Need help from a boolit designer

[338RemUltraMag]

I need some help designing a heavy for caliber boolit for my 416 Rigby. I would like one to be as close to 450 grains as possible, and it needs to work with a 1-17 twist. I know woodleigh makes a 450 gr RN and the Rigby can plug one along at 2300 FPS. I have played around on the Mountain Mold website with a few designs buthave never made a boolit before and want one that will be easy to get accuracy from (I know some designs give people fits)

I took some measurememts from my rifle as best I could w/o cerrosafe.

Max mag OAL 3.815
Neck length .480
Max bullet dia .418
Throat length .129

I assume the boolit will have to have a fairly long nose to get close to 450 gr. If that weight is too much for a 1-17 twist then as close to 450 as possible would be great.

Thanks to any designers out there that help a feller make a good elk boolit!

[41 mag fan]

Get ahold of Tom at Accurate Molds, I bet he can design and set you up with something you have in mind.

[338RemUltraMag]

I was going to have him make my mold, but I did not know that he designed them also.

[RobS]

If you email to tell him what you are looking for he will design what he thinks you are after and adds the new design to his catalog. You then can look at things and decide if you want changes or if the design is what you are after. He has no problems making changes to the design; I had him make changes two or three times. His response to emails is good so you should have what you are looking for in a short order. Tom at Accurate Molds is really easy to work with and is knowledgeable in the trade.

[338RemUltraMag]

Sweet thanks guys!

[Tom Myers]

I need some help designing a heavy for caliber boolit for my 416 Rigby. I would like one to be as close to 450 grains as possible, and it needs to work with a 1-17 twist. I know woodleigh makes a 450 gr RN and the Rigby can plug one along at 2300 FPS. I have played around on the Mountain Mold website with a few designs buthave never made a boolit before and want one that will be easy to get accuracy from (I know some designs give people fits)

I took some measurememts from my rifle as best I could w/o cerrosafe.

Max mag OAL 3.815
Neck length .480
Max bullet dia .418
Throat length .129

I assume the boolit will have to have a fairly long nose to get close to 450 gr. If that weight is too much for a 1-17 twist then as close to 450 as possible would be great.

Thanks to any designers out there that help a feller make a good elk boolit!

I worked this up this morning but got called away before I could post it.
I wasn't quite sure of your definition of a throat and there was not bore and groove size posted, so I used SAAMI specs for some of the dimensions.
If your chamber dimensions are different than the ones shown and you would like a redraw to those specs, just post the dimensions and it isn't much of a chore to do a redraw once the initial drawing is made.
55695556965569755698

Hope this helps.

[338RemUltraMag]

Thanks for that, I sent you a pm, this looks good!

[MtGun44]

Have you checked around to see if the twist will stablilize this boolit? Seems
REALLY slow twist to me for a boolit that has this aspect ratio, but I have not
run it across Greener's formula.

Bill

[338RemUltraMag]

Have you checked around to see if the twist will stablilize this boolit? Seems
REALLY slow twist to me for a boolit that has this aspect ratio, but I have not
run it across Greener's formula.

Bill

I know that the Woodleigh 450 gr FMJ is made for the 416 Rigby and they sit at 1.510 inches long, I need to check the formula and see what happens!

[338RemUltraMag]

I checked a simple Greenhill formula and with a 1-17 twist I should be able to stabalize a bullet up to 1.650 inches long. Any input is appriceated and if anyone gets different numbers by all means let me know!

[338RemUltraMag]

I worked this up this morning but got called away before I could post it.
I wasn't quite sure of your definition of a throat and there was not bore and groove size posted, so I used SAAMI specs for some of the dimensions.
If your chamber dimensions are different than the ones shown and you would like a redraw to those specs, just post the dimensions and it isn't much of a chore to do a redraw once the initial drawing is made.
55695556965569755698

Hope this helps.

If I send you a cast can you make the boolit fit my throat?

[Tom Myers]

I checked a simple Greenhill formula and with a 1-17 twist I should be able to stabalize a bullet up to 1.650 inches long. Any input is appriceated and if anyone gets different numbers by all means let me know!

The formulas below are modifications of the Greenhill equation that consider the muzzle velocity of the bullet.
Let

V = Muzzle Velocity
D = Bullet Diameter
T = Twist Rate ~ inches for one complete twist
3.5 = Constant for calculations

If the muzzle velocity and the bullet length and bore diameter are known then this formula will be used to make the calculation:
T = ( 3.5 * SqRt( V ) * D² ) ÷ L

If the barrel twist rate and the muzzle velocity are known then this formula will be used to make the calculation:
L = ( 3.5 * SqRt( V ) * D² ) ÷ T

If the barrel twist rate and the bullet length and bore diameter are known then this formula will be used to make the calculation:
V = ( L * T ÷ D² ÷ 3.5 )²

So, the minimum calculated muzzle velocity needed to stabilize a 0.416" dia bullet that is 1.415" long in a 1 in 17 inch twist barrel would be 1,577 fps

1,577.25 = ( 1.415 x 17 / 0.416 / 0.416 / 3.5 ) x ( 1.415 x 17 / 0.416 / 0.416 / 3.5 )

[Tom Myers]

If I send you a cast can you make the boolit fit my throat?

