RPM Test; a tale of three twists, Chapter 2

[Larry Gibson]

Ralf

Excuse but what does your question have to do with a test of 3 different twist barrels? Absolutely nothing. Yes they are probably different with 4 different burning ratesd to the same velocity. What the heck is your point. My test was the same load to the same pressure to the same velocity. I tested the difference that RPM makes. The test demonstrates it is RPM. Please come back with a more pertinant question or quit wasting my time with rediculous comparisons that are not valid.

Read the test Ralf, I am seriously thinking you have not done that.

Larry Gibson

[runfiverun]

i don't think it is so much the different pressures
but when where and for how long.
like bass [i believe] said about 3000 posts ago pressure at the muzzle has an effect
also.
10000 psi at a bad crown is way worse then 4000.
a hard slam into a short throat, is probably not as bad IMO as it will be re-worked some in the bbl [ possibly for the better] any way.

bad is still bad, and rpm's is the killer.
i dont think it is the end-all but it sure don't help.

[Tiger]

Ralf

Excuse but what does your question have to do with a test of 3 different twist barrels? Absolutely nothing. Yes they are probably different with 4 different burning ratesd to the same velocity. What the heck is your point. My test was the same load to the same pressure to the same velocity. I tested the difference that RPM makes. The test demonstrates it is RPM. Please come back with a more pertinant question or quit wasting my time with rediculous comparisons that are not valid.

Read the test Ralf, I am seriously thinking you have not done that.

Larry Gibson

First your test only proved there was a difference in accuracy in your particular rifles and only for the powder/powders you selected, along with the loads. That's hardly conclusive and representative of all the different rifles and loads and bullets out there. How can you be sure the barrel harmonics were exactly the same with all the test rifles especially when the twists are different. They say the harmonice or vibrations of a barrel upon firing are like a sinew wave on an oscilloscope. The accuracy depends and what position that muzzle is in when it releases the bullet. You have no test to determine that. Perhaps you could affix such a tuning device to your muzzles and then shoot for the best accuracy with each twist.

What was my point on the different powder burns rates? To point out and to get you think that there are more then one , two, three, or more influences on the bullet that cause it to do what it does do.

Waste time? From watching the forum it's obvious to impress many members with elaborate tests. Many have gotten accuracy at higher rpm then you ...45 2.1, Bass...and others who probably don't care to mention it, but you can not accept that.

Runfiverun

All those things you mentions in your last post are still connected to pressure one way or another.

Ralf

[onceabull]

A "newbie"with nary a post except on the latest "RPM" thread ??? a water carrier for ?????..... Onceabull.....

[runfiverun]

tiger

larry is testing rpm's
he knows how to make a rifle shoot
what he has/is doing is making everything as comparable as he can

same brass boolits powder and bbls as close as anybody can reasonably get them.
i personally think that what he has shown so far has proved this out.

as far as the velocity / pressure question it would mostly show up as
vertical dispersion mostly anyway.

[leftiye]

Sorry about that double post as I was trying to edit the one.

Runfiverun I'm not saying that rpm has nothing what so ever to do with the accuracy, I'm saying the damage, if any is occurring, is happening in the barrel. Then of course rpm will amplify that damage outside the barrel. The different versions of 4895 are so close to one another I don't think there would be a difference either, but I did say four powders with different burn rates meaning entirely different burn rates, which you did answer too.

So why do you think with the four different burn rate powders the accuracy would be different? Will you tell me because of the different pressure applied to the bullets?

Ralf

Ralf, we all have said that (probly several times) before about the RPMs probly having an effect both inside the barrel, and later. I think it is interesting that there is Nothing that we can do about RPM besides buying a barrel with a slower twist, or slowing the velocity - if rpms were THE culprit - with a given alloy boolit. On the other hand, there are myriads of things concerning alloy, lube, powder burn rate, gradual versus sharp leade and other reloading factors that will make higher velocity boolits shoot more accurately. Ironically, when we buy that slower twist barrel it itself may not shoot cast well, and our money may be wasted.

Larry, Concerning 28 grain load being accurate, and 30 grain load not grouping well- "That is usually indicative of the bullet's rpm ecxeedingits threshold" (OR SOMETHING) not necessarily, your opinion.

[runfiverun]

if larry's tests prove out here
it would sure simplify load start.

think about it , boolit hardness ,pressure, twist rate, velocity.
it would sure make picking a starting load close to where you want to be
a lot easier.

if you remember to write down a few simple formulas
[ which i will have to find again]
to figure your leads compressability, your loads reduced pressure.
your twist's rpm's.
pick three or so powders that all fit the bill and start them all
in the same place, put them over a chrono. and tweak the best one.

