My Secret to HV Cast

[hivoltfl]

This whole thread has been one HE@@ of a good read, I tip my hat to you guys on this one, it should be archived.

Rick

[Pat I.]

Felix,

I agree and disagree with what you're saying. The way it's been described to me and what I've read in a bunch of books is that accurate shooting is being able to place a shot where you want it on a target, like score shooting. Precision shooting is being able to place a bunch of shots close together anywhere on the target, like group shooting. Of course we both know everyone just uses the word accurate to describe both and for the most part don't bother with score shooting, although for a hunting gun it's probably be a better system than shooting groups.

Doing something like you said wouldn't seem a good way to find out how accurate,precise, a gun is because conditions, light, coffee intake, a butterfly flapping it's wings in the Amazon Rain Forest, and a bunch of other things could make a lot of difference where the group ends up if you're shooting on different days. You can chase a shot to make a precision group but you can't call back one shot if you're testing for accuracy.

Sitting down at a bench and shooting four five shot groups isn't going to tell you how well a gun will shoot in the long haul but it's a heck of a lot better than basing what you're saying on one three or five shot group and ignoring the other twenty or the "Called Flyers" we all seem to get after finding a shot out of the group.

Pat

[Pat I.]

Pat, If you ever want to know specifically what I am referring to, PM me and I will tell you or even take pictures if you want.

It'd be nice if we could discuss things without getting down and dirty but maybe that's not possible.

Bass you seem like a very patient guy and I like you for it but I'm gonna have to pass on going to PMs. Who knows maybe someone will be able to pluck a diamond out of the trash heap we're building here!!!

Pat

[Scrounger]

Joe, there is some ill-mannered person making posts using your handle. You might want to look that person up and talk to him about being respectful.

[Maven]

At the risk of getting dampened by this urination tournament/discussion, I have several questions to ask. (1) How do you determine RPM's for a given rate of twist? (2) Do RPM's also vary with velocity? (3) How do you know the pressure (psi) a given load combination, twist rate, chamber dimension and barrel condition develop? Are you using a strain gauge? a computer program? or are you just guessing? (4) I'm not sure I grasp this, but when accuracy (as defined by the shooter) degrades, how do you know that it's due to RPM. If it is the latter, can you quantify how much of said degradation can be explained by RPM alone and not some other variables? Help me understand this please.

[Bret4207]

This assumes that the word taker has no critical faculty means can't distinguish BS from the real world; and that Dr. Felix is often right. I can and he isn't. If you want to believe that he said something, God bless you. As usual, he didn't.
joe b.

Okay Joe- Enough ***** footing around. Personally, I was all for you coming here and fishing for information. Now I see it was a mistake to let you mine for information. You got here a few months ago and haven't contributed much, just mined for information. Felix has been around for nearly 10 years, knows his stuff, has the creds to back it up, has been helpful to anyone who asked and has NEVER stooped to such a low level as you have in this and other threads! In other words he has conducted himself like a gentleman. You sir, have not. If you can't behave in a decent manner and keep from this insulting behavior then I suggest you find someplace else to find the information you need for your book.

[Larry Gibson]

Maven

(1) How do you determine RPM's for a given rate of twist?

There are several ways; I do it this way. Divide your twist in inches by 12 inches (that the "feet") which gives you a constant. divide the velocity in fps by the constant which gives revolutions per second. Multiply that answer by 60 (60 seconds in a minute) and you get the RPM.

Example; for a 10" twist divide 10 by 12 and you get .833 for the constant. That is only good for the 10" twist. Each different twist will have a different constant.

Velocity of 1800 fps divided by .833 gives 2,160.8 revolutions per second. Multiply that times 60 and you get 129,652 RPM

(2) Do RPM's also vary with velocity?

Yes, that is why the faster the fps the greater the RPM and the more effect it has on any defectd in the bullet.

(3) How do you know the pressure (psi) a given load combination, twist rate, chamber dimension and barrel condition develop?

Are you using a strain gauge?

I don't.

a computer program?

I don't usually get excited about pressure with cast bullet loads.

(4) I'm not sure I grasp this, but when accuracy (as defined by the shooter) degrades, how do you know that it's due to RPM.

If the shooter is working up loads and his groups are doing ok then tighten up and then open up again he has; one, reached an efficient burning of that powder. two, reached the optimum accuracy for that load combination and three, exceeded the RPM threshold for that alloy with that pressure. With medium to slow burning powders this is generally in the 130-145,000 RPM range. Compute it out and you find find most who report accuracy with a 1-10" twist '06 for instance report best accuracy in the 1750 to 1850 fps range. That is 126,050 to 133,253 RPM. Above that and their groups open. Those who are using medium/slow powders with hard cast bullets that fit the chamber/barrel well report good accuracy at 2000 fps or so. Above that accuracy is lost. That is 144,000 RPM.

