1 in 15 twist for a 6PPC

Given one caliber and jackets the same length and runout, wouldn't we have less
CG offset with those having lighter cores ? Say 65 vs 68. There is certainly less
off center mass in the lighter
 
Depends on which you think has the greater contribution to CG offset. We've been talking about jackets, so if there was less core and the jacket specs remained the same, the bullet CG offset would be greater with a lighter bullet.

Edit:
Put it this way. If the location and amount of the "defect" remains the same, but the overall mass goes down, the CG offset is greater.
 
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JonathanK said:
I think James Mock would be a great person to test it out as well
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One barrel won't prove much - THAT is one of the BIG issues with BR 'experimenting': conclusions drawn based upon too many 'samples of one'!:eek:

As AlinWa pointed out, and as hinted at in Greman's comments (quoted above), precession, is a necessary attribute of stability. With MARGINAL stability (< Sg 1.4), the bullets never 'goes to sleep' thus, impact, relative to varying conditions, even at short range BR, is less predictable in the wind: the angular drag (drift) component varies from shot-to-shot, producing patterns, vs. groups, as the condition is 'missed'. A fully stabilized bullet WILL display more angular (vertical) movement (precession) as the bullets 'drifts' back-and-forth in varying vectors/velocities, BUT, comparatively, will shoot GROUPS along this 'string', thus making 'hold-off' more predictable . . . how often do we compete in ZERO conditions . . . or, even 'light' ones?:p;) How many barrels have you owned, which shoot in the relative still early AM/late PM,, only to 'blow-up' during match conditions - could this be as much about stability (or, lack there of), as opposed to 'tuning'? :confused:

Overlooked here is also the fact that heavier bodies are stable at lower RPM - a positive attribute of larger calibers; the sole negative for larger bullets is recoil.:D The historic bell-curve representing [so called] 'hummer' 6mm barrels is pretty poor - something like 2/10ths being of 'killer good', or, 'BIG Match' quality, while the 30 Cal. bell lumps a large majority of barrels in the latter category, with only the occasional ho-hummer or, bummer. Could this be due to the fact that the bullets from the contemporary 30 Cal. model are exiting the muzzle at Sg ranging from 1.4 - 1.9 (the "MAGIC WINDOW"), at sub 150,000 RPM, while the 6mm model produces sub 1.4 [Sg], at 180,00 plus RPM?:p;) Except in 'tunnel-like' conditions, 'proper' twisting for 6mms should produce an over-all increase in grouping performance (smaller AGGS) - as with our thirty caliber experiment, the more barrels you try, the more pleased you'll be - there can always be a bummer barrel - but, when it comes to hummers, you'll beat the hell out of the 2 out-of-ten model.

Oh, and, for the thirty, GREATER stability, at lower RPM, combined with 'better' bullet balance (a lower PERCENTAGE of Cg off-set): see the notes (above) by the two Als! Damn that recoil! :confused::rolleyes:

RG
 
One barrel won't prove much - THAT is one of the BIG issues with BR 'experimenting': conclusions drawn based upon too many 'samples of one'!
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Right.

Wasn't what I was after, Randy, but my fault I didn't hit the *bold* enough. The first thing to establish is "That didn't hurt it any." Once you get a few "that didn't hurts," you can get enough people willing to try to establish how much, or under what conditions (if any), it helps.

The psychological downside is if barrel number one does hurt (the grouping), that is taken as proof of something. Of course, the proper response if the first one "hurts," is once again, you have only one data point. If I had the resources, I'd hand out 10 barrels -- but I don't.

Even if all this is correct, there will be occasions where it demonstrably hurts. When you're riding the ragged edge and things are working, the ragged edge is a good place to be.

A more general conclusion would be, when you go to a big match, if you're taking 14 and 15 twist barrels, have a good 12 or maybe 13 in the bag -- you never know when it'll come in handy.

If James wants to give it a try, that's OK with me. But it isn't suppose to be just a "free barrel." It'll take work to do any comprehensive evaluation even with one barrel, and "I'll pass" is a perfectly reasonable response.
 
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Charles E said:
Right.

