Power chambers | Hank's Message Board

ballistic
Senior Member

Posts: 386

Power chambers Nov 20, 2023 8:44:06 GMT -5 via mobile sew and mitch like this

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Post by ballistic on Nov 20, 2023 8:44:06 GMT -5

Gents
I believe it’s not just the threads -it’s the size of the hole (I.D) diameter of the 5/8 vs the 9/16. I swapped a 9/16 to a 5/8 plug and picked up 20 fps on speeds. The primer also looked like it had less pressure on it.
I don’t have my notes with me right now on powder volumes for each plug - but I believe the plugs powder volume was 3.5-4 grains more in the 5/8 plug. That in itself provides a mini powder chamber. (Short and fat)

Combine the 5/8 plug with its larger powder chamber cut vs the 9/16 and you will see greater speeds with less pressure. Think of a centerfire magnum fat case vs the std .308 case.

I also increased the size of my powder chamber this spring. I picked up 35-40 fps and no longer use a wad. The barrel hardly has any residue when I clean it. Primers show noticeably less pressure signs. Speed deviation is better.

Would a 11/16 or larger plug (if you could fit it / you can’t) offer even less pressure - I’m absolutely sure it would.
Just something to think about as well as the thread size comparisons

Last Edit: Nov 20, 2023 8:47:47 GMT -5 by ballistic

Hank
Administrator

Posts: 2,806

Power chambers Nov 20, 2023 9:05:08 GMT -5 sew, cajunnavy337, and 2 more like this

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Post by Hank on Nov 20, 2023 9:05:08 GMT -5

It is not the shear strength of the threads we need to worry about, both plugs will hold more pressure than the barrel will. I’ve seen several barrels completely explode; I've never seen a plug stripped of its threads. What we need to be looking at is the overall minor diameter. On the 9/16 plug it is approx. .500 on the 5/8 plug it is approx. .540 subtract .250 from these and then divide into half and you have a wall thickness of .125 on the 9/16 plug and .145 on the 5/8 plug. Yes, this is only a .020 difference, but that will make a big difference in shear strength. I have seen both plugs separate at the head, but I see more of the 9/16 plugs do this than the 5/8 plug. Not to mention, if you put in a powder chamber (even a small one) the 5/8 diameter powder chamber will produce less pressure than the 9/16 powder chamber will.

mitch
Junior Member

Posts: 90

Power chambers Nov 20, 2023 9:06:21 GMT -5 via mobile sew and ballistic like this

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Post by mitch on Nov 20, 2023 9:06:21 GMT -5

Sure thing Ballistic, and good points. When I get a chance to run some numbers on the thread strength I’ll be doing the comparisons in the basis of EQUALL PRESSURE (sorry for all caps, would have bolder but can’t figure out how to do that on my phone haha) for consistency, but that will ignore whether different systems generate the same pressure or not.

I’m taking baby steps, one thing at a time ;-)

hillbill
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Posts: 4,144

Power chambers Nov 20, 2023 9:59:38 GMT -5 via mobile sew, ballistic, and 1 more like this

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Post by hillbill on Nov 20, 2023 9:59:38 GMT -5

Also keep in mind a powder chamber with the 9/16 plug in a .45 bore is a waste of time due to drill size, you’re gaining almost nothing
Yes you could use a boring bar to cut the chamber in front of the plug bore but?
I’ve used several 9/16 plugs and all have been for break actions or a smaller shank .40 cal