Three Rifles Three Different Rifling Twists

[vzerone]

Has anyone read Bryan Litz's test of the title of this post and how he went about it, plus the results, in his Applied Ballistics For Long Range Shooting? It's very interesting and I can post a shortened excerpt here that sums it up.

[Larry Gibson]

I have read the book, several times and still refer to it often.

[vzerone]

Yes I know you have. His test was much more professionally done and there were no differences between the three rifles because as we both know he used a swap barrel. Do you remember the chart where he gave the averages of the three different twist and going from 10 to 12 twist the group actually enlarged? Why?

[Larry Gibson]

pages you are referring to?

[vzerone]

Larry I have a library of electronic books. With the book we are talking about for some reason (maybe I'm using something wrong) Kindle doesn't show the page numbers. With that said the chapter is Chapter 5 Effect Of Twist Rate On Precision.

Here I'll just post it so you and everyone else can read it:


LIVE FIRE TESTING

All of the theory is well and good, but it’s about time for some shooting! Will the math hold up? Let’s see. One of the challenges to exploring dispersion with live fire is isolating the variables. If you have a 1:8” twist rifle, a different 1:12” twist rifle, and you know someone you can borrow a rifle with a 1:10” twist barrel from and shot them all for groups; that would be a poor test. You wouldn’t know how much dispersion was due to twist rate, and how much was due to the differences in barrels, stocks, scopes, triggers, etc. Although it’s never possible to conduct perfect testing in the real world, we do our best to minimize as many variables as possible. For this test, I employed the same Savage platform, HS Precision stock, NightForce scope, and Bartlein barrels used in the previous studies. The Bartlein barrels are all the same length, contour, and have chambers cut with the same reamer by the same people on the same day. The test was run by shooting the same batch of ammo out of each barrel in turn, changing the barrels out on the same platform using the same gages to headspace each barrel. The test was conducted over several hours during calm conditions by the same shooter. In this way, all the variables which could reasonably be controlled were minimized, leaving twist rate alone as the deliberate focus.
The 3 Bartlein barrels were all 24” long, 1.125” straight contour with SAAMI 308 Winchester chambers in 1:8”, 1:10” and 1:12” twist all with 5R riflings. Ammo was loaded using all the same components except for bullets. One batch of ammo was loaded with Berger 175 grain OTM Tactical bullets, and the other batch was loaded with Sierra 175 grain MatchKings. We want to see if the difference in dispersion can be resolved for high vs. average quality bullets as suggested by the math (this assumes there is a difference in balance for these bullets). The test procedure was to start with thoroughly cleaned barrels, then fire 5 fouling shots prior to the record groups. After fouling each barrel, I fired 5 groups of 5 shots (a Benchrest agg) with each ammo/bullet type. The barrels were not cleaned in between bullet types, but I did alternate the order they were fired. The 1:8” and 1:12” twist barrels were the first and last to be fired and for these, I fired the Berger loads first, then the Sierra loads. For the 1:10” twist barrel, I fired the Sierra’s first then the Bergers. There didn’t appear to be any degradation in accuracy over the 60 shots fired in each barrel after cleaning (5 foulers, and 25 shots of one bullet).
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Figure 5.3 shows the test target with all the groups. Seeing the groups can give you a sense of what’s going on, but it’s difficult to really see the trends clearly. Only the big obvious trends are apparent by looking at groups. For example, look at the 2nd and last rows which show the Sierra bullets fired from 1:8” and 1:12” twist barrels. It’s visually clear that the slower twist barrel produced better average groups than the faster twist barrel.
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In order to really see what’s going on, you have to measure the groups and look at the statistics. We’ll start with the results for the Sierra bullets. Figure 5.4 shows a plot of the average groups fired with the Sierra bullets for each twist rate. Error bars are shown which indicate +/-2 Standard Errors. What that means is; if the test were repeated, there’s a 95% confidence level that the average group size would fall within those error bars. In other words, the true average is 95% likely to be within that range. Note this is different than saying any specific group will fall within that range, but the average should fall within that range.

****I'm skipping ahead here in Mr Litz's article for a summary paragraph:
Remember that this test is intended to isolate dispersion due to twist effects as much as possible. However, the reality is there are many other components of dispersion affecting the groups. Things like atmospheric conditions, quality of aiming and shooting, consistency of ammo, etc. These variables all contribute to the baseline dispersion which, in a good test, affects all groups the same. In other words, if we had access to bullets that were perfectly balanced, and had no dispersion due to twist rate, there would still be some level of baseline dispersion which would dictate the minimum group size.

