Was Mr Greenhill Wrong ?

M

murphy

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Ever since smokeless powder become popular rifeling twist rates have been coming down. I know that some of the reason this happens is because of better bullets, but can not help thinking that manufactures build obselesence into their rifles by giving them slower twist rates than needed. Popular thinking in the 1960s was that bullets could be easily overstabilised but my own tests do not bear this out. Conversly I have had plenty of understabilised bullets go through the paper sideways and give on again, off again accuracy. What twist rate are the current crop of benchrest rifles using, and did Greenhill know what he was talking about when he formulated his calculation?)chill(
 
Mr. Greenhill wasn't wrong when bullets were lead pills and velocities were lower, but longer bullets are less dense because of air space or polymer tips and require more twist for the length. A good sourse of info is Applied Ballistics For Long Range Shooting 2nd Edition by Bryan Litz. The Don Miller twist formula takes into account length, mass, caliber, velocity and atmospheric conditions. I made my biggest gains in reloading when I started matching bullets and twist a few years ago. - nhk
 
murphy said:
What twist rate are the current crop of benchrest rifles using, and did Greenhill know what he was talking about when he formulated his calculation?)chill(
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You need to get comfy with Sg values. Benchrest shooters go for an Sg of somewhere between 1.2 and 1.5 -- 1.2 if they shoot in a temperature controlled super dome, 1.5 if they expect to encounter temperature changes.

Aside from gyroscopic stability (Sg), there is also dynamic stability (Sd). The latter's what you need to explain why your 168-grain Sierra Internatinal Match bullets keyhole at 1,000 yards.

We have better models than Greenhill now, but he was not "wrong." If you like math, try Robert McCoy's books. He did a lot of testing for the Government at Aberdeen. Brian Litz is maybe a better read for 2010.

http://www.appliedballisticsllc.com/Book.htm
 
Many thanks boys, I will definately get a hold of Brian Litz vol #2.
 
For a no-math answer, this isn't too bad. As he says, rate of twist is a compromise, as with most everything in shooting. A fast twist isn't as accurate as a slow twist, right up to the point the bullet becomes gyroscopically unstable.

Again, benchrest shooters, particularly the short-range variety, are concerned with anything that loses them .05 MOA or so. Hunting is an entirely different story.

http://bisonballistics.com/articles/barrel-twist-and-bullet-stability
 
Charles, That article is an absolute gem, and yet I have three hunting rifles that shoot short varmint bullets quite a bit better than regular hunting bullets of similar quality. My rifles are a 270 that does best with 90g sierras out of a 1in10 twist. A 300win mag that shoots best with 110g Sierra varminters or 125g noslers out of a 1in 10 twist and a 7mm/08 with 1 in 9 twist that likes 100g sierra varminters. The 7mm/08 is a fairly new Savage model 16 and the difference is particularly noticeable. This rifle often shoots 3 shot 100yd groups of around .3" or better with 100g Sierras, yet after extensive tests 145g Speer Hot Cores are lucky to better 1". I do not just look at the smallest groups but at the overall load development profile of the entire procedure and can determine fairly quickly if a bullet is a winner or not. I am not a scheptic but what in the name of god do the manufacturers do to those stubby varmint pills that makes them shoot so well when in theory they should be in a state of over stability.
 
It is somewhat harder to maintain good balance a longer bullet. The cores may also be a factor. Vaughn noted a couple of problems with the cores in his .270.

If you don't shoot benchrest, it can be difficult to get a handle on the level of accuracy needed to win in competition. It is absurd from a hunting rifle point of view.

The notion that hunters should turn to benchrest for accuracy answers has a limit. You have to know when we're chasing a factor just not significant, or worse, a bad compromise from a hunting perspective.

Many of us get drawn into benchrest -- some to the competition, some for the quest for accuracy for its own sake -- but it is a mistake to think what we find has universal application.

Edit:

BTW, I shoot .30-caliber, 210-grain boat tails at 1,000 yards with a 1:12 twist barrel. No problems. Last match I had a 4.2 inch group -- ten shots at 1,000 yards. Not always that good, of course. The case has the capacity of a .308 Norma Mag, a bit smaller than your .300 Win Mag.
 
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Thank you Charles for taking the time to listen,it is difficult to come to terms with the increasing desparity between Benchrest in it's purest form and the needs of accuracy conscious hunters and varminters.
 
To Charles E and other interested parties, Have had a good think about the concept of the slower rifling twist and the obvious advantage to long range benchresters. Am thinking that barrel profile may have something to do with the fact that they can get away with a slower twist. A 300 Win Mag with a #3 profile barrel must have a lot of whip and oscillation and quite frankly it is a wonder that they can shoot well at all but they do, especially with light varmint type bullets. Am thinking that maybe excessive spin may actually be an advantage in a rifle with a light and perhaps not as well crafted barrel. Maybe the faster twist actually helps to mask some other inequities. What do other folks think about this, could I be on the right track. If barrel profile is part of the equation it should be factored into the formula?
 
