Another kind of RPM Test [Archive]

Bass Ackward

03-30-2008, 07:00 PM

For this weekend, I took my wife's 22" barreled Howa in 30-06 and 4, 150 cast bullet designs. Her rifle has a shorter throat to make this possible. The designs were a 311466, 311440, 311440 hollow point, and my 152 grain LBT Spitzer. The 311440 hollow point weighs 146 grains. These represent round nose, wide flat, hollow point, and spitzer designs at roughly the same weight.

I loaded three of each design with ACWW and the same mix water dropped and hardened for two days. All were sized .3095 using a nose first sizer and seated lightly into the lands. All will be loaded to within 50 fps of each other using 56 grains of RL19 as the high base for 2500 fps velocity in this gun. No loads leaded.

My objective was to change no variables and keep RPMs constant. Bullets were weighed and varied by 1.2 grain with my LBTs being the same as the others, blemished slugs were shot in the order they came. I used reamed and turned brass with loaded rounds spun for less than .002 runout measured on a sized band with all designs. My sizers ARE round. Powder charge did not have to be adjusted more than 1 grain to stay with in 50 fps of 2500 fps with the lighter hollow point needing the extra charge.

I also chose 18 grains of 2400 for a low 1700 fps target and will hold this RPM level. No load work up is occurring on either end. Just RPMs as a constant. I will swap brass later. Temperature was 30 to 50 degrees over the two days.

Quickload predicts muzzle pressure at bullet exit to be 7000 psi with the high loads and 3800 psi with the low loads and fast powder.

311466- 156 gr dressed
High: ACWW - 5 1/2". WDWW - 3 1/4"
Low: ACWW - 1 5/8". WDWW - 1 1/4"

311440 Solid 154 gr dressed
High: ACWW - 12". WDWW - 6 1/2"
Low: ACWW - 2". WDWW - 2 1/4"

311440 Hollow point 146 gr dressed
High: ACWW - 1 5/8". WDWW - 1 3/8"
Low: ACWW - 1 5/8". WDWW - 1 3/4"

LBT Spitzer 155 gr dressed
High: ACWW - 5 1/4". WDWW - 1 1/8"
Low: ACWW 1 1/4". WDWW 1 1/4"

Now I took standard cases that were not prepped just right out of the box for the last two bullets. Loaded just as carefully, run out was now .005 to .007.

311440 Hollow point 146 dressed
High: ACWW - 3 3/8". Ran out of bullets.

LBT Spitzer 155 dressed
High: ACWW - 7". WDWW 2 1/2"
Low: ACWW - 1 5/8" WDWW - 1 1/2"

Took one more design as I had some 311467s sitting here in both ACWW and WDWW confugurations. Powder charge was raised to 58 grains for the same RPM and Quickload predicted pressures 6000 psi higher at 40,000 psi to do this.

311467 185 grain dressed
High: ACWW - did not hit paper. WDWW 4"
Did not shoot low as I knew this would be dramatically better.

To be continued.

Larry Gibson

03-30-2008, 07:13 PM

Bass Ackward

03-30-2008, 07:46 PM

This was interesting as I did not know what to expect from this rifle really. And the results were not totally as I expected they would be.

The results were sorta startling in that the 311440s that are the same except for the hollow point that shot remarkably well in both the ACWW and WDWW hardness's while the solid design that is the SAME was the worst of all designs tested. Is it the 10 grains less pressure or the hollow point nose that is supposed to put a better air flow on the slug? Another argument. But the hollow point results were the same as I had with handgun tests too.

What was clear. Launch bad bullets and you get what looks to be an RPM effect. But the LBT that was 1 grain outta balance shows me that if I match hardness to the pressure and fouling that it will encounter at the higher velocity, so that I launch good bullets, that RPMs has virtually no effect on that amount which is fairly substantial as a percentage of bullet weight. So either RPM effects everything or it doesn't.

Weirdly enough, meplat size and shape had little to do with accuracy either when you look at all the tests. When hardness failed, and all designs went squirrely, all bullets reacted pretty much the same way with remarkably pour grouping with the most aerodynamic of these, the 311467 going the wildest. Coincidentally, it has the highest muzzle pressure too at just over 12,000 psi

But if you look at the lightest 311440 and the heaviest 311467, clearly the lighter bullet has the higher velocity potential. Even though the bearing area is longer / stronger on the 311467 to fight that force in the bore, so it has to be elongation of the pressure curve for the lighter slugs at the same hardness even though the powder would be thought to be slow with both slugs.

What was remarkable too was that run out had as much effect on accuracy as pressure destroyed / outta balance bullets. But this means a base out of square just as if pressure distorted it. Apparently it doesn't take much. How a base distorts appears to be a mute point, the higher the muzzle pressure, the wilder the group. Which also supports PB limits theory when in the RPM zone.