*****My summary: I don't believe that this test can be done accurately with cast bullets. There is no cast bullet that is even going to come close to be as perfect as match jacketed bullets. As you seen in the chart that gave the averages of the groups there is very little difference between the twist rates. In fact going up from the 10 twist to the 12 twist actually had an increase in the group size. For just shooting varmints, to hunting, to just casual target shooting there's not enough difference to give a hoot. Now for serious benchrest competition there is. If member here doesn't have good consistent cast bullets that don't have a large weight variance faster twists are going to really spread your groups.

This was just a small excerpt from Bryan Litz's book Modern Advancements In Long Range Shooting Vol 1

VZ

[Larry Gibson]

Litz's tests validate my own with both jacketed and cast bullets. I have run the same test with 8, 9 ,12 and 14" twist tests in the .223. I have run the same test in the 30-30 with 10 and 12" twists. I have run the same test in the .308W with 10, 11, 12. 13 and 14" twist barrels. I have run the same test in the 30-06 with 10 and 12" twists. Yes I used different rifles but all the rifles were moa or better capable with quality jacketed bullets. The same load and bullets were used in each cartridge. In every single test the slower twist barrels produced the best accuracy with both jacketed and cast bullets with the same load........every single test.

Since no one else would ever have a test rifle exactly what was used by Litz or myself what matters is the trend which is simply; the slowest twist that stabilizes the bullet will give the best accuracy with a given load and velocity, especially with cast bullets. With cast bullets the velocity can be increased with the slower twists until the RPM is the same in all twists. Then accuracy will be fairly close to equal. That's why you can shoot cast bullets faster in slower twist barrels while maintaining accuracy.......

Believe what you will but the facts remain consistently the same. Further reading of Litz's book (I have the 2nd edition) you will note (page 181) he state's; "The fact that the bullet is spinning around 200,000 RPM magnifies the dispersion effect of any imbalance." In effect the higher the RPM the greater the dispersion (group size), the lower the RPM the less the dispersion (group size).

[vzerone]

Larry did you have a swap barrel setup? I know the one test you used three different rifles like Litz said not to use.

Reading Litz's book, in addition to conversing with him via email, he said the dispersion from a fast twist is not enough to make a difference at 1000 that only the most expert best shooters in the world would notice. He said you definitely are not going to miss the entire backer board and that he wouldn't tell me the twist that it would take to make a bullets spin so fast that it would indeed go wild and crazy. Now I've known some twist down in the 1 in 6 range that shot well and weren't crazy, so I'm thinking Litz was talking about something like a 1 in 3. Like I said he wouldn't tell me because I would say he was crazy. Now both Mann and Pope fooled with twist starting from 1 in 1 and up. That boggles my mine.

Litz has a good section in there about dispersion and a formula. The formula was with some of the best match core and jacket bullets and the dispersions just throwing in the different twist wasn't much at all. I'll believe what Bryan Litz has to say. Also there is no such thing as a perfect bullet and cast bullets are as far from it that you can get. Like I said a different twist test with cast bullets is plum crazy.

[Larry Gibson]

"[I]The formula was with some of the best match core and jacket bullets and the dispersions just throwing in the different twist wasn't much at all/I]."

That is correct and so is Litz. However, Litz isn't using cast bullets. My tests were with cast bullets and jacketed bullets. No the difference in accuracy between the fast and slow twists using quality jacketed bullets "wasn't much", as litz says, but a difference was still there. The difference was much greater with cast bullets because cast bullets are much softer than jacketed bullets and no matter how well we cast them they are not as balanced as quality jacketed bullets. That difference with cast bullets becomes rather apparent at the RPM Threshold of the components you are using, especially when shooting past 100 yards.

[vzerone]

That softness with cast hasn't anything to do with what you are talking about if it's started straight into the bore. A good example of that is paper patched bullets. They shoot very well accuracy wise. One of the major problems of imbalance is variance in weights between the bullets. You yourself said that you learned to cast better bullets not too many years ago. I believe according to your better casting of bullets time period was after you did the rpm tests.

