curves for optimum MV I posted in Reply #8 take into account the slowing of the slug over distance, you will note that the horizontal axis is the muzzle velocity, and the charts are calculated by the MERO ballistics calculator for 300 yards.... It is true that as you increase the range, the ideal MV increases, but not as much as you might think, since most of the angular wind deflection occurs in the first part of the slugs flight.... At 700-800 yards, the optimum only increases to about 1050 fps....

I realize that you are very much a "results oriented" shooter, and that is a good thing, as when your results disagree with theory, it pushes us to find a better theory to explain your results.... You are correct, it should never be a case of "I told you so", but rather of working together to further our understanding of our sport.... All the best....

Bob

[JungleShooter]

Just a great thread.
Bob delivers as usual.
Thanks for taking the time and effort to give us what no-one else would.

And this thread gets me closer to my dream of XLR (eXtreme Long Range shooting). 🤩

I just read about the best velocities.

And half an hour ago I bought the perfect (within my budget) scope for it.

Now I just need the RIFLE!!! 😄

Matthias

[Spacebus]

So you finally figured the science out why we have said that shooting faster than your charts tell you we get smaller groups at distance aka less wind drift.

This is why I always stick to the tested facts and not on theory alone. Theory is a good starting point but when pushing the envelope a little you might find something that was not as the theory suggests.

Not here to say told you so, just to remind to ask why do they have this point and could the chart be faulty. Always question the theory if there are some that get different results that they should.

Edit: oh yeah forgot, the sweet spot should be around 1000fps, but consider the distance and how long you stay in that sweet spot?
The muzzle velocity can be significantly higher.

Marko

None of the local competitive 22br shooters are using supersonic ammo. I was the only one a few weekends back and got the lowest score 😂 I would be very curious to see any really completive shooters that are using supersonic ammo.

[K.O.]

" I would be very curious to see any really completive shooters that are using supersonic ammo. "

BPCR long range guys tend to load stuff like .40-60, .45-70, .45-90 to 1300-1400 fps...

[rsterne]

BPCR long range guys tend to load stuff like .40-60, .45-70, .45-90 to 1300-1400 fps...

Most likely a case of trajectory trumping wind drift....

Bob

[Spacebus]

" I would be very curious to see any really completive shooters that are using supersonic ammo. "

BPCR long range guys tend to load stuff like .40-60, .45-70, .45-90 to 1300-1400 fps...

I meant in the context of 22br competitors. There are plenty of long range centerfire shooters going supersonic, but usually their projectiles stay supersonic until the target. The 22br is much closer to the real of PCPs

[ballisticboy]

Firing anything with a muzzle velocity between about 1070 ft/sec and 1170 ft/sec is normally reckoned to be a bad idea due to the rapid changes in all the aerodynamics with small variations in muzzle velocity. Real life has shown this is true as well as the maths, whether it be bullets or 155 mm shells.

Of course, if you have a gun with zero MV variability firing bullets with zero yaw or yaw rate, then they will fly at these speeds just as well as anything else.

[MJP]

" I would be very curious to see any really completive shooters that are using supersonic ammo. "

BPCR long range guys tend to load stuff like .40-60, .45-70, .45-90 to 1300-1400 fps...

I meant in the context of 22br competitors. There are plenty of long range centerfire shooters going supersonic, but usually their projectiles stay supersonic until the target. The 22br is much closer to the real of PCPs

Just wondering, jow many of those 22LR shooters are shooting 200m and beyond distance?

One thing most if all powder burners lack is the consistency in velocity of a modern PCP, we have guns with velocities within single digits of variation.
None of the 22LR match ammo can come close to that.
Just shot my  .457 and ten shots with same 291m/s velocity. And velocity at 50m was within 2m/s due to wind, same trend going up to 100m

We have the tools and valves to make it, but the harmonics are where we are still loosing the game on big bores. That stupid hammer strike before the bullet even moves sending a shockwave throughout the frame.

Just something to think about.

Marko

[sb327]

I agree 100% that the harmonics within hammer/valve system is the most significant issue in the modern pcp.

Dave

[Spacebus]

" I would be very curious to see any really completive shooters that are using supersonic ammo. "

BPCR long range guys tend to load stuff like .40-60, .45-70, .45-90 to 1300-1400 fps...

I meant in the context of 22br competitors. There are plenty of long range centerfire shooters going supersonic, but usually their projectiles stay supersonic until the target. The 22br is much closer to the real of PCPs

Just wondering, jow many of those 22LR shooters are shooting 200m and beyond distance?

One thing most if all powder burners lack is the consistency in velocity of a modern PCP, we have guns with velocities within single digits of variation.
None of the 22LR match ammo can come close to that.
Just shot my  .457 and ten shots with same 291m/s velocity. And velocity at 50m was within 2m/s due to wind, same trend going up to 100m

We have the tools and valves to make it, but the harmonics are where we are still loosing the game on big bores. That stupid hammer strike before the bullet even moves sending a shockwave throughout the frame.

Just something to think about.

Marko

My local club shoots at 50m. Any competitor I've seen/heard talk about long distance shooting with rf or CF all say to keep it sub or supersonic if you want MOA or less accuracy. I haven't encountered any competitive shooters that use ammo entering the transonic range during flight.

[K.O.]

