“Finding That Node”

 

This Week’s Tips or Tricks…

 

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Note: all below CBTO measurements noted were taken using a Hornady Bullet Comparator attached to a Hornady Dial Caliper as shown below.  Please also note that for all CBTO values documented below, I would also need to subtract 1.0035” from every CBTO measurement to get the corrected CBTO length.

 

Example: I measured CBTO with the Hornady Bullet Comparator attached to the Hornady Dial Caliper and noted the value as 2.8250”.  To find the length that you will need to subtract for your particular tool to get corrected CBTO, close the Dial Caliper jaws all the way down with the Bullet Comparator Tool and the correct size comparator inserted and document the value of the Dial Caliper when fully closed, in the case of my particular tool this value was 1.0035” when fully closed.  So to find corrected CBTO I would then calculate 2.8250” – 1.0035” = 1.8215” CBTO.  If you are using a digital caliper, simply close the jaws and press the ‘Zero’ button on your calipers to achieve your corrected CBTO.

 

 

                    

 

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Q:  What is a “node” and how do I find it???

 

A:  A “node” or “sweet spot” is the right combination of bullet weight, powder charge, and velocity that your rifle or handgun likes the best…hence the ”sweet spot”.  So why not just call it the “sweet spot” then, what does a “node” have to do with anything???  OK, rather than try to explain this in some complicated way, I’m going to explain it to you in a way you are sure to understand.  The back straps and tenderloins are the “nodes” that you look for on your harvested deer, elk, moose, etc.  These meats both have different characteristics and come from different areas of the animal, but because the tenderloins may be your favorite…the tenderloins are your “sweet spot”.  So let’s take this concept and apply it to your reloads.  Your firearm may have multiple “nodes” or sweeter spots, but because there can only be one true “sweet spot” we use the term “nodes” to describe multiple weights, charges, and velocities in which your firearm will perform the best and most accurately at.

 

For example, I fired a series of (14) strings of different loads (5 shot groupings each) with varying seating depths and Hodgdon H4895 powder charge weights and here were the results for the same common bullet weight of 77 grains:

 

Shooting String                       ES                    CBTO                           Charge             Node - ?

Group A – String #1                1-5/16”            2.825”             @         20.0 gr.            No

Group A – String #2                1-1/8”              2.835”             @         20.0 gr.            No

Group A – String #3                1-3/8”              2.825”             @         20.5 gr.            No

Group A – String #4                1-1/2”              2.835”             @         20.5 gr.            No

Group A – String #5               9/16”               2.825”             @         21.0 gr.            YES

Group A – String #6                1-13/16”          2.835”             @         21.0 gr.            No

Group A – String #7                15/16”             2.825”             @         21.5 gr.            No

Group A – String #8                1-3/16”            2.835”             @         21.5 gr.            No

Group A – String #9               1/2”                 2.825”             @         22.0 gr.            YES

Group A – String #10              1-15/16”          2.835”             @         22.0 gr.            No

 

Group B – String #1                13/16”             2.825”             @         19.0 gr.            No

Group B – String #2                13/16”             2.835”             @         19.0 gr.            No

Group B – String #3                3/4”                 2.825”             @         19.5 gr.            No

Group B – String #4                7/8”                 2.835”             @         19.5 gr.            No

 

Now, take the above data for my Colt Competition AR with Match Grade 18” barrel, 1:8 twist, MAX CBTO of 2.836” to the lands, and shooting the 77 grain Berger OTM Tactical Bullets and you will notice I found (2) “nodes” where the firearm performed well, but there was one sweeter spot of the strings:

-Both nodes performed best at a CBTO of 2.825” having an SD of 0.316429” and ES of 7/8” whereas the CBTO of 2.835” had an SD of 0.408378 and ES of 1-1/8”.

-String #5, performed well at an Extreme Spread (ES) of just 9/16” at 100 yards with 21.0 grains of H4895…making it Node #1.

-However, String #9 performed 1/16” better coming in at an ES of just 1/2” at 100 yards with 22.0 grains of H4895…making it my Node #2, but this one was the “sweeter spot” of the two nodes for this particular test!

 

So now just (70) bullets into my box of 100, I have already found a 1/2 MOA grouping recipe setting me up for success in this rifle with (30) rounds yet to go in the same LOT!  From here, if I want to try and pursue potential improvement even farther for my rifle, I would start by backing off my seating depth with another string at 2.820” and 2.815” at 22.0 grains of H4895…but why???

 

1.)    If we compare every one of the Strings above against Seating Depth vs. Seating Depth, you will notice a pattern that all the 2.825” performed identical at worst but predominantly better than the 2.835”…so the next logical step here for the best return on my efforts and time would be to start backing off the seating depth slightly in 0.005” increments for 2-3 more strings to see if I can improve that 1/2 MOA grouping...maybe I can, maybe I can’t with this particular bullet and powder combination, but either way with 100 rounds or less I will have a complete expected DNA analysis of what my rifle can be expected to perform like with this particular bullet, charge weight, and velocity.

 

2.)    Since just going from 21.0 grains up to 21.5 grains opened up my shot grouping by 3/8” and moving from 21.5 grains up to 22.0 grains moved my shot grouping back in by 7/16”…it is pretty safe to say that by attempting to vary my powder charges in between the ranges of 21.0 grains and 22.0 grains would likely be fighting an uphill road both ways and thus a pretty safe bet that this would prove at a lost cause with little to no return or improvement!!!

 

Note: above I didn’t even factor in velocity as a variable for arriving at my best plan of attack in this particular scenario because I didn’t have a Chronograph with me.  Now why do I mention this???  I tell you this because if I had a Chronograph with me and would have been able to record each shots velocity…the velocity results alone could completely change my plan of attack outlined above and here is why…

 

1.)    Let’s say that String #9 did in fact prove to have the best Velocity SD between String #5 and String #9, my plan of attack would remain the same proceeding onward with String #9.

 

2.)    However, if the SD of the Velocity for String #5 were in fact far less than that of String #9, then I may have a better potential for greater return and improvement by moving forward with String #5 instead since the SD of the Velocity is far better, which will certainly increase my chances for greater returns and improvement in accuracy.

 

3.)    There is always option three right!  Since we now have only used up (80) of our bullets since we continued on with String #9, we could just say to hell with it and proceed with a side-by-side comparison of String #5 vs. String #9 and just see what happens…worst case scenario, we still have (4) strings left in total meaning (2) per each; however, if you proceed this way the next box of bullets you open could be from a different LOT and potentially skew your results…so just be conscious of your strategy here!!!  

 

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Do you have a Tip or Trick regarding reloading that you would like to see posted?  Please send us your Tip(s) or Trick(s) and we will see about getting them posted!

 

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Written By:  Kyle R. CEO of Broken Box R LLC

 

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