I've seldom see the "true" ballistics on this one.Figures as one can see on the board,Nickudus datas , could not be the only datas available in a case holding so much more. So my question is naturally what is this cartridge potential(570 gr.,600 gr.,525 gr.originals)in a modern case(like Horneber or bell mast tech.) ??!

PER 577,
I went to 2450 with the 570 & 600 grainers with no ill effects other than groupsize opening up. I've seen the following loads posted on the Internet from various sources:

150 Gr. H-4831 for 2500+ fps - 600 grain bullets.
135 Gr. RL-22 for 2300 fps w/ 525 Gr. Woodleighs.

Guns & Ammo / February 1989 - Jack Lott - The .505 ... When Is �Enough Gun� Too Much?
From Ryan Breeding:
152 Gr. IMR 4831 with 600 grain Barnes soft nose for 2,578 fps. Unreal
132 Gr. IMR 4831 with 700 grain Barnes soft nose for 2,260 fps.

Really Nic the .505 gibbs is neally as powerful as the .585 Nyati from those figures. The difference between the two is minute really. The gibbs is a fantastic looking case as well.

Thank you very much fellas,i appreciate your info.
But i'm not sure what you mean by 'unreal'(2578 fps@600 gr.),,Nickudu,,sorry my IQ,, limits but did you mean overloaded,,or ?

I think what he means is......holy s#*t almost 9000 ftlbs of muzzle energy!

Db Bill is correct. I had put the notation there some time ago and failed to notice it prior to posting, Sorry about that!

[ 09-22-2002, 19:32: Message edited by: Nickudu ]

Nick, those are outstanding results with the .505.

Do you get any pressure signs such as sticky cases?

I managed to get out in the country to do a little shooting yesterday, and one of the things I did was to finally shoot off a few .510-.505 Gibbs loads that I had put together with WC 852 (slow) surplus powder that I had purchased from Jeff Bartlett. This powder is supposed to behave like IMR 4831, though I suspect it is a little bit slower.

The rifle is a P-14 with a 32" 1-3/8" heavy barrel, and no brake. The ammunition was put together with Bertram cases, CCI Magnum primers, 700 grain M2 ball bullets, and appropriate amounts of foam filler. The ammunition had been sitting for about 3 months since I had loaded it. The bullet was seated to the top of the cannelure, which allows a one-tenth inch jump before the rifling is engaged.

I was wandering through Home Depot one day, and I found packages of cylindrical polyolefin (?) insulation, slightly more than 1/2" dia., and twenty foot length. Useful for filler in .510" cartridges.

Increasing the powder charge in one grain increments and firing one round at each charge weight:

120: 2111 fps
121: 2171 fps
122: 2203 fps
123: 2178 fps
124: 2213 fps
125: 2275 fps
126: 2193 fps
127: 2272 fps
128: 2242 fps
129: 2319 fps
130: 2310 fps
131: 2343 fps
132: 2313 fps
133: 2359 fps
134: 2356 fps
135: 2365 fps

Previously my fastest load had been 2075 fps with 145 gr. (slightly compressed load) of the very slow IMR 5010 powder.

It was really hot yesterday (North Texas), and I had trouble keeping the ammunition cool, and the rifle was allowed to cool for 1/2 hour after every five shots. Up to about 130 grains, small quantities of crushed foam could be found on the outside of the case just below the mouth, suggesting that the neck was not immediately blowing out to press firmly against the chamber walls, and thus very low pressure loads? There were no problems with extraction and the cases look normal. There seems to be plenty of potential for increased powder charges and velocities. With the foam filler, there were no hangfires. IMR 5010 loads without filler had hangfired up to 135 grains.

I find it relatively easy to fire 2100 fps loads from prone. The 2300+ fps loads exceed my definition of fun from prone. I am a slightly built fellow of just 190 lbs and 75 inches without much padding on my frame. The rifle needs to be restocked out of the plastic Choate stock with the slip-on recoil pad and into something much nicer. And I will have to start shooting from a sitting or standing bench.

A very important detail is often overlooked with the big cases. True, they have awesome velocities when pushed, but the rearward bolt thrust in pounds force (not PSI!!!) can get to the limits of the receiver design and metallurgy.