There are better designs for high velocity than others. The idea is to elongate the pressure curve with lighter bullets, slower powders, or slower twist rates, load more concentric ammo or all of the above. Launch a bad bullet at 1800 fps and you only have 3800 psi to disturb it. Launch a bad bullet at 2500 fps and you have 7000 - 12,000 (311467) psi to affect it.

But what ever it takes, DON"T launch bad bullets at any RPM or pressure level.

Bass Ackward

03-30-2008, 07:52 PM

Appears Bass is proving the existance of the RPM threshold.

Bass, I would have to ask if you chronographed those loads or are going off the guestimate of Quick Load?

One other thing, what does "dressed" mean? I only asked as that is not a term I've seen before when refering to any type of ammuntion.

Larry Gibson

Larry,

Look close at the data. All designs were outta balance, but two designs failed to show any RPM effect. The hollow point didn't care how outta balance it was as it shot soft as well as it did hard.

Loads were chronographed. But Quickload did estimate within 50 fps of the chrono, so I believe the muzzle pressure figures to be close.

Dressed means that bullets were weighed with check and lube. My bullet naked were within 1/2 grain, but people often forget that checks aren't all the same and air pocketes can be trapped in lube as well. It all counts, so if you are going to weigh, then you need to weigh dressed which I did.

NSP64

03-30-2008, 07:55 PM

So if I look at this right a gc maynot be needed for lead prevention as much as to keep the base uniform at higher preasures.

felix

03-30-2008, 08:01 PM

Very good, John! Absolute terminal pressure is as important as the pressure curve is from beginning to end. Perhaps even more so, eh? ... felix

felix

03-30-2008, 08:03 PM

Yes, gas checks are required to maximize performance. To go better, paper patch. To go even better, use condoms. All assuming the same quality of projectiles. ... felix

Larry Gibson

03-30-2008, 08:29 PM

Basss Ackward

"Look close at the data. All designs were outta balance, but two designs failed to show any RPM effect. The hollow point didn't care how outta balance it was as it shot soft as well as it did hard."

I did look closely at the data. I don't believe you are seeing what it is telling you. Yes "all designs were outta balance". All bullets, especially cast bulletsare "outa balance that is why (once again) we shoot bullets into groups instead of one hole. Obviously the HP stayed in balance. This could be an anomaly groop as you don't mention the number of shots per group or if you repeated any of the tests. Anomaly groups do happen, quite often acutally, and they should be retested if they appear to be "too good".

"Loads were chronographed. But Quickload did estimate within 50 fps of the chrono, so I believe the muzzle pressure figures to be close."

Thanks for the answer; the QuickLoad muzzle pressures should be fairly close.

"Dressed means that bullets were weighed with check and lube. My bullet naked were within 1/2 grain, but people often forget that checks aren't all the same and air pocketes can be trapped in lube as well. It all counts, so if you are going to weigh, then you need to weigh dressed which I did."

"Dressed"; I like that! I had not heard it used that way before, I shall enter that definition into my library, thanks.

"What was clear. Launch bad bullets and you get what looks to be an RPM effect. But the LBT that was 1 grain outta balance shows me that if I match hardness to the pressure and fouling that it will encounter at the higher velocity, so that I launch good bullets, that RPMs has virtually no effect on that amount which is fairly substantial as a percentage of bullet weight. So either RPM effects everything or it doesn't"

Launching "bad" bullets or the fact that they get "bad" during accelleration is not relelvant; It is the RPM that adversly affects the ("bad") imbalanced bullets. 1 gr weight differance does not make the bullet imbalanced either. An imbalanced bullet is when the center of form does not coincide with the center of gravity. Weight in this case has nothing to do with "balance". The balance is in relation to the spinning of the bullet. If the center of form of the LBT bullet coincides with the center of gravity of the spinning bullet the .0066% (the 1 gr) is not a "substantial difference. That 1 gr is not a "substantial difference even as far as weight varience of .30 caliber cast bullets goes. RPM does in facte(a)ffect the bullets.

"Weirdly enough, meplat size and shape had little to do with accuracy either when you look at all the tests. When hardness failed, and all designs went squirrely, all bullets reacted pretty much the same way with remarkably pour grouping with the most aerodynamic of these, the 311467 going the wildest. Coincidentally, it has the highest muzzle pressure too at just over 12,000 psi"

Not "wierd" at all. When the alloy hardness went the bullets sustained greater imbalance (obturation and distortion) during accelleration and the RPMs centrifugal force had a greater affect.

"There are better designs for high velocity than others. The idea is to elongate the pressure curve with lighter bullets, slower powders, or slower twist rates, load more concentric ammo or all of the above. Launch a bad bullet at 1800 fps and you only have 3800 psi to disturb it. Launch a bad bullet at 2500 fps and you have 7000 - 12,000 (311467) psi to affect it."

That is true but all that only occurs in the barrel during acceleration. It is the RPMs centrifugal force that causes the inaccuracy during flight.