If it is the latter, can you quantify how much of said degradation can be explained by RPM alone and not some other variables?

The "other variables" are the alloy the quality of the cast, how well the bullet fits, etc, etc, etc. All those have to do with how much the bullet deforms during accelleration creating an un balance bullet. Also keep in mind that our cast bullets are no perfectly ballanced no matter how well we cast them (some are a whole better than others). The faster the bullet spins (higher RPM) the more these imbalances cause yaw, pitch and wobble. It is the increase in yaw, pitch and wobble that causes groups to open. Higher RPM increase the yaw, pitch and wobble.

Help me understand this please.

Hope you do now.

Larry Gibson

[leftiye]

Larry, any idea how much RPM is necessary to pull the alloy apart? It may well be the RPMs in your example. A little different than the BHN X 1400 thing, this deals with tensile limit of elasticity. Should be possible to calculate out directly. I'd need to know how to calculate centrifugal force and how to set up units of weight to convert into lbs. or whatever. Also how to calculate cross section being stretched on the surface of a cylinder by rpms. All of which I don't, never had any Calculus.

[Bass Ackward]

Paul,

(1) How do you determine RPM's for a given rate of twist?

Muzzle velocity X 720 divided by twist rate in inches = RPMs.

(2) Do RPM's also vary with velocity? Yes, see the formula

(3) How do you know the pressure (psi) a given load combination, twist rate, chamber dimension and barrel condition develop? Are you using a strain gauge? a computer program?

I use Quickload. Since velocity is proportional to pressure, once verified with a chronograph, I can assume the pressure listed is what is producing my velocity.

(4) I'm not sure I grasp this, but when accuracy (as defined by the shooter) degrades, how do you know that it's due to RPM. If it is the latter, can you quantify how much of said degradation can be explained by RPM alone and not some other variables? Help me understand this please.

The easiest accuracy occurs at sat 1500-1800 fps in 30 caliber with cast. AND .... jacketed too. Above that you start to increase the factor of harmonics because you are increasing friction. Just like the volume of a wine glass gets louder when you rotate your finger around the rim and push harder, your barrel begins to whip more also. This makes accuracy more difficult. The difficulty does not make the accuracy any poorer. The lowly 22 LR has been proven to have harmonics in rifle barrels. Jacketed demonstrate harmonics from vibration caused by friction. Why wouldn't large caliber HV lead bullets create harmonics? Answer: They do, that's the point that gets over looked by RPMers.

So are you just moving off a harmonal node or is RPMs getting you? The key is that some guys can destroy PB bullets at 800 fps. It ain't RPMs that got them there, it's pressure. It's pressure right up until some magical point it becomes RPMs, but no one on earth can tell you where that line is. And if it's different for 22s than 30s, so then it isn't a line period. The only difference is inertia.

[Pat I.]

I think an easier way to find RPM is velocity x 720 (constant) divided by twist. 1800 x 720 = divided by 10 =129,600

I don't know if I'm reading leftiye's post right but if so I don't think bullets are being pulled apart or anything like that by overspinning them I just think the built in defects open the group more the faster you spin them. Smaller calibers can take more spin because the defects are closer to the centerline. No examples to back this up and there's not going to be any but I'd bet 45 caliber bullets in a 10 twist at 2100 fps would have guys at the next bench ducking.

[Pat I.]

I think an easier way to find RPM is velocity x 720 (constant) divided by twist. 1800 x 720 divided by 10 =129,600

I don't know if I'm reading leftiye's post right but if so I don't think bullets are being pulled apart or anything like that by overspinning them I just think the built in defects open the group more the faster you spin them. Smaller calibers can take more spin because the defects are closer to the centerline. No examples to back this up and there's not going to be any but I'd bet 45 caliber bullets in a 10 twist at 2100 fps would have guys at the next bench ducking.

