Twist rates, the Juenke and accuracy.

[Tony Z]

Late last year i aquired a Vern Juenke bullet spinner out of the US. For all these years i have measured and batched bullets by bearing length, ogive profile etc and had some reasonable success at long range with it. I have never fired bullets in competition with the use of the Juenke spinner. So before it goes up for sale i wished to see for myself if there is merit in this devise. Well so far from a short range perspective for me there is, to a point. Recently i did a bit of work with a 22BR and 6BR and a well known commercial bullet brand and did convince myself that bullets that spun less than 5 units did shoot one hole groups and those that were over 10 units on the scale did group rather ordinary. In this case it was possible to batch commercially made bullets that would give true BR accuracy out to 200 yards. The down side was that there was a 75% cull rate where out of a box of 100, 25 were worthwhile and the rest were only good for the crows.

Now here comes the anomaly to this bullet spinning thing. For a number of years i have shot a 30BR with a well known brand of custom bullets. In my 18 twist barrel these bullets will wipeout the dot in a Hunter target with the right driver in good conditions. Groups below 0.250" are easily achieved at 100 yards with this combination. Then a little while ago i decided to spin these bullets on the Juenke, and guess what? They were not all that much better than the above mentioned commercial bullets. Now i checked the batches, and sure enough, they were the same ones that drill holes in the 18 twist 30 BR barrel. So they spin poorly, but still shoot well enough to net a 747.xx at the Innisfail 300 shot a few years back where they shot a 500.32 at 100 and 200 agg. So i know this combination shoots very very well, but the Juenke says they shouldn't. So yesterday i decided to shoot these bullets out of my Maddco 14 twist 3 groove 30 BR barrel. At 100 yards it shot a 249.6, which with the 6x scope class is a reasonably competitive score. Those bullets shot were no better than 10 units and averaged about 15 units. Some were as high as 25 but i did try and use these just for foulers. The one shot dropped was a very skinny 12 o'clock 9. The rest were skinny 10s and there was nothing convincing about this setup. I was surprised that 249 was the score as there were a lot of peripheral shots that just cut the ring. Shot again, i doubt i would have been so lucky.
At 200 yards, the 10 ring was very elusive and 9 points were dropped. No dots were hit, not even close and no single bullet hole was completely inside the ten ring. All 10s were line cutters which is not a good sign for Hunter. These same bullets shot out of the 18 twist just flatline across the target giving a wind weather report of the day. At 200 yards the one target was used and groups of five shots were fired for score on each roundel. All five of these groups were very poor with the same pattern at 100 being evident where the groups were very open and all had some shots that were well outside the 10 ring with one just cutting the 8 ring at 11 o'clock and heading for that seven ring. Lastly i shot a group of these same bullets that did spin 5 units or better and the rifle was completely different. That one group was half of the best of the Hunter targets score groups and more importantly was only a couple of calibers in height.
My conclusion with this is that the Juenke can determine a bullet both good and bad, but i am pretty convinced so far only in a short range application where bullets just spun on this machine will not necessarily be uniform for bearing length or ogive profile. Even using the pointer location as an indication of ogive position is deceiving as a full 15 units of scale is way less than half a thou of an inch of jacket thickness on a 30 cal bullet. Bullets that are less than 5 units in jacket concentricity, but may be 5 units apart on the scale, still shot through the same group when shot at short ranges. With a six mil or 22 that may be different.
As for long range, that is for another test i will be doing shortly for my last hoorah. From what i have seen so far bullets just spin tested will still give ordinary groups, mostly vertical, if shot at 1K with no other batching process. This is where i think the Juenke has become maligned as there have been many disillusioned with the machine as they just do not produce the desired result at 1K. But at shorter ranges, even to 500m they do look very impressive and deceptive at the same time. That much i already know for sure.