"But what ever it takes, DON"T launch bad bullets at any RPM or pressure level"

See Bass, you are learning about RPMs, aren't you.

Larry Gibson

runfiverun

03-31-2008, 12:04 AM

what i got here also
is that the externally hardened boolits shot much better
hmmm.
stripping, maybe / nose slumping, probably
wonder how 5/5 or other mix would compare here?

Larry Gibson

03-31-2008, 02:39 AM

Bass

Since you chose to only test a 10" twist to keep the RPMs consistant along with the pressure let me ask you one more simple question;

Remembering that pressure is the same and consistant with the 10" twist barrel; If you were to also have used a 14" twist barrel and the loads/pressures were the same and ALL the HV groups fired with it were the same size as the low velocity groups could we not then say that since the RPM was considerably less (128,000 RPM at 2500 fps and still within the RPM threshold) that it was the RPM that caused the greater inaccuracy in the 10" twist barrel at HV? Remember now, the pressure is the same in both rifles.

Larry Gibson

Bass Ackward

03-31-2008, 07:33 AM

Remembering that pressure is the same and consistant with the 10" twist barrel; If you were to also have used a 14" twist barrel and the loads/pressures were the same and ALL the HV groups fired with it were the same size as the low velocity groups could we not then say that since the RPM was considerably less (128,000 RPM at 2500 fps and still within the RPM threshold) that it was the RPM that caused the greater inaccuracy in the 10" twist barrel at HV? Remember now, the pressure is the same in both rifles.

Larry Gibson

Larry,

The pressure is the same. What is different is the elongation of that pressure curve. Instead of peaking at say two inches of barrel travel, it may peak at 2 1/2" of barrel travel. What that means is that the bullet has another precious 1/2" of travel gaining velocity as it goes. If you were going to get rear ended by a car that is coming on at 25 miles an hour, would you rather be rear ended going 10 miles an hour or 20 miles an hour? The least damage of coarse is the 20 mile an hour example. Same with the bullet.

So not only are you raising pressure, you are also peaking it faster and closer to the beginning. Sort of as if you were increasing twist rate. If one was to use an AR platform that used pressure to cycle the bolt, thus reducing muzzle pressure, you would see a wider HV accuracy spectrum. Not that pressure won't destroy bullets, but they have much lower muzzle pressures with shorter barrels to affect results.

Want to know then why factory bullet designs fail so low in general? Most factory molds have a tapered base to facilitate putting on the checks that grip at the top. That means that only air remains inside the check to maintain that pressure seal as that bullet is exposed. The crime occurs upon exit when that bullet exits. Unless that base deforms to fill the check putting the bullet outta balance again. That little copper cup isn't materially stronger than lead unless it is supported. And if it is gripping at the top of the check because the lead is tapering away under it, you will see check rotation stripping occur as it remains the only thing left in the bore. Especially if it had to scrape lead too. Think that soft copper cup deformed where it wasn't supported? And if the base was pushed in, didn't the top then spring out like a parachute? Ooops, whats holding it now?

Easiest accuracy does occur at the earliest levels that will stabilize a certain length bullet using a certain twist rate and then it becomes harder from that point on. Why? Cause lube means more, hardness is becomes critical, more friction so more barrel vibration, a thousand reasons, not one.

Here is the bottom line. Two new guys can have the same twist rifles and want to shoot HV.

One guy can understand the process and work to achieve accuracy at HV if he thinks logically and takes steps to correct.

The second guy blames his results on RPMs. What does he do next?

Larry Gibson

03-31-2008, 11:52 AM

Bass

You failed to answer the question.

It is obvious you know the answer and just don't want to answer (admit) it. However we shall soon see. I am not going to use cars to hypothesize about pressure in different barrels. In the test i am going to conduct I will measure the pressure including the time pressure curve and I will measure the effects on the bullets flight using 3 different twists. You already admit that your test here ("And the results were not totally as I expected they would be.") gave different results than you expected. There are many theories and hypotheses that may sound good (like your pushing the car) but when actually applied to something else (like the pressure curve of shooting a bullet) they may be different and not applicable at all.

Your test simply provides us with the same information we've known all along. Is the inaccuracy caused by pressure (or a different time pressure curve) or is it caused by RPM? I could be wrong or you could be wrong or we could both be right. With a slower time pressure curve along with reduced RPM accuracy could be enhanced, that's the third option here. We shall soon see what the actual differences are, if any, when the same bullet is fired out of a 10, 12 and 14" twist barrels at the same presure. Then we won't then have to hypothesize about it.

Larry Gibson

Bass Ackward

04-01-2008, 06:51 AM

You failed to answer the question.

Is the inaccuracy caused by pressure (or a different time pressure curve) or is it caused by RPM? I could be wrong or you could be wrong or we could both be right. Larry Gibson

Larry,

I am the greatest advocate of no laws when it comes to cast. So how can I answer any question as a fact. :grin:

You miss the point here also. This is not a matter of me being right. Just you being wrong. :grin: I suppose that we have seen people lining up on both sides of the fense, but I only want to see that the next fella be able to imporve or succeed if he wants to try.

