TAC in .308 Win ?

[hounddawg]

honestly not I worried about "over spinning" the bullet. I use quality bullets for the most part and most of those studies are quite old in manufacturing terms. With advancements in machining almost everything in commercial firearms has improved. Barrels 40 years ago were not even close to what todays factory barrels are.

here is a good study on bullet cant and accuracy for anyone that is skeptical about concentricity

http://nielsonbrothersarms.com/22%20Concentricity.htm

[Bart B.]

22 rimfire barrels and ammo made over 40 years ago hold all of the prone 40-shot records at 100 yards using scopes and most of the 50 yard ones.

The primer mix was changed in the early 1980's reducing accuracy and wearing out barrels faster.

[hounddawg]

when records stand for 40 years my thought is that it was neither the gear nor the shooter but just a case of the sun, the moon, and the stars aligning for that one fateful moment. There have been thousands of matches shot since then by a lot of top tier shooters with elite gear and it might be another 40 years before those records are broken. That is why I don't set store much in records. A lot of them are set by one hit wonders

[Unclenick]

I have a partial box of Remington Match ammo that is from the 1950's. One day I took it along with boxes of the supermatch Federal ammo made for the (92?) Olympics, and Eley 10X and several other boxes of match ammo I had to see what my old Winchester model 57 sporter would shoot best. They were all about the same except the ancient Remington Match, which shot groups half the size of any of the others.

Regarding bullet tilt, some more careful explanation for how it affects good, symmetrical bullets is in order. In the simplified and exaggerated drawing below, you can how tilt moves the center of gravity (aka, the center of mass) off the boreline. In that position, you can see the CG orbits the boreline as the bullet spins. This is like spinning a weight in a circle on the end of a very short string. When you let go of the string, the weight takes off sideways at a tangent to the circle of spin. In the rifle, the "string" is released when the bullet clears the muzzle. The bullet is also going forward very fast at the time, but that tangent motion has momentum that is independent of the forward momentum and it drifts the bullet off the center of the group being printed on paper.



Two important things that affect the result:

1. The further forward the CG is from the center of tilt and the more degrees of tilt, the bigger the radius of the CG orbit around the boreline, so the faster the orbit is and the more drift it introduces.
2. The faster the rate of spin, the faster the orbit and the resulting drift it introduces.

From the above, a couple of things will be apparent:
Since tilting the bullet in the bore squeezes one front edge and its opposite rear edge of the bearing surface against the bore, there is a limit to how far you can tilt the bullet before the force against those opposite edges is great enough to straighten out any further tilt. Bullet tip tipping on the order of four or five-thousandths off-axis (0.008"-0.010" TIR) is a typical limit. Longer bearing surfaces will allow less tilt.

The amount by which CG's are offset by tilt is typically under half a thousandth of an inch, so it takes some fast spin to develop the centrifugal effect that lets the bullet take off sideways.

If there is no distance between the CG and the center of tilt of the bearing surface, as is the case with a double-ended wadcutter, for example, then tilting the bullet will not move the CG away from the bore line and no drift effect will be introduced at any rate of spin.

In the case of the 22 Long Rifle, several things suggest bullet tilt should have little effect on it. The blunt shape will not put the CG very far from the center of tilt. It's not a wadcutter, but most modern high power rifle designs depend on a long Spitzer nose to pull the CG forward of the center of tilt at the bearing surface center and this causes the lateral drift effect to be a significant issue when concentricity is poor.

Second, the 22 LR spin rate is low, with a 16-inch rifling pitch and velocities in the vicinity of Mach 1. Where a 40-grain bullet from a 223 Rem barrel with 9" twist at 3200 fps will be spinning at 256,000 r.p.m., a 1200 fps 22 LR from a 16" twist barrel will be spinning 54,000 rpm. So, even if the 22 LR bullet had a long, pointy nose to pull the CG forward, it would only cause that CG to orbit the bore centerline at about a fifth the speed the 223 example does, and that would cut the drift velocity to about a fifth of what the 223 sees.

On the other hand, the 22 LR TOF is longer, but not five times longer. So the effect will be there, but overall probably only on the order of a tenth of what you would see with the 223.

[hounddawg]

I have a partial box of Remington Match ammo that is from the 1950's. One day I took it along with boxes of the supermatch Federal ammo made for the (92?) Olympics, and Eley 10X and several other boxes of match ammo I had to see what my old Winchester model 57 sporter would shoot best. They were all about the same except the ancient Remington Match, which shot groups half the size of any of the others.

probably had a lot to do with the base to ogive measurement of that particular ammo more than anything.

