RPM Test; a tale with three twists

[btroj]

If the threshold is entirely exterior ballistics how can it be "moved" by changing powder speed or alloy?
You state that the threshold isn't a limit but rather a point where accuracy becomes more difficult to attain. If the threshold is entirely external ballistics then wouldn't it be a hard limit?

I think alloy, pressure curve, and bullet design all have a huge role to play in accuracy at higher velocities. It is about finding balance within a system of variables.

Thus those RPM threshold figures are not hard and fast as some things like a too soft alloy or too fast a powder can lower the threshold. Conversely, other things like a harder alloy or a slow burning powder can raise the threshold.

[Larry Gibson]

Btroj

How many times must it be explained. Slower powders are used to slow the time/pressure curve to lessen the imbalance done to the bullet during acceleration which is in the internal ballistics phase. During the external ballistics phase the centrifugal force acts on those imbalances. At a certain level of RPM the centrifugal force causes accuracy to deteriorate rapidly. That is the RPM Threshold of that bullet with that load out of whatever twist barrel is used.

It does not adversely affect the stability of the bullet as a few of you seem fixated on.

Larry Gibson

[btroj]

Btroj

How many times must it be explained. Slower powders are used to slow the time/pressure curve to lessen the imbalance done to the bullet during acceleration which is in the internal ballistics phase. During the external ballistics phase the centrifugal force acts on those imbalances. At a certain level of RPM the centrifugal force causes accuracy to deteriorate rapidly. That is the RPM Threshold of that bullet with that load out of whatever twist barrel is used.

It does not adversely affect the stability of the bullet as a few of you seem fixated on.



Larry Gibson

The portion in red in my post is taken directly from your first post in this thread. Your words.

Changing alloy and pressure curve are purely internal ballistics and YOU say those things can move the rpm threshold.

Now you seem to be saying that "a few" don't understand that the threshold is all about external ballistics.

Which is it?

Personally I think it is silly to try and remove one from the other. Everything we do to a bullet in the barrel has an effect on it once it leaves the barrel.

As for changing pressure curve not affecting bullet stability, what? So a bullet that is damaged during the ignition and pressure rise isn't less stable than one launched with little to no deformation?

If the pressure curve is irrelevant, as you seem to be saying, then how can it possibly be used to move the threshold?

If the threshold is entirely about external ballistics then for a single bullet it would be a hard limit. Bullet can't be changed, rpm is purely velocity/twist related so at a certain velocity accuracy detonates. Period.

Problem is we know that isn't the case. You yourself said we can move it. We can move it by altering interior ballistics. Those interior ballistic changes all have one effect, reducing damage to the bullet during it's time in the barrel.

Are you saying that what we do to the bullet n the barrel has zero effect on the threshold? If not then in what way are people stuck on interior ballistics? If they matter then shouldn't we be fixated on them?

[Digital Dan]

[44man]

Remember the Juenke system? A little machine to check bullet out of balance. I understand some of the better bullet makers still use it to test lots.
However it won't work on cast. I can't even use my run out tester on the boolit, need to measure case necks. Just too hard to have a round boolit, then there is the parting line.
The amazing thing is that we get cast to shoot as good or better then jacketed. I get superb accuracy from revolvers with bullets and just using the same techniques with lead, it has proven very easy to match groups.
It has also proven that the faster twists of BFR's can not be matched.
To stray to stuff like too soft lead has been nothing but failure, Soft throwing fliers from boolit damage and ruining fit. To use an "M" die to prevent boolit sizing while ruining tension is a failure.
The FCD is a failure as is any over crimping.
Yet all you will read is to make the boolit softer or to crimp the devil out of it. My premise was to duplicate jacketed in every way.
What it came down to was interior ballistics, boolit integrity and letting the boolit be the guide into the bore and reaching the spin a boolit needs.
A gun needs a boolit at the right stability and adding more velocity over that results in groups opening. Cast works the same as jacketed so let us say you shoot jacketed at 2700 fps from a certain twist, can you use the same rate to shoot that bullet at 3800 fps? How about 900 fps?
Once you change the twist or velocity with cast, accuracy will go away so there is nothing to measure beyond the stability point, the threshold is that point only for a given boolit in a given twist. You exceed it with any change.
The only thing to be found is the range a boolit can be shot from a certain gun or what velocity is needed for a range of boolit weights. Each will need a different load but is far easier then trying to make one boolit do what it can't.
I never found pixie dust to make a boolit go faster or slower then stability.
Garbage in, garbage out!