We got a 22-250 in this last week that won't hold 4 " with factory copper. Cleaned the copper out and it's back below MOA. The point here is that, regardless of the bullet material, the sure way to increase fouling is to increase velocity. Eventually everything is over come.

Fouling plays a big part. And lube acts like a hydraulic sizer the faster you go too effectively sizing down the bullet and reducing rifling height. This is seen with the results with the LBT Spitzer using ACWW in the first post. So hardness is not only for pressure, but fouling too. I expected you to jump all over that, but you let it pass.

Get above 80 degrees where the lube is thin and used up do to temperature and friction and that load comes back MOA where the softer lead can be used for groundhogs. But only above 80 degrees. I spent 3 years trying to get a lube not to thicken in the cold to work with ACWW and couldn't. Which is why I use semi wadcutter designs now for hunting as the sharp shoulder will keep the fouling clear a little farther up the velocity scale to ward off that RPM monster than an olgival will. This is why I suspect the 311440 did well with both ACWW and WDWW as the shoulder held up at that level.

Ever wonder why you see so many semi wadcutter (handgun)/ bore ride (rifle) designs in factory molds unless the bullet is designed for low velocity use?

joeb33050

04-01-2008, 07:14 AM

Bass;
I wish I had the theories that some of you guys have, but I'm still trying to understand the test.
How many shots in each group?
How many groups were shot with each load/bullet/hardness?
What was the range?
Thanks;
joe b.

For this weekend, I took my wife's 22" barreled Howa in 30-06 and 4, 150 cast bullet designs. Her rifle has a shorter throat to make this possible. The designs were a 311466, 311440, 311440 hollow point, and my 152 grain LBT Spitzer. The 311440 hollow point weighs 146 grains. These represent round nose, wide flat, hollow point, and spitzer designs at roughly the same weight.

I loaded three of each design with ACWW and the same mix water dropped and hardened for two days. All were sized .3095 using a nose first sizer and seated lightly into the lands. All will be loaded to within 50 fps of each other using 56 grains of RL19 as the high base for 2500 fps velocity in this gun. No loads leaded.

My objective was to change no variables and keep RPMs constant. Bullets were weighed and varied by 1.2 grain with my LBTs being the same as the others, blemished slugs were shot in the order they came. I used reamed and turned brass with loaded rounds spun for less than .002 runout measured on a sized band with all designs. My sizers ARE round. Powder charge did not have to be adjusted more than 1 grain to stay with in 50 fps of 2500 fps with the lighter hollow point needing the extra charge.

I also chose 18 grains of 2400 for a low 1700 fps target and will hold this RPM level. No load work up is occurring on either end. Just RPMs as a constant. I will swap brass later. Temperature was 30 to 50 degrees over the two days.

Quickload predicts muzzle pressure at bullet exit to be 7000 psi with the high loads and 3800 psi with the low loads and fast powder.

311466- 156 gr dressed
High: ACWW - 5 1/2". WDWW - 3 1/4"
Low: ACWW - 1 5/8". WDWW - 1 1/4"

311440 Solid 154 gr dressed
High: ACWW - 12". WDWW - 6 1/2"
Low: ACWW - 2". WDWW - 2 1/4"

311440 Hollow point 146 gr dressed
High: ACWW - 1 5/8". WDWW - 1 3/8"
Low: ACWW - 1 5/8". WDWW - 1 3/4"

LBT Spitzer 155 gr dressed
High: ACWW - 5 1/4". WDWW - 1 1/8"
Low: ACWW 1 1/4". WDWW 1 1/4"

Now I took standard cases that were not prepped just right out of the box for the last two bullets. Loaded just as carefully, run out was now .005 to .007.

311440 Hollow point 146 dressed
High: ACWW - 3 3/8". Ran out of bullets.

LBT Spitzer 155 dressed
High: ACWW - 7". WDWW 2 1/2"
Low: ACWW - 1 5/8" WDWW - 1 1/2"

Took one more design as I had some 311467s sitting here in both ACWW and WDWW confugurations. Powder charge was raised to 58 grains for the same RPM and Quickload predicted pressures 6000 psi higher at 40,000 psi to do this.

311467 185 grain dressed
High: ACWW - did not hit paper. WDWW 4"
Did not shoot low as I knew this would be dramatically better.

To be continued.

Bass Ackward

04-01-2008, 08:48 AM

Bass;
I wish I had the theories that some of you guys have, but I'm still trying to understand the test.
How many shots in each group?
How many groups were shot with each load/bullet/hardness?
What was the range?
Thanks;
joe b.

Joe,

Sorry. I should have included that. Knowing you, this isn't scientific enough for true accuracy purposes. It wasn't meant to be. Only looking to show a pattern. One thing that you can be sure of, is that if you get a bad group with 3, you can pretty well rest assured that 10 shots ain't going to improve it.