Here's something to think about. One thing you might notice is that the deflection depends on time of flight, not range. That’s because when the bullet exits the muzzle, it’s basically given a lateral kick, which gives it a lateral velocity. The resulting deflection is then velocity times time. As a result, if you were to consider the deflection example above at 1000 yards, it would not be 10 times the 100 yard deflection. It would be based on the 1000 yard time of flight which is more than 10 times the 100 yard time of flight.

I don't believe you ever brought that up. Haven't you led us to believe that for example a 1 inch group dispersion at 100 yards would be 10 times that at 1000 yards?

[vzerone]

Litz said this: All of the theory is well and good, but it’s about time for some shooting! Will the math hold up? Let’s see. One of the challenges to exploring dispersion with live fire is isolating the variables. If you have a 1:8” twist rifle, a different 1:12” twist rifle, and you know someone you can borrow a rifle with a 1:10” twist barrel from and shot them all for groups; that would be a poor test. You wouldn’t know how much dispersion was due to twist rate, and how much was due to the differences in barrels, stocks, scopes, triggers, etc. Although it’s never possible to conduct perfect testing in the real world, we do our best to minimize as many variables as possible.

What don't you understand about that? No matter how good your rifles are that's not as valid as test as the way he did it. That's why Bryan Litz wrote that in his book so we wouldn't be doing such test which don't give as precise data.

[Larry Gibson]

vzerone

That softness with cast hasn't anything to do with what you are talking about if it's started straight into the bore. A good example of that is paper patched bullets. They shoot very well accuracy wise.

Yes PP bullets can be very accurate. However, the hardness of the alloy still plays a part as the PP jacket still is not as hard or as supportive as a brass alloy jacket. With jacketed bullets an almost pure lead core can be used to well over 3000 fps. To the contrary with PP'd bullets as you get above 2000 fps a harder alloy must be used. The plain cast bullet (sans any type of jacket) does not have the support during acceleration that the jacketed or PP'd bullet has regardless of how straight it is started into the bore.

I cast quite good cast bullets at the time of the initial RPM tests. I learned to cast better bullets because of the later tests pushing the RPM Threshold and accurately shooting the 30 XCB and 311466 to 2600 to 3000+ fps. If you question the validity of my initial RPM tests you are free to get yourself a switch barrel action and 3 alike barrels with 10, 12 and 14" twists. Camber them with SAAMI spec .308W reamers. Get a 311291 mould and cast up some decent bullets using COWWs + 2% tin. get some 4895, some decent .308W cases ands some LR primers and duplicate the test. Then shoot 10 shots each for each rifle of 26 through 38 gr of 4895 in 1 gr increments with a Dacron filler. Test them at 100 yards with 10 shot groups. Come back with the results.

Given the fact that the velocity of the loads I tested was the same the time of flight was the same. What varied was the group dispersion because the deflection caused by the bullets imbalance was greater with the faster twists.

No, I have not led you nor anyone else to believe is linear to 1000 yards. What I have been saying, which apparently you've not been understanding is that group dispersion can be quite close to linear to 600 yards but then group dispersion opens up in a somewhat parabolic curve. The reasons are varied and Litz covers them in his book as do most other ballisticians. What is linear is MOA; 1" at 100 yards (not exact but is the generally accepted figure) will equal 10 times at 1000 yards.



One of the major problems of imbalance is variance in weights between the bullets. You yourself said that you learned to cast better bullets not too many years ago. I believe according to your better casting of bullets time period was after you did the rpm tests.

Here's something to think about. One thing you might notice is that the deflection depends on time of flight, not range. That’s because when the bullet exits the muzzle, it’s basically given a lateral kick, which gives it a lateral velocity. The resulting deflection is then velocity times time. As a result, if you were to consider the deflection example above at 1000 yards, it would not be 10 times the 100 yard deflection. It would be based on the 1000 yard time of flight which is more than 10 times the 100 yard time of flight.

I don't believe you ever brought that up. Haven't you led us to believe that for example a 1 inch group dispersion at 100 yards would be 10 times that at 1000 yards?[/QUOTE]

[Larry Gibson]

Litz said this: All of the theory is well and good, but it’s about time for some shooting! Will the math hold up? Let’s see. One of the challenges to exploring dispersion with live fire is isolating the variables. If you have a 1:8” twist rifle, a different 1:12” twist rifle, and you know someone you can borrow a rifle with a 1:10” twist barrel from and shot them all for groups; that would be a poor test. You wouldn’t know how much dispersion was due to twist rate, and how much was due to the differences in barrels, stocks, scopes, triggers, etc. Although it’s never possible to conduct perfect testing in the real world, we do our best to minimize as many variables as possible.