[leftiye]

run5run, I disagree. The only thing that larry's "principle" does is to help us further understand inaccuracy. ALL of the things that one does about inaccuracy remain the same. We're still faced with the situation that accuracy at slower fps is easier to attain, and that if you want to go faster, you have to do better (do your homework). The better you iron out the variables that reduce deformation, the better you'll do at high velocities. (RPMS only act upon the defects anyway - Ironically, if you were to have perfect boolits, and perfect loads, accuracy more than likely wouldn't be perfect anyway). Most of this at present constitutes a basic formula or framework guiding us on how to proceed. After that you must analyze your results and adjust your loads, and rifle, etc..

Another side trip - if you just want to shoot paper, speed is somewhat not an issue. If you want to shoot game, and want boolit expansion, very high velocities aren't needed or wanted as soft lead is needed (relatively), and you will either make a surface wound with insufficient penetration, or mutilate your dinner. Pure lead boolits at 2000 fps. make excellent varmint boolits, but you won't hit anything without a paper patch (or similar) and maybe not then, and you won't want to eat it afterwards.

[Tiger]

A "newbie"with nary a post except on the latest "RPM" thread ??? a water carrier for ?????..... Onceabull.....

Newbies be forewarned the Onceabull Department of Knowledge must certify your knowledge before you can post freely or acquire 10,000 posts.

I don't see you contributing anything to this thread. Probably because you can't.


Ralf

[runfiverun]

leftiye
do my homework?
pay attention to the test please, what larry is doing is homework.
i don't think i ever heard him say that all tests are being cut off at 1800 fps
i believe he said he will test to see at what velocity/rpm that each twist rate will lose
accuracy. [ i believe he also said he will try slower powders to try and get it back,
as well as other sn/sb nixes]

which is fine with me as i usually shoot most of my g/c rifle boolits in the 2000-2400
fps area anyway.
depending on how they regulate with my sights @100 + yds
if you are thinking
that either i or others [larry] believe that you can just pour up whatever
lead you find , into what mold ya got, and shoot it to x amount of rpm's
because that is in the magic rpm range.
you are totally missing the whole point here, what larry is doing is defining what
causes the "sweet spot" in load development.

this is what i am taking from these tests.

[leftiye]

Boy, did you lost me! The homework referred to was what we have to do in getting a load right or improving it (nothing to do with you personally). Sorry if I wasn't more clear, no offense meant to you anywhere in my post. But Larry don't need no help in defending hisself. Don't see 1800 fps anywhere in my post.

[Tiger]

runfiverun

That sweet spot post you just done sounds a lot like a barrel harmonics situation.

I have been doing some searching back through the old post and it's a lot of work. I believe it was Buckshot that has done lots of shooting with the Swede. It appears that the Swede is difficult for many to achieve good accuracy with especially at the higher velocities. If I read correctly Buckshot set a limit of about 1900 fps and still maintain decent accuracy. That gives the bullet an rpm of 182400 which is outside of Larry's rpm range. We know that the 6.5 bullet has been a problem caliber to shoot accurately at higher velocities, but yet judging from Buckshot's pictures of his targets he has done well at 1900 fps and 182400 rpm with a long small diameter 6.5 bullet. That's not to say that all his targets were fired at that same 1900 fps. I also read that he was experimenting with some other bullets for higher velocities yet, but ran out of them before he could verify a conclusive test. It looked like what he had achieved more then likely did up the velocity level. That means even more rpm for that 6.5 bullet. Today I was also looking at the Lyman cast book. I was in the 6.5 caliber section and the 6.5 Mannlicher data stuck out. They had quite a few loads in the higher velocity bracket say 2200 fps. The rifle they used had a 7.5 twist so that gives us 211200 rpm. A load for the 25-06 gave a velocity of 2677 fps (at 44,700 psi too). It had a 10 twist which gives us 192744 rpm. There are more examples. All out of Larry's rpm range. What is my point? Lyman, which tested all these loadings, would not publish loads that were unacceptable as we know this would come back on them. Unacceptable would mean no usable accuracy or either barrel leading up badly.

So is it okay that I disagree with Larry? Some say no. Who can explain the above result by Lyman?