The test is also unfair in that the 311466 was really meant for a larger bore. It improves dramatically for HV use, if you have a 30 with a .311 bore as the grooves will still hold lube. Lube is the key to fighting pressure and friction that results. Lube becomes the enemy when it is left in the bore and becomes fouling as velocity increases.

Every segment outlined was simply a 3 shot group to get through it with the bullet supply I had on hand. Plus I had to load some of these over a couple of times to get the .002 or less run out. The 311466 was particularly bad about that cause it's tapered. Hard to load a tapered slug and get alignment in the case which is why I sized smaller and seated into the lands.

My range is 100 yards.

BABore

04-01-2008, 10:14 AM

Geeze BA, I bet your one of them guy's that drives around "Road Closed" signs and tears the "Do Not Remove" tag off of mattresses. [smilie=1:

Larry Gibson

04-01-2008, 11:34 AM

Bass

"I am the greatest advocate of no laws when it comes to cast. So how can I answer any question as a fact."

That is a cop out! How then can you state anything as "fact".

Regards your test; those being 3 shot groups I can agree that what appears bad probably is. Conversely, I have shot enough very good 3 shot groups with some very inaccurate loads to know I'm not making any assesments on your test. The only thing I could say is it gives you places for more tests which are complete.

Care to conduct a more difinative test on those bullets? Only comment to be made is "close, but no cigar".

Larry Gibson

leftiye

04-01-2008, 09:07 PM

What a great surprise.

joeb33050

04-02-2008, 07:16 AM

Bass:
You know, and we all know, that shooting one 3-shot group doesn't tell us much, if anything.
However, I've looked at your results, over and over, and tried to draw some information from the tests and groups. Make believe that it makes sense to shoot 1 3-shot group.
First, it looks like harder bullets shoot better than softer bullets at 2500 fps. Didn't we already know this? I did. This is why we use ex. lino at high velocities, n'est ce pas?
Second, lead bullets of any hardness shoot more accurately at low velocities than high velocities. Didn't we know this? Isn't this why CBA shooters shoot at lower-than-2500fps-by-far velocities. I knew it. So did you.
I don't understand how you-all of you-can derive any other information from these tests. RPMs or lube-as-fouling or pressure as the bullet leaves the uzzle or anything about pressure. Aside from first and second above, how do you get the info to make all the other statements. Please, explain this to me. To us. Where does it come from?
joe b.

QUOTE=Bass Ackward;316533]Joe,

Sorry. I should have included that. Knowing you, this isn't scientific enough for true accuracy purposes. It wasn't meant to be. Only looking to show a pattern. One thing that you can be sure of, is that if you get a bad group with 3, you can pretty well rest assured that 10 shots ain't going to improve it.

The test is also unfair in that the 311466 was really meant for a larger bore. It improves dramatically for HV use, if you have a 30 with a .311 bore as the grooves will still hold lube. Lube is the key to fighting pressure and friction that results. Lube becomes the enemy when it is left in the bore and becomes fouling as velocity increases.

Every segment outlined was simply a 3 shot group to get through it with the bullet supply I had on hand. Plus I had to load some of these over a couple of times to get the .002 or less run out. The 311466 was particularly bad about that cause it's tapered. Hard to load a tapered slug and get alignment in the case which is why I sized smaller and seated into the lands.

My range is 100 yards.[/QUOTE]

joeb33050

04-02-2008, 07:34 AM

Basss Ackward

"Look close at the data. All designs were outta balance, but two designs failed to show any RPM effect. The hollow point didn't care how outta balance it was as it shot soft as well as it did hard."

I did look closely at the data. I don't believe you are seeing what it is telling you. Yes "all designs were outta balance".

All bullets, especially cast bulletsare "outa balance that is why (once again) we shoot bullets into groups instead of one hole.

I don't know that out-of-balance bullets are THE cause of inaccuracy. Does anyone have a cite that shows this to be true?

Obviously the HP stayed in balance. This could be an anomaly groop as you don't mention the number of shots per group or if you repeated any of the tests. Anomaly groups do happen, quite often acutally, and they should be retested if they appear to be "too good".

"Loads were chronographed. But Quickload did estimate within 50 fps of the chrono, so I believe the muzzle pressure figures to be close."

Thanks for the answer; the QuickLoad muzzle pressures should be fairly close.

Quickload does a great job of estimating MV. It does NOT do a great job of estimating pressure. I have data.

"Dressed means that bullets were weighed with check and lube. My bullet naked were within 1/2 grain, but people often forget that checks aren't all the same and air pocketes can be trapped in lube as well. It all counts, so if you are going to weigh, then you need to weigh dressed which I did."

"Dressed"; I like that! I had not heard it used that way before, I shall enter that definition into my library, thanks.

"What was clear. Launch bad bullets and you get what looks to be an RPM effect.