What don't you understand about that? No matter how good your rifles are that's not as valid as test as the way he did it. That's why Bryan Litz wrote that in his book so we wouldn't be doing such test which don't give as precise data.

Here's what's not understood by you; Litz was shooting and talking about the highest quality jacketed match bullets available. Litz did not test cast bullets nor did he consider cast bullets in his writings. Instead of reading something into his writing that isn't there run the test mentioned my previous post. See if you get any different results that I did.

What is your point to all this?

[vzerone]

Larry you threw a lot of stuff and questions at me. Let me see if I can wade through them and address, although it maybe not be in order. Let's tackle your good bullet casting. You said this in one of the post above: "I cast quite good cast bullets at the time of the initial RPM tests. I learned to cast better bullets because of the later tests pushing the RPM Threshold and accurately shooting the 30 XCB and 311466 to 2600 to 3000+ fps." How can you cast quite good bullets and then learn to cast better bullets? Here's a post of yours from January of this year on the CBA forum, supposedly when you're casting "better bullets: "Of the 542 bullets weighed 22 were rejected for a visual defect or because they weighed less than 186.9 gr which means the weighed ones had passed the visual inspection but still weighed way lite. The remaining 520 XCBs were weight sorted into separate bins of .1 gr increment from 186.9 gr to 188.0 gr......a 1.1 gr spread." This picture accompanied that post and showed your weight sorting setup.
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That many bins??? I pm'ed you not long ago and tried to help you cast better bullets. Yes folks, Larry and I pm one another. I told Larry at that time I had just cast a bunch of 30 Sil bullets and the weight variance was .1 grain. If I were to sort them I'd only need two bins. One for the main weight bullet and the other for the ones that were only .1 grain different. Larry that is what you call good bullets. The bullets you suggested for me to try the three different rifles with three different twists were at the most mediocre good bullets. They are old Lyman designs. In your XCB shooting did you use those bullets you suggested? No, you and others designed the 30 XCB bullet. You done this because you learned by now you have to have a better fitting bullet. For the members if you're just doing the standard cast bullet shooting in your rifles and not the high velocity shooting for accuracy those bullets Larry named are then good. What those bullets do lack though is they don't fit the throat as well as the new current designed bullets such as Larry's XCB bullet and 45 2.1 30 Sil to name two. Maybe your three different rifling tests would have looked much different had you cast real better bullets and that the bullets were better designs such as your XCB or the 30 Sil. It doesn't matter if it's a jacketed bullet or a very well cast good designed bullet that enters and exits the bore straight, but I have to concur with Bryan Litz you cannot do a accurate test with three different rifles like he said. I conclude talking about you casting good bullets.

Next you said this in an above post: "The plain cast bullet (sans any type of jacket) does not have the support during acceleration that the jacketed or PP'd bullet has regardless of how straight it is started into the bore." Some of that is is true and a lot of it isn't. If a soft cast bullet has the proper support and started into the bore straight it will should accurate if the rifling supports it too. Way back in the 70's when the NRA wrote the Cast Bullet Book they shot a 300 Win Mag to just a tad over 3000 fps with very good accuracy, plenty good enough if you were to hunt with it. Of course with that velocity I wouldn't use it on big game, but varmints it would be okay.

I'm going to address these last things and finish. That is what is my point? You have talked in the past to other that if a cast bullet is a very good one and started straight into the bore and exits properly that rpms don't affect it's accuracy. The point is it doesn't matter if a bullet is cast or jacketed rpms only disperse a bullet only if it has imbalances and that dispersion is based on time. I mentioned all that in a post above. Cast bullets are only going to have large dispersion's if they are imbalanced by whatever means. This statement above "What is linear is MOA; " makes no sense in the way you wrote it. MOA isn't a bullet it's a measurement, but I believe what you meant to say is linear dispersion can be measured in MOA. Linear dispersion and rpm dispersion are two different things. The rpm dispersion, as I posted, is measured in time and not multiplied the distance, were as linear dispersion is X's the distance.

VZ

[popper]

Don't want to rain on anybody's parade but it's the rotational energy of the boolit that causes dispersion. Faster spin, higher rotational energy. If that energy is NOT aligned with the trajectory vector, (strength of boolit, wind, poor boolit/design, etc.) dispersion occurs. Just normal gyro effects.