Ralf

[runfiverun]

buckshot isn't the onlyone 45 2.1 , manley j.t. and others have
worked with the 6.5 swede with good results, lots of others have had many,many
problems with it if you can find it probably on page 2 or so
there is a thread on the 6.5 that started all this testing.

i am forming an opinion that the smaller calibers fare better with cast as higher
rpm's. just don't have any tests to pull memory from
i do have a 7mm mold coming so i can try it against a 30 cal

same boolit design from same pot of 4/6 mix g/c and going to try twist etc...

and i know that larry doesn't need any help!!!!
no offense taken
i enjoy hearing all this stuff from everybody it is all different opinions and some valid facts
you know, the well then how come this, and the how come that.
it is all the fun we have and the reason for this web site.

hell ifit works for one guy it ought to work for everybody?
the more we find out from the more sources may point to what we should be doing
or what may be wrong if what we tried doesn't work.

as far as the lyman manual thing i don't know i do know that they will show higher velocities

at times and then disclaim their data saying that excessive leading occured at xxx velocity
with cast data they give you boolit weight and velocity data.
they have no way of knowing what lead you are going to use and if you have any problems
you will be told that you didnt follow their recipe exactly.

[Larry Gibson]

Ralf

Lyman doesn't test it's loads for accuracy by shooting groups. The "accuracy" loads are judged so based on internal ballistics, i.e. constistancy of pressure and velocity. Because loads are listed does not mean they are accurate.

Perhaps besides actually reading the test I've done so far you should read the Lyman Manual too.

Larry Gibson

[leftiye]

My experience too. - Many of lyman's loads are way hotter than will shoot well. Pressures may be consistent, but you might (some remote possibility LOL) , just MIGHT get a little (?) leading.

[carpetman]

Larry Gibson "consistancy" of pressure. No longer impressed it's consistent so therefore consistency.

[Tiger]

runfiverun

It's harder to shoot the larger calibers at higher velocity because if you do they usually have a lot of recoil to them. That of course depends on the caliber but say 35 caliber and up the bullets are much heavier most the time so they start to hurt the shoulder. Too they normally don't have a fast twist if one is wanting to see if the rpm is what destroys accuracy.

Larry

Are you a politician by chance? Did you see anywhere that I posted that Lyman tested by shooting groups? No matter by which means they gather their data they still are not going to publish real bad data.

I remember Bass speaking about the pressure on the base of the bullet as it leaves the muzzle. We know the gases are trying to escape too. I am sure some of you have examined recovered bullets. Me too. I noticed on the low pressure ones the gas checks did not look too bad. Another story on the higher pressure bullets. The gas check, if they were still on the bullet, look like they go through holy hell. You may have noticed that it seems the gas pressure gathers, collects, or peaks in the center of the base and pushes in there making the gas check look like a cup. I think I saw a post by Felix saying he agrees with that. So what I am getting after is the more I think of this cupped or somehow damaged gas check the more I think what Bass said. Larry you know well that factory jacketed bullet bases rarely ever have this condition. So many Bass is right about the pressure on the base of the near the muzzle and as it leaves the muzzle huh? I would agree that an undamaged base whether it is a jacketed bullet one or a gas checked one is not going to be as accuarate as an undamaged one.

All of you see that there are way too many variables involved in cast bullet shooting to make a conclusive decision about what causes accuracy to go bad.

Ralf

[runfiverun]

so we aren't going to try and test what variables we can, to try and see which
ones work. better.?
the only ones trying to better castboolit shootin are cast boolit shooters.
when i bought my last rifle there were no instrucions as to what bullets to shoot in it
cast or otherwise, it didn't even say what twist rate the bbl had.

but my next one will probably be built out of parts that i pick and choose and then have assembled how i specify.

[Larry Gibson]

Larry Gibson "consistancy" of pressure. No longer impressed it's consistent so therefore consistency.

I'm tellin' ya, this computer doesn't know that!

Larry Gibson

[oso]

There must be an advantage to rifling or we'd all be shooting muskets with 0 rifling. We might all agree, or without too much argument, that 32 tuns/inch is probably too much twist. Greenhill came up with a formula to find "optimal" twist rate for bullet weight, diameter, specific gravity, bearing length and velocity (one factor is 150 for slower bullet velocity and 180 for faster velocities.) As I see it Larry is experimenting to see if bullet velocity could be fine tuned as a factor to consider for .30 cal cast bullet accuracy for the average caster with the twists he has available. He's doing some great thinking and testing. He's not writing a new gospel and no one has to use the information presented. The real problem here is that some think he is not getting enough non-constructive criticism. Thanks Larry for the information, and I appreciate your patience.