[grouch]

I'd still like to hear Larry's results.
Grouch

[Larry Gibson]

I believe this site is hacked. I can't post from my PC or 2 laptops. Can only post from smart phone so posting is limited. Appears my IP is blocked.

Larry Gibson

[Larry Gibson]

I'd still like to hear Larry's results.
Grouch

PM your email and I will show you results.

Larry Gibson

[Larry Gibson]

As to 45 2.1, Byron and now 44man; same old arguments and erroneous assumptions over and over. Old Indian say; waste of arrow to shoot at buffalo already falling off cliff. ...........I'm tired of wasting arrows. Instead of arguing simply because my name is on the post or hypothosizing non relevance try conducting the simple test with a 30-06 that I've mentioned numerous times. You will find the RPM Threshold.

Larry Gibson

[btroj]

Jay Carney couldn't have said it better

[cainttype]

"I must be missing something.
Larry has attempted to illustrate through multiple posts, for a long time, that this "RPM threshold" is an area where average cast shooters, using average firearms, and employing basic loading procedures are likely to see a deterioration of accuracy as velocities are increased if the standard grease-grooved cast projectile exceeds 140,000 RPM. He has, as far as I'm aware, always maintained that this "threshold" is NOT a limit, and can be exceeded by various means...better casts, better loading techniques, better component choices, better firearms, and better ammo-to-firearm fit.
The theory didn't originate with Larry, as he has explained before, but he has done some serious testing that has obvious interest to the average cast rifle shooter. The simple point that it is EASIER to achieve accuracy with higher velocities by using a slower rate twist is very important to the casual shooter who has no desire to get terribly technical, but likes to enjoy his firearm with a minimum of fuss.
I very much appreciate anyone that takes the time to methodically test anything that interests me and shares their results. Whether I agree with their conclusions is irrelevant, I appreciate their generosity.
By the way, Larry, you're welcome to shoot with me anytime, as are any others that even attempt to dessiminate information in an effort to help others."


That was posted 01-08-14... Six months ago.
Nothing has changed. Larry attempts to offer results of pretty well documented tests that he's conducted himself. All the while, being taken to task by others that have yet to answer a simple question I've asked several times ( except 44man, who has stated his position)... So I'll ask AGAIN.... Has anyone else tried to use slower twist rates in an attempt to achieve higher velocities, while maintaining accuracy, with standard grease-groove cast bullets in rifles, and did you find it to be an advantage?
Larry details the non-linear accuracy results that occur whenever the "threshold" of a given load has been pushed too far... Has anyone else done the testing on their own to look for these signs?

I hear, and have heard, the dissenting yammering. As of yet, what I haven't heard is anyone else detailing their own trials.
I already know there are those of "us" (whoever that is) that have seen it all, done it all, and know it all, but I'm not aware of anyone that tries harder to help and mentor members on this site than Larry Gibson.
Thanks, Larry... I count you as a friend.

[Newtire]

It is pretty disappointing to see an interesting study about to take place by someone who's trying to help us along as a group by perfoming a series of time consuming tests being sniped at. Fer crissakes guys, let the guy get off the ground and go do his test and come back, turn in the "flight report" and hear the findings. If you feel so adamant that someone is wrong, go out and make your own experiment and then compare results.

It is what it is, sure there are vaiables-from what I gather, this is what the test is trying to find out isn't it?

Larry's always done some pretty straight up kind of reports. Let the guy get off the runway before you try to shoot him down.

It's easy for someone to sit behind a computer keyboard and theorize. Larry's going to get up, go out and shoot some boolits. There's a big difference.

I'm interested in the "Real Deal". Nuff Said.

[waksupi]

It is pretty disappointing to see an interesting study about to take place by someone who's trying to help us along as a group by perfoming a series of time consuming tests being sniped at. Fer crissakes guys, let the guy get off the ground and go do his test and come back, turn in the "flight report" and hear the findings. If you feel so adamant that someone is wrong, go out and make your own experiment and then compare results.

It is what it is, sure there are vaiables-from what I gather, this is what the test is trying to find out isn't it?

Larry's always done some pretty straight up kind of reports. Let the guy get off the runway before you try to shoot him down.

It's easy for someone to sit behind a computer keyboard and theorize. Larry's going to get up, go out and shoot some boolits. There's a big difference.

I'm interested in the "Real Deal". Nuff Said.

