RPM Threshold

[joeb33050]

Harry Pope, and his contemporaries, never did really settle on wheter gain twist was better or not. I'm with them.

I certainly can't prove it, but the ASSRA scores/groups improvements in the past few years might just have something to do with those Smith (and other) gain twist barrels.
Something happened, so that we see multiple 250s shot in matches.
joe b.

[felix]

Again, Joe, shorter the boolit (engraving section) , the better the gain twist works. Also, the tougher the boolit, the better it works. Gain twist requires that the boolit comes back to normal after changing from being twisted at different rates from front to back within the engraving section. .... felix

[joeb33050]

Again, Joe, shorter the boolit (engraving section) , the better the gain twist works. Also, the tougher the boolit, the better it works. Gain twist requires that the boolit comes back to normal after changing from being twisted at different rates from front to back within the engraving section. .... felix

Shorter = works better. Any data?
Tougher = better. Any data? Bev Pinney, PBB winner, used 30:1, Smith gain twist. Duane Jenner used 25:1, Smith gain twist. These were the two gain twist guys at the 2007 CBA NM

I don't know what your last sentence means.
If the gain twist gains at all points along length, then the front of the bullet is being twisted faster than tha rear, but imperceptibly in any normal = 1" bullet length. There is always this, and always the angular delta per inch of barrel increases.
Starting with the bullet breech seated, the front of the bullet has been turned at some angle theta and the rear has been turned at theta-D for difference.
As the bullet moves down the barrel, twist increases, theta increases, and theta-D increases.
With a gain twist barrel, the first derivitive of theta or theta - D WRT L = barrel length, is a positive number. With a constant twist barrel the first derivitive is zero.
Pope wrote that the constantly changing angle kept the bore-bullet interface sealed. Or sealed better. This of course was before the invention of obturation.
I don't know if the gain twist helps accuracy, results are mixed.
I do think that in a good bolt gun, a breech seated bullet may shoot better, and it may shoot even better in a gain twist barrel.
And, the gun is available, unlike the DeHaas Miller actions that are as close to unobtainable as possible.
A stock Savage 308 with breech seated bullets is easy to try, and the twist is fast enough for long bullets. A breech seater can be ginned up by a competent machinist or hobbyist.
If that worked, changing the gun to switch-barrel and using a ?Smith gain twist barrel in 30BR or a cartridge similar to 32MS in volume and shape would allow a first-look estimate of the effect.
The Savage is approximately infinitely more available than any competitive SS rifle, and 1/4 to 1/6 the cost, and years faster to acquire.
At my age I have to consider the gunsmith velocity if I'm having a gun built. Answers to the analysis are not encouraging. I may get the gun before I croak, but will I know why I ordered it and what to do with it? Or my name?
Anyhow, why doesn't someone tell me where I can read about the Government testing having to do with RPM???
Larry? Anybody???
joe b.

[Pat I.]

How do you know Bev or Duane are using gain twists? I don't and I know them both. Why don't you find a 6.5 Carcano to play with? If you decide instead to have a Smith GT barrel put on one of your guns, it doesn't have to be a Savage to see the results, keep me posted since I'll be wallowing around doing things without thinking them through.

[Larry Gibson]

joeb33050

The tests were conducted by the U.S. Ordnance Technical Committee. They recommended the adaptation of the T65 cartridge (7.62 NATO) in a rifle with 1-12" twist. I'm not sure where to find their published report on it as it's been years since I read it. It is most often erroneously published that the T65 cartridge was to replace the M2 cartridge with it's attendant velocity of 2800 fps. That is not the case. First of all the Arsenals did not produce any M2 ammo that attained 2800 fps. That was the plan but the M1 cartridge superseded the plan to up the M1903 ammo velocity to 2800 fps (originally 2700 fps). Problem was the M1 ammo’s range exceeded the maximum the range fans of most military ranges allowed. M2 ammo came about when the arsenals were asked by the War Department to load some equivalent ammo to M1903 ammo for “practice” stateside as the WWI produced stocks of M1903 ammo had been exhausted. M2 Ammo was loaded to nominal 2650fps by the arsenals to meet this requirement. I’ve a copy of the memo directing such velocity BTW.