There is most definitely an accuracy advantage with twist rates as a bullet that measures poorly still measures poorly no matter what barrel it is shot in. But the difference of RPMs between a 14 twist and an 18 twist is enough to mask a lot of bullet CG offset. If i was to stay in this Hunter game, i think that the way i would head with a barrel for a 30 BR would be like the yanks did in the early days and head off to 19, 20 or even 21 twist back when the 0.925" jackets were being used. Nowadays the bullets are most likely on the 1.000" jackets like the BIBs and 19 twist may be the limit. Which ever way you look at it, bullets shot with this much jacket eccentricity in any other caliber or same, and with more regular twist rates exhibit similar groups at 200 yards and are not worth a cracker. The way slower twist rate takes a lot of the bullet CG offset moment out of the equation and gives a very different outcome at the target. This has long been the theory and in this example seems to be the reality.

There has long been the two factions in long range. Those that go with minimal twist to get the job done and those that use more twist than required in the others view with the object of getting a SF of 1.5 or better. With a good batch of bullets, i doubt that an inch or less in twist rate choice that is within the parameters would have any great bearing either way. For me, the Juenke has confirmed known good shooting bullets in many calibers, and maybe shown why some other batches have not been so good. There has long been the question asked by many of what the machine actually measures and also the question of if in fact it is worthwhile. Put very simply, the machine measures bullet jacket concentricity. For short range use, just the Juenke alone seems to be able to deliver the results. For long range, i know for sure it will give a bullet that will group well when tested at shorter ranges, but also know that this is only one half of the the total equation and groups at the longer ranges are average at best when no other qualification is used. As i said earlier, this machine goes up for sale shortly, but before then my curiosity wants me to try and determine its value at 1K where bullets spun alone are shot, bullets just qualified as i have done for years are shot, and then finally a combination of both is used. There is no doubt that there is a direct correlation between bullets that are qualified as junkers by measurement with my methods, but there are also good measuring bullets that show big numbers of units on the Juenke. So a perfect measuring bullet using mechanical means in not always a perfect bullet when measured electronically using the Juenke. My guess is that the use of both methods will produce the best outcome.

I hope this little chapter has given a little insight on a machine that is not written about all that often. And possibly a little insight on the role twist rates play in accuracy.

Tony Z.

[Curtley78]

G'day Tony,

Very interesting topic. There seems to be so many variables though such as weight.

I weighed 2 packets of Berger 155.5 Full Bore the other day and found 3-4 variations of weight, admittedly the variation was in tenths of grains, I also weighed 2 packets of Sierra 95 grn Match King and again found 5 differing weights (94.5-6, 94.7-8, 94.9-95) I then assorted these projectiles into three groups.

Do you believe that it is worth while batching projectiles into specific weight categories for long range BR and would the half grain deviation between projectiles have any significant impact upon accuracy?

Regards

Sean

[jimbo]

I spin all of my 6mm match grade bullets......usually at around 13.75 inches for every revolution, all the way to the target.

[Mick]

I always thought it was odd that people relied on only the Juenke without qualifying the bullets by bearing surface etc.

Just seems like common sense to me. The thing measures jacket concentricity. There are much more important factors to batching bullets than that I'd thought.

[Curtley78]

....The thing measures jacket concentricity. There are much more important factors to batching bullets than that I'd thought.

That is what I was thinking. Such as the theory of consistency by equalising pressure, weight & velocity.

Regards

Sean

[Tony Z]

So Brendon, i was told you spun all your Elfs before you went over to NZ where you went on to win the two gun at the world champs. No truth to that?

Tony Z.

[Ackley Improved]

Tony.. what are you going to be chasing in $$$$ for the machine?

Cheers

[jimbo]

So Brendon, i was told you spun all your Elfs before you went over to NZ where you went on to win the two gun at the world champs. No truth to that?

Tony Z.

Absolutely correct. I have a Cantech bullet spinner, and every Elf that I took to NZ in 2001 had passed the test - less than two tenths of run out.

The Roosters that I took to South Africa? I started to spin a few, but the consistency was that good, I gave up on that and used them straight out of the box.

