I'm designing a 700 grain cast bullet for the .550 Magnum and need some cartridge dimensions. I need the COL, case length and neck length.

Thanks

col is 3.8
case is 3"
there is no neck/parallel neck
but..
if you are designing for all the 550s, do your crimp grove .720 back from the nose, rather than .820, as that will allow all of them to use it

I think you need the throat specs to add to what Jeffe has posted:

Throat =
Parallel-sided free bore (length and diameter)
+
Leade angle

Or, for a "no free bore" throat:
Throat = leade angle and diameter at start of throat

This would be very interesting for someone with a reamer drawing to supply these specs for public admiration.

What Jeffe said, mostly. My 550 Gibbs Magnum case is 3.130 max length, I trimmed to 3.100". That case capacity is 198 grains or so.

I personally think in terms of two bullet weights, the same length, 1.275"-1.300"; but one round flat nose with a .450" meplat and single grease groove for maximum weight around 760-775grains, and the other a truncated cone with a meplat about .430"-.450", about .725" long, and the back half about with equal length bearing bands .001" over groove diameter, and grease groove depth about .530", very slight radius on the back end...driving band there about .200" long. That one might come in about 100 grains lighter, say 625-650 grains.

I'm not asking much am I?

My barrel mikes about .542" and .550".

If you go to the 550 pictures and video you can see the RFN 715gr bullet I have been shooting. I would BUY that bullet by the box at 760-775 grains and be happy with just that design for a heavyweight. For my 550 Gibbs throating (Gorgeous reamer set by Dave manson and reloading dies by Hornady, BTW) that bullet needs to be seated in the crimp groove to fit the chamber throat. My cast loads oal at 3.670", but feed and fit perfectly at that length. If the nose area were about .548" instead of a rather chubby .5515" it could have another .100" beyond the crimp groove.
The meplat is a dismal .320" and no shoulder for the "slap" effect on game. Design the bullet with a shoulder somewhat like a pistol SWC design, and set it to crimp on the back edge of that shoulder, and call it good.

My magazine box will take loaded rounds at 3.800" and I have already shot that 715gr bullet at 2250+fps with zero leading issues for 4-10 rounds. Maximum (IMHO) weight/velocity balance for Dangerous Game. The T/C would be the "anything but the African Big Three" bullet, and run out 2400+fps. If you wanted to gas check it, another 200+ fps might be reachable. At 2250-2300fps it would be a fun 12 lb rifle to take a box of twenty loaded rounds to the range and shoot up.

With a Bhn of 22-25 I would take the 775gr at 2300fps to Africa and try on Buffalo and Elephant. Regardless of what you take, from 9,3X62/74 on up to a .600 OverKill: if you muff the shot even a little, the PH is going to throw down on the animal if he has any concerns. With a bore of .550" and that bullet weight and speed, if you show the PH you can shoot it accurately, I do not think he would have any issues with the cast bullet.

If all goes according to plan, I will get to Africa next spring to test my theories out on Buff and Elephant. I will take the .550 Gibbs Magnum, and my 416 Rigby as the second rifle.

These are my thoughts and rationale for the designs and weights I wish for...

I have been modifying the 881 grain NEI mould bullets, to experiment with. I cut them from 1.480" long to 1.228" and shortened/flattened the nose. They also got a T/C front that features a .420" diameter meplat and the tapered section is roughly .330" long. I also took .050" off the base length. That bullet weighs 735 grains before lube. I would leave it .050" longer on the nose and 760-775gr and be one deliriously happy camper. I made up half a dozen, within .010" and 2 grains, and shot them 2278fps first load testing.

If it took less than ten minutes and taking it out of the lathe chuck six or seven times to check length I would make up a hundred and do all the velocity testing with it. These bullets feed perfectly, and 35 grains heavier would be THE PERFECT .550" caliber projectile, from my experience. Since I have the only 550 Gibbs magnum for another month at least...that makes me the Bull Goose Looney here. Since RNS has done some work with an 800gr jacketed bullet, this weight would be fine in his .460Wbee/550 Magnum as well. I will send JeffeOsso pictures of the 715 gr RFN and my 735gr custom to post here tomorrow sometime. I got a gunshow in Boise at 9am, and the BSU game comes on my bigscreen at 1pm...

Rich
DRSS
Knowledge not shared is knowledge lost...

I don't remember the freebore and throat, and I can't find my drawing.. but i'll get back to you...

Excellent!!! I wish I could see a photo of the 715 grain RFN.

Thanks everyone!

KDM,

check your Email.

Rich
DRSS
Knowledge not shared is knowledge lost...