THE DREADED TRANS-SONIC REGION UNMASKED

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joeb33050 posted this 28 January 2020

There is a popular notion that if the bullet passes through the TRANS-SONIC region; then accuracy suffers. This notion is accompanied by mention of scientific-sounding contentions, but little or no data. Fortunately, data can be rooted out and examined, if the rooter has any interest in fact over popular drivel.

We need enough data to convince, data that shows whether or not accuracy is diminished by bullets passing through TRANS-SONIC world.

We need data on accuracy of a lotta bullets going through TSR, and other bullets NOT going through TSR.

We got it. Rimfire Central, a forum with lotsa experimenters, has a lotta data about 50 shot groups, at 200 yards, with rimfire bullets.

https://www.rimfirecentral.com/forums/showthread.php?t=1129343

Some 22lr cartridges send the bullet of at speeds less than the speed of sound, about 1125 fps. Others send the bullet of at mv greater than 1125 fps, and, accuracy of these through-the-TSR must be affected-for any 22rf bullet starting above 1125 fps will be below 1125 fps at 200 yards. 

No such accuracy effect is seen.

Some examples:

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RicinYakima posted this 29 January 2020

JoeB,

I can't figure out the chart, sorry. What was the group size shot while the bullet was still supersonic, what was the group size when it was falling into the transonic zone, and what was the group size subsonic? The same shot fire through three different targets each at different range.

Website only shows groups at 200 yards. We don't know what is happening to the bullet prior to hitting the one target.

Ric

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joeb33050 posted this 29 January 2020

Is this more clear?

 

Do groups enlarge after bullets go through the trans-sonic region?

 

The speed of sound ~1125 fps.

 

See page 536 of the 2020 Gun Digest, (or the back of ~any gun digest). 22lr hv bullets, mv = 1255 fps, 100 yd v = 1016 fps. 22lr hv hp bullets, mv = 1280 fps, 100 yd v = 1001.

 

Looking at this page, see that all 22lr hv bullets go through the trans-sonic region between the muzzle and 200 yards.

 

If groups enlarge after bullets go through the trans-sonic region; then we would expect 22lr hv 200 yard groups to be larger than 22lr standard velocity, <1235 fps, groups.

 

We have much data about 22rf 200 yard 50 shot groups, here: https://www.rimfirecentral.com/forums/showthread.php?t=1129343

 

Examples:

 

Armscor Precision 36 grain CPHP 22lr, mv = 1201, group size ~8.3”

 

Armscor Precision 40 grain SV 22lr, mv = 1060, group size ~13.8”

 

 

 

CCI AR Tactical 40 grain CP 22lr, mv = 1219 fps, group size ~10.2”

 

CCI Clean Polymer Coated 40 grain SV 22lr, mv = 1050 fps, group size ~9.1”

 

 

 

Review of the 50/200 data shows that there is NO large increase in group size with hv bullets over sv bullets, suggesting strongly that there is NO large increase in group size when bullets go through the trans-sonic region over those that do not.

 

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There are two competing theories about the trans-sonic bullet story.

 

Some bullets at some velocities at some ranges become less accurate over a short change in range.

 

 

 

Ex:  over a 10% increase in range, group size increases 20%. Over this 10% increase in range the bullets may or may not drop below the speed of sound.

 

 

 

There is general agreement that this occurs.

 

 

 

One theory contends that the bullet velocity dropping below the speed of sound causes the bullet to vary from their course and make big groups.

 

 

 

The other theory says that as the bullet RPM drops, the bullets becomes unstable and less accurate; and if it happens around the speed of sound-that is coincidence. (I have proven that slow twist barrels make ever larger groups as velocity falls, and can make it happen on demand.)

 

 

 

Exponents of both theories have no supporting data that I’ve been able to find.

 

 

 

 Measurement of the 50/200 groups: measure group size with a plastic ruler with 1/10” graduations, measure 6” of the picture ruler with the plastic ruler. Group size ~ plastic ruler group size X (6/plastic ruler 6&rdquo.

 

If the picture group measures 4”, and 6” of the picture ruler = 3”, then the true group size ~ 4” X (6/3) = 8”.

 

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If group size varies as the cube root of the number of shots / group, and it ~ does from n = 2-10; then 50 shot groups are 2.15 times the size of 5 shot groups.   