I have experimented with bullets up to five tenths run out, using a rail gun, and can find no real problems. Over that the average group size tends to increase. Not much, but enough in our game.

[Curtley78]

The last time I was rostered out at Silverdale a few of the BR boys were using these 'Elfs' unfortunately I didn't ask who is the importer for them and where I could get some?

Regards

Sean

[Ackley Improved]

Elf's = Australian.

[jimbo]

The last time I was rostered out at Silverdale a few of the BR boys were using these 'Elfs' unfortunately I didn't ask who is the importer for them and where I could get some?

Regards

Sean

Erik Nielsen from Dunedoo (NSW) was the guy behind the Elf brand - he made bullets for many years, and they were at the time the best bullets made in this country. He made one shape and one weight, and there was very little variation between each batch. I shot them by the thousands and won a shit load of shoots with them.

A few years back Erik developed arthritis in his hands and could no longer pull the levers. The dies were sold to Peter Fleming up in Coffs Harbor. I shot some of Peter's and they were just the same - bloody excellent.

Unfortunately, Peter has the same complaint and his hands are giving him heaps. So, when he has finished making himself a 'life time supply' of bullets, I understand he will sell the dies and bullet making set up.

He is o/seas at the moment so don't go chasing him up yet.

[RDavies]

Jimbo, when you say 5 tenths of runout, is that half a thou? About 2-3 thou seems to be what I always end up with (with an occaisional one about .006" out), what sort of difference will that make?
I would suppose the Juenke users are already sorting by bearing surface as well as using the machine? Jeeze, I,m flat out getting time to reload at all.
Something else I have been thinking with twist rates is that it pays for us Southerners to use slightly faster twists. Up in Atherton and mareeba with its altitude and warm weather (giving less air density) People might be able to get by with longer barrel twists. I have had a few barrels (In .224 and 7mm) which were supposed to be 9" twist ,but are closer to 10". I found on nice warm days, these will shoot the 175 Sierras (or 70gn Berger in .224) well, but if it is a cold day, (Dense air) the 175s dont shoot as well, but the shorter 168s (or 68gn flat base .224s) loaded to identical velocity go great. I was thinking the bullets are only marginaly stable in the 10" twist barrels in the denser air

[jimbo]

Jimbo, when you say 5 tenths of runout, is that half a thou? About 2-3 thou seems to be what I always end up with (with an occaisional one about .006" out), what sort of difference will that make?
I would suppose the Juenke users are already sorting by bearing surface as well as using the machine? Jeeze, I,m flat out getting time to reload at all.
Something else I have been thinking with twist rates is that it pays for us Southerners to use slightly faster twists. Up in Atherton and mareeba with its altitude and warm weather (giving less air density) People might be able to get by with longer barrel twists. I have had a few barrels (In .224 and 7mm) which were supposed to be 9" twist ,but are closer to 10". I found on nice warm days, these will shoot the 175 Sierras (or 70gn Berger in .224) well, but if it is a cold day, (Dense air) the 175s dont shoot as well, but the shorter 168s (or 68gn flat base .224s) loaded to identical velocity go great. I was thinking the bullets are only marginaly stable in the 10" twist barrels in the denser air

Five tenths of a thou on run out. The modern benchrest rifle will/should shoot 'sub one',ie less than 0.100 five shot groups, but there are very few sub one shooters.

However, the rifle is so highly tuned that it will pick up any discrepancies like variations in the bullets. Factory over the counter bullets can sometimes shoot down under half an inch - I am taking aggregates here - like five x five shot groups...not one fluke group. When we start to get into the realms of competition shooting we are talking about shooting 100 yard aggregates under two tenths of an inch.

In New Zealand in 2001, I shot four consecutive groups under .150 at 100 yards - the agg went within one shot of the smallest ever shot anywhere by any class rifle in the world - my .15 something agg is still the WBC record. I tell you this not to blow my trumpet, but to give an idea of how much difference there is between normal rifles and these formula one jobs. Every bullet had been spun on a bullet run out guage and spun up near perfect. I did weigh them, but I have found that for short range benchrest, a couple of tenths of a grain makes no difference.