Where is the RPM effect in the test data? Please explain!

But the LBT that was 1 grain outta balance shows me that if I match hardness to the pressure and fouling that it will encounter at the higher velocity, so that I launch good bullets, that RPMs has virtually no effect on that amount which is fairly substantial as a percentage of bullet weight. So either RPM effects everything or it doesn't"

Launching "bad" bullets or the fact that they get "bad" during accelleration is not relelvant; It is the RPM that adversly affects the ("bad") imbalanced bullets. 1 gr weight differance does not make the bullet imbalanced either. An imbalanced bullet is when the center of form does not coincide with the center of gravity. Weight in this case has nothing to do with "balance". The balance is in relation to the spinning of the bullet. If the center of form of the LBT bullet coincides with the center of gravity of the spinning bullet the .0066% (the 1 gr) is not a "substantial difference. That 1 gr is not a "substantial difference even as far as weight varience of .30 caliber cast bullets goes. RPM does in facte(a)ffect the bullets.

"Weirdly enough, meplat size and shape had little to do with accuracy either when you look at all the tests. When hardness failed, and all designs went squirrely, all bullets reacted pretty much the same way with remarkably pour grouping with the most aerodynamic of these, the 311467 going the wildest. Coincidentally, it has the highest muzzle pressure too at just over 12,000 psi"

Not "wierd" at all. When the alloy hardness went the bullets sustained greater imbalance (obturation and distortion) during accelleration and the RPMs centrifugal force had a greater affect.

"There are better designs for high velocity than others. The idea is to elongate the pressure curve with lighter bullets, slower powders, or slower twist rates, load more concentric ammo or all of the above. Launch a bad bullet at 1800 fps and you only have 3800 psi to disturb it. Launch a bad bullet at 2500 fps and you have 7000 - 12,000 (311467) psi to affect it."

That is true but all that only occurs in the barrel during acceleration. It is the RPMs centrifugal force that causes the inaccuracy during flight.

How do you-any of you-know that muzzle pressure has anything to do with accuracy? Is there data or a cite?
There is no such thing a centrifugal force. Look it up.

"But what ever it takes, DON"T launch bad bullets at any RPM or pressure level"

See Bass, you are learning about RPMs, aren't you.

Larry Gibson

Is this all opinion, or is there any body of fact-test-information that I'm not understanding?
joe b.

Bass Ackward

04-02-2008, 08:19 AM

1. First, it looks like harder bullets shoot better than softer bullets at 2500 fps. Didn't we already know this? I did. This is why we use ex. lino at high velocities, n'est ce pas?

2. Second, lead bullets of any hardness shoot more accurately at low velocities than high velocities. Didn't we know this? Isn't this why CBA shooters shoot at lower-than-2500fps-by-far velocities. I knew it. So did you.

3. I don't understand how you-all of you-can derive any other information from these tests. RPMs or lube-as-fouling or pressure as the bullet leaves the uzzle or anything about pressure. Aside from first and second above, how do you get the info to make all the other statements. Please, explain this to me. To us. Where does it come from?
joe b.

Joe,

Yes we know this. But there are no constants here. And if you think this theory is hair brained, it's not mine. It belongs to a man that was named Marshall.

Larry believes it's RPMs. But at different temperatures I can make RPMs go away. Look at the ACWW figures for the LBT Spitzer. Group size was 5 1/4". That was at 50 degrees. Now if I shoot that over 80 degrees with the SAME .... EXACT hardness. It will be MOA or less. Over 90 degrees, it's is always less. Personally, I believe that I am using up the lube that at some point, as you went up in temp, would then start to lead.

This is what I asked you about that year that they had the high temps in Kansas for the Nationals. People were stymied why so many were shooting way better groups than they normally did even though it was hot. Well, my guess was that they were over lubed and simply weren't realizing it. Heat uses up more lube. I mean this is the theory of lube purges huh?

Marshall believed that they best accuracy occurred just before leading began. I think he is right as this bears out time and time again. That means lube is used up by the bullet that is carrying it and the next bullet doesn't have to fight it to pass unsized. Cause lube is not compressible and creates hydraulic forces too. The faster you go, the greater the sizing force. Huh? Effectively reducing rifling bite into the bullet.

This particular test, this one load, says that it isn't only RPMs. Or that it isn't only hardness or balance to survive pressure. So Joe, if we are taught hardness is a required constant to prevent outta balance, and RPM forces are a constant that can't be over come, why does accuracy improve so dramatically with temperature? What's your theory then?

Larry,

To be polite, I couldn't answer the question because I couldn't figure out what the question is?

Is it about defeat? I am ready to admit defeat in one area. And that's changing you. I am beginning to believe that you simply want to claim that a glass is half full. You sure you don't live in Missouri?

Care to borrow my mold for your upcoming testing? I lend it to you if you promise to give it back. :grin:

Succeed just once, JUST ONCE, and that glass is going to change and be half full. :grin:

Larry Gibson

04-02-2008, 11:32 AM

Is this all opinion, or is there any body of fact-test-information that I'm not understanding?
joe b.