Back to the point; T65 ammo was designed and loaded to match the trajectory of M1 ammo (174 gr FMJBT at 2640 fps) out to 1200 yards (1100 meters). The 147 gr M80 or the M59 150.5 gr bullets were loaded to 2750 fps 78 ft from the muzzle. It was found a 12” twist gave the best accuracy at maximum range over a 10” twist. Note: many also think the max effective range of the M14 was/is 450 meters (500) yards but that also is not correct. The 450 max effective range is the max effective range using hold over with a battle sight zero (250 meters). Maximum effect range actually is 620 meters for the M14 and 1100 meters for the M60 GPMG. With the rear sight of the M14 properly zeroed it is quite possible to adjust the sight (that’s what the elevation scale is for on the elevation knob) and hit an E target 80% of the time at 700 yards (the 620 meters).

Palma Matches were originally shot with issue rifles and ammo provided by the host country. Palma Matches are belly matches fired at 800, 900 and 1,000 yards. Since 7.62 NATO was the ammo in use by the host nations the ball ammo of 145-155 gr was used. The rules changed that allowed the visiting nations to bring their own rifles, initially service rifles and then any rifle, in 7.62 NATO as the host nation continued to supply issue service ammo. The match shooters picked up on slower twists not accentuating the defects due to RPMs. Initially the match rifles had 12” twists but then they lengthened the barrels to 27 ½ - 32” to obtain maximum velocity. This increased RPM and accuracy with ball 7.62 ammo was adversely affected. It was quickly found that a twist of 13 or 14” dramatically improved the accuracy of 7.62 Ball. Some equivocate this with rounds that “go to sleep” but it actually is different. The adverse affects that RPM has on bullet imbalances is a proven fact.

Larry Gibson

[Bass Ackward]

The adverse affects that RPM has on bullet imbalances is a proven fact. Larry Gibson

Twist rate is determined by the range that you want to fling a certain weight / length / ballistic coefficient object in a stabilized fashion. The more screwed up or less aerodynamic the projectile, (the wider the meplat) the more velocity you will need to start it out at. If your velocity ceiling is limited, then you will need to increase your twist rate to stabilize it farther out. (wadcutters) This is external ballistics and why nose shape / meplat size eats up twist rate. Or lowers RPM ceilings.

Internal cast ballistics dictates that a slug trying to accelerate is retarded by a twist rate angle in the bore. The more the rate angle is increased, (faster twist) the more that bullet will be held back and pressure will work on the base. In effect, it's the same as using a faster powder and we all know that slower powders do allow higher velocities. Also the more barrel time it will have exposed to that pressure. And the result will be the more barrel vibration and greater harmonics will take place. That is also why the lightest bullet per caliber achieves the highest RPM. And why softer bullets can be used with slower twist rates. And why larger case capacities lengthen pressure curves. Not because of stripping or bullet damage as most believe.

So, when you lose cast accuracy is it because of external ballistics or internal ballistics at short ranges? Actually both. You work to mold to achieve perfection and your twist rate fights to destroy it. Pressure does the damage.

[Larry Gibson]

Bass

It would it appear that you agree with the statement of mine you quoted! I've no arguement with your discertation as it quantifies the quote.

Larry Gibson

[sundog]

Gain twist is just that. BUT, you really need to know the start and end twist... 10 to 12? 13 to 14? AND what bore? .308ish, 32ish, ??? Otherwise it doesn't mean much. Gradual, abrupt?

Anyone know for sure the start/end for the Smith bbl?

I shot today in the big wind. S20-G40, light rain showers, and VERY overcast.

