Range Report Beyond Sonic

[WDL]

My 19 year old grandson shot & killed a woodchuck last summer at a confirmed 884 yards with my Savage 22-250. Terminal velocity was 1089 FPS. I don't know whether that is trans-sonic or sub-sonic, but in either case, the groundhog didn't care.
After reading about the British sniper and the crazy things that happen to a pointed bullet when it goes into the trans-sonic region, I wonder if the 55 Nosler BT hit the woodchuck point first. Again, he didn't care.
Comments?

 

[LRS_Ranger]

Re: Beyond Sonic

I would think that if the bullet turned around to fly base forward, the accuracy would have gone all to hell.. Just one shot, maybe, but if you are grouping out that far I bet you are still flying point first.

168 SMK's are known for losing stability when going transonic.. From my personal experience at about 1100 yards, 168's start flying god knows where, when they are grouping ok at 1K. The ones that do hit the target at 1100 are quite often sideways.

 

[WDL]

Re: Beyond Sonic

No groups, just one shot. The range was an educated guess on my part. My grandson cranked up 22 inches of elevation on the scope and squeezed off the shot.
Obviously some luck involved, along with skill - he is a natural shot.

 

[Redmanss]

Re: Beyond Sonic

Your speed of sound for your trans-sonic transition is dependent on the temperature of the air. The colder it is, the lower the speed of the sound barrier is. At 20*F the speed is 1074fps, and at 80*F it is 1140fps.

Speed of sound in air calculator

In answer to your question about what part of the projectile hit first, probably still the nose. When we used to shoot the 173gr M118, it was always subsonic at 1000yds. The holes were still pretty much round on the target, and I never heard of one impacting sideways unless it skipped off the berm first. Sometimes the hole would be a bit elongated and was possibly due to the dropping trajectory at that range, but mostly round. They may spin off axis a bit going trans-sonic, but they won't go tumbling in my experience.

 

[armymedic.2]

Re: Beyond Sonic

good link redman thanks

 

[mattmc40]

Re: Beyond Sonic

good info! I agree the chuck didn't care

 

[WDL]

Re: Beyond Sonic

Thanks for the info, Redmanss. I estimated terminal velocity at 1089 FPS and the air temp was probably ~80*. So I guess the bullet was sub-sonic, but only briefly.
I read somewhere that once a pointed bullet goes sub-sonic, the bullet wants to swap ends since center of gravity is near the base of the bullet. But what I don't know is how long does the process take after going sub-sonic.

 

[Redmanss]

Re: Beyond Sonic

Calling Bryan Litz.....

Until he gets here, I'll take a stab at it with my basic knowledge.

The effect on a bullet at transonic speeds depends on the specific bullet design. Some will start to tumble, as I've read it's more those with a steep boat tail angle, shorter OAL, or are light for their particular caliber. The 168gr SMK (steep boat tail, short OAL, somewhat lighter round) is a bullet that doesn't handle it well and is the reason people recommend them for <600yds. Most modern match rounds perform well in the transonic region, or at least better than other older designs. Heavier/longer bullets are better for handling the transonic shift.

To the best of my knowledge, there aren't a whole lot of physical studies that have been conducted on the subject, or at least nothing published I can find. Maybe one of the really smart guys will come along and throw in what they know as my experience/knowledge is limited to what I've seen on the range and the little info available on the subject.

The transonic effects start around Mach 1.2, so for your temp of 80*F it started the effects around 1370fps. Out of curiosity, what's your MV and altitude? I plugged in a couple guess numbers and I think your terminal velocity may have been a bit higher than what you're thinking, but again I'm only guessing on your specs.

 

[WDL]

Re: Beyond Sonic

MV was 3870 fps. Altitude was 972 AMS

 

[WDL]

Re: Beyond Sonic

Bullet was a moly coated 55 Nosler BT which I would consider a middle of the range for caliber. Not sure how the boattail would be described.

Edit: BTW, my grandson that made the discussed shot is enlisting in the USMC.

 

[Redmanss]

Re: Beyond Sonic

OK, running those numbers and using the G7 BC of .130 for that projectile, I'm coming up with a velocity of 1141fps at 900yds. For pressure I used the ICAO standard of of 28.86in/hg and guessed at 20% humidity. This is using the Point Mass Ballistics Solver program.

Not too far off of what you had and still well within the transonic range of effects not to mention right at the fringe of the actual sound barrier. That round has a 14* angle to the boat tail which is pretty steep in comparison the the heavy boys. I'm not all that experienced with the 22-250, but I know the 77gr SMK out of my 5.56 MK12 is outstanding at the longer ranges, and will dispense with vermin just fine too.

I highly recommend Bryan Litz's book "Applied Ballistics for Long Range Shooting". I reference it often and am still trying to absorb all the information it contains, and it also comes with the ballistic program I referenced earlier. http://www.appliedballisticsllc.com/index_files/Book.htm

All science aside, outstanding shot by your grandson, and I wish him luck in his potential USMC pursuits!

 

[WDL]

Re: Beyond Sonic

Thanks for taking the time, Redmanss. Your information has been very informative. I will have to order the book the next time I place an order at Midway.

And thanks for the best wishes for my grandson.