It's the bullets, generally. While I've resisted the temptation I'm surrounded by friends shooting 30BR's mostly in our winter league matches and their utilization of longer bullets, 110-115gr in twists from 1-15 to 1-18. As most know they're trying to push the envelope for the absolutely slowest twist to consistantly stabilize the long bullets right on the edge. Several have tried the 18 twists which shoot great.... right up to the point when the temp drops below about 20deg and just that slight amount of velocity lose with a case full of N130 and it's sideways holes, unstable slugs time and again. Everything else being equal the 17 twists work. 16's are safest for when it really gets cold. Again, every other single caracteristic is the same. Want to shoot the lighter shorted slugs you're OK with the slow twists but you end up giving away too much wind resistance.
 
Please forgive my ignorance,but when I moved to the bush some 7 years ago I lost touch with what is happening in the benchrest world. Back then everyone at my local rifle range were using 6ppc with 70g bullets and 1 in 14 twists. Are we talking about the same level of competition or is this a different dicipline? Now I generally shoot alone on my own private range but I still enjoy experimenting.
 
The 30's are shot primarily for score but folks still shoot them for group, a lot of them in winter league type matches. The 30 BR's are very close to the PPC except you really can't shoot free recoil so few shoot them in registered group matches since they can be tough over several aggs/days.
 
Tim,

My God, you Yankees are a tough bunch. When it's less than 50 degrees outside, I find all sorts of reasons not to spend the day sitting at a bench, shooting. 1:18 works just fine for me. (But I do shoot the .30BR free recoil. I guess us westerners/come southerners do have some toughness...)

Edit:

For a bit of parity, how are you guys when the heat and humidity are both in the 90s?
 
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Well we load/clean inside but go shoot 20-30 minutes at a time, still you haven't lived until you try a 2 oz trigger when its about 5 deg.

We're multi taskers Charles, this summer I was lucky enough to win the NYS champs 2 gun with a mid .2 agg & at that match Jim Borden laid down an .046 probable new world record, and that was with a couple thunder storms thrown in.
 
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I'm not a group shooter. I shoot varmints and do some LR score shooting, which means I don't load at the range. Since I don't know what exactly what conditions I will be shooting and my ammunition has to be loaded before hand I don't select a bullet/twist combination of less than Sg 1.4 and use powders that aren't too temperature sensitive. Most of my loads are Sg 1.7-1.8 and perform under all conditions. My LR .308 load has an Sg greater than 2.0. The lower BC bullets will still show some differences in groups over a temperature range. My criteria for accuracy is sub .5 MOA and that's generally where I am.

I've experimented by purposely loading to reduce Sg below 1.0. I've seen groups open up immediately and at about Sg 0.8 holes are oval and it doesn't get any better past 100 yards even though I've been told stability improves down range. - nhk
 
Charles E said:
99.44% sure the answer is no.

It's the bullets.

Try some Berger Match Grade bullets.
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is there some specific formula for getting Berger's to shoot? I have an 11 twist Krieger (.308) that will shoot everything but a Berger. I have tried 5 different powders and they all look terrible.
 
@AMMASHOOTER -- No, some barrels just don't like some bullets. But when you say "Bergers," that covers a lot of ground. Do you mean the VLDs? If you've been jamming them, try jumping them .020, then .040. Or try the hybrids, or non-VLDs. The reason "Berger" gets tossed around a lot is they are the closest thing to a custom from the big manufacturers. Which doesn't mean someone else's bullets wont shot just fine in you rifle.

* * *

@nhkuehl:

nhkuehl said:
. . .Most of my loads are Sg 1.7-1.8 and perform under all conditions. My LR .308 load has an Sg greater than 2.0. The lower BC bullets will still show some differences in groups over a temperature range. My criteria for accuracy is sub .5 MOA and that's generally where I am.
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I don't think this a benchrest shooters perspective. And a long-range .308 load suggests highpower, with the 2-MOA 10 ring, 1-MOA x ring. Huge honking rings. Nor will you get sub .5MOA at 1,000 yards, particularly with a .308. Or I've never seen it. If so, enter matches, you'll win the year-long aggregate comptitions most years.

For records, see.

http://internationalbenchrest.com/records/long_range/index.php

But what I suspect is you're giving a short- to mid-range highpower perspective, no?
 
Now I have the general idea, The climate here in Queensland Australia never gets below 50 Degrees farenheit. You guys should come out one day and have a go at Belmont rifle range in Brisbane, that sea breeze can be very interesting!
 
Sub .5 MOA

Charles E;657887I don't think this a benchrest shooters perspective. And a long-range .308 load suggests highpower said:
Yes I'm aware of records. I'm an aspiring (poor, but a$piring) F-T/R shooter (.5 MOA X ring). I can only verify my groups at 200m locally and sub .5 MOA is not difficult there with a 1000 yd reduced to 200 target. The rifle (Remington 700)* definitely out shoots me and a thing called wind (Mariah?). There is always more horizontal than vertical. I shot a 600 yd practice match and the guy pulling my target commented on how little vertical I had. I've only shot it at 1,000 yds once at Raton and the wind beat me. I also shoot a 6-18X40 $cope. I shot the .308 at the Gateway Dynamite Shoot and exploded a pop can at 400 yds (.6 MOA?) in two shots, the spotter called the first shot and I adjusted. I connected at 600 yds with my Savage .243 in two shots are well (.4 MOA?). Most of my practice comes from prairie dogs on wide expanses of range land and no wind flags. - nhk

*A friend that is a lifelong hunter and hunter education instructor called it the most accurate rifle he's shot.
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