Chargar's Lee 311291 in the .303 over 18.0/surp4759 and dacron wad went less than half inch by 4 inch vertical for ten shots. GT line is 360 (wind directly at back). Thinking about bumping it a grain.

Also shot 03A3 scoped sporter with 25.0/4198 and dacron wad with Beagled SAECO 301 WQ, Beagled 311284 WQ, and 314299 HT. 311284 was purdy good, but as usual the 314299 was the best. It and the 311299/40.0/4895 WQ can hold the white of the old gieser target at a hunert for five shots. Worth the trip to the range.

[sundog]

Oooo,, actually a gain twist would be something like 14 to 12, number has to reduce to speed up the spin....

Sorry 'bout that.

[Pat I.]

I won't bet my life on it but I think you can choose the start and end twist with the Smith barrels, like 19 to 11 or 20 to 14. If I remember right the Carcano's was something like 19 to 8 and would be a cheap way for Joe to test it out.

[joeb33050]

How do you know Bev or Duane are using gain twists? I don't and I know them both. Why don't you find a 6.5 Carcano to play with? If you decide instead to have a Smith GT barrel put on one of your guns, it doesn't have to be a Savage to see the results, keep me posted since I'll be wallowing around doing things without thinking them through.

"How do you know Bev or Duane are using gain twists? I don't and I know them both."

I consulted the Nov Dec 2007 Fouling Shot, looked in the NM equipment lists, and, as they say, voila!!

I think I'll try breech seating a bolt gun, I mentioned the gunsmith velocity which keeps me from trying to have a gun built. The famous Competitor SS pistol that was to be delivered in under 10 weeks is now 17 weeks underconstruction and no news.

joe b.

[Pat I.]

[QUOTE=joeb33050;252629 I consulted the Nov Dec 2007 Fouling Shot, looked in the NM equipment lists, and, as they say, voila!! joe b.[/QUOTE]

Well ya got me there for sure! Guess it gives credence to the old saying that even a blind hog can find an acorn once in a while.

[Bass Ackward]

Bass

It would it appear that you agree with the statement of mine you quoted! I've no arguement with your discertation as it quantifies the quote.

Larry Gibson

Larry,

Not always. Remember, the 115 grain Speer example. If something can be beaten just once, then it isn't a fact. A better term might be "inflexible trend". The real question is how flexible (anal) do you want to be?

What's the most accurate cartridge in the world? A 30 PPC at 100 yards? A 300 Win Mag at 1000? Or a 303 British at 1319 meters? (I think that distance is correct.) Can a palma rifle compete to win in any of these categories with generic bulk ammunition regardless of twist rate? Who expects to do well at a 1000 yard match with a 20" barrelled 30 PPC? Or someone at a bench rest competition with a military 303. So why can't we consider a cast as another possibility to make use of our desires instead of using only a set amount of variables to draw up .... "easy" limits?

So why when we come to lead, is the limit the lead because of a single variable? RPMs? Don't we match hardness to the pressure to defeat it? And if going up in hardness by just 6 BHN requires .001 down sizing in bullet diameter for me to get the same groups, can I not be anal (sometimes you don't have too as some guys can find HV almost by accident.) to try something else instead of just blaming it on RPMs?

In other words, if just one guy can, ask why can't " I "? The answers are advancing. If you accept an RPM level as "your" guide, you trivialize the shooting and reloading process to blame your or your guns failure. Simple as that. So all of this jumps around the hot button issues. We don't define accuracy standards. We don't define poor or defective cast guns. And we don't define anal. And without that, we can't develop an RPM ceiling without including .... defective and limiting data. (statistics)

So your test to find best "average accuracy" with what's "reasonably" available off the shelf or steps that are taken is fairly useless. If you want to prove "easiest accuracy" that a slower twist is more .... "idiot proof" and minimizes errors as a reloader and shooter of cast, save your components, I'll give you that. Cast or jacketed as your palma post shows.