BPCR long range guys tend to load stuff like .40-60, .45-70, .45-90 to 1300-1400 fps...

Most likely a case of trajectory trumping wind drift....

Bob

Hi Bob... I think it was about mid to late 1980's that modern BPCR started and had a friend that had a .45-70 and is about then was exposed to it... have talked with a few BPCR competitors/shooters since then... it is a little about trajectory but is more about the belief that the increased rpm is needed to stabilize the very heavy/high sd rounds... Basically to make up for a tad too low of a twist rate out at the 400-500 yard area...  that between about Mach 1 about the same twist rate needed as about 1300 fps is the attitude I picked up, right or wrong...

 I did some looking to see if that attitude still holds true... here is one example I found...  http://www.texas-mac.com/40_Caliber_BPCR_Accuracy_-_Twist_Rate_vs_Bullet_Length_vs_Velocity.html

so for us well is a moot point anyways I just do not think we could match getting a .348 SD (.410" 410g)  round to go that fast... even in .172 the psi/volume would be !!!  hmm .348 sd...is it possible to get a 72g .172 to 1350 fps with even helium...?

even a blunt-ish nose 1.1" .172 round is only about 67g...   http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=in.&weight_unit=grains&bullet_name=Custom+bullet&re_calculate=yes&boundary_layer=L%2FT&entry=return&diameter=.172&length=1.1&nose=.25&meplat=.04&drive_band=.172&base_diameter=.172&angle=0&boat_tail=0&secant_radius=&weight=69.2&density=11.4

  so yep trying to get to 1300+ fps with even a light round would not make much sense for us...

but it is very common in bpcr competition... they would send lead faster but no gas checks allowed...can't run boattails cause of jetting...

I still think what they do lobbing rounds at high transonic is pretty amazing especially with sights and period correct scopes only...
just can not help loving  single shot .45-70 n such..

[K.O.]

I guess guys what I am saying is... it is just not that simple as stay super/sub sonic... sure as a general rule it can hold generally true...but there are a lot more transonic stable bullets at high altitude than at sea level..

predicting transonic stability well in Brian Litz words it is a bit mysterious... 

I have always been fascinated by bullet design (what works for what use, in what and why) and a big part of that is due to the those seeming exceptions to general rules that exist in the finer points...

https://bulletin.accurateshooter.com/2014/09/practical-thoughts-about-transonic-bullet-stability-and-accuracy/ 

but I also love that sub optimum also has it's use...  it is fun to once in a while pump up my Makeshift MK1322 to max and send 30g BBT out at 550 fps   ... No can is safe within 50-60 yards..   a quarter is not safe at 30.. it is very much capable of taking jackrabbits at 40 yards...Better than the Benji green tin at about 18 fpe  I used in the 1980's... less buttoning and deflecting going thru bone, that meplat with 30g behind it will just punch thru...
 the BBT at 250 fps less fps still handles wind more predictably... the BBT 30g has done well to very well in a variety of platforms at a variety speeds and twist rates...
 
and no supply chain worries if you recycle...

and thanks to other pioneers like NSA now we have 10 to 20 grain .177 slugs of different makes now... down to about 20g in .22...  each will react to conditions, altitude, with that also variable at different speeds and twist rates...   heck a 980 fps 10g KO is still a bit of a leaf in the wind, the shape makes me think darty/less predictable over slower fpe equivalent lobbed 16g  H&N... 

and 

 would bring a grin...  having a budget 20 ish fpe, 1.5-2 moa to KO cans at 100 yards...    https://www.gatewaytoairguns.org/GTA/index.php?topic=207173.80

[mackeral5]

How does this higher velocity shooting affect a round such as the Altaros ATP Smooth .25, 49.5gr?  I've seen many posts where those "in the know" state Altaros designed these to run in the high high 800-900fps range.  I currently shoot them in my .250 Bulldog, at 850fps using  a 700mm Superior Heavy liner, 1:18 twist. 

In comparing the above setup to King Heavies shot in a STD superior liner (1:24 twist) and right  at 900fps, the King Heavies are pushed 4-6" by a light cross wind at 100 yards.  The ATP's at 850fps seem largely unbothered by wind in the same conditions. 

Soon I will begin setting up a more fitting platform to shoot the ATP Smooths and I am curious if it makes sense to target velocities in the upper 900-1000fps range.  I find that 850fps out of a longish barrel tends to be easy to achieve good efficiency at whatever energy level is produced for a given caliber/projectile weight, this almost universally applies for me and my tuning style, across all calibers/energy levels.  So I am curious with my preferred projectile, the ATP Smooth, what is there to gain in going somewhere closer to 1000fps vs the mid-high 800fps range, other than the flatter trajectory.  My rough guess is most platforms will consume 1.5-2x the volume nitrogen pushing 1000fps vs 850fps.

I am very new to this area of our hobby and do appreciate your sharing of experience.

[ballisticboy]

You may find that the stability suffers at higher speeds, specially over 1050 ft/sec.

[sb327]

We are going to have to be honest with ourselves here. The changes in accuracy due to the speed of the projectile being in the transonic region will probably not affect in a great way the ‘acceptable’ accuracy developed by a bpcr at 500 yds with open sights. At least that’s how I see it in my bpcr shooting.

Dave