[vzerone]

Don't want to rain on anybody's parade but it's the rotational energy of the boolit that causes dispersion. Faster spin, higher rotational energy. If that energy is NOT aligned with the trajectory vector, (strength of boolit, wind, poor boolit/design, etc.) dispersion occurs. Just normal gyro effects.

Popper Bryan Litz covers that and still the bullet doesn't deflect that much to make a hoot at 1000 yard.
Here the formula for figuring the deflection which as you see include the twist for the spin.

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You notice that .0001 figure? That's the imbalance number of the bullet. If you play around with that formula and the larger the number the more deflection. If you bring it to zero the deflection is near zero.

[Ballistics in Scotland]

Further reading of Litz's book (I have the 2nd edition) you will note (page 181) he state's; "The fact that the bullet is spinning around 200,000 RPM magnifies the dispersion effect of any imbalance." In effect the higher the RPM the greater the dispersion (group size), the lower the RPM the less the dispersion (group size).

Most of have heard of the accidentally "incorrectly" rifled Springfields General Hatcher mentioned, which gave superior accuracy with a particular military bullet, until that irregularity was discovered and the machines set to the standard 10in. twist. I am sure it was true, but unlikely to be due to velocity of rotation or "overstabilisation".

These things can happen, and are a complex iinteraction with bullet weight and shape. A wobble may or may not be induced, and may settle down as the bullet travels downrange, or deteriorate to the point of tumbling. It doesn't surprise me in the least if a slow twist sometimes produces this kind of effect less than a fast-twist one.

But there is also a far more consistent and predictable reason for error on target. If the bullet's centre of mass is even a thousandth of an inch off-centre, it is travelling in a helical curve while the outside of the bullet travels in a straight line. When the bullet emerges from the muzzle it obeys Newton's First Law. Not being constrained into that helical path, the centre of mass flies off in a straight line. But that straight line is the last direction in which the helix was pointing.

Imagine if that .002in. helix could be unrolled into a flat rectangle, ten inches long. The end would be π (i.e. about 3.142) times .002, i.e. .00628in. The angle between a diagonal and the long side will be equal to the angle of the bullet's departure with the bore axis.

At 1000 yards (4320 times that 10in. twist), the bullet deflection will be 4320 times .00628in., or 27.143in.

A wobble may occur, may bear some relation to the rifling twist, and will add to the 27.143 group if it does. But the reason described for the 27.143in. part of the inaccuracy will make its size inversely proportional to the rifling twist, and independent of bullet weight, length and velocity. Create that bullet imbalance by drilling tiny holes into the jacket, and position them at 3, 6, 9 and 12 o'clock in the chamber and you can make a four-leafed clover or even four separate groups on the target.

When I built my medium-heavy P14 Enfield .300H&H, I had in mind the 190gr. Sierra MatchKing and similar softpoints. It performed well with these, but gave at least as good accuracy, a consistent 1⅛in. at 200 yards, with 125gr. Spitzers at over 3550 ft.sec., which translates to 255,600rpm. I interpret this as meaning that the angular deflection was happening, but a significant wobble wasn't.

This also proves that the bulletmakers are making them within better than a fifth of a thousandth of perfect concentricity of mass, and the small specialist firms who cater for benchresters very much better than that. It is quite a performance.

[Larry Gibson]