Question that should be asked, are you interested in generic accuracy or specialized and specific accuracy? One requires more than the other. But just because you choose to run your two mile PT test with a 35# ruck on your back filled with beer for the trip, don't blame me when your times don't meet the standard. And that's what your test is really talking here. I want this without having to do or meet that. Fortunately, cast accommodates everyone and the HV guys are changing the stereotype.

[joeb33050]

joeb33050

The tests were conducted by the U.S. Ordnance Technical Committee. They recommended the adaptation of the T65 cartridge (7.62 NATO) in a rifle with 1-12" twist. I'm not sure where to find their published report on it as it's been years since I read it. It is most often erroneously published that the T65 cartridge was to replace the M2 cartridge with it's attendant velocity of 2800 fps. That is not the case. First of all the Arsenals did not produce any M2 ammo that attained 2800 fps. That was the plan but the M1 cartridge superseded the plan to up the M1903 ammo velocity to 2800 fps (originally 2700 fps). Problem was the M1 ammo’s range exceeded the maximum the range fans of most military ranges allowed. M2 ammo came about when the arsenals were asked by the War Department to load some equivalent ammo to M1903 ammo for “practice” stateside as the WWI produced stocks of M1903 ammo had been exhausted. M2 Ammo was loaded to nominal 2650fps by the arsenals to meet this requirement. I’ve a copy of the memo directing such velocity BTW.

Back to the point; T65 ammo was designed and loaded to match the trajectory of M1 ammo (174 gr FMJBT at 2640 fps) out to 1200 yards (1100 meters). The 147 gr M80 or the M59 150.5 gr bullets were loaded to 2750 fps 78 ft from the muzzle. It was found a 12” twist gave the best accuracy at maximum range over a 10” twist. Note: many also think the max effective range of the M14 was/is 450 meters (500) yards but that also is not correct. The 450 max effective range is the max effective range using hold over with a battle sight zero (250 meters). Maximum effect range actually is 620 meters for the M14 and 1100 meters for the M60 GPMG. With the rear sight of the M14 properly zeroed it is quite possible to adjust the sight (that’s what the elevation scale is for on the elevation knob) and hit an E target 80% of the time at 700 yards (the 620 meters).

Palma Matches were originally shot with issue rifles and ammo provided by the host country. Palma Matches are belly matches fired at 800, 900 and 1,000 yards. Since 7.62 NATO was the ammo in use by the host nations the ball ammo of 145-155 gr was used. The rules changed that allowed the visiting nations to bring their own rifles, initially service rifles and then any rifle, in 7.62 NATO as the host nation continued to supply issue service ammo. The match shooters picked up on slower twists not accentuating the defects due to RPMs. Initially the match rifles had 12” twists but then they lengthened the barrels to 27 ½ - 32” to obtain maximum velocity. This increased RPM and accuracy with ball 7.62 ammo was adversely affected. It was quickly found that a twist of 13 or 14” dramatically improved the accuracy of 7.62 Ball. Some equivocate this with rounds that “go to sleep” but it actually is different. The adverse affects that RPM has on bullet imbalances is a proven fact.

Larry Gibson

This is hard for me to understand. Is this what happened?
"The 147 gr M80 or the M59 150.5 gr bullets were loaded to 2750 fps 78 ft from the muzzle. It was found a 12” twist gave the best accuracy at maximum range over a 10” twist. "
This having to do with the M14 rifle with ??24"?? barrel. Yes? No?

Then
"Initially the match rifles had 12” twists but then they lengthened the barrels to 27 ½ - 32” to obtain maximum velocity. "
"accuracy with ball 7.62 ammo was adversely affected. It was quickly found that a twist of 13 or 14” dramatically improved the accuracy of 7.62 Ball. "

So, at M14 velocity the 12" twist was shown to be more accurate than the 10" twist.
At greater velocities due to longer barrels accuracy decreased.
With the longer barrels slower twist brought the accuracy back.