Wasn't what I was after, Randy, but my fault I didn't hit the *bold* enough. The first thing to establish is "That didn't hurt it any." Once you get a few "that didn't hurts," you can get enough people willing to try to establish how much, or under what conditions (if any), it helps.

The psychological downside is if barrel number one does hurt (the grouping), that is taken as proof of something. Of course, the proper response if the first one "hurts," is once again, you have only one data point. If I had the resources, I'd hand out 10 barrels -- but I don't.

Even if all this is correct, there will be occasions where it demonstrably hurts. When you're riding the ragged edge and things are working, the ragged edge is a good place to be.

A more general conclusion would be, when you go to a big match, if you're taking 14 and 15 twist barrels, have a good 12 or maybe 13 in the bag -- you never know when it'll come in handy.

If James wants to give it a try, that's OK with me. But it isn't suppose to be just a "free barrel." It'll take work to do any comprehensive evaluation even with one barrel, and "I'll pass" is a perfectly reasonable response.
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Ooops, I hit the post button too soon!:eek: I'm with you 100% here Charles - not many of can afford to test a statistically valid sample size.
For the thirty caliber model, we now have 14 seasons of data: is the 'sure-fire' stability THE [not so] salient issue?

In reference to the highlighted (RED) quote, yes, assuming that one is a SUPER condition doper . . . but, what about the rest of us?:confused:;)

And, I assumed that, in my statement above - "Overlooked here is also the fact that heavier bodies are stable at lower RPM" - people would understand that this is in comparison to bullets of differing caliber, but, equal sectional density and similar proportions. RG
 
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65-grain bullets

Brady Knight and J. D. Denoff both make killer 65-grain bullets on .750 or .790 bullets that work equally well in a 13.5 or 14 twist barrel at 100 or 200. Several shooters were using them at Riverbend this weekend, and J. D. has a pending LV 100 agg world record from this weekend.
 
1 in 16

I have a barrel that Allan King used to use on his 6x39 heavy gun and it is supposed to be a 1 in 16 (Hart barrel, I know out of favour cause it is button rifled). Now Allan was no fool and he shot 83 grain McCracken bullets in that gun. I always shot 75 grainers out of it cause that is what I had at the time.

I had that barrel rethreaded and chambered for the 6 PPC, but I have never fired it. It is a .261 neck and I just never got up the desire to do the necessary case work. Only had it for maybe 20 years.

What is all this stuff you guys are talking about with temperature and altitude? Sounds to me like some smart ass came up with a way to psych out the competition by getting them into navel gazing instead of concentrating on the conditions of the day.

The smallest group I have ever witnessed was a .070. Even by today's standards that is a small group. It was shot with folded reject (read free of charge) bullets that weighed both 68 and 70 grains (which the shooter did not even know until the next day). When Al Mirdoch was making McCracken bullets he would throw the folds in a box and then he would often just give them to us poor young bucks.

DDDave
 
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damascusdave said:
I have a barrel that Allan King used to use on his 6x39 heavy gun and it is supposed to be a 1 in 16 (Hart barrel, I know out of favour cause it is button rifled). Now Allan was no fool and he shot 83 grain McCracken bullets in that gun. I always shot 75 grainers out of it cause that is what I had at the time.

I had that barrel rethreaded and chambered for the 6 PPC, but I have never fired it. It is a .261 neck and I just never got up the desire to do the necessary case work. Only had it for maybe 20 years.

What is all this stuff you guys are talking about with temperature and altitude? Sounds to me like some smart ass came up with a way to psych out the competition by getting them into navel gazing instead of concentrating on the conditions of the day.

The smallest group I have ever witnessed was a .070. Even by today's standards that is a small group. It was shot with folded reject (read free of charge) bullets that weighed both 68 and 70 grains (which the shooter did not even know until the next day). When Al Mirdoch was making McCracken bullets he would throw the folds in a box and then he would often just give them to us poor young bucks.

DDDave
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Dave,
With all due respect, there is no way that 83 grain bullets will stabilise in a 1 turn in 16 twist barrel. I suggest you check that Hart barrel with a tight patch and a good cleaning rod.

