I'll repost this over here. I'm sure this has been done but I' guessing for African game. I would like to do this with .50 BMG and VLD bullets in mind. I would like to know the ideal barrel length, load data etc. Thanks for any info.

HEAVY -- no, seriously, make everything HEAVY if you are going to build a sniperish rifle

if it were MINE< it would be a brake 30" 1:15 or 1:10 twist, and a long talk with Dave Manson on throat.

load data? I seriously doubt anyone has anything but conjecture/quickload for that.

my 500 AR will go right around 1950-2000FPS with 645gr milsurps .. have not shot any amax's

I have a 32-inch barrel .51 Gibbs made with the stock Clymer reamer, which seems to have an ideal throat for the M2 ball 700-grain bullet. It has been down for restocking for about four years, owing to a substantial enlargement of the honey-do patch. It is the .505 Gibbs necked up to .51, with no other changes.

I never did finish working up loads. I wasn't exactly sure where to stop, anyway. Some load data below.

135-140 gr of IMR 5010 completely fills the case for 2100fps, depending on how much tapping you do to settle the powder.

Seems to me I tried WC872 up to 140 gr with cotton ball for the same velocity. 135gr or less of WC872 with no cotton ball hangfires about half the time. There was plenty of room for more powder, because the ball powder packs much tighter than the sticks of extruded powder. I would like to know what a full case would have done.

135 gr of WC 852 (slow type, I think it approximates the 4350 powders) produced 2365 fps. The wisdom of such a load I leave to the judgment of others. Without access to pressure-tested load data, my best guess was that 2400 fps was safe.

Online twist calculators say I barely have enough twist (15 twist) at 2400 fps. Of two shots I fired at 2100 fps at 5000 feet of elevation at a target 650 yards away, one seems to have hit the target sideways. The other hit point first. Based on these results and your inclination to use long VLD drag bullets, a 10 twist seems more sensible.

Thanks guys. Between 1:10 and 1:15, which would be the bets for 750 BMG bullets as well as 880 gr. solids?
Also, is this feasible as a single shot from a Magnum Mauser? Thanks again.

Not sure but I think .458win has one of these also. Recently I sent a CZ550 which is similar in size to a "magnum mauser" out to be re-barrelled in .500 AccRel {.510" bore}, although the .500AccRel will fit standard length actions with 535 grain bullets, I want to take advantage of the overall length of the CZ for the ability to use the longer mil-surp and VLD bullets also. These will be very long overall and may have to be fed by hand one at a time in the CZ magnum. Need to get a measurement.
Rodney.

Another vote for "make it heavy". I think the upper-end capability of an improved 505/510 gets so close to 50BMG performance that you need a similar rig.

The other option is to go further into wildcatting and shorten the case to the point it fits and feeds in the soon-to-be-released MRC PH action. This may keep the recoil to a reasonable level in a man-portable package.

Well, hehehe, my idea is to get as close to the BMG with safe pressure limits as possible. The goal is 300-400 FPS slower than the BMG with 750 and similar bullets. Determining the optimum barrel length is the issue for me. With the recoil factor, I'd just as soon be too long than too short.We're looking at energy potential above 10K FPE here. A heavy barrel and stock as well as a couple mercury recoil reducers, and a Sorb-Ease pad should do the trick. I also have no quams about making a compensator as this is going to be an "ugly tactical rifle" not a beautiful hunting rifle. The 6-18X65 ATN will add a couple pounds too. I look forward to this project and will keep you all posted, hopefully even with pics. So far it is in the planning/research stage. Thanks for all the input gentlemen: I'll take all I can get.

This will be an interesting rifle. I like the .505 Gibbs very much also but the .510" improvement will really be doing something. Have you already found some loads for it? My little 500 AccRel will very much be in a sporting configuration, safari style rifle, but I expect it to do everything the 50 Peacekeeper and the 500 Jeffery can do. For mine I'm using a 1 in 10 barrel for slower velocities but the bigger improved Gibbs may be better suited to a 1 in 12" or 14" if they make them. I think the BMG uses a 1 in 15" as a standard, but for slower velotities a faster twist in my opinion may be better. I've had this problem even with .22 rimfire shooting heavier bullets at slower speeds as they do not stabilize in the common 1 in 16" barrels. Go long with the barrel, you can always cut it off and re-crown later. Just some thoughts. Rodney.

this single feeds fine in a ruger
ya'll tell me which pic looks best

Hey those look good, all of them. Looks like the .500AccRel case with mil-surp bullet? Be going there soon. Was messing around out in the loading room and made up an un-improved 510Gibbs case. Just a .505Gibbs expanded to .510" so here is a pic of it compared to others. .510Gibbs,.505Gibbs and .375H&H

Gotta love those 50s!
Rodney.

yep .. 645 gr on a stock 500 AR case.. 4.155 oal..

okay, that is distrubting.. it would feed FROM THE MAG on a PH action.

Forgot to mention overall length for 510Gibbs- 4.650" with 750 grain mil-surp. Need to single feed in magnum length action.
Rodney.

quote:

Originally posted by jeffeosso:
yep .. 645 gr on a stock 500 AR case.. 4.155 oal..

okay, that is distrubting.. it would feed FROM THE MAG on a PH action.

So......I can shorten a Gibbs case some, load blue tips and have an APTI repeater with my spare PH? I'm in love! I'd do an 500 AR on it but the bolt-face is set already.

I would think it to be easier to do the mag-well for a .500AccRel by far, than for a shortened 50 BMG wildcat. For me the donar action {500AccRel} already had the parent case for boltface and magwell, no problems here.
Rodney.

Harry - I bet they can "not" open your boltface past .600, if you asked quickly! Its always easier to go UP in that.

this 510 gibbs got me to thinking, and I decided to make up the dummy above .. I had shot some other pulls in the AR, and they went bang, just fine, though I'll have to use a slower powder, I think ...

One of the few places that I think a long barreled AR would be a winner .. ahhh, heck, I might have to get back on the PH list.
jeffe

Jeff, I'm convinced the 500 AR is winner and I plan to do one. It's just that both of my charter PHs have the 505 Gibbs spec so I'm currently stuck with that rim diameter.

good on ya Harry .. i am starting to convice myself that a Th - tactical hunter, could be reasonable .. ah, me..
too many projects, and not enough time in the field, though i am doing better at that these days

Speaking of tactical-hunter rifles, I do still have that 505/416 Gibbs reamer around somewhere. The poor man's CheyTac, so to speak.