9mm "transonic" region affecting accuracy?

[Visionairy]

Gentlemen, and ladies where applicable. First time poster, long time lurker here.
Hope to get some opinions, of which i'm sure there's plenty of!

Been shooting my Beretta CX4 9mm carbine at our local outdoor range at 25, 50 & 100 yds lately. I manage about 3" grps or less at 50yds pretty consistently, which is ok considering a bit of wind and cheapie factory ammo I guess. Problem is, when I move over to 100yds, my groups spread out so far it's not even funny, I can barely hit the 8 or 9" target. I've figured the drop to be approx 4" at that range but I literally am getting one out of 4 shots on the dang target.

My THEORY is that the 124 grainers I was shooting were going "transonic" about 30yds out (based on an online ballistics calculator) and that the disturbance caused by turbulence was tossing them slightly off course and that the next 70 yds gave it time for that random disturbance to be multiplied and become more apparent.

So IF that's true, I got two options, A: Use faster 115grainers or B: Use slower 147 grainers. The online calculator I used told me that in order to remain supersonic out to 100yds that I would need a muzzle velocity of 17-1800 fps which is impossible with 9mm therefore, I need to use subsonic 147gr bullets. I got some 147 gr bullets in the mail along with my sweet new powder scale & some other stuff so I'll be putting some loads together soon but I'm looking to see if anyone is buying my theory.

Thanks!!!
Mike

 

[hoodfu]

If I remember correctly, supersonic is ~1250 fps. A 9mm coming out of a normal handgun is ~950fps. Has the speed be calculated out of a 16" barrel to see what extra speed you get? I wasn't aware that any 9mm was supersonic other than maybe +p+.

 

[Visionairy]

I'm not precisely sure either. I have heard about 1170, or maybe it was 1070. I know it varies with altitude & temperature. I've also heard that there's quite a wide "region" of around 200fps or more and that you have to get below 900fps to avoid it altogether.

BUT, if it is 1170, and that's about the velocity i'm getting at the muzzle, that would mean that it's transonic immediately upon leaving the muzzle which would be even WORSE than it happening 30 yds out

I'm just on a quest to shoot the teeniest tiniest groups I possibly can with this gun @ 100yds, I'm hoping, with some careful reloading & good shootin', to get 2" or so @ 100. That'd be sweet

 

[RevolvingGarbage]

If I remember correctly, supersonic is ~1250 fps. A 9mm coming out of a normal handgun is ~950fps. Has the speed be calculated out of a 16" barrel to see what extra speed you get? I wasn't aware that any 9mm was supersonic other than maybe +p+.

None of that is even close. The speed of sound is usually around 1075 FPS depending on altitude, and most 9x19mm (115-124gr) rounds will exceed that by atleast 50 FPS out of a handgun with a 3" barrel or better.

You might try using 147gr 9mm rounds and see if the extra weight helps decrease buffeting at longer ranges (they would still most likely be supersonic out of a carbine barrel unless you reload rounds specificly to be subsonic).

 

[MachIVshooter]

Welcome aboard, visionary!

You are correct. For optimal accuracy, the bullet needs to either start out subsonic, or remain supersonic all the way to the target. This is one reason .38 and .45 dominate bullseye shooting; 9mm and .40 teeter on the sonic barrier with most loads fired from handguns.

That said, it's still gonna be real easy to start out supersonic with a 147 from a carbine. You'll have to back the loads off. Depending on altitude, you need to be around 1,050 or less

 

[brboyer]

Gentlemen, and ladies where applicable. First time poster, long time lurker here.
Hope to get some opinions, of which i'm sure there's plenty of!

Been shooting my Beretta CX4 9mm carbine at our local outdoor range at 25, 50 & 100 yds lately. I manage about 3" grps or less at 50yds pretty consistently, which is ok considering a bit of wind and cheapie factory ammo I guess. Problem is, when I move over to 100yds, my groups spread out so far it's not even funny, I can barely hit the 8 or 9" target. I've figured the drop to be approx 4" at that range but I literally am getting one out of 4 shots on the dang target.