I was a good mate of Al Mirdoch's and stayed with him in 1980 when I attended the Canadian Supershoot at Namaka. I also imported around 120,000 McCracken bullets into Australia, including quite a lot of the 83 grainers. We had to go to 12 twist barrel to stabilise them. They were unreliable in 14 twist, even out of a 243 hunting rifle.

Believe me, temperature did have an effect with the 1 in 15 barrel. Anything under about 12 deg Celcius could produce sidways holes in the target. The same barrel on the same day won the 200 yard agg at the Nationals in the afternoon (22 deg C) using exactly the same load.

Cheers

Brendan Atkinson
in South Australia
 
DDDave.
My personal experience is that with even a 1/15 twist 6mm barrel it would not stabilize a 62 grain, 0.800 bullet. Velocity was about 3320 fps. That is at an altitude of 1100 ft. Now at Raton, 6,000+ altitude that barrel shot like nothing I ever had before. Just bugholes. Now expain that.

Donald
 
Al Mirdoch

Hey Brendan

Just repeating what Al told me and what is recorded in the old benchrest shooters news issues. I know that it does not make a bit of sense and I will be the first to admit if I am in error.

I do not have the barrel right here with me so I cannot confirm the twist. I somehow forgot to register my guns and they are in hiding. I am going to feel pretty stupid getting it turned down and rethreaded and chambered if it ends up keyholing bullets. Then again I already feel stupid for having such an interesting gun that has never been fired.

One thing for sure is that shooting at Namaka in the old May shoot could be a pretty cold experience. One of my favourite memories of Al is of him shooting in his old light blue parka on May 5.

We lost a good man and a good friend when Al passed on. Just wish I could have been a better friend and got him to cut down on the JB before it got him. I will forever be thankful to him for giving me the incentive to quit.

DDave
 
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BTW Brendan did we meet at that Supershoot? Unfortunately I do have a bit of trouble remembering events from around that time. My hard drive has quite a few errors. Seems to me that was the year that Lori Mirdoch turned 20. She was a very pretty, intelligent and together lady and I blew my chance with her by being an idiot. Only person I ever knew who could spot bullet holes on a 20 yard smallbore target without a spotting scope.

Dave Wilson
 
Altitude difference

Donald said:
My personal experience is that with even a 1/15 twist 6mm barrel it would not stabilize a 62 grain, 0.800 bullet. Velocity was about 3320 fps. That is at an altitude of 1100 ft. Now at Raton, 6,000+ altitude that barrel shot like nothing I ever had before. Just bugholes. Now expain that.
Click to expand...

If we can all agree that a bullet is fully stablized at Sg 1.00 and assuming we are dealing with an unadjusted temperature of 59 degrees and the only thing that changes is the altitude then at 1100 ft the Sg is .95 and at 6300 ft (Raton) the Sg is 1.14.

At 1100 feet the temperature would have to 89 degrees to get an Sg of 1.00.

At at 6300 ft the Sg would still be 1.01 at 0 degrees. - nhk
 
damascusdave said:
BTW Brendan did we meet at that Supershoot? Unfortunately I do have a bit of trouble remembering events from around that time. My hard drive has quite a few errors. Seems to me that was the year that Lori Mirdoch turned 20. She was a very pretty, intelligent and together lady and I blew my chance with her by being an idiot. Only person I ever knew who could spot bullet holes on a 20 yard smallbore target without a spotting scope.

Dave Wilson
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We might have. I remember that there was a beer strike on at the time and Wayne Miller brought a whole trunk load of beer and hard stuff over from Saskatchewan in that big V8 car of his. He loaned me that sucker for the time I was there. The Saturday shoot was held in good conditions, but on Sunday it was bloody freezing and my wife spent most of the day sitting in Wayne's car with the heater on. I think Bill LePer won the 2 Gun, and I still have a cap on the wall from Precision Guns and Sports (Lethbridge?) for winning the 200yd HV agg.
Many years ago, eh? Al was a great guy with a wicked sense of humour. A good mate.

BA
 
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