CHP 7 Expansion of Ideas

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RBinAR

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8) Today I?m going to mention what happens in a number of cased rounds. Normally cased loads don?t translate to smokeless muzzle loading very well but if you will bear with me there are some ideas that we can eventually put to use.

The first idea I?d like to discuss is called ?expansion ratio? in a technical sense it?s defined as the chamber volume plus the barrel volume divided by the chamber volume. That?s a lot of volumes isn?t it? Fortunately it can be expressed simply but with a few more words.

The best way to understand this is to compare cases that shoot similar amounts of powder with different caliber bullets. That?s easy to do because people like to stick with a well known type of case. A 30-06 case for instance is often adapted to shoot bullets in .257, .277, .284, .308, .338, .358 and .375 caliber (I could have left one out). If you use a bullet that is the same sectional density (SD) you get a good comparison of what happens to a load when you change the bullet caliber.

In the 25-06 and 270 Winchester the powders used to shoot our bullet (SD = .26 or 120 and 140 grains) are very slow burning the slowest of which is Retumbo and H1000. Retumbo and H1000 are slow burning big magnum powders. If you go to a larger caliber such as the 280 Remington or 30-06 faster powders like H4831 and H4350 are needed to reach maximum pressure for the case capacity. If you go to a still larger bullet like the 338-06 and 35 Whelen even faster powder must be used such as Varget and BL-C(2).

All the cases listed have the same capacity and the bigger bullets are heavier but as the caliber grows the powder burning speed must speed up. It sounds contradictory doesn?t it: bigger bullet, faster powder? That?s expansion ratio. Simply put it means a bigger caliber bore has more space. When you turn gun powder to gas a lot of things determine the pressure but none is more important than how much space the gas has to expand into. With a larger space you need a faster powder to maintain pressure even if the bullet is heavier.
expand-copy.jpg

If you put the same amount of pressurized gas in each container the smaller container would have a higher pressure. If you put the same amount of gas in two barrels the smaller diameter will have a higher pressure.

In modern shooting this is fairly well understood by most shooters up to about a 45 caliber bore. But did you ever notice most reloading manuals don?t have a rifle caliber bigger than 45? So there are few who have shot and understand how expansion applies all the way up to 50 caliber and above.

In 50 caliber slow burning powders are almost unheard of except if you shoot tremendous energies. You will find them in 50 BMG shooting but I think a bullet with a SD of .411 and shooting to 13,000fpe qualifies as tremendous energy. In any normal load such as the 50 Alaskan (shooting 4000fpe) a faster powder such as H-4198 would be normal.

Another quality of a case is ?engraving pressure? I have spoken of this before so let?s just say it takes some extra energy to force a bullet into the barrel?s shape. When you load a bullet from the muzzle you don?t have that extra energy so an even faster powder would suffice as in a case.

When you see how different a 50 caliber rifle is compared to others it should be no surprise when early 10ML load developers thought there was no chance to shoot powder that was slower than pistol caliber speed. I can still remember hearing reports of shooters trying Imr and H-4198 well into the 50 grain levels and still having a load slower than BP speeds.

If it?s hard to make pressure because you have a giant expansion ratio and no engraving pressure that will happen but it did not mean 4198s were useless. It meant we didn?t know how to use them.

As time rolled on it was soon discovered that trying to use a small or moderate amount powder was not possible with normal propellants. Someone had to try moving up to a useful range. I was schooled enough to know what should happen as I first tried it but because of the unknown and prevailing fear of the day I still shot the loads from my safety rest. That allowed me to be several yards from the rifle at ignition.

With time it was soon learned that several powders of slightly different burning speed would shoot to a useful pressure if enough powder was used. Today you will hear of at least 8 to 10 different powders shooters are having good results with depending on how heavy a bullet and how fast they prefer to shoot.

Still, I always wondered if there was not a way to overcome the extra large expansion area of the 50 caliber barrel. One day the answer occurred to me but I wasn?t trying to develop a load or understand powder burning speed I was trying to shoot a 40 caliber bullet in a 50 caliber bore.

Trying to shoot a small bullet in a big sabot is difficult, far more difficult than accounting for the 50 caliber expansion ratio. I was so determined I was ready to try extraordinary measures (like reinforcing sabots and special sabot plastic formulas) to get it accomplished. Yet all I accomplished was the establishment of ?Rick?s Rule?: a bullet less than .060? the size of the bore is extremely difficult to shoot accurately at speed in a sabot.

With my disappointment came the answer: use a bore that?s close to the size of the bullet to work. It was time to begin experimenting with a 45 caliber smokeless muzzle loader. Sure enough, the results were excellent as the bullet was now well inside of the .060? diameter limit but something else happened that it took time to understand.

The loads for a 212 grain bullet (count the sabot) were much more like those listed for light weight bullets of a 45 caliber rifle than expected. That was the case for two reasons, a 212 grain bullet is not terribly far from the normal lightest weight bullet used in the caliber (250 grains) and the 45 caliber has a lot less expansion so it is much easier to make pressure.
4550-copy.jpg

54 to 58 grains of H-4198 shoots such low pressure it's nearly useless with either the 300 (left) or 250 grain (center) common sabot-ed bullets in 50 caliber. However the 200 grain (right) bullet shoots very well with that amount in 45 caliber reaching 2600+fps at the top load.

Powder choices for the 45 caliber smokeless muzzle are not much different for a standard 45 case such as the 450 Marlin. We still have no engraving pressure so they are not exact but it?s very close. So a load of 55 to 65 grains of powder in the 45 caliber barrel shoots to a very useful pressure and speed just as the 60 grain case capacity (45 Marlin again) of a 45 caliber rifle. Besides that powder selection is the same (H322 or H-4198).

All was good in the world. We were able to shoot a light weight bullet to a very good speed (2600+fps) with an understandable powder charge. However discovery would not allow for relaxation.

Some of my best ideas are copies. I would have to say what happened next was total plagiarism. I saw that some were using jacketed bullets in a muzzle loader without a sabot. Henry and Bill Ball did this before I owned a smokeless muzzle loader and Bad Bull rifles beat me to it also. All I did was realize it could be done without shooters having to resize their bullets. Since we are mostly lazy so called sabot-less shooting was doomed to obscurity (and may still be) until some one could come up with a bullet you can buy and load. Thankfully the Parkers at Parker Bullets were well ahead of the curve.

With the Parker Hydracon and Ballistic Extreme bullet 45 shooters can simply put in the powder insert a wad, bullet, ram it all home and shoot. It?s as simple (if not easier) as a sabot and pistol bullet.

The Parker bullets weigh 250, 275, or 300 grains. Those weights are all normal light weight models that are shot in this caliber. With the extra weight and smaller expansion area of the 45 loads can now perfectly mirror data published for a cased round. Bullet speeds are slightly lower (no engraving pressure again) but not by much so almost perfect correlation is achieved. Now we are back to shooting real rifle powder in realistic amounts.

The 45 caliber may not be the smallest available. Things may still have some ways to go in development stages but that is next time. I have to save some space for another chapter.
 

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