I don't know why I love this debate, but...
Maybe it's because I thoroughly enjoy big bore revolvers, and these two cartridges in particular. Both are fine performers, and offer a lot of flexibility for a wide range of uses.
It seems that everyone has their own ideas as to how these two should be compared, so for what it is worth, here is my take.
A few posts have touched on some of what I will cover, but have also failed to address the subject in full. First, what to compare? Factory loads only? Handloads for Rugers and similar? Five shot guns, or only six shooters? IMHO, if what we really want to compare is only the cartridges themselves, the only fair way to do that is to assume that each gun is capable of safely handling the maximum pressure that the cartridge case can safely handle. If you do otherwise, all you are really doing is comparing the strength of the guns, not the performance envelope of the two cartridges.
If this is the comparison to be made, I think you would be hard pressed to show that the .44 has any advantage at all. The .45 enjoys more case capacity, and a bullet with a larger surface area for pressure to work with. This is important because an increase in pressure does not give a linear increase in velocity. In other words, increasing pressure by "X" amount, will not always yield a velocity increase of "Y". However, by increasing the area on which pressure acts, you always get a predictable and linear increase in work capacity, or force. Pressure x area= total force. Exert more force, and you get more work done. No exceptions. Thus, the .45 can produce more gas volume (larger case capacity) to drive the bullet down the bore, and that gas is pushing on a surface area that is roughly 10 1/2% more than the .44. I don't see any way that the .44 can overcome this advantage except by exceeding the pressure of the .45 by at least 10%.
So, which case is stronger? That's a good question, that so far, I have not found an answer to. Although, another poster did provide a link to information on .45 Colt 5 shot loads that exceed 50,000psi. I have cut open several cases, both .44 and .45, and taken careful measurements of all dimensions that I could. This was done using and optical comparator, and what I found was that I could not find any significant difference in most brands of brass. I have the data here somewhere, but not sure where just now. I will post it if I can come up with it in my mess of ancient notes and data. This leads me to believe that the cases themselves are capable of containing similar amounts of pressure.
John Linebaugh uses a load generating 59,000psi (verified in a Hornady test barrel)for proof testing. This is for his five shot guns, and is certainly beyond what would be safe in any six shooter of either caliber. Suffice it to say, that either cartridge will probably handle more pressure than any sane reloader is willing to attempt. Can you load the .44 to 10% more pressure than the .45 case will handle? Maybe, but I'm not willing to find out.
Now, for those that want to compare the two cartridges in the same gun, say a Ruger Blackhawk; John Linebaugh has written an excellent article in which he has done exactly that. It can be found here
http://www.customsixguns.com/writings/heavyweight_bullets.htm
here is a quote from the above article
Whatever the .44 Magnum will do, the .45 Colt will do with roughly 1/2 the barrel length, pressures being nearly identical. From the limited pressure testing we have done, we have found that whatever the .44 Magnum will do, the .45 Colt will duplicate with about 5,000 psi less pressure. This is with standard bullet weights. As the slugs get heavier the gap widens.
If you choose to read the article, you will find that this conclusion was reached after testing guns in both calibers to the point of structural failure, and then assembling hand loads that maintained a 100% safety margin for the respective failure pressure. In other words, they were both loaded to 50% of the pressure that resulted in the firearms failure to contain the pressure. The .45 won out. Could you have increased the pressure in one over the other? Sure, but then you have decreased the safety margin for one, but not the other, and made it a skewed comparison.
Having said all that, I still don't load my .45s to this level of performance. Neither do I load my .44s to their full potential either. When I need more performance, I step up to a larger caliber, with a heavier bullet, that is loaded short of it's full potential as well. I have found this to be easier on the shooter, and just as deadly on the game pursued. .357 not enough? Reach for a moderately loaded .44. Still not enough? grab the .45. Need more still? Break out the .475. More yet? REALLY?! What the hell are you hunting?
I'm glad that I don't have to choose only one caliber, but if I did, I would b hard pressed to make the choice between the .45 and the .475. The .44, while a fine cartridge, just doesn't have the flexibility of the larger calibers. Given the choice between a .44 and a .45, I'll take the .45. But, I wouldn't throw stones at the .44 either!
JW
I would give more credence to writers such as Ross Seyfried, who has probably done more heavy load work with the .45 Colt than anyone.