 

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If 100 yard group size is 2.4 times 50 yard group size, and if good 50    yard 5 shot group size = .5”; then 200 yard group size ~ 2.4^3 X .5 = 6”; the kind of numbers we see in the 50/200 data. Reality check.

 

 

 

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RicinYakima posted this 29 January 2020

"Review of the 50/200 data shows that there is NO large increase in group size with hv bullets over sv bullets, suggesting strongly that there is NO large increase in group size when bullets go through the trans-sonic region over those that do not.

 There are two competing theories about the trans-sonic bullet story.

 Some bullets at some velocities at some ranges become less accurate over a short change in range.

 Ex:  over a 10% increase in range, group size increases 20%. Over this 10% increase in range the bullets may or may not drop below the speed of sound.

 There is general agreement that this occurs."

The above is what I believe also. It is the question of WHEN the great increase in group size occurs, not the striking of the target group size.

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Squid Boy posted this 29 January 2020

It is a very interesting thread on the rimfire site but everything is shot at 200 and outdoors. That's great for testing the relative accuracy between the various brands and types of ammo but does little to settle this particular argument I believe. No actual data points are established by shooting at intermediate ranges that would definitely show any change in the rate of dispersion. There are assumptions made for closer ranges but not targets. I think it needs more definitive study.

I am limited at my own range to 25, 50 and 100 yards and generally don't shoot at 25 because the little hole doesn't tell me anything. However, during my own 22 ammo testing the average group change was about 2.5 times between 50 and 100 yards. Some started sub-sonic and others dropped out of the sonic range at various distances to the target. 

If I recall correctly Dr. Mann tested bullets through paper set at very close regular intervals out to 100 yards but never commented on any suddenly going wide along the track. i believe the test was more to detect a tip more than anything. 

Just my own experience and thoughts on the matter. Squid Boy 

"Squid Pro Quo"

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Larry Gibson posted this 29 January 2020

I think that plotting 22LR statistics attempting to prove accuracy is not lost in the trans-sonic region for all bullets of different cartridge, caliber, BC, bullet shape, ranges the transition occurs at and velocity levels is a bit of a stretch perhaps?

LMG

Concealment is not cover.........

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Ed Harris posted this 29 January 2020

A clear demonstration is to stand in the pits and pull targets for someone shooting 168-grain M852 at the 800 yard stage of the Palma Trophy Course, to observe full-profile keyholes and 6 foot groups, then change to M118 and repeat the test and note the round holes and reasonable group size.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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Squid Boy posted this 29 January 2020

It seems to me that there was a problem with the M852 from the onset. however it might not have been the bullet or the point it went trans-sonic. There are references to very good accuracy out to 300 yards or so and then bad from there out. The bullets were supposed to be commercial match 168 grain HPBT starting at 2600 so I would think they would still be supersonic past 300 and hit trans-sonic at around 500+. But keyholes show a complete loss of stability somewhere along the line. The M118 stays point on as you point out but why? Is there a difference in rifles being used perhaps or barrel twist rates? Thanks for bringing this up but just adds more things to consider. I really like these mind exercises. Squid Boy

"Squid Pro Quo"

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Ed Harris posted this 30 January 2020

Dr. Robert L. McCoy at the US Army Ballistic Research Laboratory at Aberdeen Proving Ground published a BRL Report summarizing Aerodynamic Stability Data for Small Arms Projectiles in the late 1970s or early 1980s.  Maj. Bruce M. Wincentsen and I assisted in real-range firing done at night shooting backwards, (aiming at a red lightbulb), into the transonic aerodynamic range (built in an old "blimp" hanger) at 500, 600, 700, 800, 900 and 1000 yards firing USMC M40A1 sniper rifles and a Hart 1A heavy benchrest switch-barrel gun which enabled replicating the tests using various twists of rifling. 

The M40A1 rifles were 1:10", 1:11" and 1:12"  twist.

The Hart bench gun was tested with 1:8, 1:10, 1:12 and 1:14 twist barrels.

Ammo included UK and Canadian 144-grain NATO ball, 146-grain German DAG, and US 168-grain M852, 175-grain M118 Match and handloaded Sierra 168, 180 and 190 MKs. The Sierra 175-grain MK now used in the M118 LR and the 155-grain Palma were developed after evaluating the results from this testing.

