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barrabruce
08-11-2014, 02:46 AM
G'day
Trying to figure out the ballistic co-efficient of the ideal 309241 pb 150grb 30 cal mould.
I have tried looking it up and too dumb to figure out one of those b.c. calculator programs.

I'm figuring about 0.250 b.c. as a rough estimate.
Anyone actually know what it actually is ?

Thanks
Barra

Digital Dan
08-11-2014, 06:43 AM
You might want to poke around on this ballistics calculator. It isn't that precise but will put you in the ballpark.

http://www.handloads.com/calc/

It isnt' displaying properly for me at the moment....maybe later?

Or this one, isn't that difficult to use.

http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi

barrabruce
08-11-2014, 07:14 AM
Thanks d Dan I will give it a go

fouronesix
08-11-2014, 08:56 PM
barra,
The current Lyman bullets have BCs assigned, but the 309241 is not in the current listings so a BC reference probably doesn't exist. If it is the round nose cousin to the 311291 then I'd guess (pure guess) it would be somewhere between .20 and .25. With some range time at both 100 and 300 yards, along with a chronograph and using the JBM ballistic calculator you could come pretty close. Probably quite a bit of sweat equity involved though.

barrabruce
08-12-2014, 04:27 AM
http://castboolits.gunloads.com/attachment.php?attachmentid=45999&d=1341869824
This is the beatsy here.
The driving bands are 310 on mine and the nose starts at 0.301 and tapers down to the broad round nose.
Driving band length is 0.510 and nose is 0.370 long.
mines got the crimp groove before the nose thou.

Getting conflicting b.c.'s
What would you call the nose in the jbm calculator???
I got a bc of 263 or 241 .
I haven't a chronograph so I was hoping I could dope out the velocity with drop at range.
It was only blowing 15-30 and gusting and twirling ..not good for load development testing and figuring.

Shall keep trying.
Bruce

fouronesix
08-12-2014, 08:59 AM
Good question as to what it's called.

The way I'd estimate the BC would be:

Find muzzle vel with a chronograph. Shoot at 100 yards. Shoot at 300 yards and find center of group. Measure the drop between 100 and 300. Enter a best guess BC (maybe .225) in the JBM Simplified Traj Calculator. Look at the JBM predicted trajectories out to 300. Compare between predicted and actual. If the actual drop at 300 was the same as the predicted, then .225 would be very close. If the actual drop was less than the predicted drop, the BC would be a little better than .225. And so on.

Using some extrapolation or interpolation between the actual and calculator predicted, you could probably come very close to assigning a BC to that bullet at that velocity.

barrabruce
08-12-2014, 09:18 AM
Yeah that's about the only. Way I can figure it out too
May see if I can loan a crony.

HARRYMPOPE
08-12-2014, 09:54 AM
I have shot it and the 311291 side by side to 200 yards at 1150-1200.both dropped the same from 100 to 200.I came up roughly 12 moa to get the 200 yard zeros.

Tom Myers
08-12-2014, 10:03 AM
This is the beatsy here.
The driving bands are 310 on mine and the nose starts at 0.301 and tapers down to the broad round nose.
Driving band length is 0.510 and nose is 0.370 long.
mines got the crimp groove before the nose thou.

Getting conflicting b.c.'s
What would you call the nose in the jbm calculator???
I got a bc of 263 or 241 .
I haven't a chronograph so I was hoping I could dope out the velocity with drop at range.
It was only blowing 15-30 and gusting and twirling ..not good for load development testing and figuring.

Shall keep trying.
Bruce

Bruce,

Using your image and some old Lyman catalog bullet images, I scaled out some dimensions that seem to be a fairly close match to the Lyman bullet. (The original mold apparently was manufactured with a choice of different weights)

The dimensions were entered into the Precision Bullet Design ~ Advanced (http://www.tmtpages.com/#Advanced) software and also into the Precision Bullet BC (http://www.tmtpages.com/cast_bc.htm) software. Each software package uses a slightly different algorithm to calculate the bullet B.C. but the two calculation results of 0.2298 and 0.2319 are quite close so an average of 0.230 could be a close estimated B.C.

The images below will show the results of the scaling and calculations. Both software packages have consistently returned values that are always quite close to the BC values that Lyman has advertized for their bullets.

Now, having said and done all that, it needs to be stated that these values are just calculations, and although these values are very useful when setting up initial sight setting and trajectory applications, actual chronograph and careful target analysis data are necessary to achieve the real world Ballistic Coefficient for a bullet-fireaream combination.

