Chronograph results, need input please

bpost

March 01, 2006 15:34

OK, I have been working on the loads for my 6BR Encore, 19.5" Bullberry barrel.

The best accuracy load I've found so far is 70 gr bal tips with 31.3 of Varget.

Here are the results of that load;

2940FPS avg
19.95 ES
8.88 SD

Groups hover about .3

Now trying to get more speed here is what I have;
31.9 varget 70 nosler match HP.

3022 FPS avg.
45.46 ES
17.29 SD

Group was .4-.5

Why is the SD and ES climbing?

I have some loaded with 75 V-MAXES for tomorrows testing and I went up to 32.2 with the nosler 70 Bal. Tips.

Then it will be testing with N-133.

This is fun! A plus is I have not shot the chronograph; yet.

0

• 

  JustC

  March 01, 2006 16:09

  The reason your chrono numbers i.e. "reality" are growing is because you have progressed past a harmonic point. If this load is close to max, then that is the top you will get from that load/barrel combo. If it is a low-to-mid range charge, then you can continue up the ladder and will most likely find a harmonic point at a higher MV as well, with the same great numbers. Your first load numbers are great,..match worthy[8D]

  0
• 

  nononsense

  March 02, 2006 05:07

  bpost1958,
  
  JustC has you pointed in the right direction as far as harmonics is concerned. Your accuracy isn't necessarily falling off in huge amounts but your numbers are indicating that you're getting further away from the node. As you increase or decrease the powder charge, the numbers and sometimes the groups, look like a sine wave.
  
  
  
  What we look for is the load that produces the most consistant internal ballistics so that the bullet leaves the muzzle at the same place and the same time. In essence, it vibrates the same each time you pull the trigger. The changes are usually brought about by differences in the charge weight when tuning but can obviously be affected by any change in components, barrel length and barrel diameter.
  
  
  
  As the benchrest folks have taught us, short, thick barrels have wider tuning nodes than the longer, skinny barrels do.
  
  This is a good article for reading on load development:
  
  http://www.frfrogspad.com/loaddev.htm
  
  The other thing to take into consideration here is that your loads that are producing fine accuracy are at the lower end of the pressure scale in your project. As you increase the charge weight, you're starting up the curve away from the lower node but progressing towards another node higher up in the pressure scale. I think you'll see that if you continue with the Varget tests. But, again I will say that the Varget won't give you the cleanliness and efficiency of the N-133 powder. 'Nuff of that.
  
  Please keep us posted on the tests, they're getting interesting and should provide us with some good information.
  
  Thanks!
  
  Best.

  0
• 

  Reddot47

  March 05, 2006 23:01

  Fantastic post!

  0

Please sign in to leave a comment.