And during my work with the Oehler M43, I have learned that "reading the case" is no sure way to judge pressures. As the powder charge goes up, so does the pressure, and so does the rearward bolt thrust.

I also have an Excel Spreadsheet that calculates the rearward bolt thrust for a variety of big bore cartridges in the popular action used today. I have ran seveal iterations of pressure combinations. Can get real scary reading the figures.

Over 2500 ft/sec with a 600 grain bullet makes nice discussion material, but IMHO pushing this cartridge to this level is overextending the rifle action, plus bullet performance may suffer, both expanding type and maintaining the straight path of a solid. Needless to say the recoil increase and controllability of the rifle for a fast follow shot becomes an issue. And how about a stuck case, when you are looking some beast in the eye and need another shot?

Just be safe out there guys, and I absolutely advise everyone that is involved in pushing the big cases to high velocity to give serious thought to obtaining a means of pressure testing the loads. I will be running some M43 data with Paul Hail's 500 Jeffery in a month or so and will post the results.

I have seen a couple of receiver failures due to high loads. One was a lanyard fired pressure gun and the receiver ring split. The other was a Winchester P-14, had a real bad case failure and gas escaped everywhere, most of it came down the left lug raceway wrecking the rifle. The P-14 has horrible gas control!! Only thing saving the shooter's eye was a pair of sunglasses.

[ 09-22-2002, 18:49: Message edited by: John Ricks ]

John, excellent post regarding thrust force. How do yo calibrate the Oehler M43? I have often wondered this and haven't known anyone who owned one to ask. So if you do not mind sharing this I really would appreciate knowing the calibration method used.

Thanks,
Axel

Axel, John Ricks,
A question, please. I have a loading for my .505 Gibbs which chronos at 2325 fps with both the 570 grain "X" bullet and the 600 grain Barnes Super Solids. I am intentionally using a faster than usual powder in RL-15 and 4 grains of Dacron filler. Have you a guesstimation of the pressures I am working with here? Using the Horneber brass, I am 4 to 5 grains below any physical indication of high pressure, the first being a slight
"stick" when the fired case is extracted promptly. While I was hoping this loading is, let's use the term "moderate", I agree with your comments relating to case size/surface area as it relates to pressure. I use the CZ-550 action.

Nickudu, I would estimate that your load is in the 52000 to 54000 psi range. That would generate a thrust force of 9700 - 10,100 lbs.

CZ specifies their CZ550 Magnum action to a thrust force of 9300 lbs! Therefore, you are pushing the action above CZ's specified maximum thrust load. To keep the thrust force below CZ specified maximum your max velocity with the 600 grain bullet would be 2230 fps. Maximum pressure would be 49000 - 50000 psi.

Axel

John, how many pounds of rearward bolt thrust is safe in a P-14? How much stronger is the CZ-550? One poster a year ago noted that the P-14 lugs were small for various applications. I think my P-14 bolt was switched for a P-17 bolt when it was built because it was determined that the striker hole in the P-14 bolt was slightly off-center.

Given that the .505 Gibbs has about .322 sq. in. of cross-sectional area at the case head right in front of the extractor groove, we could then multiply the safe lbs. of rearward bolt thrust by 3.1 (1/.322=3.1) to get the safe psi?

Given that the loads are assembled properly with optimal powder selection and a 32" barrel, what velocities with various bullet weights (600, 650, 700)give maximum safe psi's? I figure I get an extra 120fps from a 32" barrel in comparison with the typical 26" pressure barrel.

In reading the A-Square manual I noticed that the larger (.372 sq. in. of cross-sectional area at the case head right in front of the extractor groove).577 T-Rex cartridge is loaded to a modern pressure level of 65000 piezo psi. The manual also says the A-Square Hannibal rifle in which the T-Rex was chambered was built on a P-17 action? This would then imply a safety margin for a .505 Gibbs loaded to the same pressure level in the same action?