Larry you threw a lot of stuff and questions at me. Let me see if I can wade through them and address, although it maybe not be in order. Let's tackle your good bullet casting. You said this in one of the post above: "I cast quite good cast bullets at the time of the initial RPM tests. I learned to cast better bullets because of the later tests pushing the RPM Threshold and accurately shooting the 30 XCB and 311466 to 2600 to 3000+ fps." How can you cast quite good bullets and then learn to cast better bullets? Here's a post of yours from January of this year on the CBA forum, supposedly when you're casting "better bullets: "Of the 542 bullets weighed 22 were rejected for a visual defect or because they weighed less than 186.9 gr which means the weighed ones had passed the visual inspection but still weighed way lite. The remaining 520 XCBs were weight sorted into separate bins of .1 gr increment from 186.9 gr to 188.0 gr......a 1.1 gr spread." This picture accompanied that post and showed your weight sorting setup.
219563
That many bins??? I pm'ed you not long ago and tried to help you cast better bullets. Yes folks, Larry and I pm one another. I told Larry at that time I had just cast a bunch of 30 Sil bullets and the weight variance was .1 grain. If I were to sort them I'd only need two bins. One for the main weight bullet and the other for the ones that were only .1 grain different. Larry that is what you call good bullets. The bullets you suggested for me to try the three different rifles with three different twists were at the most mediocre good bullets. They are old Lyman designs. In your XCB shooting did you use those bullets you suggested? No, you and others designed the 30 XCB bullet. You done this because you learned by now you have to have a better fitting bullet. For the members if you're just doing the standard cast bullet shooting in your rifles and not the high velocity shooting for accuracy those bullets Larry named are then good. What those bullets do lack though is they don't fit the throat as well as the new current designed bullets such as Larry's XCB bullet and 45 2.1 30 Sil to name two. Maybe your three different rifling tests would have looked much different had you cast real better bullets and that the bullets were better designs such as your XCB or the 30 Sil. It doesn't matter if it's a jacketed bullet or a very well cast good designed bullet that enters and exits the bore straight, but I have to concur with Bryan Litz you cannot do a accurate test with three different rifles like he said. I conclude talking about you casting good bullets.

Next you said this in an above post: "The plain cast bullet (sans any type of jacket) does not have the support during acceleration that the jacketed or PP'd bullet has regardless of how straight it is started into the bore." Some of that is is true and a lot of it isn't. If a soft cast bullet has the proper support and started into the bore straight it will should accurate if the rifling supports it too. Way back in the 70's when the NRA wrote the Cast Bullet Book they shot a 300 Win Mag to just a tad over 3000 fps with very good accuracy, plenty good enough if you were to hunt with it. Of course with that velocity I wouldn't use it on big game, but varmints it would be okay.

I'm going to address these last things and finish. That is what is my point? You have talked in the past to other that if a cast bullet is a very good one and started straight into the bore and exits properly that rpms don't affect it's accuracy. The point is it doesn't matter if a bullet is cast or jacketed rpms only disperse a bullet only if it has imbalances and that dispersion is based on time. I mentioned all that in a post above. Cast bullets are only going to have large dispersion's if they are imbalanced by whatever means. This statement above "What is linear is MOA; " makes no sense in the way you wrote it. MOA isn't a bullet it's a measurement, but I believe what you meant to say is linear dispersion can be measured in MOA. Linear dispersion and rpm dispersion are two different things. The rpm dispersion, as I posted, is measured in time and not multiplied the distance, were as linear dispersion is X's the distance.

VZ

Yes, I have learned to cast much better bullets over the last 8+ years. As usual you quote me out of context leaving out important facts stated in the rest of the post such as; all the bins shown in the photo were not used. The majority (347/65%) were "match selected" bullets and were within +/- .1 gr. Another 15% were just .1 gr below that and were used as fouler/sighters. The rest were rejected. I deal in actual results as measured by bullets from mould to target. I do not deal with results simply measured from keyboard to screen. When you can push any ternary cast bullet at 2900 fps and shoot moa or less 10 shot groups at 600 yards (target shows 11 shots at 600 yards into 5.9") then you can talk to me about how to cast better bullets.

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As to the PP bullets the NRA used in the 300 Win Mag. Colonel Harrison conducted that test and recommended and alloy with at leas a BHN of at least 16 - 20 BHN in not harder for PP'd bullets used above 2500 fps. Because....guess what? The PP does not provide sufficient structural support for a softer alloy during the acceleration at that velocity level. Softer alloy in 12 BHN range is recommended for up to 2000 fps.

BTW, MOA measurement is linear measurement. As I stated 1 MOA is considered to be 1" at 100 yards. So 1 MOA at 200 yards is 2", at 300 yards it's 3" etc. and at 1000 yards 1 moa moa is 10". Linear group expansion would be 1 moa at 100 yards (a 1" group), 1 moa at 200 yards (a 2" group), 1 moa at 300 yards (a 3" group) etc. out to 1 moa at 1000 yards which would be a 10" group.

Now if you actually read my posts concerning the 30 XCB in the 30x60 rifle you'd see it consistently shoots (with 10 shots or more) 1 moa at 100 yards, 200 yards, 300 yards and at 600 yards (see picture above). That is linear group and moa dispersion to 600 yards. Note with the RPM at 2900 fps with that load out of the 16" twist barrel is below the RPM Threshold.