[felix]

Excellent! The more inertia a boolit has (bigger diameter), the easier it is to "blow it up", "pull it apart" by rotation (both inside and outside of the barrel). This requires the twist be slower using a 45 caliber for the same accuracy as could be had with a 30 caliber. Making the rotational inertia the "same" by changing the RPM for the two boolits individually, the accuracy with them should be identical (assuming barrel interference is the same, and the distance is compatible with each of the boolit's form factor (Ingall's research). ... felix

[felix]

Thanks, Bret. It is hard to advance the other cheek, but that is what I have been trying to do during the interim between his and your posts. ... felix

[felix]

Pat, yes, you can shoot the 22's quite fast RPM wise and get away with it for the reason you stated. Besides, it is easier on the boolit to reach those higher velocities because of the inertia value being so low when compared to a 30, for example. The accuracy actually can be less, though, because of the outside-of-the-barrel infractions. Not enough weight to get out there and touch something, as you well know. ... felix

[Pat I.]

See Felix, I thought I finally came up with something so profound I had to say it twice!!!!

I don't know whats happening here but I can click on buttons til I'm blue in the face and nothing happens, sabotoogie perhaps!

[Larry Gibson]

Larry, any idea how much RPM is necessary to pull the alloy apart? It may well be the RPMs in your example. A little different than the BHN X 1400 thing, this deals with tensile limit of elasticity. Should be possible to calculate out directly. I'd need to know how to calculate centrifugal force and how to set up units of weight to convert into lbs. or whatever. Also how to calculate cross section being stretched on the surface of a cylinder by rpms. All of which I don't, never had any Calculus.

I have had Hornady 55 SXs and Sierra Blitx's disintegrate in flight when push to 3300+ fps from 1-12" twist barrels and over 3500 fps from 14" twist barrels. They go "poof' and you see a big puff of lead about 30-40 yards from the muzzle.

However I can say that I've not had a cast bullet disintegrate to my knowledge. I have pushed them right up to 3000 fps but all at least "hit the target" (most often a 24x24" paper at 100 yards). They make improved cylinder patterns actually instead of groups. I have also seen what indicates that some part of the bullet may be breaking off; the little comma's in bullet holes and a couple small chunks of lead (no it wasn't the bullet Bass LOLs) imbedded in the chronograph screens.

To answer the question I have no idea what it takes to spin the lead alloys apart.

Larry Gibson

[felix]

Me too, Larry. Even with the Sierra's 45 grainer simi-pointed at about 3500+. Prolly more like 3700 for these because they were loaded down some when using a 22-250. BR boolits stayed together at 3900+, and this is only because of the heavier jackets they typically wear. These boolits use almost pure lead, right? That would be heavy with little strength to hold up, and would find the first leak in a jacket and use it for escape. Ah, forgot: 14 twist. ... felix

[Bass Ackward]

Take and put a light coat of oil on those bullets and try again. They are being torn up INSIDE the barrel which is causing the dramatic effect once air is encountered.

I use this on jackets:

http://www.lubricationspecs.com/Whatsnew.htm


Warning: Once you start to use this oil on jackets, it's going to make you think about cast. Same thing as putting lube on a Barnes Triple shock.

[Bass Ackward]

I think an easier way to find RPM is velocity x 720 (constant) divided by twist. 1800 x 720 divided by 10 =129,600

I don't know if I'm reading leftiye's post right but if so I don't think bullets are being pulled apart or anything like that by overspinning them I just think the built in defects open the group more the faster you spin them. Smaller calibers can take more spin because the defects are closer to the centerline. No examples to back this up and there's not going to be any but I'd bet 45 caliber bullets in a 10 twist at 2100 fps would have guys at the next bench ducking.

Pat,

Very Good. That's why you need deeper grooves or taller rifling if you want to maintain the same percentage of .... grip on a 45 as compared to a 22 caliber with a .004 bite.

If you bite it, it will rotate. Just look at all the guys who buy older military rifles. Do they want a good rifling or a shot out one?

[joeb33050]

Okay Joe- Enough ***** footing around. Personally, I was all for you coming here and fishing for information. Now I see it was a mistake to let you mine for information. You got here a few months ago and haven't contributed much, just mined for information. Felix has been around for nearly 10 years, knows his stuff, has the creds to back it up, has been helpful to anyone who asked and has NEVER stooped to such a low level as you have in this and other threads! In other words he has conducted himself like a gentleman. You sir, have not. If you can't behave in a decent manner and keep from this insulting behavior then I suggest you find someplace else to find the information you need for your book.

I've been here since the site started, since the old shooters site went away. The book, Cast Bullets For Beginner And Expert, Second Edition, has contributions from many on this site. See the list of acknowledgments.
You say that it was a mistake to let me mine for information. Is "mining for information" your phrase? Is it meant in a negative connotation? Sounds like Chas Hamilton to me. I'm here and elsewhere looking for information, to be written down to provide a source for CB info for all. If that's not allowed here, let me know.
Fishing for information? Sure. Let me know if no fishing is allowed.
joe brennan