Subs going supersonic

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wwburb
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Subs going supersonic

Post by wwburb »

New to 300 Blk. Just received an Aero 16” upper. Using my 30 cal AAC suppressor I tested to loads and both went supersonic.

Winchester 200gn Super Supressed 1040 fps spec
Grind Hard 194gn subsonic 1050 fps spec

Any ideas why?
Tks.
imashooter2
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Re: Subs going supersonic

Post by imashooter2 »

Too much powder in too long a barrel.
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dellet
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Re: Subs going supersonic

Post by dellet »

wwburb wrote: Wed Dec 22, 2021 10:08 pm New to 300 Blk. Just received an Aero 16” upper. Using my 30 cal AAC suppressor I tested to loads and both went supersonic.

Winchester 200gn Super Supressed 1040 fps spec
Grind Hard 194gn subsonic 1050 fps spec

Any ideas why?
Tks.
Are those actual velocity numbers from your rifle, or off the box? You need to verify actual velocity to start diagnosing.

Many manufacturers no longer label ammo as subsonic for this reason, only give a velocity guess. Too many complaints.

If those are true velocity readings when you were shooting, then it must have been sub zero temps to be close to going super.
Or just the normal crap ammo that needs to be reliable in every Frankenbuild out there, uses a powder that will cycle anything, but is extremely loud even suppressed. A lot of noise comes out the ejection port of an AR. This is the most likely cause.

If you are new to suppressors, 300 Blackout or worse, both. You will find factory ammo extremely disappointing to use. It just ain’t Hollywood.
300 Blackout, not just for sub-sonics.
ReadyAimDuck
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Re: Subs going supersonic

Post by ReadyAimDuck »

I'll just add that the speed on the box is an average/estimate at some barrel length, that may or may not be mentioned on the box by the manufacturer. it may be below 1060 fps for a 9" barrel but 1100 fps for a 16" barrel, as a rough idea. Yesterday, the speed of sound was somewhere around 1060 - 1070 fps where I live in the early morning. The week before it was around 1100. It varies with the air temperature. If its somewhere in the 1060 range, I can see how some rounds claiming to be 1050 fps, may go above 1060. My subsonic reloads deviate quite a bit more than +- 10 fps, and occasionally I hear a supersonic crack when it is very cold out.
wwburb
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Re: Subs going supersonic

Post by wwburb »

Yes those numbers were off the boxes. Outside temp was 43F at sea level. I’ll run though Chrono tomorrow. Tks everyone.
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dellet
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Re: Subs going supersonic

Post by dellet »

Probably should have given you this earlier. Speed of sound calculator, tables don't copy well, but at 43 degrees it's about 1100 fps.

https://www.weather.gov/epz/wxcalc_speedofsound
300 Blackout, not just for sub-sonics.
ReadyAimDuck
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Re: Subs going supersonic

Post by ReadyAimDuck »

At 45 degrees Fahrenheit the speed of sound should be around 1100 ft/s. Looking forward to the chrono results. What barrel length, by the way?

Edit: Sorry, just saw you already mentioned it was 16".
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