2750 fps 10" twist = 198000 RPM
2750 fps 12" twist = 165000 rpm
correct to MV from 78", a guess:
2800 fps 10" twist = 201600
2800 fps 12" twist = 168000
correct to long barrel, a guess. 32-24 = 8 X 30fps = 240 fps+2800 fps = 3040 fps in palma guns
3040 fps 10" twist = 218880
3040 fps 12" twist = 182400
3040 fps 13" twist = 168369
3040 fps 14" twist = 156343

Am I understanding what happened? Not why, still working on what.
Thanks;
joe b.

[felix]

Looks good to me, Joe! ... felix

[Ricochet]

...think about why you NEVER see a free floated military barrel.

That overlooks the many Mosin-Nagants with free-floating barrels. The Finns in particular practiced that quite deliberately by shimming the actions on their rebuilds to float the barrels, and they were doing that way before the '50s. I have standing beside me as I type a 1943 Izhevsk M91/30 that free-floats when the action screws are properly adjusted. Shoots a whole lot better that way than when the front screw's overtightened and pulls the barrel down against the tip of the stock, too. Or when it's benchrested too far out on the skinny front part of the stock, pushing it up to touch the barrel.

[Larry Gibson]

.......So, at M14 velocity the 12" twist was shown to be more accurate than the 10" twist.
At greater velocities due to longer barrels accuracy decreased.
With the longer barrels slower twist brought the accuracy back.

2750 fps 10" twist = 198000 RPM
2750 fps 12" twist = 165000 rpm
correct to MV from 78", a guess:
2800 fps 10" twist = 201600
2800 fps 12" twist = 168000
correct to long barrel, a guess. 32-24 = 8 X 30fps = 240 fps+2800 fps = 3040 fps in palma guns
3040 fps 10" twist = 218880
3040 fps 12" twist = 182400
3040 fps 13" twist = 168369
3040 fps 14" twist = 156343

Am I understanding what happened? Not why, still working on what.
Thanks;
joe b.

That is it exactly regarding how RPM is lowered to lesson the effects on accuracy caused by imbalanced bullets. I don't think anyone here thinks issue ball bullets are that well made to be considered "balanced".

The initial testing, for a new service rifle/cartridge, criteria was for a 22" barrel. That is what the M14 has on it.

Larry Gibson

[felix]

Military bullets are about worthless for BR work. I have tried many different ones because they were/are cheap. I would say offhand they would be close to equal hurried-up cast boolits at best. Now we are talking 3250 (circa 55 grainers) versus 2400 (circa 60 grainers) respectively here, the appropriate speeds for each type in this particular bench gun. 14 twist: 170K versus 125K RPM respectively. So, you can get 50K more RPM with military boolits for the same accuracy (in this gun). ... felix

[Larry Gibson]

Bass

The question here is rather straight forward;

Why is it the average reloader when he gets a regular mould from Lyman, RCBS, Lee or Saeco for his rifle can get accuracy at a certain velocity yet loses accuracy above that velocity?

With the 30-06 for expample he gets good accuracy in the 1700-1900 fps range but above that he gets poor accuracy. He casts the bullets of WWs or an alloy like #2 as mentioned in Lyman's or RCBS cast bullet manuals and uses normal loading techniques as per the manuals. I believe the reason is that above a certain threshold of RPM (the threshold is a range of velocity of 125-140,000 RPM not a specific "limit") accuracy deteriorates with such cast bullet loads as the increased RPM accentuates the inbalances in the bullet (caused during casting, by poor fit, excessive obturation during accelleration, etc.). The increased RPM causes the yaw, pitch and wobble to be increased and accuracy suffers as the higher the velocity the higher the RPM.

