Author Topic: ? for Fred M (Read 697 times)

BIGBOREFAN · « **on:** December 27, 2004, 04:23:07 AM »

Fred can you tell me what the case head thrust is on a 45-70 operating at 28,000 CUP's and then a 223 operating at 50,000 CUP's. I'm curious to know if there is much difference in the thrust since the the rim diameter on the 45-70 is bigger than the 223. I think the thrust would be close to one another since the 45-70 case head is bigger and operates at lower pressure but the 223 operates at higher pressures but with a smaller case head. Any idea.

BBF

Mac11700 · « **Reply #1 on:** December 27, 2004, 05:48:28 AM »

BBB:

While this isn't exactly what you are looking for...it does pertain to it...

Quote

To put it as simply as possible it is the actual loading onto that standing breech which is a function of total case pressure times the diameter of the case head. A small diameter shell will push backward less than a large diameter shell even though both have the same total chamber pressure. It is this back pressure that is the reason T/C came out with the Encore to cover the rearward loading the Contender cant handle even though several of the Contender chamberings are for high pressure rounds. If you do a study you will find that some Contender frames were actually stretched because of case head pressures that were to high for the frame to handle.

To put it another way 65,000 PSI (Pounds per Square Inch) will not push as hard on a1/2-inch area as it will on a 3/4-inch area or a 1-inch area.

That is also the reason the SB-1 action cant handle the same rounds as the SB-2 can. Its action is of a different material that isnt as strong so cant take the same amount of rearward movement.

The entire thread can be read here...http://www.graybeardoutdoors.com/phpbb2/viewtopic.php?t=46555&postdays=0&postorder=asc&highlight=thrust&&start=35

There's some good info there...

Mac

Fred M · « **Reply #2 on:** December 27, 2004, 09:04:21 AM »

Bigborefan.
Your point is well taken, and the published cup figures are to be taken into consideration with bolthead thrust in actions with lesser action strength like the Handi. As mentioned by Mac we went through this before. But here is an update.

As usual the best conversion I have seen converting psi to cup has evaded capture on my computer. But 52kcup = roughly 60kpsi.

The amount of pressure that can be transmitted to the boltface or standing breech is determend by the inside diameter of the case at the pressure ring which is about 0.200" above the bottom of the case head.

The case walls at that point vary but are in general about 0.037" to 0.042" for the 223. I assume the 45-70 has a similar case wall thickness at the pressure ring.

OD of the 223 = .375 - say 2x40 = .295 ID. = 0.068sq/in x 60kpsi= 4098lbs against the boltface/standing breech.

The 45-70 OD= 0.505 " - 2x40 = 0.425" ID = 0.142sq/in
(28000cup x 1.516) -17902 = 24546 psi x 0.142 = 3495 lbs on the breech face

It follows that the 45-70 at the above pressures will develop 12% less force against the breech than a 223.

By comparison the 25-06 at 60kpsi developes 7536 lbs back thrust.

I saw Qick having a conversion table maybe he can enlighten us on the right figures.

Quote

Note: Addendum . A better conversion. That changes the above 45-70 calculations which I amended.

Thanks to Denton you can convert PSI to CUP by the formula:
PSI=(1.516 X CUP) -17902. It follows by this that the lower cup values are nearly the same as psi. This makes it difficult when comparing apples with oranges, one quotient does not apply to all. Sorry for the false info at the start.

BIGBOREFAN · « **Reply #3 on:** December 27, 2004, 09:45:11 AM »

Fred M your a genius. Thanks very much for the info. I knew if anyone could figure it out it would be you.

BBF

quickdtoo · « **Reply #4 on:** December 27, 2004, 10:14:04 AM »

PSI to CUP in a nutshell, well, not exactly... :-D
http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

Fred M · « **Reply #5 on:** December 27, 2004, 11:18:05 AM »

Quick
I did find the right formula on my computer. So I changed my post accordingly. I don't think it serves much of a purpose to convert from one to the other, since there is no straight line correlation.
The formula is perhaps quite realistic but has flaws on either end of the pressure spectrum. I feel the cup system should be done away with.

I corresponded with the Hodgdon ballistic man about the same subject a few years ago. He said you can't convert cup to psi. period. He also said they can't afford to scrap all the cup barrels, that is why they still use the system.

It is best for a hand loader to use a program such as Quick Load or stick to published data. Specially when loading for a rifle like the Handi. My idea of 49kcup or 55Kpsi is the most that ever should be used in a Handi if reliable function is expected, and what is wrong with that.

That again is dependent on the diameter of the cartridge base as demonstrated above.

Paul5388 · « **Reply #6 on:** December 27, 2004, 03:10:52 PM »

Fred,

Using your numbers, the .357 Max, that a lot of folks have been reaming their .357 Mags out to, developes 3852 lbs on the standing breech. That's only 246 lbs less than a .223. That's 94% of the .223, which I would think isn't enough to be too concerned about.

Fred M · « **Reply #7 on:** December 27, 2004, 03:35:40 PM »

Paul.
Please carefully read that full article, the one that Quick posted. It seams to me that shotguns and pistol cartridges do not fall under this conversion.

I only skimmed over this article since I never use these conversions.
Quick who posted the URL may be able to fill you in on that one. I hate to make any more statements about cup verses psi.

The reason for this is that, if have 15000cup x 1.5 minus 18000 you get to near zero psi. That is why this system is nuts. Don't use it please.

Since the 357 max has nearly the same inside diameter than a 223 at thge pressure ring it should produce similar interior ballistics.

Donaldo · « **Reply #8 on:** December 27, 2004, 06:05:22 PM »

I too had conversation with one of the companies that put out reloading manuals about cup vs. psi. I got the same reply, "you cannot compare the two, period". One is one and the other is something else. Best I can estimate in the 40 to 50 thousand range, cup is about 8,000 lbs less than psi, but that is very rough. Best bet is just to use the manuals, don't exceed the max. And a bit of common sense don't hurt either.

Paul5388 · « **Reply #9 on:** December 27, 2004, 06:53:57 PM »

What is even more interesting is when you compare the .357 Mag cup numbers from Speer #10 (46,000 cup) and then use Speer #13 at 35,000 psi.

Here's a site that has the SAAMI cartridge specs listed and the .223 is only 55,000 psi instead of 60,000 psi.

It's harder to hit a moving target, like SAAMI specs! :eek:

Fred M · « **Reply #10 on:** December 27, 2004, 08:14:18 PM »

Donaldo and Paul.
The various reportings of pressure is quite understandable. No two pressure guns. chamber, bores. grooves are the same and will not produce the same readings. Nor will they produce the same signs of pressure on a case. Operators have good inspection apparatus and will report pressures in line with their findings. They are not about to stick their neck out.

So 5000psi difference is quite normal and is in the range of 10%. Perhaps you will remember that I have talked about that before. As a handloader you have to be able to read pressure signs and interpret them. They can be quite different in a Handi because of the flex in the action.

What may be perceived as pressure may not be be a pressure problem at all. There should be no attempt in reaching bolt action velocities or loads.