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Discussion Starter #1
I'm pondering the  benefits or lack of benefits as it relates to using a slow burning powder or a fast, if both would give me the same velocity.
These figures are pulled out of the air and have no basis in reality.
If I were to load my 45-70 with Unique and achieved a velocity of 1300 fps and I could do the same with a much larger quanity IMR 5010 for the same velocity, is there an advantage to using one over the other, aside from cost? To make it more specific lets say they both shoot into one inch at 100 meters.
Jim
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I am probably not the most informed person to comment on this but...

There are several very good resons for using the bulkier powder. Powder position at the moment of ignition is important for shot to shot consistancy. This will result in lower extreme spreads in your velocity readings.

With some powders reduced loads are considered dangerous. I have been doing a lot of thinking about the post from IDShooter on the ignition problems with what apear to be starting loads with IMR 4350. (i am not familure with loading for the 300 Rem Ultra Mag). Ignition problems can result from powder position with slow burning powders.

Charles Petty had a very interesting article in Handloader a few years ago about the"solving" of the "SEE", Sudden Explosion Effect by PMC. PMC experianced a huge pressure spike due to a bullet stopping in the throat of a 6.5 X 55 cartridge.

I would be very worried if I had any cartridge with ignition problems.

Back to the subject, slower powders can also cause an increase in muzzle pressure, the pressure at the muzzle when the bullet exits, this can increase velocity while actualy decresing chamber pressure.

Interestingly,  most powder charges are 90% consumed in the first two to three inches of bullet travel. Think about that. Peak pressure does not last long with any powder. Lloyd brownells series of articles in Handloader years ago were compiled into a book called Firearms Pressure Factors (I think) by Wolfe Publishing), You can probably get it on an interLibrary loan, good book.

Muzzle pressure is just as important a consideration in choosing the correct powder for your application as is breech pressure. This can be verified by looking at the load recommendations for contenders chambered for rifle calibers. The loads generating the highest velocities usualy require the traditional rifle powders rather than the fast pistol powders.
The reason, in my opinion, that many beginners have trouble with cast bullets is that they are using fast powders in big cartridge cases, and they experiance leading. A starting load for jacketed bullets would probably have given better results.

I'm sure there are people here with more experiance than I have on this very interesting subject. This is an important area of disscussion for the short barreled Guide Guns and Timber rifles.
 

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arky: when you say they both shoot into one inch you take away the one variable that really keeps us looking for select loads. At the velocity level you are referring to there are a number ofways to get there. With the fast burners a loader has to use a great deal of caution to ensure that the powder charge isn't accidentally doubled. Every case needs to inspected and the charge depth in the case should be physically measured. Some fast burners are position sensitive so inert fillers are sometimes required to keep the powder at the rear of the case or the rifle may have to be tipped up in the air before shooting. There has been all kinds of discussion on the merits/hazards of fillers, particularly various fibers such as dacron or poly batt. I've used most of them without problems but you hear stories of ringed chambers etc. from improper method of use.
So. at 1300 economy almost dictates using the fast burners given equal target results. Other considerations may have to be included in your loading processes to make it actually happen though and to prevent accidents.
A powder which does not require fillers is Accurate's 5744. My dealer has not been able to find a wholesaler in B.C. who is stocking it however.
 

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Discussion Starter #4
I'm mostly curious about the internal ballistics for the difference.
Does the fast powder cause the bullet to upset faster and obdurate with a better gas seal. Does the slower powder's gas more gently get the bullet moving down the barrel?
I've used Unique to make spitball loads for the 45-70, with 255 grain 45 Colt cast bullets. These loads did right well out to 50 yards, and had the recoil and report of a 22 RF.
Maybe better put.....
Lets say we have two powders both fill the case to the base of the bullet. One is a fast burning powder and the other is slow burning. They both accelerate the bullet to 1300 fps and both give the same accuarcy. Is there any advantage to having a powder that accelerates the bullet to the 1300 in the first 6 inches of barrel or does the powder who achieves the same velocity in the full 24 inches of barrel.
Jim
 

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arky: I think I see what you're getting at although a case full of a fast burner would/could be a blow -up happening but I think you know that. Well I can't prove it but for a rifle I would prefer one that develops its pressure slower and maintains it all the way down the spout. My feeling is that this is easier on a cast bullet in terms of maintaining tight land to bullet tolerances. As I generally use gas checks I think the obturation aspect is minimal  especially if hardened bullets are used.  Most shooters prefer their cast bullets to be slightly larger than bore size as well so there doesn't seem much room to get things much tighter. With a plain base or hollow base bullet of softer metal such as may be used in a revolver or target pistol (or even a rifle at low velocities) the opposite may be the case if in fact the difference is measurable as far as powders go.  The effect may be of most benefit as it enters the forcing cone in keeping blow by minimized. Perhaps Marshall can enlighten us a bit on this.  I must admit to not previously giving the subject much thought and zero objective testing. Probably have had a preconcieved notion of what would be right and went from there. (ignorance is not necessarily bliss) besto.
 

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Arky,
    I don't know about your hypothetical situation, but here is a real-world one. In my SBH, I have used the Hornady swaged lead SWC with AA#2 and AA#5. When I use each powder to push that bullet to +/- 850 fps, the load using AA#2 leads and the load using AA#5 does not. #2 is very fast, #5 is medium fast. So obviously the powder speed affects the bullet base differently. Hope you can extrapolate this information to figure out your puzzle.                                IDShooter
 
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