Now as to your comment on twist rates. Some benchresters were using (me included) Maddco 15 twist 6mm barrels. They shoot great in weather above 15 deg C. However, a few of us found out that if the weather is cold, like Silverdale or Para on an August morning, you can get bullets going through the target sideways. As soon as it warms up, the same load works just fine. Marginal stability!

John Giles (PSECO) and Neville Madden (Maddco) won seven four gun National Championships in benchrest using the 308 cartridge with a 168 gn bullet in a 1 in 14 twist barrel - the bullets must have been bordering on unstable but they sure did shoot. They also had to use powders like IMR 4895 and IMR 3031, and did not get the velocity that we can achieve from the modern stuff.

You need to chronograph your loads in varying temperature, because yes they will vary.
Benchresters often adjust their load for changing weather conditions. Some have a temperature sensor down in the powder in the measure. Some shoot H322 in the cooler morning, but in the afternoon switch to Benchmark 2 (the latter seems to work even better in hot weather). Those who shoot Vihtavouri N133 can be constantly tweaking the load during the day. Complicated, isn't it?

In South Africa we only had access to one powder - the local stuff, SomChem S335. It was filthy stuff to use and caused us all sorts of fouling problems, but I found two 'nodes' in it which worked just fine. One was red hot, and the other mild. You work these things out.

But..as I always say, if it was easy, everyone would be doing it.


Cheers

Brendan

[albow]

Hi Jimbo

I find it interesting what you have to say about the adjustment of loads to keep them shooting in the varying temperatures etc and was wondering how big a variation you have to make with your load. Also what was the variation in the load in SA between the two nodes?

I used to have about +/- .4 gns on the load for my LR gun for it to still group well but earlier this year had a stretcher tube fitted and all I can say is this is what you want.

When I went out and did some limited testing for a load and I say limited because there was no point shooting any more than the four groups I did. What we need to keep in mind here I already had a load so I started .5gns below my old load and it shot great and I then worked up 2 full gns from that and it still shot. The only difference in the groups was they were each printing slightly higher on the paper with the increase in speed and the only reason I stopped where I did was due to pressure but now had a full 2 gns of load window.

If you get a chance put one of the tubes on your gun, it will be the best thin you do

Alternatively you could do a story on a rifle. Shoot it in the bare form and then add a tube to see the difference.

[jimbo]

Stretching, compressing or tensioning barrels has not really taken on in short range benchrest.
In sporter and light varmint you might have a problem staying under the weight limit, but there might be scope for it in heavy. I have seen this system used on an unlimited class rail gun, but that did not set the world on fire. The best in World were shooting at the WBC in South Africa, and no-one was using this system there.

The load window was 1.2 grains apart - this is a given for N 133, as the nodes come out at 1.2 gn. My load was 29.8 for the Rooster 67's and 31.0 if I went to the Copperhead double ogives. The lighter charge did not give great velocity (around 3200 I would guess), and sometimes at 200 yards it was like shooting a rimfire - gee, it was touchy, but boy was it accurate! That range is at 4200 feet above sea level, and every morning it was BLOODY COLD!!!

The dirty powder caused us to change our cleaning routine, and we had a Hawkeye bore scope on hand to check the internals after every clean to make sure we were getting it all out. We were patching out with Butch's Black Powder Solvent for the first patches until they came clean, then switched to Butch's Bore Shine. That took care of most of the powder fouling but the copper fouling was mind boggling - these were new barrels that did not foul when run in in Oz. So...we got stuck into the bore with Iosso bore paste until it was clean.
Everybody in our team was having trouble with the copper fouling, so it was not specific to just one barrel. The really odd thing was that nearly all of the copper was in the last two inches of the barrel. Yes, we were using moly coated bullets.

We also weighed every charge, as there was so much static around that we were getting .6 grain variations in powder measures that back home run faultlessly.

Like I said...if it was easy....