Bottom line, to shoot a 168 Sierra at 1000 yards and hit anything shoot it from a .300 Winchester Mag.

In the .308 Win. the current 175MK and 180MK worked well best from either a 1:11" or 1:12" twist, the 190 MK needs a 1:10"

The M118 Match FMJ and Sierra 175MK now used in the M118LR gave the best results out to 1000 yards in either 1:12", 1:11" or 1:10" twist barrels.  

Ordinary NATO light ball was most accurate in the tight-bore, Australian Omark-Sportco spec. 1:14" twist barrel on the Hart action.  

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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joeb33050 posted this 30 January 2020

http://www.snipercentral.com/history-m118-ammunition/

It appears that the M118 cartridge varied greatly over time, there wasn't/isn't one, but there were several/many flavors.

However, tales of testing/shooting various rifles/cartridges don't bring me any closer to the answer to the question. Something happens sometimes to some gun/cartridge combinations at some ranges, sometimes after the bullet speed drops below the speed of sound.

Does bullet rpm fall below the required stability level and bullets become unstable?

or

Does going through the trans-sonic region cause bullets to become less accurate?

or

?

 

 

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TRKakaCatWhisperer posted this 30 January 2020

Mann writes about the instability in a region of velocity (hence in a region of distance) where the bullet is unstable AND then (often) will re-stabilize.  Therefore, merely looking at 100 and 200 yard scores could miss the entire region of instability.

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joeb33050 posted this 30 January 2020

Mann writes about the instability in a region of velocity (hence in a region of distance) where the bullet is unstable AND then (often) will re-stabilize.  Therefore, merely looking at 100 and 200 yard scores could miss the entire region of instability.

For 22lr hv bullets, the trans-sonic region is included.

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Larry Gibson posted this 30 January 2020

"Does bullet rpm fall below the required stability level and bullets become unstable?"

That may or may not happen. However, that is not the reason accuracy can be lost during a bullets transition from sonic to sub-sonic velocity.

"Does going through the trans-sonic region cause bullets to become less accurate?"

Joe, there is no simple answer to your question as there are many variables.  Bullets transitioning from sonic velocity to sub-sonic velocity get buffeted around by the turbulence.  Bullet shape, sectional density, BC, the angle of the bullet in relation to direction of flight (some bullets don't nose over at long range), where the transition takes place in the trajectory, etc. are just a few of the variables. Some bullets/loads many times will lose stability also the M855, which is the military 7.62 loaded with the Sierra 168 MK, being an excellent example.  That round, as previously mentioned, does go sub-sonic in the 900 yard+/- region most often and many of the bullets will lose stability.  Many times, also as previously mentioned, the bullet is simply buffeted around yet maintains stability.  When the transition is complete and the buffeting stops the bullet continues on still stabilized but it's flight path has been slightly changed.  If that [loss of accuracy/group is larger] occurs close to the target little loss of accuracy may be noted.  However, if it occurs some distance from the target a large loss of accuracy/group gets larger than it should [not stability] will be noted and the shot most often called a 'flyer".

In the case of your 22LR with those that are sonic at the muzzle the transition is usually before 100 yards.  Ergo, groups at 100 and 200 yards occur post transition and won't demonstrate the accuracy loss caused by the transition.  They do demonstrate that HV 22LR, because it starts out sonic, is almost always  less accurate than the 22LR that starts out sub-sonic.  

LMG

 

 

 

 

 

Concealment is not cover.........

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Squid Boy posted this 30 January 2020

Ed, they didn't call the place Aberdeen Play Ground for nothing. I was there for training and should have stayed when invited.

Great thread,lots of good stuff. Squid Boy

"Squid Pro Quo"

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joeb33050 posted this 31 January 2020

The Winchester 69A, with Federal HV Match 719 22lr, can be adjusted to vary mv from 1204 to 935 fps. Today I plan to check accuracy at ~1204 fps, and ~1069 fps-at 100 yards.

The 1204 fps setting will cause the bullets to go through the (dreaded) trans-sonic region on the way to the target, the 1069  setting bullets start sub-sonic.

If bullets lose accuracy after going through the t-s region, I expect to see larger group sizes.

