Tumbling

[DeltaBravo]

Tumbling Picture

Since no one has posted a picture of the "tumbling" or "key-holing" in question, I dug around and found my last target for the 87 grain V-maxes. When you look at this picture, keep in mind that I was actually AIMING at many of those bullseyes, but you can see the failure to group! Also look at all the oblong/oval bullet holes.

I have no idea what the issue was, but I got tired of wasting powder and bullets and moved on to the Berger 80 grain Varmint Match and haven't looked back!

Dennis

 

[Charles E]

It can be hard to say with certainly, but the pictures of targets posted show what looks to me to be more like bullet blowup. The jackets have come apart, and remains of "everything" are cutting large & irregular holes.

"Tumbling" usually gives a print of the bullet, often in profile. I Goolged the topic & got

https://www.google.com/search?q=tar...GoBQ&ved=0CAcQ_AUoAQ&biw=785&bih=501#imgdii=_

Of course, some of those look like blow-ups too, but there are a lot of "prints" -- in profile & otherwise -- of bullets that tumble; where the gyroscopic stability (practically, rate of twist) is the culprit. Again, the practical difference is changing the rate of twist won't do anything for blowing bullets up -- except a faster twist makes things worse. On the other had, it will stabilize a long bullet that tumbles when the twist is too slow.

* * *

The formula's Berger Bullets uses -- and a lot of people, are based on the work of the late Robert McCoy at the Aberdeen testing facilities (U.S. Army), coupled with the work by the late Bill Davis at Tioga Engineering, designer of the VLD bullet & a friend of Walt Berger.

While Dan Lilja has posted that the Tioga programs are no longer available
http://www.riflebarrels.com/products/tioga_info.htm

essentially the same programs can be gotten from -- or run online -- at JBM ballisyics

http://www.jbmballistics.com/index.shtml

specifically for Gyroscopic stability, at

http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi

* * *

Bryan Litz (also now at Berger) covers these & other topics on his site & in his book. Mr. Litz's work should probably be considered the latest word; practically, he's the guy that gave us the hybrid bullets, aimed at a bullet with essentially the same drag as the VLDs, but less fussy to load (seating depth). That's the theory at any rate, and the hybrids do seems to shoot awfully good.

http://www.appliedballisticsllc.com/

 

[DeltaBravo]

Charles,

I looked at the backs of the holes and it looks like they're intact as a single hole, just a bit oval in shape. My guess is that the bullet was either over or under stabilized, and entered the target before "going to sleep" - none of the holes on any of my targets appear to be round/circular. I think Harold Vaugn's book on rifle accuracy facts calls it "precession" and he says the bullet is basically cork-screwing until it settles down. That would certainly explain the oval holes, at least in my mind. Of course that may or may not explain the atrocious lack of any kind of accuracy; I was actually AIMING at those bulls-eyes but the bullets were going everywhere!!

I finally just gave up and tried the Bergers and voila, all is well.

Dennis

 

[shinny]

Off the subject..forgive me please.

Charles E,

I sent you a PM several days ago and was wondering if you received it.

Thanx

Shinny

 

[shinny]

On the subject this time.

A friend of mine purchased a Remington 700P LTR in .223. He couldn't get it to shoot a decent group @ 100yd and he couldn't figure out what was wrong. He asked me what he could be doing wrong.

He had some ammo that he had loaded himself, so we went back to the range. I asked him about the powder charge, which was fine but he didn't know for sure what bullets he used. I could tell they were Hornady's, but had no idea what ones.

I suggested we go to the 25yd range to start. I bore sighted the rifle and fired one shot (Target attached). Now, this is tumbling.

He was shooting 75G bullets in a 1 in 9 twist barrel (Right at the cusp)..............We loaded a few rounds with 65g bullets and the rifle came alive.