223 load results question

[AK Eggy]

Last winter I loaded some 223 with 55 gr. FMJ BT. I trimmed all the cases to the same length (1.755") and loaded to the same overal length (2.223"). I crimped all of the rounds without moving the die at all and I charged with Varget from 23 gr. to 26 gr. in .5 gr. intervals.

I was able yo use a chrongraph this weekend so I took these rounds with me. I shot 5 rounds of each powder charge through the chronograph from a bench with the rifle on a rest. As I shot, the velocity increased roughly 100 fps over the previous powder charge (again, .5 grain increments between charges). Then I got to 25.5 grains of powder charge and the velocity jumped about 400 fps. That surprised me, but OK...I guess that's OK. Then I shot the rounds with 26 grains of powder and velocity dropped about 150 fps. 26 grains was the max. load in the book I was working with, so I stopped there.

So my question is...Is that a normal finding...A "large" velocity jump, then a decline with the next larger charge? I haven't noticed that before with handgun loads, but then again I was using a rented chronograph and the numbers weren't very consistent for the handgun stuff and this weekend the numbers I was gettin were much more consistent.

 

[steve4102]

My guess it was just a "false" reading due to something like sun light, muzzle blast etc.

 

[JimKirk]

The only way to know for sure ... is to run the test again, maybe under different light conditions. I would shoot some factory rounds(control) to get an idea and then compare to the results you are getting. I mean if you get 3000 fps average out of a test group of factory, then you get 2600 fps out the lowest load and then 3000 fps or a close number from the suspect load ... then you'll know.

I would suspect the light on the chronograph as to what that is giving the +/- results.

Jimmy K

 

[AK Eggy]

More info

Thanks for the suggestions.

I did measure 3 different factory loads (again, a string of 5 to get an average). They were all 55 gr. FMJ BT projectiles as were my reloads. Here is the average velocity for a string of 5 rounds for each powder load. Chorograph was about 10' away from the muzzle. It was a completely clear day and I had the diffusers installed.

There was a large caliber gun a couple of spots over that would throw an error code on my chronometer when he fired, but I realized that pretty quickly (I had someone watch the readout while I was shooting) and removed those readings from the string before calculating the averages.

Brand #1---3076.2
Brand #2---2928.8
Brand #3---3864.0

Reloads
23 gr.----2430.4
23.5 gr.--2502.2
24 gr.----2577.2
24.5 gr.--2641.6
25 gr.----2754.2
25.5 gr.--3162.4
26 gr.----2982.8

There was a noticeable difference in the feel of the rifle when firing the 25.5 gr. load. A more crisp, more defined feel to the action (semi-auto rifle). This feel was consistent through all of the rounds charged with the 25.5 gr.

Thanks again, and in advance, for everyone's input.

 

[ssyoumans]

Seems like you got your loads reversed on the loading block? Have you loaded up a second batch of reloads? I haven't seen that behavior with Varget, TAC, BLC-2 or W748.

 

[cougar1717]

Your 26.0 gr. data appears to be an anomaly since it is a "knee" in your data if you plot it. The problem is, you've already said that the chrono is suspect and you've only tested 5 data points at this loading. The most important thing is that five data points at 26.0gr are not enough to draw any sort of conclusion about that load. If you're content with the 25.5gr, use it and happy shooting. If you desire to work it up again, you would need at least two groups of five for each loading to have something to analyze. It would also be desirable to use two chronographs to check the values.

 

[AK Eggy]

ssyoumans...I thought about that and when I came back home I took a bullet from each of the containers (25.5 and 26 gr.) and took them apart to re-weigh the powder...They were labeled correctly.

cougar1717...Sorry, I meant to say the chronograph I was renting from the range before I used this one was not giving me the numbers I expected and there was a large spread in the measured velocities for like loaded rounds from the chronograph I rented. I didn't shoot for accuracy when running these rounds, so I don't know which one shoots better, I was just playing with the chronograph and seeing how my loads compared to factory. I just noticed the more "crisp" feel of the rifle when I fired the 25.5 gr. loads and when I looked at the numbers (someone else was recording them for me...I couldn't see the read-out from where I was shooting), I was surprised to see the big jump.

Just today I started putting my table back together so I'll have a chance to put some more rounds together so maybe I'll get a chance to try again before it gets too cold.

 

[NCsmitty]

Brand #1---3076.2
Brand #2---2928.8
Brand #3---3864.0

Is #3 a typo or the real deal?

I use 15ft from the muzzle to avoid muzzle blast giving erratic readings.



NCsmitty

 

[AK Eggy]

oops

yep...typo. But it is still higher at 3364.0. Sorry 'bout that.

 

[m33p0n3]

It really doesn't explain the decrease at 26, but around that charge (25.5 grain) is where some manuals start calling for a compressed load with Varget. I'm still really new to reloading rifle, so I'm just throwing it out as a possible explanation.