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Squid Boy posted this 31 January 2020

Joe, I have no clue on this so I have to ask, how does one adjust the velocity on a 22 rim-fire rifle? Thanks, Squid Boy

"Squid Pro Quo"

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joeb33050 posted this 31 January 2020

The Winchester 69A has a 10-32 threaded hole about 1" forward. Various valves and screws allow varying mv from ~1204 hole closed to ~ 935 fps, hole wide open, with Fed HV Match 719.

 Shot 1/31/20

 

Left 1203 fps, 100 yards, 18 in 4.5", 17 in 3.1"

Right 1094 fps mv, 100 yards, 21 in 3.05".

Chronographed while shooting.

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RicinYakima posted this 31 January 2020

Thanks for shooting that for us Joe!

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Ken Campbell Iowa posted this 31 January 2020

there is a ton of stuff regarding bullet instability to be googled on the opinion-net ...

and even you-tube ...

i have spent a few hours * trying * to digest that information .. i have arrived at the conclusion that the results are pretty much what happens to everything else that we digest ...

**************

hey, for fun only ::

... a HP bullet takes about 3 seconds to travel 1 thousand yards ... if you do a Dr. Mann thing and set a bullet tip down  on a glass ... spinning at 100,000 rpm ... it will spin nicely ( with a teensy wobble )  for way more than 3 seconds ... probably minutes .............. so in our near-vacuum our bullets aren't running out of spin in 3 seconds ..

but at 3000 fps, our air looks more toward a swimming pool than a vacuum, so dammit anyway all of a sudden we have a complex situation where now that little wobble that didn't matter much in a vacuum is now exposing varying areas in varying locations to varying pressures causing varying forces .... eeeek ! ....

... and remember that the propagation of sound varies with the density of the medium ... crap ! ... at 3000 fps, the medium that counts ( as the bullet sees it ) varies from the shock compressed area to the almost-vacuum laminar flow area ... 

as Omar puts it .. " something happens to some bullets " when the inputs are changed during the transition time ...  probably not running out of spin, so probably has something to do with more force on one side of the bullet ... that un-balancing force has to be fairly large ... but remember, our bullet is still traveling 700 mph in a swimming pool ...

complex indeed 

i give up ...  maybe we should just shoot some bullets and see what happens ... ( g ) ... oh, google mentions that short bullets are more resistant to becoming unstable ...   like 22 rf, for instance.   

anybody tried high speed roundball at 1000 yards ??  do cannonballs achieve ultra-sound velocities and then become transitionally unstable ?  where would that mysterious force act on a round ball ? all the surfaces are the same and the cg is always in the middle ... 

******************

joeb's vari-pressure 22 rf gun is fascinating .... but maybe those roundish 22 rf really don't ever wiggle much through transition ...  oh, i might mention that if you change the velocity of your load , you have to change the barrel tuner setting if you want to test for best groups. 

do 3118 castings out of a 32-20 ( ok, 32 Fed. Mag )  ever go erratic through transition ?  some fun with a 32 mag for someone.   don't forget to adjust your tuner.

just some thoughts ... ken

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John Alexander posted this 31 January 2020

Joe,

Ken has a point about the barrel tuner. We don't know if the super and sub velocities groups have the same precision before one of them transitions.  How about seeing those same cartridges and velocities group before one goes through Mach 1.  Groups at fifty yards maybe?

Easy to think up work for you but then I don't have a rifle with a valve in the barrel.  I guess I could try to do it by hand loading super and sub velocity loads.  That sounds like fun and would see what longer higher BC bullets do. Hmmm, when the weather gets a bit warmer maybe.

John

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joeb33050 posted this 31 January 2020

Joe,

Ken has a point about the barrel tuner. We don't know if the super and sub velocities groups have the same precision before one of them transitions.  How about seeing those same cartridges and velocities group before one goes through Mach 1.  Groups at fifty yards maybe?

Easy to think up work for you but then I don't have a rifle with a valve in the barrel.  I guess I could try to do it by hand loading super and sub velocity loads.  That sounds like fun and would see what longer higher BC bullets do. Hmmm, when the weather gets a bit warmer maybe.

John

 

The bullet starts at 1203 fps, and we're reasonably sure v < 1135 at 100 yards. I don't know v at 50 yards. Anyone?

I think 25 yard v> 1135 fps. ??  Anyone? A ballistic calculator shows @25 yards, v is right around 1135 fps. I don't know a range , reasonable, where v> 1135. ??????????//

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