Yes, happy to help if I can.
Using the Precision Bullet Design and Chamber Drawing software, I can generate bullet dimensions that will closely fit a chamber from dimension measured from either impressions or castings.

Impact impressions are much more reliable and stable than Cerrosafe castings. It is often difficult to obtain accurate headspace dimensions from only the castings as the rim cut or chamber end is never defined enough to accurately measure distances.

With the help of dimension recorded by a very thorough test performed by another poster(wish I could remember his handle but CRS Syndrom is my constant companion these days), I have developed an algorithm that can reliably convert the continually changing Cerrosafe radial dimensions back to the original chamber dimensions based upon the time elapsed since the casting.
The instructions that are commonly supplied for the expansion factor are taken from an old properties sheet that lists the dimension changes in a Cerrosafe casting that has dimensions of 1/2" x 1/2" x 6" and is relevant only to a casting of those dimensions.
If anyone is interested, this is the formula that I use to calculate the expansion of a Cerrosafe casting and it works well.
Let H = the hours elapsed since the casting was made.
Let D = the dimension that is measured on the casting.
Let C = the actual dimension of the chamber.

Then

C = ( H x D x 177.62 ) / ( H x 178.31 - 1 )


If the castings are crisp and well filled out and an un-sized, fired case is provided along with the time of casting, a credible set of chamber dimension can be obained. From these dimensions, close fitting bullet dimensions can be obtained.

Chamber impact slugs work a whole lot better and are easily made if one has access to pure lead and a steel or brass rod that is a reasonabley close fit to the bore diameter of the barrel. The most difficult part is the initial forming of a bore diameter, pure lead slug.
What I have found that works very well for me is to obtain two blocks of hardwood, clamp them together and then, using a bit diameter that is a close fit in the barrel bore, bore a hole on the centerline of the clamped blocks about two inches deep and then simply pour the melted lead into the makeshift mold.
Next find a metal rod or hard wood dowel that is a slip fit in the neck of an unsized fired case and cut it to a length that will allow it to set in the case positioning the top to within about 1/4" - 3/8" from the end of the case.
Place the dowel or rod in the case, place the lead core in the neck and chamber the assembly in clean lightly oiled chamber of the firearm. Then close and lock the bolt.
Wrap the brass or steel rod with electritian's tape at intervals along the rod so that it is a sliding snug fit in the bore and then, using a heavy hammer and with firm strokes, strike the rod untill the sound of the impact changes, indicating that the slug is completely impacted and filling the throat and bore of the barrel.
Open the action, while lightly tapping on the rod, carefully extract the impacted cartridge and slug from the chamber.

Please don't feel that only an impact impression will get results. A crisp Cerrosafe casting along with a fired case and the date and time of casting will work quite well.

If you do send either a casting or an impression, before placing it in a shipping box with packing or padded envelope be sure to wrap each item separately and tightly in cotton or foam then wrap with paper and then wrap with tape. You would not believe what can happen to the impressions and castings while riding in the back of a semi trailer for a couple of days and nights.

The bullet length of 1.415 should stabilize well as long as the muzzle velocity is above 1,578 fps.

http://www.tmtpages.com/LinkSkyImages/forum_images/416Rigby/Twist%20data.png

[338RemUltraMag]

Bump so I can find it, I am making a chamber impression on Monday.

[338RemUltraMag]

Made an impression, it took a while because of the Christmas season.

http://i1270.photobucket.com/albums/jj609/joshaaronelli/gun%20and%20game%20pics/20130103_171939.jpg

[338RemUltraMag]

Ok, bore ride is .409, total bore is .417

[338RemUltraMag]

Throat diameter is .418

[338RemUltraMag]

http://i1270.photobucket.com/albums/jj609/joshaaronelli/gun%20and%20game%20pics/20130103_173346.jpg


Brass length is 2.883

[338RemUltraMag]

http://i1270.photobucket.com/albums/jj609/joshaaronelli/gun%20and%20game%20pics/20130103_173442.jpg

Total chamber length is 2.925

[338RemUltraMag]

http://i1270.photobucket.com/albums/jj609/joshaaronelli/gun%20and%20game%20pics/20130103_173759.jpg

From brass end to rifling start is .120

[338RemUltraMag]

http://i1270.photobucket.com/albums/jj609/joshaaronelli/gun%20and%20game%20pics/20130103_173620.jpg

From chamber end to rifling start is .076

[Tom Myers]

From brass end to rifling start is .120

Looks like you did a great job with the impact impression;

Your dimensions indicated a few changes and resulted in a slight change in the design:

http://www.tmtpages.com/LinkSkyImages/forum_images/416Rigby/338RUM_418-408-450_Rot.bmp

http://www.tmtpages.com/LinkSkyImages/forum_images/416Rigby/338RUM_418-408-450_445_gr_Sketch.png

http://www.tmtpages.com/LinkSkyImages/forum_images/416Rigby/416_Rigby~~338RUM_418-408-450_Design_Throat_75%25.png

In order to make fabrication as easy as possible for the mold maker, where possible, the software rounds non critical dimensions to the nearest 0.005"

Look it over and see what you think.

[338RemUltraMag]

Tom, that boolit looks great! I am gonna send Tom @ Accurate Molds a link to this thread so he can see the design, thanks again for your help!