http://i148.photobucket.com/albums/s30/Unionvillelacrosse10/overstab.jpg

Today I was shooting 55 grain FMJ Hornadys from a 1 in 7 twist Colt HBAR at 25 yards. I began to notice these small pinholes above some of the main bullet holes. Is this indicative of overstabilization

I would say either you change your sight picture or you need to watch your breathing, but that's just my opinion.

What is your backstop behind the target because those holes/tears look like they have the exit  in front of the target and are not entry holes.

I agree it looks like those small holes or tears and from the backside and not from a projectile.

Good point.  The backstop was plywood that was really chewed up (shot up) and rough.  But, we did notice it only happened with some shots.

What was behind the target?  Looks like you hit a rock or something hard behind the target and got debris flying back.  

ETA:  Little slow writing that up.  Agree with above.

I get that a ton when shooting with PW backing.

So they were secondary projectiles. pieces of plywood exploding off of the impact site. that would make sense.

Overstabilization would not manifest itself at that range.  Overspinning the bullet to the point of disintegration is another matter.

In any case, you got good answers above.

As I said earlier. I get that all the time where I shoot. We work a ton of construction sites and get sheets of the stuff all the time. So we usually just tack targets to the plywood and shoot it until we get too lazy picking it up. BUT the shrapnel out the back is brutal! Plus it also forces pieces out the front.

That is pretty common when targets are on plywood

I don't think you can "overstabilize" - that doesn't make sense.

Spin it too fast, exceed the limitations of the projectile, and it will fail.  Or you can do the reverse.   Same result
458

I understand that, but a projectile that disintegrates is hardly "over" stabilized.

Agreed, looks like shrapnel blast from hitting the backstop...



 

I shot on plywood Saturday but taped cardboard on the front to make it easier to pull staples when I pulled targets. Just a thought for you.

I've shot much lighter bullets from 1/7 without ever having "overstabiliization".  It's usually something people worry about that don't have anything better to worry about.  I hear it's possible with some ballistic tip 45's but I've shot 45's before and never had a problem.  Just keep shootin!

If you under stabilize a bullet it will become unstable and tumble.  We all know that.  If you over stabilize a bullet it does have an affect but not until long range.  There was a long article done on this in the FCSA VHP magazine.  Let's say you are shooting at 1000 yards.  With a bullet properly stabilized the centerline of the bullet would stay in the line of travel along the arc.  Bullet nose pointing up as the bullet goes above the line of sight, then pointing down as the bullet falls back toward earth (target).  In an over stabilized bullet the bullet nose would be pointing up even though the bullet itself was traveling down.  The impact on paper would look like a keyhole or slight keyhole, depending on the angle of the bullet impacting the target.  This is really hard to type out and I cannot do drawings.  The best way I can describe it is you know that if you are shooting at very long range, you are shooting so the bullet is traveling up above the line of sight.  So as the bullet arcs up its nose is pointed up.  At the top of the arc where it flattens out a little, in a normal stabilized bullet the point of the bullet would flatten out the same as the arc, and as the arc started down the bullet point would start pointing down also.  In the over stabilized bullet the bullet tip continues to point up instead of down but it does not tumble.  
I hope I have not botched up the explanation too much but if you can find an index of back issues of VHP and find the article they do a lot better job of describing it and they have pictures.

Lol another ARFCOM expert

Not over-stabilization.  

Your explanation is very clear.

agreed

Although I will add this:

You can spin the jackets off shitty bullets with a 1/7 twist barrel. American ammunition brand for example. I made the sorry mistake of shooting some of this stuff through a suppressor. It really screwed it up (gilding metal separated and struck the baffles). This also resulted in really poor accuracy, of course. When it did hit the paper I didn't see any spattering like you show. I have seen spattering like that when the backstop was something that couldn't be penetrated. I get it a lot with my steel plate targets, the kind that use an electric motor to reset. I made them out of inconel plate left over from some grain handling equipment I built for the farm but I suspect anything that stops the bullet with very little penetration would do it. Bullet fragments would still have a lot of energy and have nowhere to go but back the way they came.

Over stabilization. Think about what you just said.

I agree.  Poor choice of terms.  I think most posters get what I was asking––were the marks I referenced in the photos the result of the 55 grain FMJs we were shooting coming apart and fragmenting because the 1 in 7 twist barrel was too fast.  Consensus was no, which was all I really wanted to know.

I'll just leave this here.  

overspin [′ō·vər‚spin]
(mechanics)
In a spin-stabilized projectile, the overstability that results when the rate of spin is too great for the particular design of projectile, so that its nose does not turn downward as it passes the summit of the trajectory and follows the descending branch. Also known as overstabilization.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Agreed.