Air Gap Question?

[edge]

I understand that with BP an air gap will cause a problem, but I don't get where a small gap ( bullet not quite down ) with smokeless causes this problem!

I can shoot a .458 Win Mag in a .458 Lott rifle since the Lott is the same cartridge but longer by 0.300

If I take a compressed charge of H322 ( 83 grains ), using a 300 grain bullet, I should get around 2777 fps and an estimated 50.636 psi. ( .458 Win Mag )

Now if I throw the same charge into the larger Lott case I am now only 89% of case capacity ( AIR GAP ) and get a velocity of only 2644 fps and pressure of 40,265 psi.

I don't know any situations where a compressed charge does not reach a higher pressure than a non compressed load.

Any thoughts?

edge.

[Richard]

I am sure you are aware that slow burning powders are not recommended for light, reduced velocity, loads......in general. These have been know to blow up barrels/actions. Not too common but has happened on rare occasions. This could be an area where a non-compressed load spikes the pressure.
Richard

[edge]

The way I understand that problem is that the powder ignites and when the bullet moves a short distance the pressure drops and the bullet stops and the pressure spikes as if the bullet were an obstruction.
You get a small spike and then a large spike. I have not heard of this when using the correct range of powders in a reasonably full case. Some powders specifically warn to not drop weight more than 10%.

edge.

[whyohe]

years ago i talked to hodgens about h110 for my 44mag pistol cause there where such a wide variety of min and max loads buy different bullet manufacturers books. he said you have to be careful cause if you get the load too light its (for lamens terms) explodes or pressure spikes fast rather than burnes. this powder works better under compressed loads. IMO i think it depends on the powder as to how a little air gap might effect the pressure spike.

[rbinar]

8-)I have done more than one series of tests with an air gap between the sabot and the powder. These tests were long enough in the past to be done with the 50 caliber rifle.

The only oddity I ever saw was a hang fire with a large air gap and H322. The shot was a snap wait fraction of second then boom. In all other cases the shot fired exactly as normal or did nothing. I have tried to blow this gun up in so many ways simply because I wanted to be certain.

In one of my test I loaded 70 grains of H4198 and a 300 grain bullet then started with the sabot 5 inches off the powder. Most shots were misfires but one or two out of 20 would go off. They shot with little difference than a normal shot.

I noticed that the Speer reloading manual has a section where it doubts the so called cases of "detonation" and also states it can't repeat such conditions in a lab settings.

When it appears in a post or whatever I allow for others opinion and don't comment, but I have my opinion as well.

[jims]

;Drbinar: You purposefully tried to blow one up (I am not sure if you succeeded) and I did not want to blow mine up but did. Something does not seem quite fair to me. ;D
I am glad however you have done all the testing on these smokeless poles, your research and efforts have helped us all here.

[rbinar]

Mar 31, 2009 21:15:48 GMT -5 jims said:

;Drbinar: You purposefully tried to blow one up (I am not sure if you succeeded) and I did not want to blow mine up but did. Something does not seem quite fair to me. ;D
I am glad however you have done all the testing on these smokeless poles, your research and efforts have helped us all here.

Yes I honestly have a safety rest that allows me to fire any rifle from many feet away with a string. And yes I have PURPOSELY tried to blow a 10ML to pieces MANY times.

One thing I have limited what I'd try was a load that I knew already would be outrageous (I wouldn't load 85 grains of a shot powder). All the duplex loads and many of the heavy bullet loads I've shot were first tried on the safety rest. I don't mind blowing up a $400 rifle if I can learn something that makes it worth the effort. But my fingers and toes are different.