The questions above are honest requests for information. I want to have safe fun and keep my eyesight. I am not a ballistician or an engineer or a physicist or a mathematician. My level of involvement is to carry the parts and the reamer down to the gunsmith and ask him to put it together in the next six months or so. I've got enough skill to put together 1/4 MOA rifles and ammunition. I've been handloading for nearly 20 years and loading nonfactory cartridges for perhaps 10 years. I don't shoot much, though, so the actual number of rounds loaded is less than that period would imply.

I have also put together a few loads that have stuck, however, I was using factory components and the Speer #11 Reloading Manual. My recollection is that the .300 Win. Mag. IMR 7828 190gr. HPBT maximum loads, reduced 10%, stuck. And the .44 Mag. IMR 800X 200 gr. JHP loads, reduced more than 10% from 21gr. to 18gr., stuck. Because of this I have some experience with sticky case extraction, which according to the A-Square Manual will not occur until after safe pressure levels have been exceeded.

SDS, the bolt face diameter is of little consequence with regard to thrust force. Thrust force is determined by the inside diameter not the outside. Since the bolt face diameter is an outside dimension in means nothing.

In order to understand the actual thrust force you need to section your brass and measure the diameter of the flat section at the base of the cartridge. This diameter will be smaller than the groove diameter. In most instances you will find that the ID of the brass is approximately .130" - .150" smaller than the OD.

The maximum allowable thrust force per CZ for their CZ550 Magnum is 9300 pounds. That limits a Gibbs sized case to a maximum operating pressure of around 49000 psi. This is most likely a conservative value, but it is what the manufacturer has specified.

Axel

If this is true that actions will set back, then all those 378 Wbys out there would not need to have the locking lugs lapped

What about the bolt face itself? How thick is the bolt face. After all the bolt face must tranfer the force from cartridge head to locking lugs.

Mike

Axel,
Thanks for the response. A variable that I should have mentioned is molycoated bullets and the moly bore-prep I use from "Midway". Is it not likely this might reduce pressure/bolt-thrust to some degree? I know my max loads in any caliber have heavier powder charges using molycoated bullets than those with non-coated bullets.

Nickudu, it takes a certain force to accelerate the mass to a given velocity. So since force is pressure times area and the area is constant the pressure to accelerate your bullet to velocity "X" is also a constant. Moly coating can reduce the coefficient of friction between the bullet and bore thus reducing the pressure for a given powder charge, but as you have stated you needed to add more powder to get our velocities back up.

This is due to the fact, that I stated in the beginning. It will take 52000 to 54000 psi to accelerate that 600 gr bullet to 2325 fps.

Moly coating IMHO is good only to reduce copper fouling. Then again you are only exchanging copper for moly fouling in the end.

Axel

Axel, Yes. Sorry, I didn't have my thinking cap on when I posed the question.

Molycoating: I find a few other things about it that appeal to me. Groups seem to be good right away, as opposed to some of non-moly loads that often require wiper shots or some bore fouling before the groups tighten up. Also, I'm nearly convinced that coated solids penetrate better than non-coated solids.

Nickudu, don't apologize! There is no such thing as a stupid question, except for the one never asked that is. I admit to having very little experience with moly coated bullets. I tried to molycoat some here at home with dismal results and gave up. I was not smart enough to figure out the tricks to the process I guess.

Your comments about tighter groups "outa the box" so to speak intrigue me. Are you coating your own or buying precoated factory bullets? How BIG a difference did you see?

Thanks,
Axel

I use the molycoating products from "MidWay" and a dedicated tumbler. There have been instances, where I've found that loads that normally needed 6 or 8 rounds to "settle down" in a clean barrel would shoot as tight, or even a bit tighter, after a single wiper shot, through a clean barrel with molycoated bullets. Often, I've needed to add a grain or two of powder just to equal the velocity of the uncoated bullet and then found I could go on to exceed the previous uncoated max velocity by a good margin, at similar pressures. This being the reason I posed the above question as to whether or not you thought molycoated bullets might be a factor in regard to bolt thrust.

Nickudu, the molycoat may in all actuality help reduce peak pressures therefore allowing a greater average working pressure to be generated. This would explain higher velocities with equivalent pressure signs. I do not pretend to have all the answers, but the above does make some sense.

Axel

Axel, I'm sort of glad it makes some sense. If we knew all the answers it wouldn't be such fun.