Joe b

There will be soon. The test I about to start using a M43 (waiting on weather) will provide facts on internal ballistics and external ballistic. Thus we will know what is going on inside the barrel and during flight. The target will provide terminal facts. The three different barrels will provide the different RPM. The M43 will provide pressure information.

I will be conducting the test in what ever weather is suitable. We do know that colder weather adversely effects lube. It is however the lube in the barrel. Have you shot groups in colder weather and noticed the first shot out of a fouled barrel was a flyer but the other shots went into group? I think we all have. The reason is the lubes we use harden in cold weather. The first shot was shooting over this hardened lube fouling. The other shots went to group because the lube fouling in the barrel hadn't hardened yet and was still soft. Much the same reason BP shooters go to great lengths to keep the fouling soft in their barrels.

I am constantly amazed with what Bass comes up with. To get HV with cast bullets Bass claims numerous things that do effect accuracy of the bullet in flight and we all pretty much agree with those. However, to shoot cast bullets at HV above the RPM threshold among many essoteric things one had to do was: first it was bullet design needed to be perfect, then it was the barrel "nodes", then it was a throated barrel to match the bullet and now it is lubes that are only good above 80 degrees!

These things, even if they are successful with Bass, do not help the rest of us who wonder why our regular cast bullets do not shoot as accurately at HV as they do at low and medium velocity when we shoot them in our regular rifles. I do not really perceive that 99.9999999999999% ad nauseam of cast bullet shooters are wanting a specially throated rifle that shoots a specially designed bullet only when the Sun, the Moon, the stars and the planets are all aligned and it is over 80+ degrees out. I think what they really want is a HV load for hunting (that usually means cold weather), for long range shooting, for recoil equivalent to jacketed loads for practice and a few other reasons. All of these shooters want to be able to pick up their rifle (mostly unaltered rifles), a box or two of cast bullet reloads and go shoot regardless of the weather. They expect their cast bullet loads to have a consistent level of accuracy every time out. Do we really believe they (or we for that matter) will go through all the effort that Bass, 45 2.1 and a couple others insist they must do to shoot 5 1/4" on one day and maybe, just maybe, if they wait for those 80+ degree days that load might shoot 1 1/2" groups? I, for one, think not.

Larry Gibson

felix

04-02-2008, 11:44 AM

Marshall believed that they best accuracy occurred just before leading began. I think he is right as this bears out time and time again. That means lube is used up by the bullet that is carrying it and the next bullet doesn't have to fight it to pass unsized. Cause lube is not compressible and creates hydraulic forces too. The faster you go, the greater the sizing force. Huh? Effectively reducing rifling bite into the bullet. ... BA

Yep, right on!!! ... felix

Larry Gibson

04-02-2008, 12:55 PM

Bass Ackward

"To be polite, I couldn't answer the question because I couldn't figure out what the question is?"

Your failure to understand the question is, no doubt,why you also fail to understand how RPM effects a bullet in flight.

"Is it about defeat? I am ready to admit defeat in one area. And that's changing you. I am beginning to believe that you simply want to claim that a glass is half full. You sure you don't live in Missouri?"

Lets' say my test were to give a clear demonstration that it was RPM that adversly effected the bullets accuracy above the RPM threshold. Would you then change your mind (that's a pretty simple question)?

I seriously doubt you will change your mind regardless of any facts presented. I've already stated that I am quite willing to change my mind. If the tests do not show RPM to be the reason for the inaccuracy above the RPM threshold then will change my mind. I am not from Missouri but it appears you may be.

"Care to borrow my mold for your upcoming testing? I lend it to you if you promise to give it back. :grin:"

I still have 26 of your bullets left. I will use the load that is that has already demonstrated excellent internal ballistics and accuracy in the M70 (1.5" group at 2505 fps on a 60 degree day). I will shoot a 7 shot group with each of the different twist .308s. I will also shoot one 5 shot group out of my 10" '06 with your load of 56 gr RL19. Of course the '06 will also be attached to the M43 so we shall have all the pertinant data on that load.

If your LBT bullet really excells and I change my mind I will probably buy a LBT mould of that design. However I am interested in seeing how it stacks up against the 311466. While my mould drops at .314 when cast of linitype it sizes down to .308 quite nicely. The lube grooves are deep (.292) and hold sufficient lube after sizing down as far as .308. Both bullets are very close in weight, both have about the same bearing surface and both have just about the same length nose. Note attached picture.

