Sub sonic amm turning super sonic

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shooter65

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Sub sonic ammo turning super sonic

Has anyone evr experienced this:

A debate from another forum...

After cleaning a rimfire barrel the reason you get flyers is because the subsonic ammo will go supersonic after cleaning causing flyers.



The gentlemans opinion....

It may have to do with the fact the match ammo we shoot is 1080 fps, if I remember the velocity correctly. It is just under supersonic, so it starts off as fast as possible, but never has to transition through the sound barrier, causing bullet instability. I don't know why it happens, it just does.

You have to remember that velocity is also a function of: barrel length / bore condition / bore size / chamber / throat / smoke in the barrel / and a million other things. Which goes back to the original question in this thread - why is the first shot out of a "cold" barrel out of the group? = velocity.
 
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I'm not sure which of two conditions you are talking about.

Most rimfire guns shoot the first shot from a clean barrel high to 11 o'clock. At fifty yards about 1/2 inch. Mine do that, but not always? I always suspected the first shot is of higher velocity for some reason. I have seen this with perhaps 8 barrels in two rifles. Others have told me of the same experience. Never paid much attention to my plinkers. Back in late 2000 I had some 10x that shot the first shot supersonic. I remember I was shooting next to Fred J and he acted as though this was not uncommon. (for a senile old guy how do I remember that?) Lapua Midas only went high never supersonic. Never had another ammo that went supersonic. Although I use a chronograph to measure velocity and SD sometimes I have never measured that first shot as I always put 4 or 5 shots through the barrel before I start measurements. Its not a cold barrel as a dirty barrel can be left to sit for a while and the first shot might be off, but not high at 11 o'clock for me.

Now after that first shot some barrels take longer to settle down than others. It depends on the ammo and how they were cleaned. It is supposedly how long the barrel takes to lay down a layer of lube where each shot has the same lube. Its been my experience that factory barrels take longer to stabilize than custom barrels. A good bench gun shouldn't take more than a few shots where some factory barrels may take 20. But that I don't think is higher velocity but irregular velocity till the lube gets consistent.
 
Just was wondering if it is possible after cleaning a barrel that it is possible for subsonic ammo to go supersonic.

I personally do not see how this is possible given a particular rifle has a fixed barrel length and you are using the same subsonic ammo such as Lapua Midas M or Master????
 
Get this all the time.

When cleaning any barrel, you remove all the fouling and lubricant. The load report, is just that, I doubt that the bullet is going sonic. You must re-season the bore once cleaned for the barrel to settle down. If worried that first shot will ruin your group, after cleaning, then don't shoot that first shot for score. Otherwise, observe if it doe the same every time it cleaned, and hold off an appropriate amount. Like Rich said, most barrels will need several shots to settle it down after cleaning.
 
is there such thing as a Cold Barrel match..where only one shot is fired every twenty minutes, or am i dreamin ??
 
Yes

But we shoot 3 shoots every hour or so. Most of us never clean our barrels and those that do, maybe once a year. We are allowed to fire a fouler into the pit first if we desire. These are not Bench Rest Matches.
 
Gambler-cold barrel match

Some people shoot a milk bottle cap match here in the East. It is usually at night and indoors and it takes a dial indicator rig to determine the winner. It is cold barrel....one shot and put your rifle back on the shelf. Sight in for a cold conditioned bore.

Maybe Harry Deneen will chime in on this. My mind is fuzzy with senility, but I sort of remember an article about this in Precision Shooting some years back.
 
three shots per sixpack only ifn it's informal:D

i know guns and booze don't mix:eek:

and i highjacked a nuther thread
 
The norm

The only place I ever saw Beer and Ammo mixed, were at the German Schuetzen Clubs. A little like Larry the Cable Guy at a funeral.
 
"is there such thing as a Cold Barrel match..where only one shot is fired every twenty minutes, or am i dreamin ?? "

I've heard of cold barrel matches in sniper competitions.
 
I have a home range...home is on the edge of town and neighbors frown on the crackle of rimfire practice. I practice with 1050fps MV ammo, through a muffler which "silences" the muzzle noise to an unassuming "Pfft". 1065fps ammo, shot through the same muffler, will break the sound barrier with a ear-catching "crack" down range.

My first shot, or two, after cleaning will get the same down-range "crack"...means to me that they are getting out faster than 1050fps. Low humidity will also let speeds increase, as well as low air temperature...at least in my back yard.

Jeff518
 
Has anyone ever gathered any data after cleaning a barrel then shooting through a chrongraph to see if this is possible at all?
 
Jeff,

That observation regarding humidity is intriguing. My ballistic tables report that the higher, the humidity the higher the velocity. I wonder if that is only related to supersonic speeds.

Bryan?

John
 
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