Tell me more about the 550 Mag....what is the parent case and dimensions, etc. Hate to reinvent the wheel.

Anything wrong with necking the 450 A-square Short to 510 and making a standard 510 Mag?

This would nearly eliminate the shoulder and make it a fine feeding round, while allowing a 20 inch bbl to deliver full velocity.

COL would run 3.38 inches like the 458 Win Mag. The short case would be very efficient, and would handle reduced loads well.

Full pressure loads would be at the upper end of the useful power scale at 7400 FPE with 600 grain bullets clocking 2360 fps. However, a far more useful load would be a 500 grainer at the same velocity, especially if driven by 55 grs of XMP 5744 giving 458 Lott power with 458 Win recoil.

Sabot-

I believe that A-Square has already been down this road...

They developed the .495 A-Square, designed for actions that would not handle a round longer than 3.60". IIRC, it was straight or had a "ghost" shoulder. Their published ballistics were about 150 fps slower than the .510.

Bob

i believe the 495 will match the 500 jeffery factory loads...

ch4d sells the dies, and can find you a reamer.. this is kinda the reason i am so wrapped up in a 550mag kurtz, so it will fit in just about anything

jeffe

Sabot, if I hear you right, you're not talking about the 495 A-Square, but a 460 case cut to ~2.5" right? Sounds like a fine idea, within it's limits, of course.
You'll never get a 600g to go 2400 with a 20" bbl, but I bet you'll have quite a thumper nonetheless. More like a 50-110 on sever steroids.
Efficiency would be the theme, rather than raw power.
Goferit!

Take it down to 2.25" and you will have 500 Whisper, which will fit in a short action with "normal" hunting type bullets and get a 535 grain pill to 2150 fps!

That's the idea...shorter than the 495, and the same length as a 458 Winnie. Just a FAT Winnie, thats all. Held to COL 3.38 inches, it will hold 93 grs of AA2230.

Shoulder would be .570, like the 460 Short, where the 495 tapers down to about .545. The 460 Short gets 6670 fpe from a 500 gr .458 and the increase in bore to .510 is good for a 13% increase in energy...that's 7500 ft pounds. The 500 gr .458 is the same length as the 600 gr .510, so the capacity is constant.

The 495 uses IMR 4895 and IMR 4320 which are a bit slow, so I think the rated 6925 fpe is associated with slightly lower pressure than one could get with AA2230. Still, all things considered...including RECOIL...it might be more useful at lower pressure and 6500 fpe or so. Best candidate for testing this out is a Savage 110 action in 458 length with a replacement bolt face screwed on. Weight should run 12 lbs without optics. It if pans out, one could then invest in controlled feed and a nice stock.

Expansion ratio would be identical to the .458 Win Mag, so any bbl length that works there would work for the 510 Short. Say 22 inches as a compromise. Again, the short fat case should do well with XMP 5744 and the lead or jacketed 50-110 bullets out there, particularly the Barnes 450 grainer with a .247 SD. This should do 2000 fps with only 50 grs of this powder. This is a nice even 4000 fpe with 34 FP of free recoil...right there with a 300 Win mag or 338 Win. Given the diameter, authority would be similar to the 458 Winnie. Not bad for the level of recoil.

Finally, there is the pure fun of punching paper with lead and jacketed 300 grainers at 1400 fps and 28 grs of 5744...

We could have TWO stocks giving the 12 lb and an 8 lb weight to make the fun shooting more....FUN! No sense in building this unless fun is kept in mind...the full bore 600 gr loads run 94 FP free recoil...

I also agree that the calculations are optomistic. I would think 600 gr @ 2200 fps is a more realistic level when loaded to safe prudent pressures. Remember, most actions cannot handle the weatherby case at the same pressure levels as a belted mag case, due to increased bolt back thrust, as well as less hoop strength around the chamber, due to less metal for the bigger hole.

I've used Unique to launch 470 gr cast @ 1050 to 1150 fps from my 500 Jeffrey, lots-o-fun, and relatively mild recoil.

If you want a fat "winnie" just go with the 550 Magnum
Short that is being developed. Then you have exact same configuration, Simple and straight.Work with 600 grain
bullets and give max powder capacity in the OAL you are
planning on.Ed.

Just to give an idea of what you might expect, this case is significantly shorter, but the seating depth is reduced with several of the bullets as well. While the objective of this cartridge was different from what you are going for, it might be indicative of performance. The rifle is an AR-10 with 24" PacNor 1 in 9 twist stainless barrel, operating at about 55K psi. Aside from the 750 AMax loads, the rounds feed from the unaltered magazine

http://feistyrooster.com/500phantom/500phantomloaddata.html

Now those are believeable ballistics!

Sabot- Just a straightened out 460 wea brass.A slight

taper.Check the threads in Big bore forum and RNS' site

that he lists on his postings.Forums and site has

the info. Got companies making bullets, barrels, dies ,

complete guns, etc.And guys.. making short versionsEd.

Thanks Ed, if there are folks making 550s with COL 3.38 inches I am definitely reinventing the wheel. Love to see a version with 75 to 80 gr H2O capacity with a 525 grainer seated to 3.38 inches COL.

Believe it or not this puts one into the Lil' Gun powder burn rate, as long as one is looking for 2400 fps or so. This remarkable powder solves many of the problems with underbore loads not having enough capacity. It has the longest, flattest pressure curve in the history of fast powders...ideal for the right big bore. If usable capacity divided by the bore squared is around 300, there is a chance the powder will work well.