I took 15 different .22 LR ammos from Eley Tenex to CCI std velocity and measured the base to ogive on 15 rounds of each and averaged them. They ranged from .782 on CCI Blazers to .752 on Eley Tenex with the others somewhere in between. The best ammo in my CZ 452 was the SK Pistol Match Special with a average base to ogive of .765. Other ammos which had a base to ogive between .0761 to .767 also did well but any outside that .006 window did not shoot worth a darn regardless of box price. That includes high end RWS 50 and RWS 100 ammo which had base to ogive averages of .755 and .756

[Unclenick]

That's interesting. Did you also do the traditional rim thickness measurement? If so, did you see a pattern there?

I think I still have some that ancient match. I know I've got some of the Federal ammo and the Eley 10X. I've also got SK rifle match as well as CCI and Federal standard velocity. I'll have to look at the base-to-ogive number. Were you using the standard Hornady 22 Cal comparator insert?

[hounddawg]

standard 22 insert, did not bother with measuring rims. I operated off the assumption that .003 in BTO could make a difference in CF why not rimfire. If you want a copy of the spread sheet I will try and see if I can find a way to post it. About three hundred rounds of ammo died to make that spreadsheet

it would be interesting to retest on a indoor 50 yard range

edit pretty sure I have some of each of the lot #'s I used if you want to compare your lot # measurements to mine. I'll check if you are interested in pursuing this theory farther. I went into 2020 with more .22 LR than I did primers lol, I just knew it going to be a SHTF couple of years

[Bart B.]

Originally Posted by hounddawg

when records stand for 40 years my thought is that it was neither the gear nor the shooter but just a case of the sun, the moon, and the stars aligning for that one fateful moment. There have been thousands of matches shot since then by a lot of top tier shooters with elite gear and it might be another 40 years before those records are broken. That is why I don't set store much in records. A lot of them are set by one hit wonders

Best 22 rimfire match ammo made since about 1980 is not as accurate as earlier years.

[old roper]

http://bulletin.accurateshooter.com/...-at-200-yards/

https://riflebarrels.com/winners-world-records/

[hounddawg]

http://bulletin.accurateshooter.com/...-at-200-yards/

https://riflebarrels.com/winners-world-records/

never let facts get in the way of a good narrative

that accurate shooter article was pretty amazing, I would be happy to get that group at 100, never mind 200. I do a lot of 200 yard shooting with 22's for practice and a 2 MOA group at 200 with a factory rifle is considered good

[Bart B.]

Originally Posted by old roper

http://bulletin.accurateshooter.com/...-at-200-yards/99.99% luck as all the other groups are bigger.

https://riflebarrels.com/winners-world-records/

More luck.

How are those groups measured; outside dimensions or centers of the two widest shots?

The NRA record for 50 yards prone with a scope is 400-40X plus 165 more record shots totaling 205 record shots touching the .391 inch diameter X ring. At a match some years ago, 1995?, I asked the holder, Mary Stidworthy and her Dad, George, about the RWS ammo used. It was tested at about 3/16 inch extreme spread 40 shots at 50 yards. After Eley, Lapua and RWS changed their primer mix in 1980, their best ammo tested about twice as big. I think Mary Stidworthy strutted her stuff in 1980 when she shattered the any sight National Championship record with a score of1600-154X with the same ammo.

Lapua had an explosion at their Helsinki rimfire ammo plant killing a few dozen people and the European Union governments tasked Eley to make a safer primer formula for all rimfire plants. The new mix had more abrasives that wore out barrels faster and was less accurate.

See post #79 in:

https://forum.accurateshooter.com/th...4031871/page-4

Very few competitors shooting prone can keep the point of aim and shot calls inside 1/4 MOA single round loading 40 record shots.

I understand why folks who are not competitive shooters in smallbore rifle disciplines nor follow the scores are often skeptical about the accuracy attained. I was very skeptical until I started shooting them. After shooting 40 Xes in a 50 yard match I was allowed to continue shooting for record. 3rd shot in the shootout was called a deep X at 9 as the wind gusted from 3 o'clock. Bullet missed the X ring by a 20th of an inch. Eley Tenex ammo was made in 1979.