I'm attempting to answer that question; is that too hard to understand? I think it is not as you've already conceded that RPM does have an adverse effect on accuracy of cast bullets; " So your test to find best "average accuracy" with what's "reasonably" available off the shelf or steps that are taken is fairly useless. If you want to prove "easiest accuracy" that a slower twist is more .... "idiot proof" and minimizes errors as a reloader and shooter of cast, save your components, I'll give you that." BTW; the use of the slower twist is to keep the RPM under the threshold while attaining a higher velocity. Our example shooter is not going to get another barrel for his favorite '06, he wants it to shoot as is.

Now as to the rest of your last post; yes you can get around the RPM threshold by getting "anal". There are a number of things one CAN do, but the average cast bullet shooter isn't going to do them. He neither has the equipment, the knowledge nor the desire. He just wants to cast bullets, load them in the rifle that he has and go shoot them. He is not going to get a different rifle, new molds, a lot more casting equipment or make some exotic alloy. He just wants to know why his bullets won't shoot accurately above 1900 fps or so out of his '06. And by just casting and shooting regular bullets he is not going to get accuracy above the threshold, now is he. The reason he won't get accuracy above a certain velocity with his 10" twist '06 (or any other rifle of 12" twist or faster) is EXACTLY what we are talking about, isn't it?

The question isn't about getting anal is it, it is about why normal cast bullet loads almost all cast bullet shooters use don't shoot as accuately above a certain velocity as they do below at or below that velocity. THAT is the question I am preparing to answer by shooting over 500 rounds, using 2 different cast bullets, 3 different powders (4895, RL15, H4831SC) loaded in 1 gr increments to give velocties from 1800 through 2500+ fps with each powder and bullet. Identical loads will be fired through 3 accurate rifles of .308 Winchester and each 5 shot string of a particular load will be chronographed and the group measured. Each through a rifle with a with a different twist; 10, 12 and 14".

The test IS NOT to show which rifle is more accurate but at what RPM accuracy deteriorates. Thus the test I am doing is to show at what RPM accuracy deteriorates in each of the 3 rifles with the 2 different bullets loaded over 3 different powders. Given the different twists of the rifles the RPM will be different for each rifle at any given velocity. If accuracy deteriorates in the 10" twist at 2000 fps but doesn't in the 12 and 14" twists then that is an indicator that RPM is the culprit. If at 2200 fps accuracy is still worse in the 10" twist and deteriorates in the 12' twist also but doesn't in the 14" twist then that is even more of an indicator that RPM is the culprit. Then if at 2400 fps accuracy deteriorates in the 14" barrel and we compare the RPM when accuracy deteriorated in all three twist barrels and find that it is close to the same then that would be a good bet that RPM was the real culprit.

So Bass, if you insist my test is "fairly useless" then I challenge you to come up with a comprehensive comparable test to show us how "the HV guys are changing the stereotype." Please SHOW me/us how your '06 holds accuracy from 1800 fps through 2600+ fps and that best accuracy DOES NOT come in the RPM threshold with that 154 gr LBT bullet but at the higher velocity/RPM of 2500+ fps. The choice of alloy, lube, size, barrel bedding or any of the other "anal" things you want to do are ok with me. Pictures of targets and chronograph results please. Shouldn't take more than 10 five shot strings to cover 1800 to 2600+ fps. The guantlet is at your feet. All you have to do is pick it up.

Nothing like a friendly little shoot out, eh?

Larry Gibson

[mainiac]

Thought i might chime in here with a test that im going to make. In previous posts, i alluded to a 22 hornet that shoots up to 2800 f.p.s. with acceptable accuracy. Im about to start testing my 222,s. The difference is that the hornet has a 16 twist, and my 3 222,s have 14 inch twists. Will my deuces shoot as high a velocity as the hornet will, with the same bullet? My benchrest guns have barrells with the slowest twists possible. 15 inch, with 1.080 jackets in 6mm, and 17 twist with 1.000 jackets in .30 caliber. These are on the bare edge of stabilization, but it is the most accurate way of shooting registered br. Anyway, when i get my test done,i will report back. BTW, one of my 222,s is a old sako vixen,with micro-groove barrell. This should be intresting.