Could you be so kind as to quit misconstruing what I say specifically regarding dispersion based on RPM. If the velocity is the same out of 10, 12 and 14" twist riffles then the time of flight will be essentially the same. There can be a difference because the BC, actually measured, will be lower in the faster twists. It is not very much over short distances such as out to 300 yards. The dispersion caused by RPM on imbalances in the bullet given the same velocity and thus the same time of flight will be greater with the faster twists because the RPM is greater. That is ballistic fact and is what Litz said in the quote you posted from his book.

[Larry Gibson]

Popper Bryan Litz covers that and still the bullet doesn't deflect that much to make a hoot at 1000 yard.
Here the formula for figuring the deflection which as you see include the twist for the spin.

219585

You notice that .0001 figure? That's the imbalance number of the bullet. If you play around with that formula and the larger the number the more deflection. If you bring it to zero the deflection is near zero.

That 0.0001 is the center of gravity offset from the geometric center by .0001". That is based on the best of the best of high quality jacketed match bullets. Cast bullets, even the best ones anyone can cast will have a much larger offset straight out of the mould. Sizing the bullet does not improve it. The offset is also much larger when the bullet is launched. The "3000" is the velocity.

Excellent observations by popper and Ballistics in Scotland.

[vzerone]

I've never disputed the higher rpm on imbalanced bullets causes more dispersion, only the fact that the dispersion doesn't amount to a hill of beans. Litz also spoke of some bullets in his book with a .000073 imbalance.

Larry when you can cast bullets with .1 grain or less weight variance come talk to me.

MOA is just a measurement, it doesn't do anything except give you a measurement of linear dispersion.

[vzerone]

That 0.0001 is the center of gravity offset from the geometric center by .0001". That is based on the best of the best of high quality jacketed match bullets. Cast bullets, even the best ones anyone can cast will have a much larger offset straight out of the mould. Sizing the bullet does not improve it. The offset is also much larger when the bullet is launched. The "3000" is the velocity.

That's 100 percent correct Larry and the exact reason I've said earlier that the any rifling twist test done with cast bullets is flawed data. It's only correct for the bad cast bullets that the person doing the tests did.

[Larry Gibson]

vzerone

I've never disputed the higher rpm on imbalanced bullets causes more dispersion, only the fact that the dispersion doesn't amount to a hill of beans.

Conduct the test.....you'll see. Show us how good your bullets are. We know you can post pictures, show us some bullets and, most importantly, actual targets......?

MOA is just a measurement, it doesn't do anything except give you a measurement of linear dispersion.

And THAT is EXACTLY what I said.

[vzerone]

I already said such a test is stupid using cast bullets. We already know from physics that there is a rpm dispersion on imbalanced bullets. To do with it with the best match bullets available only proves that the dispersion doesn't amount to a hill of beans. Litz kind of done that, I posted the results here and if you have the books you read it.

The main thing is that if a cast bullet is hopefully imbalanced (and other negative influences) it's not going to shoot off into wonder wonder land like many in the past have claimed here on this very forum. For that matter one can take imbalanced flawed cast bullets and shoot so half decent groups at 100 yards. Notice I said 100 yard. They would be plenty good enough for deer too!

[Larry Gibson]

vzerone

The main thing is that if a cast bullet is hopefully imbalanced (and other negative influences) it's not going to shoot off into wonder wonder land like many in the past have claimed here on this very forum. For that matter one can take imbalanced flawed cast bullets and shoot so half decent groups at 100 yards. Notice I said 100 yard. They would be plenty good enough for deer too!

Said the same thing many times. Unbalance bullets can indeed give pretty good accuracy out to 100 yards if under the RPM Threshold. If over the RPM threshold they also can give very usable accuracy to 100 yards for hunting deer size game.

Nice to see we are in agreement......:drinks:

[vzerone]

vzerone

The main thing is that if a cast bullet is hopefully imbalanced (and other negative influences) it's not going to shoot off into wonder wonder land like many in the past have claimed here on this very forum. For that matter one can take imbalanced flawed cast bullets and shoot so half decent groups at 100 yards. Notice I said 100 yard. They would be plenty good enough for deer too!

Said the same thing many times. Unbalance bullets can indeed give pretty good accuracy out to 100 yards if under the RPM Threshold. If over the RPM threshold they also can give very usable accuracy to 100 yards for hunting deer size game.

Nice to see we are in agreement......:drinks:

Appears you are agreeing with me!