My THEORY is that the 124 grainers I was shooting were going "transonic" about 30yds out (based on an online ballistics calculator) and that the disturbance caused by turbulence was tossing them slightly off course and that the next 70 yds gave it time for that random disturbance to be multiplied and become more apparent.

So IF that's true, I got two options, A: Use faster 115grainers or B: Use slower 147 grainers. The online calculator I used told me that in order to remain supersonic out to 100yds that I would need a muzzle velocity of 17-1800 fps which is impossible with 9mm therefore, I need to use subsonic 147gr bullets. I got some 147 gr bullets in the mail along with my sweet new powder scale & some other stuff so I'll be putting some loads together soon but I'm looking to see if anyone is buying my theory.

Thanks!!!
Mike

Been shooting my Beretta CX4 9mm carbine at our local outdoor range at 25, 50 & 100 yds lately.

How? From a rest? What type if sights?

 

[Visionairy]

Seated, off sandbags, next to a guy shooting a LOUD a$$ mosin next to me LOL. Some of those 54R cartridges are real screamers man! Factory Iron/Peep sights.

 

[Jumping Frog]

Is there any reason you decided to spell your screen name with an extra "I", as Visionairy instead of Visionary? Just curious.

 

[brboyer]

Seated, off sandbags, next to a guy shooting a LOUD a$$ mosin next to me LOL. Some of those 54R cartridges are real screamers man! Factory Iron/Peep sights.

So you ruled out vision issues, trigger control, breathing issues, etc. before you went with transonic turbulence as a probable cause?

 

[Visionairy]

"Is there any reason you decided to spell your screen name with an extra "I", as Visionairy instead of Visionary? Just curious."

I'm in the optical business, back in the day 10-12 years ago there was an eyeglass frame with that name, spelled that way and I liked it, been using it ever since.

"So you ruled out vision issues, trigger control, breathing issues, etc. before you went with transonic turbulence as a probable cause?"

Being in the optical business, I know that my vision is better than perfect. I was paying attention to breathing and trigger control the best I know how and it's served me well shooting the handful of other higher powered rifles I've shot.

The main reason I suspected something else was that my groups were 5x the size at 100yds than at 50. All other things being equal, 2x the group size at 2x the range should be possible, I figured 3x maybe just for a margin of safety but it was waaaay worse than that even so I was just searching. I know that this transonic issue is a huge problem for 22lr rifles at ranges beyond 125yds or so so I figured why not, what's the diff?

 

[rfurtkamp]

16" and 10" barrrels, hitting pop cans and clay pidgeons at 100m is trivial with my Uzi. It's almost not fun.

Same with the MP5k-PDW with a 5.5", although it has much better adjustable sights.

I suspect there's zeroing error, wrong sight picture, or the sights themselves aren't conducive to accuracy at longer ranges, any of which could cause problems.

You've got a rail on the thing, try a scope zeroed for 100m.

As it stands you've latched onto a technical explanation without exhausting your other diagnostic criteria.

Perhaps there's something about stance, trigger pull, etc. that really shows up at longer ranges - you need to examine everything else first.

 

[Tenacious B]

Just to clarify, the speed of sound is dependent on temperature and the gas that is being considered, obviously air in this case. The temperature of the atmosphere varies with altitude.

 

[Oro]

Just to clarify, the speed of sound is dependent on temperature and the gas that is being considered, obviously air in this case.

Yes, but if you play with the equations, you will see that it will take some extremes of elevation or weather to alter the speed very much. 1,075fps is a very good approximation of the speed of sound for practical purposes.

A boat-tail bullet will be the biggest benefit for transonic issues - it dramatically decreases buffeting. Unfortunately, "area-rule" geometry can't be applied to bullets like it can to aircraft.

 

[zxcvbob]

Are you reloading? Try using Red Dot powder and load it near the upper end of its range (so it will burn cleaner.) Red Dot gives pitiful velocity and great consistency in most handgun cartridges, which is exactly what you want for target loads.