Thar ya go. He's putting up. If you're not, shut up.

[freebullet]

I read through 10 pages of attacks and disputes with no test results. Frankly, had I gone through what Larry has in this thread I doubt I would post the results here either.

[MBTcustom]

There was a time when this site had more than it's fair share of people who were already busting caps and throwing away lead, who just wanted to talk about the way they saw the results.
Now it seems that if anybody actually plans to do any shooting/experimenting they get piled on by a whole herd of people who never posted a group on this forum, and who don't help anybody but themselves (rather generously to the service we provide) and they pile on anyone who doesn't think about this sport in exactly the narrow way that their mind is capable of comprehending.

I also want to hear what Larry has to say (matter of fact, I was going to do almost exactly the same thing till I found this thread!).
Larry has a different way of looking at cast boolit shooting. A different gauge. If you just can't stand the idea of some guy on the other side of the country who likes to measure his cast boolit success with RPM instead of FPS, then go find a place where everybody thinks exactly like you do.

Larry, if you need a cast boolit gunsmith to help you eliminate a few more variables, you've got my number. I know a lot more about building them than shooting them.
If you decide it's just too big a headache to continue, let me know. I'm going to see this done one way or the other.
I don't see any other threads here comparing the effects of different twist rates side by side, and I don't see anybody else stepping up to the bar.

Yes there are different variables with each barrel. Does that mean there is nothing to learn by running a test like this? Gimme a break fellers! I learn something with each individual boolit I send down range! In fact, I learn more from failure than I do from success. Crawl out of your rut and open your mind a little! You might not agree with the method, the results, or the conclusion but you might just learn something and apply it to your way of doing things.

What really bugs me about this thread is, I really don't think anybody is afraid Larry is wrong and wasting bandwidth. I think that people are afraid he might be right, and they would rather silence him than consider the possibility that everything that can be learned has not already been learned by (pick your guru).
Wake up and smell the coffee! This is how the old shooters found out what they did. There was a time, if you told people that you: cast your boolits oversize, fit them to the throat, let them sit for 2 weeks before loading them, make your own lube, use aluminum gas checks that don't crimp on, or use jacketed load data, you would be laughed off the range and called a moron and a weirdo. Now we all so these things because somebody took the time to fix "a problem that didn't exist".

Surely if we can have a thread that deals with purple font, or thread killers, then we can have a thread that deals with a subject like this!

[Love Life]

A man on another forum ran a test with 4 different 6mm cartridges, but all the barrels were cut from the same chunk of steel.

If a call to bartlein can be made, and they can cut 3 different 30 cal twists into 3 different barrels from the same chunk of steel, then I will buy one of the barrels for this experiment and pay to have it chambered and mounted to the test rifle.

[MBTcustom]

A man on another forum ran a test with 4 different 6mm cartridges, but all the barrels were cut from the same chunk of steel.

If a call to bartlein can be made, and they can cut 3 different 30 cal twists into 3 different barrels from the same chunk of steel, then I will buy one of the barrels for this experiment and pay to have it chambered and mounted to the test rifle.

You won't pay much if it's heading my way.
BTW, Green Mountain has barrel blanks in 8, 10, and 12 twist for $100 each. That was going to be the direction I was going to go. Straight profile, no taper, reamed matchgrade 308 to exactly the same headspace, Bluprinted action for all three to be tested on.
Yeah it would be nice if they made a 14 twist also, but hey, beggars can't be choosers.

[Love Life]

3 Barrels cut with the same reamer to the same specs ought to show a bunch of things. I might even have an action around you can use. I won't do the testing though because I am knee deep in other stuff right now.

Here is a good chance to solidify some things, and at the end of the day I'll still have a barrel to play with.

I'll shoot you a PM.

[Terrence Clarke]

Hi Larry,great post,look forward to the test result. I agree with your RPM limit on cast bullets, but my own tests have shown a lower rpm limit for best results. I wonder what effect different number of grooves in the barrel have, if any on the RPM and accuracy of cast bullets,keep up the good work.

[PAT303]

Goodsteel,I like your post,there's people on here,one in particular who does post unbelieveable groups and performances from rifles but as yet I've never seen a group posted ever,the same person does reply,usually by being critical of others and then gives replies that make no sense what so ever.I'd like Larry to just get on with and leave the criticism unless they proove otherwise,I will hopefully be doing a grease lube dry lube comparison thread soon,it takes alot of work and will be ignoring the naysayers. Pat