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# Fast and slow barrels (or is it chambers)?

#8
10-18-2004, 01:34 PM
 Writers Guild Join Date: Jul 2001 Posts: 1,459
Re: Fast and slow barrels (or is it chambers)?

Dave, interesting tests. If someone wanted to really see differences, this is how I would structure the experiment.

Talk to the barrel maker to make a 40 to 44" barrel. Cut in half to make two barrels of identical finished length. Probably as close to identical as we are likely to get.

Not cut the chambers you want. Test and see what you get with similar chamber pressures. Amount of powder and type of powder burned will make a difference. So reference to a pressure curve and muzzle pressure would also need to be analyzed and compensated for.

What I mean is that if one is a min spec chamber and uses 44gr of Varget compared to a max chamber that uses 46gr of Varget to get the same chamber pressure (same throat and leade dimensions), it would be assumed that the larger volume chamber/case would give the higher vel. Cases would be fireformed.

If using identically sized cases, there will be an error as some energy is spent expanding the small case in the larger chamber.

The vel would have to be adjusted for the difference in powder volume, etc. My guess is that once all numbers are corrected, you will get the same performance within the measuring error. There is no free lunch. Same energy into a system will give the same results.

Repeat but use the same reamer and two different barrels from the same manf. Compare that. I bet that the vel will be different. The pressure data will pretty much tell the tale.

Right now, there are just too many variables to conclude anything.

I believe that fast and slow barrels do exist. However, these barrels are not readily predictable. The same maker will make barrels that vary.

Or else, all barrels would be ...the same.

Jerry
#9
10-22-2004, 07:40 PM
 Bronze Member Join Date: Apr 2002 Location: Whittemore, MI Posts: 37
Re: Fast and slow barrels (or is it chambers)?

Dave
Another variable not often thought of is the throat/freebore area of the chamber.
Had one that was .004 (yep, 4 thou) over bullet diameter, 30-06 26" MV was 2725.
Shortend the barrel 1" and recut the chamber/throat to "min Sammi" and the MV went to 2950 with the same lot of reloads.

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