The last image shows the Precision Ballistics BC from Target Data (http://www.tmtpages.com/basbal/bal.htm) calculator. Precise, accurate target and range values can be used to get the actual bullet BC from a particular firearm-bullet combination.

http://www.tmtpages.com/LinkSkyImages/forum_images/Lyman%20311241%20Scaled/Lyman_311241_(Scaled).Jpg

http://www.tmtpages.com/LinkSkyImages/forum_images/Lyman%20311241%20Scaled/Lyman_311241_(Scaled)Data.Jpg

http://www.tmtpages.com/LinkSkyImages/forum_images/Lyman%20311241%20Scaled/Lyman_311241_(Scaled)_157_gr_Sketch.Jpg

http://www.tmtpages.com/LinkSkyImages/forum_images/Lyman%20311241%20Scaled/Lyman_311241_(Scaled)BC.jpg

http://www.tmtpages.com/LinkSkyImages/forum_images/Lyman%20311241%20Scaled/Lyman_311241_(Scaled)BC.png

fouronesix
08-12-2014, 11:27 AM
Yeah that's about the only. Way I can figure it out too
May see if I can loan a crony.

barra,
Yep, I think by doing it that way you will get to a more precise estimation of the BC. Once the muzzle vel and drop between 100 and 300 yards are known, using a simple calculator like the JBM Simplified Traj, you only need to keep resetting the BC in the calculator to "home in on" the exact BC for that bullet with that load.

barrabruce
08-13-2014, 01:25 AM
:shock: Holy cow.
Ghee Tom those precision cast bullet design software is just awesome!!!
Thanks for doing the calculations!!!
Think I'm about 20 years to late to start playing with that sort of stuff.
I think everyone's input is pretty well right give or take.
Only testing for myself will sort it out but it is a good start.
The b.c. of the 311291 is 0.202
That roughlycorresponds to what I was getting.

Embracing new technology :) here.
The last time I really done this was with charts and lines.

The wife just bought me a android??? phone so I can contact her in the boat and round about if need.(I think they just want a gps tracker to keep tabs on me.)

Any way I went and put the "strelok pro app" in it to play with .(doubt if I'll ever use all the functions but it has my reticle and zoom power on the range which may help a bit.)

That with me hand held gps and new "old" basic rangefinder I'm off into the obis of playing long range precision shooting with a 4x with short range slow moving cast bullets!!!!!
Whooohoooo!!!!!!!
Still waiting for the rangefinder to come and using the computer to do most things.
Thanks fellas
This is what makes this forum great to me.
Barra

frnkeore
08-14-2014, 02:34 AM
My mold is a Ideal, marrked 308241. I'll make the assumption that it's a little older that the other one posted, or not :). Mine has a ellipitcal shaped nose with no band on it, at all and ends at .298 dia. That nose shape raises the BC a little. The base band is wider and the OA length is shorter.

I used 20/1 lead/tin for the drawing and my bullet casts 154 exactly with my 22/1 alloy.

Frank
113493

barrabruce
08-14-2014, 06:37 AM
Mines an ideal mould with no vents in it.
Came in a small cardboard box labelled 308241 30-30
got the #7 under the 308241 on mould blocks.
Length is 0.880" long
Drive bands are 0.3118"
Nose has the scraper and crimp grooves and is 0.301 on boreriding tapering down to the start at about 0.265 to the rounded nearly flat nose.
Weighed 157.8gns with new and old clip on wheel weights. finger nail soft.

Hope the pic is good enough.

113494

Not bad for an 'ol beater!!!
Shoots pretty good and working on it
My bore and throat is a bit bigger than some.
Can push it though my 0.3117????" ish honed out lee wack'em sizer by hand to clean up the 1 thou lip from the part line an not so shiny layer of alloy.
Other than that its seems real even and concentric.
Barra
Well as you can see on the end of the nose it gets rounded out a bit on the casting but I have trouble getting it sharp there for some reason.
They (people on the board) were right when they say it casts good when it gets well hot. And positive pressure of a base pour dipper.

barrabruce
08-17-2014, 05:47 AM
Well went and tested all my new toys at the range today.
Had a good day but left the wind flags at home...brought along the sticks thou.

Made up a few rounds and they shot good but were like 8" lower at 100yrds then my projected 950 fps calculations.

Kept upping the charge of bulleye and arrived at 4 gns with about the right height.
Rezeroed at 50 yrds and shot a few over a chronograph. Ave 888fps. Ohh well give 'em a go.

Went out to 206yds according to the rangefinder.
Cranked up 33 moa as projected and shot off five.
113751
They were 4 inches wide and 5" lower than predicted. aprox 2" group 2 in one hole even.( happy as my recticle covers 2" at that distance and its not easy at 4x)
The wind was mild to 100yrds as some benchresters were shooting and I took a glace over yonder at there flags but out past that it was blowing a lot stiffer.
RE set the velocity by the phone app thingo and it comes to 860fps at a B.c. of 0.23 G1.
figures come out right with at but its only a rough job as I need more info and have to shoot more groups.
I took my last shot at the new gong put in place today at 328 yds but only hit the tyre..but its a start. Close but no burrito!! :)
All in all pretty good.
Thanks everyone for the help much appreciated.
Barra