I've been reading about the theory behind trajectory and drift and "experimenting" by playing with one of the commercial calculators, QuickTARGET. 

I'm observing that subsonic loads suffer least from wind drift. Is this true in practice? 

With subsonic muzzle speeds, do typical velocity spreads more greatly affect vertical stringing?

What sort of speeds do off-hand shooters gravitate towards and why?

I'm a bit out of the ASSRA loop, but I'll be living in Illinois again later this year, and I might try to make some of the matches one day. Are jacketed bullets permitted in the matches?

Thanks,
Karl

I'll have to disagree with that.  22 target shooting is done almost exclusively with subsonic ammuntion.  Vertical group size is no greater than the horizontal and, in fact, accuracy with the subsonic .22s is very close to the supersonic centerfires with their much much heavier bullets.  I don't think you give up any accuracy just because you are subsonic.  You might even gain a small advantage.   

Brent

boats, have you ever seen anyone try subsonic centerfire?  Could be that you ain't seen it because it's not been seriously tried and it ain't been seriously tried because no one has seen it.  I am aware of no laws of nature that suggest it cannot work.   

I'm willing to bet that a .32-20 can be shot subsonic more accurately than any .22 and may be any centerfire.   

Brent

My concern with subsonic would be in the vertical. Even if the velocity variation were the same percentage (which would require a smaller absolute span), it seems the arcing trajectory may amplify the errors downrange. Unfortunately, the trajectory calculators can't handle what happens when a given rifle fires a load which is 2% slower than another. They can't compute recoil on your shoulder and how that affects the initial launch angle. Only experience will determine if it is successful.

The low predicted wind drift for high BC bullets launched subsonic is tempting. There's some very high BC 22s and 24s these days, nearly equaling many 30s (jacketed, that is). I wonder how these flying pencils would do in practice.

Pity you can't use jacketed at the matches. The .32-20 Brent mentioned is one of the chamberings I was considering, using spitzer FMJ-BTs made for the .303 Brit. (Ok, I'm too lazy to cast and paper patch similar bullets.)

Brent tell you the truth I don't try much new. After all these rifles and methods are 100 years old.  I have to assume the kinks have been worked out of most loads normaly used in Schuetzen matches.  If matches are and have been won with 32/40's at 1450 fps that's all I need to know.

Not to be against anybody's theories or sport.  If someone wins or places well in a match with sub sonic 32 cal center fires I may give it a try.  May even consider if I saw a test that was valid showing potential. Otherwise better places to spend my time.  Conditons, postion, and trigger pull.

Why not give the 32/20 sub sonic a run showing the results.

Boats

You are right.  100 is not 200, and thus the bulls are different.  It is true with respect to wind as well as gravity.  And I don't see any vertical stringing - unless you use junk ammo (big surprise)....

Brent

Jim_Borton wrote on Jan 21^st, 2008 at 7:04pm:



Really?

What Jim Borton said!  He lives the theory and proves it each and every time he shoots another 250 or tiny group at Etna Green.  There anr not many out there who have made more of a study of trajectory, velocity, and wind effect. and...

Like I said..."what Jim Borton said"

Believe it!

boats, 
Have you seen anyone be consistently successful with supersonic .22s at 200 yds?   Have you tried supersonic .22s and how did they compare to subsonics?   

Any idea of why this should work for .22s and not .32s?

No one is asking you to shoot subsonics if it bothers you of course, but sometimes it is worth trying new things.

I think if I were into shooting smokeless centerfire, a .32-20 subsonic would be just the ticket.

Brent

The above reports of past failures with subsonic rounds has me pondering the causes. 

The existing twist rate calculators (for spitzers only) indicate the needed twist rate is higher for subsonic speeds. If one has throttled back a traditional schuetzen cartridge such as the .32-40, the twist rate may be inadequate for subsonic work, especially for speeds approaching sonic. Further, one would be running reduced loads, possibly causing greater variations in speed. (For subsonic work, pistol length cases would be a better choice.)

I wonder if the disturbance at the muzzle of the ejected high pressure gases is less orderly with subsonic than with sonic rounds?

One problem with subsonic work would be getting ideal bullets. One wants the highest BC, which would be a high SD bullet with a rounded nose and a boat tail, and I'm not aware of any such bullets. 

In looking at the more arcing trajectory subsonic requires, the trajectory calculators indicate the arc for a typical bullet would go from 9" at 1500 fps to 19" at 1000, which really isn't a dramatic difference. Speed variations seem a more likely culprit here.

It seems I'll simply have to have a special barrel made for my T/C rifle to test all this out...

Bullet design might indeed be an issue - subsonic bullets do require a different profile from supesonic bullets, a Metford-profile comes to mind...  Rounded tip about 45% of calibre, long tangent ogive (about 50% of bullet length).  Those things do help in cutting subsonic drag - but will make shot spotting quite a bit harder!

Joe, that's the sort of cartridge I was thinking of. By using a medium to high pressure, one could ensure complete combustion of a charge of the fast pistol or shotgun powders. In principle that should help ensure more uniform speeds. The downside is that the charges will be small (unless you're working with big bores), and this may cause speed variations due to errors in throwing or weighing charges.

It's an interesting optimization problem. 

