Cast bullet velocity limits?

[Larry Gibson]

With a 150 gr cast bullet (GC'd) your best accuracy will come in the 1800 - 1950 fps range depending on the powder and bullet design used given good casting and loading techniques.

Larry Gibson

[303Guy]

mauser1959, have you considered paper patching? That would give you jacketed performance and if I'm not mistaken, a 260 mold would make the right sized core. That aside, I'm also interested in how copper affects velocity.

[1Shirt]

I shoot cast for a number of reasons, and economy of course is a primary one. However, the pleasure of shooting a less recoiling rifle shooting moderate velocity cast bullets, ranks a close second. The fastest I have ever tried to push a cast in a rifle was about 2500-2600 in a couple of 22 centerfires. They shot accurately, but I realized that if I wanted those vols from a 224 or 245 bullet, I would want to shoot over 3000 or so, and would go with jacketed. Most of my 30's shoot fine between 1600-1800, and if I want to hunt them, on up to 2200 or so accurately. The driving adage that "speed kills" kind of applies to higher vol cast bullet shooting in rifles. To me it kills the enjoyment of shooting cast.
1Shirt!

[mauser1959]

I am trying to figure this rifle ballistics out , and after reading Larry realized he was on a similar page as I .I will have to send the particular rifle back to Remington for a trigger job , but i think it will make an awesome coyote rifle , especially with Ziese glass on it; Has a redfield peep on it . I am curious where accuracy is lost on a jacketed bullet , as opposed to say a bhn 25 alloy. All of these years I have shot factory rifle rounds and always figured if you slowed down the twist you could up the speed . I hate when I am the least informed in the class .......... thanks all for bearing with me .

[303Guy]

if you slowed down the twist you could up the speed

Pretty much, it seems. Unless you want heavier boolits. I'm quite pleased my Brits have a 1 in 10 twist cause I like heavy boolits. In some ways it's not a handicap if one shoots below 1800fps and it's good for subsonic heavies too. But for me high velocity would be quite difficult to attain with any semblance of accuracy. An interesting point is that going over 3000fps requires a little faster twist than below that. Air destabilization forces become quite intense as velocity increases.

[pdawg_shooter]

I have 2 458s, one with a factory 1/14 barrel and one I built with a 1/22 twist douglass barrel. With paper patching there is no difference in accuracy. I have taken a 430gr bullet over 2300 and can see no difference.

[Larry Gibson]

I have 2 458s, one with a factory 1/14 barrel and one I built with a 1/22 twist douglass barrel. With paper patching there is no difference in accuracy. I have taken a 430gr bullet over 2300 and can see no difference.

Both are still well under the RPM threshold. Doubt you'll want to take either above the RPM threshold (even if psi permitted) as recoil would be brutal.

Larry Gibson

[waksupi]

Larry, I am absolutely miserable at math, even with a calculator. Could you start a thread, and post the approximate velocity limits for various barrel twists? I realize I am asking a lot, but I think it would be a good reference for people to check, me included. It would most likely be sticky material. Heck, the thread could even be closed, to prevent any extraneous chat on that particular topic. Dissenters could start their own.
I don't want to get the old "yes you can/no you can't" argument going again. You and I know this isn't etched in stone, but the guidelines would be great to have here.

[303Guy]

Excellent idea, waksupi. I need such a table right now - I'm trying to decide which barrel to buy. Please do, Larry, it would be appreciated by many.

[Larry Gibson]

Ok guys, I can do that. I already have it done but I'm on the road for a couple months and guess where it is? I'll calculate the velocities and post a table. Wemust keep in mind though that the RPM threshold is not a "limit" as such and the RPM/velocity does vary depending on twist, bullet design, alloy and powder burning rate used. The table I'll post will be a spread of velocity for each twist that is 120,000 - 140,000 RPM. That is most often where the RPM threshold will be with regular GC'd cast bullets shot out of rifles.

Please do imediately close the thread I post with the table. If some want to complain they can start a different thread or go visit "we know who" over on AR. However, if anyone has genuine questions I will be glad to answer them on another thread or via PM.

Larry Gibson

[waksupi]

Ok guys, I can do that. I already have it done but I'm on the road for a couple months and guess where it is? I'll calculate the velocities and post a table. Wemust keep in mind though that the RPM threshold is not a "limit" as such and the RPM/velocity does vary depending on twist, bullet design, alloy and powder burning rate used. The table I'll post will be a spread of velocity for each twist that is 120,000 - 140,000 RPM. That is most often where the RPM threshold will be with regular GC'd cast bullets shot out of rifles.

Please do imediately close the thread I post with the table. If some want to complain they can start a different thread or go visit "we know who" over on AR. However, if anyone has genuine questions I will be glad to answer them on another thread or via PM.

Larry Gibson

Larry, when you post it, let me know, and I will close it. You may be able to do it yourself, scroll down on the page, and I think you can do it. If extraneous posts show up there before I can close it, I will just remove them.

[Larry Gibson]

Appreciate that, will do.

Larry Gibson

[303Guy]

Thank you, Larry.

[swheeler]

pdawg at 2300 fps you are approx 118k rpm in the 14 twist and only 75K rpm in the 1:22, good reason you can't tell any difference. I think a chart by Larry is a very good idea and will help many find a velocity where top accuracy is a easier to attain.

[303Guy]

Just a question; the spin rate of a large diameter boolit needs to be much lower than a small calibre one. Does anyone know where to find the radial force calculation?

Another question; to what extent does alloy strength and ductility affect maximum velocity and related spin?

[mauser1959]

this is one of the most informative threads that I have ever read here , in all of my years here .

[C.F.Plinker]

Here is an attempt at an RPM threshold chart that may serve until Larry has time to put a better one together. The first column is the twist in inches. The top number in the second (and third and fourth) columns are the RPM thresholds suggested by Larry in Post #110. The rest of the numbers are the velocities that will reach that RPM threshold in a barrel of that twist.

Velocities to reach RPM threshold
RPM threshold
Twist 120000 130000 140000
7 1167 1264 1361 fps
8 1333 1444 1556
9 1500 1625 1750
10 1667 1806 1944
11 1833 1986 2139
12 2000 2167 2333
13 2167 2347 2528
14 2333 2528 2722
15 2500 2708 2917
16 2667 2889 3111
17 2833 3069 3306
18 3000 3250 3500
19 3167 3431 3694
20 3333 3611 3889
21 3500 3792 4083
22 3667 3972 4278
23 3833 4153 4472
24 4000 4333 4667


Please look this over and give comments that can be used on the next version of the table. I apologize for the fromatting as I am not as computer literate as many.

[Larry Gibson]

Just a question; the spin rate of a large diameter boolit needs to be much lower than a small calibre one. Does anyone know where to find the radial force calculation?

Another question; to what extent does alloy strength and ductility affect maximum velocity and related spin?

Rinker's book on Ballistics will give you that information. I imagine researching ballistics on the internet might also.

Larry Gibson

[Larry Gibson]

I've posted the chart on this forum.

Larry Gibson

[303Guy]

Thanks, Larry. So, is that independent of caliber then? Another question, hows does boolit length effect the threshold?