"Succeed just once, JUST ONCE, and that glass is going to change and be half full. :grin"

Bass, I already have succeeded with your LBT bullet, remember? I have shot 1.5” groups with your bullets out of the 14” twist at 2500+ fps in 50-60 degree weather. But that was still in the RPM threshold at 128,500 RPM. The 12” twist M70 did not fare as well as it was over 150,000 RPM which is above the RPM threshold. We will now see how all the twists do including the 10” twist. I really don't expect the 10" twist to do better at over 180,000 RPM, do you?;-)

Larry Gibson

Bass Ackward

04-03-2008, 07:24 AM

I am constantly amazed with what Bass comes up with. To get HV with cast bullets Bass claims numerous things that do effect accuracy of the bullet in flight and we all pretty much agree with those. However, to shoot cast bullets at HV above the RPM threshold among many essoteric things one had to do was: first it was bullet design needed to be perfect, then it was the barrel "nodes", then it was a throated barrel to match the bullet and now it is lubes that are only good above 80 degrees!

These things, even if they are successful with Bass, do not help the rest of us who wonder why our regular cast bullets do not shoot as accurately at HV as they do at low and medium velocity when we shoot them in our regular rifles. Larry Gibson

Larry,

Now you understand why it can't be blamed on a single factor such as RPMs. And the 311440 showed you how pressure curves were different with just 10 grains of bullet weight on the same EXACT design. So much so that the hollow point could be shot with ACWW almost as accurately as WDWW at HV. From only 10 grains less weight! It's that touchy.

Look. I have and am doing it. I have succeeded. And these things are what I tell you I see. Sorry. Hard bullets do eliminate some of this stuff. But if you don't try softer stuff at higher velocity, you never get to understand whats affecting it. This is the same stuff I have reported and posted over the last five years or so. Just these things were never put together like they have been lately. I simply am re-posting it again so you can see why thinking RPMs eliminates so much from the process. Light bullets work better than heavy. And the list goes on.

The easiest and LONGEST accuracy begins where the bullet is launched fast enough to stabilize. From that point on up, you encounter all these other things that complicate the issue and start creating negatives that must either be addressed or results deteriorate to the point they LOOK like RPMs.

Bass Ackward

04-03-2008, 08:30 AM

Bass, I already have succeeded with your LBT bullet, remember? I have shot 1.5” groups with your bullets out of the 14” twist at 2500+ fps in 50-60 degree weather. But that was still in the RPM threshold at 128,500 RPM. The 12” twist M70 did not fare as well as it was over 150,000 RPM which is above the RPM threshold. We will now see how all the twists do including the 10” twist. I really don't expect the 10" twist to do better at over 180,000 RPM, do you?;-)

Larry Gibson

Larry,

I just used a 10 twist at the same velocity level (higher RPM level) and I can shoot 10" or 1" groups. That's 180,000 RPM. Trust me, a person trying and getting the pour results I tested says oh yea, RPMS got me. The guy who would shoot the 1s would just be all smiles. Change lubes and these results will change again.

I never said that RPMs don't have an effect. These results show the entire accuracy spectrum. The guy that wants success is going to ask how to get the 1" groups, not the 10"ers. And remember, there are folks out there that are struggling at the 1600 - 1800 fps level to produce these results.

My BIGGEST point in this is that if we want to teach others how to do well, then we can't sit around and blame RPMs or you eliminate the need for understanding all these other factors.

Someone PM'd me and said that I was never going to convince you. This is not about me winning an argument, but about anyone and everyone else that wants to learn what factors in. Some guys see this as an argument. Others read it and are thinking. Those are the guys I do this for.

In a nut shell. Everything we discuss on this WEB site factors into releasing a good bullet when it exits the muzzle. Every thing from lube, to sizing, to hardness, to fire lapping, to throat size and shape, to bullet design, to GC fit and anneal, to bedding to control vibration that increases with friction, (pressure, velocity) (RPMs) everything.

HV is the one stage that unifies all topics and puts it all together or you get the RPM effect. Learn to shoot well at HV and you DRAMATICALLY improve your understanding (and results) of what it takes to do well at lower levels. At least this is my finding.

leftiye

04-03-2008, 03:06 PM

Larry, You're "constantly amazed with what Bass comes up with." That's the whole point, there is nothing that anybody can come up with that influences your perception. They've tried everything imagineable, and it makes no impact whatsoever, EVERYTHING is about the RPM barrier/threshold.

Larry Gibson

04-03-2008, 04:44 PM

Bass

Contrary to what letiye says I am not hung up on the RPM threshold. I very well understand all the other things that influence accuracy of a cast bullet. You seem hung up on HV as the "goal" and are willing to do anything necessary to get there. I agree now as I have always that accuracy at HV is certainly attainable. However the guy who wants a regular cast bullet to shoot at HV is not going to get there with that cast bullet or his regular rifle (sans any modification; throating, bedding, etc). There is a reason for that. That reason is RPM within a certain threshold.

I made it to the range yesterday and ran the test using the 3 twists with 311291 with both H4895 and H4831SC. I have put the information together and am writing Chapter 2, Results of 311291 test. You believe RPM is not the reason? Well, I'll not jump to any conclusion until the entire test is complete. However, so far you are wrong.

Larry Gibson