It seems experiment is required. I'll have to acquire two barrels for my T/C. One for the classic .32-40 and one for .32 H&R (pistol) or similar. All this yet I'm a lousy off-hand shot. Much work to be done, and I'm stuck overseas until summer.

(You need to Login or Register to view media files and links) also estimates the twist needed, at Mach numbers from well subsonic to over Mach 3. It indicates subsonic twist rates are higher. I don't know how solid the theory underlying these calculations are, though.

I'm pretty sure fps variations are the problem with subsonic. The higher trajectory implies higher vertical descent rates when the target is reached. A given % error in fps probably translates into a given % (or % squared) shortfall in range, and with the higher descent rate, this implies greater vertical dispersion on target. In other words, the slower you go, the less the % spread in fps you're allowed. This compounds on the fact that at subsonic a given % spread is a smaller fps (absolute) spread to begin with.

Regarding a comment above on the typical Schuetzen speed possibly being the worst possible, I think it is. Drift calculators, such as at JBM's site, indicate drift is less for Mach 2 and above, than it is for subsonic. It seems the near supersonic of Schuetzen has the worst drift problem. With BP, Mach 2 isn't an option, and the fps variation problem gives subsonic apparently greater problems.

leadball, my little mental foray into the world of Schuetzen seems to have come to the same conclusion that BP target shooters in the 1800s did, namely that 1500 fps or so is about as good as it gets (with BP).

You mentioned the BR shooters striving for higher velocity. It was a question I put on a BR forum that led me to the information that wind drift declines at higher Mach numbers. The typical Schuetzen fps is worst for wind drift, but the advantage in tolerance to fps changes seems to fully compensate for this (when compared to subsonic).

Were jacketed bullets allowed in Schuetzen, the game would quickly home in on the solutions BR shooters now use, namely long pointy boat-tailed bullets at high speeds. There'd be no point in calling it Schuetzen any more, and there'd be no comparing modern scores to the old ones.

One might argue jacketed bullets should be acceptable if the fps is limited to traditional Schuetzen fps, and there might be advantages in accuracy to be gained from this. In looking at a few sites for custom bullets makers for BR, it seems even jacketed boat-tails can have problems with erosion on the boattail as the bullet peeks out of the muzzle, with this in turn affecting accuracy. Erosion may explain why lead boat-tail bullets aren't made (or at least not common). Long pointy boat-tail bullets would reduce wind drift even at Schuetzen speeds, and I must wonder if the "rebated" boat-tails some BR shooters are using would be feasible in lead bullets for Schuetzen. Wads might be a problem, though.

So, it seems I've convinced myself that the solution found in the 1800s--flat base bullets at 1500 fps--was the best possible for the technology of the day, which was BP and lead. The only way forward at BP velocities might be paper-patched, hard metal bullets. These were played with in the 1800s, but I don't think the theory of the day pointed them to the streamlined shapes we know of now. If you could get the jacket to shed neatly and get the wad to deal with the small bullet base, there might be some improvements to be had in drift dispersion in Schuetzen. A quick test would be to try the all-copper moly coated bullets from GS Custom. If the accuracy warranted it, plain sided versions for paper patching could then be made and tried.

Thanks for all the comments everyone,
Karl

That's how I see it as well, leadball; one needs to get up around Mach 2 to start seeing reductions in drift. That could only be done with smokeless and paper patching. 

Being ignorant of the rules, I wasn't aware a flat base was a requirement; it was mentioned above that lead construction is required. I assume paper patching permitted, but I doubt it will improve things much. 

When my work load drops some, I'll write out a computer program to solve the math and let me verify that fps sensitivity is what has caused the woes with subsonic; I'm pretty sure this is the problem.

Thanks for the clarification Green_Frog; I misunderstood the term "plain base."

You may be right about the practical effects of tail shape. At supersonic speeds, nose shape is generally thought to be quite important, with the tail shape less so. I had been running numbers using Hornady bullets, but it finally occurred to me to try Sierra bullets. Sierra publishes more extensive BC data than most other makers, and these include adjusted BC for speeds below Mach 2.

One might look at their 180 gn .308s, which have an SD similar to that of the bullets used for Schuetzen in the .32-40. Here are the estimated drifts caused by a steady 5 mph cross wind over a 200 yr range, with all bullets starting at 1500 fps; all stay supersonic to the target:


RN          4.3
SP          3.6
SPBT        3.0


Going to a pointy nose drops drift by 16%, and then adding a boat tail drops this another 17%. There are more radical nose and tail shapes than what Sierra uses. There are also stiffer cross winds. 

For reference, the SPBT drift at 1000 fps (subsonic) is estimated to be 2.1"; at 2000 fps, 2.3"; at 2500, 1.6"; and at 3000, 1.3". For a 10 mph cross wind, the SPBT at 1500 fps drifts 6.0"; and at 15 mph, 9.0"; so drift at 1500 appears to be pretty much proportional to wind speed (a result not unexpected).

Of course, gusts are what cause problems; a steady wind can be dialed out. How much such drift numbers mean in practice I certainly don't know. I'd guess that at Schuetzen speeds, improvements in bullet shape might be good for an inch less dispersion in annoying winds--not a lot. As mentioned, I can imagine some practical problems with BT spitzers in lead.