Thread: Accurizing: Ammunition
Retrieved: December 08, 2013
I wound up with an interesting book called "The Bullet's Flight From Powder To Target" by a guy named Mann. It's a hundred years old, and apparently was one of the primary sources "everyone" knew about, way back when.
Mann did basic research on accuracy, playing with twist, aspect ratio, bullet shape, etc. There's interesting information there, but the big eye-opener came when he put tissue-paper panels along the flight path. The bullet went through each panel in turn as it went downrange.
It went all over the place.
A bullet doesn't fly straight. It goes takes a helical path, opening up gradually as it goes downrange. As long as the bullets are all shaped the same, they will remain within the helix. A wide group is more likely to be a result of differences in velocity - the bullet hits the paper at a different position on the helix.
Google Books has a downloadable .pdf of the book:
The bullet's flight from powder to ... - Google Books
sjohnson
06-13-2010
Agreed. No bullet can be made perfect WRT both geometry and center of gravity. If the actual center of gravity of a bullet is not coincident with the theoretic, geometric center of gravity, the bullet must spiral once it has left the confines of the barrel.
And, there's no simple way to sort a batch of bullets by their actual center of gravity, so we're left with spirals and "unexplained" fliers.
I have that (musty) old book alongside my Thatchers and others. Good reading on long winter nights! And, a great 'net find, TRX!
TRX
06-13-2010
Mostly, what I got out of Mann's research was that, due to the spiral path, consistent velocity is the major factor for tight groups.
That makes me think the guys who sort cases by volume and break powder grains in half to more accurate loads might not just be turd polishing.
And for you guys who haven't read the book - Mann tried some other stuff, like mangling the fronts of some bullets with pliers. The mangled bullets grouped right with the perfect bullets. But even a tiny imperfection at the base caused fliers. Which is reasonable, since at supersonic speed the shock wave is attached to the back of the bullet.
For best accuracy, pick the bullets with the best bases over the ones with the best points.
1biggun
06-13-2010
And for you guys who haven't read the book - Mann tried some other stuff, like mangling the fronts of some bullets with pliers. The mangled bullets grouped right with the perfect bullets. But even a tiny imperfection at the base caused fliers. Which is reasonable, since at supersonic speed the shock wave is attached to the back of the bullet.
For best accuracy, pick the bullets with the best bases over the ones with the best points.
HMMMMMM Im not so sure about that. when I was getting slightly deformed bullet tips from the bullet guide accuracy was not as good as when they were loaded in the barrel by hand. Consistancy is the key to accuraate ammo Every thing must be the same and correct. Ill have to see if I can find the book. Bullets have come a long long way in 100 years.
Rahatlakhoom
06-13-2010
I noted how modern snipers use their spotter to track the supersonic wake as the bullet is in flight. This path is clearly helical. I really had not given it any thought until you mentioned this book by Mann. That is some quite interesting stuff.
partsman
06-14-2010
I thought Newton said a rotationg object would rotate around it's center of gravity no matter where this center was. Eg. A bullet 1 foot in diameter with a true center of gravity 5 inches off the dimentional(sp) center would rotate around this center and hit the target + or - 5 inches every time. An object in motion will remain in motion in the same direction until acted upon by another force. This is why a deformed bullet will be less accurate than one with a misplace center of gravity.
kendwell
06-17-2010
From this, how could one design a better bullet, for example, 7.62 x 39,
new barrels from DSA hammer forged, nitrided, with 1-14 twist, a hp hard cast bullet designed to have minimum diameter spiral?....
partsman
06-17-2010
Several months ago, Someone told me about a 3 or 5 grove barrell. I brought it up in the ak section and was told there were no barrells with this configuration. At that time there were some guys that seemed to know about this and said it helped stabilize the bullet because it didn't " squeeze" the bullet between grooves and there fore it wasn't as deformed going down the barrell. Just my 2 cents.
Lunyfringe
06-17-2010
This is also reasoning behind polygonal rifling- less sharp edges on the rifling = less sharp grooves on the bullet.. 3 or 5 groove is common in polygonal rifling.
Other reasoning is that it cleans easier, and seals better- resulting in higher velocity for the same barrel length..
FWIW, I've never heard of a polygonal rifled AK barrel
TRX
06-17-2010
Polygonal barrels go *way* back, though some people have the idea H&K invented
them. Lancaster rifles of the mid-1800s had them, as did the Whitworth rifle.
The idea was that the lack of sharp-edged grooves would prevent the barrel from leading, but that didn't work out in practice. Back before hammer forging, you had to remove a lot more metal for a polygonal barrel than for a conventional type, so most manufacturers went back to conventional rifling.
allesennogwat
06-17-2010
I did download that same book a month or two ago from Google books. I found a lot of interesting old books with information that is still valid. I'll have to go through my Google book collection and see what I have. Some Google books aren't available as PDF downloads but if they are "full view" you can use the Google book downloader program for Windows which is a type of file sharing program, to download and save the books in PDF format.
chipmechanic
06-17-2010
Originally Posted by TRX
Polygonal barrels go *way* back
The idea was that the lack of sharp-edged grooves would prevent the barrel from leading, but that didn't work out in practice. Back before hammer forging, you had to remove a lot more metal for a polygonal barrel than for a conventional type, so most manufacturers went back to conventional rifling.
I see no practical use in polygonal rifling. I find it annoying that I can't use lead bullets in my Glocks unless I switch barrels to conventional cut rifling like the lone wolf barrels use.
Lunyfringe
06-17-2010
Originally Posted by chipmechanic
I see no practical use in polygonal rifling. I find it annoying that I
can't use lead bullets in my Glocks unless I switch barrels to conventional
cut rifling like the lone wolf barrels use.
Glock doesn't recommend reloads at all... apparently because they're perfect
polygonal rifling may be old, but it's making a comeback- Noveske makes them for AR15s (among several others) for the reasons I stated... it's true that it leads more easily, but copper jackets are the norm with rifles anyway (I know some have experimented with lead bullets, but with high velocity (over 2000fps), it leads anyway.
I think it's only a marginal improvement, if any, over a quality barrel with conventional rifling.. FWIW, in SBRs, they do see a marked improvement in velocity over conventional rifling of the same barrel length.. and they're reportedly easier to clean (not a big deal)
allesennogwat
06-17-2010
Originally Posted by chipmechanic
I see no practical use in polygonal rifling. I find it annoying that I
can't use lead bullets in my Glocks unless I switch barrels to conventional
cut rifling like the lone wolf barrels use.
It's not the polygonal rifling that promotes lead fouling in Glocks, it's the Tenifer surface treatment. There is a company in Austria that makes polygonal Glock barrels with a different finish that doesn't foul with lead. There are other polygonal pistol and rifle barrels. Usually they are known for increased velocity for the barrel length.
allesennogwat
06-17-2010
I found when I downloaded this book. It was the 7th of June this year.
The bullet's flight from powder to ... - Google Books