223 Load Ladder Head Scratcher

[Fishinfiend]

I did a load ladder today with my 223 which was using Reloader 15 and Rem 7.5 primers. Can anyone try to explain this to me?

I was using a Prochrono Chronograph and us ing a pair of flashlights for lighting starting on 22.6 grains NATO.

Thanks for the help in advance.

 

[supercorndogs]

You are probably going to have to explain, "what you want explained." If it is inconsistent reading from your prochrono, that is to be expected.

 

[Fishinfiend]

First thing I am wondering about is the 100+ fps change from one side to the other. Second why does the velocity increases then drops then goes up and drops again?

Also, all shots were with in an hour starting with the low charge NATO and going to the top with that then doing the STD in the same order.

 

[gunsnjeeps]

Are those group averages, individual shots, what load, what bullet, what rifle, brass prep, same brass or mixed brass?

Trend is increasing velocity. Could be chrono reading and variations in loads. I don't see that big of a swing on my ProChrono but I wouldn't doubt a combination of both.

 

[Howland]

How many shots at each charge weight? If only two, it's not really enough data points to draw any conclusions. Do the two columns represent two different projectiles?

Assuming no other variables are variating, one explanation might be that you are reaching the point where the excess powder is not being burned until the projectile has left the barrel - that is until you start hitting excessive pressure.

I'm not familiar with that powder and have limited experience with .223. Also, you don't indicate what bullet weight. Perhaps someone with experience with Reloader 15 will weigh in. What does your manual list for start and maximum charge weight?

 

[Fishinfiend]

It is one shot at each charge weight two different grasses everything else is the same.

The bullet is Nosler Custom Competition 77gr HPBT.

All the shots were shot out of a 700P with 26" barrel.

I went through some of my older chrono data (unly up to 22 gr.) and the velocities somewhat matched the STD numbers. So, would you toss out the NATO group numbers?

Alliant says 24.1 and Nosler states 24.0 for Max.

 

[Howland]

A sample of one won't give you useful information. It is more likely to throw you off track.

If you did a group of five - ten would be better - at each charge weight and took the average of each group, you would likely see a steady increase upward as you increase the charge until you begin to approach the point of dangerous pressure. On the other hand, the first sign could be a very loud Boom with scattered parts. Velocity is not really what you look for with the chronograph. You're really looking to measure the variability of velocity.

What you are probably seeing is that normal upward progression but with a high standard deviation. It might be that the bullet / powder combination just isn't the best but for all I know it might be the combination of choice of shooters much better than I. It could also be some other variability. Uniformity is key to accuracy.

One variable is two different brass headstamps. Also, military brass usually is thicker, meaning less case volume, meaning you can reach maximum safe pressure with a lower powder charge. The brass on the right has 5.56x45 on the headstamps. That doesn't mean it is a military brass, but it could be.

 

[Fishinfiend]

The one I call NATO has the cross in it directly across from the words.

With that powder I would have a nice SD one 5 round groups then the next it would be bad, so I was trying to find a velocity node.

Also, I don't want my gun to go boom, but I do wear Oakley Shooting Glasses just in case.

 

[Howland]

I used to do Measurement System Analysis when I worked for an automotive supplier. A standard deviation calculated from a sample size of 5 is not really valid. They preached a minimum sample size of 30 for a valid calculation. It would not be unusual at all for one sd to be small and the next large with sample sizes of 5. I don't think anyone uses thirty rounds at each charge weight, though. I would use 5 and carefully put them on target and measure group size. When I found the range of tight group size, then I would load groups of ten to find the exact charge. Once I'd done that it was time to experiment with seating depth.

What is really important is the group size. With every load I worked up group size would shrink as I increased the charge until I would get to a point they started to open up. At that point I pulled all remaining test rounds because I had already found my optimum charge weight. I had absolutely no interest in finding out what happens beyond that point. Doing that kept me from seeing signs of high pressure.

 

[gunsnjeeps]

I'm not sure about 30 round samples, but 5 rounds will get you close. I typically load 5 per charge at an increment to test to start with then 10 of the what looked good and 5 a tenth of a grain either way to check. I'm copying the NATO/STD designations. I missed RE15 for powder. Not to just throw out conventional wisdom but a 77 with 24 grains of RE15 or Varget is a fairly common load. Brass may move you a tenth or so one way or the other.

To share chrono experience, I was working up a .45 ACP load with Green Dot and loaded them by .1 grain. The velocity of the groups over lapped highs and lows but had a definite change in average at each load.

 

[spife7980]

It goes up incrementally but your reloading practices aren't good enough to have them all be at the exact velocity so as said before, it's going to have some over lap in individual numbers but trends up.

If if you're wondering why two different types of brass give different velocities then it's because it's two different types of brass. This is why it's important to pass along all info when relating reloading information. One charge in one could be way too much in another.

Also, this isn't a ladder test. Where's your target board? Read what that tells you first because that's what you're interested in. How it shoots.

 

[Fishinfiend]

Thanks for all the replys so far.

Now I just looked up the specs for the Prochrono and it says +/- 1% and with my calculations that is 25 fps if the bullet is traveling 2500 fps.

So, am I correct to assume that in theory a 5 shot group with a max spread 50 fps could actually 0 fps?

 

[spife7980]

Theoretically but not realistically.

 

[demonjigger]

look at the 10 shot load development video by the 6.5 guys and Scott Satterlee on YouTube. It might help you. I would say try 5 at 23.6 grains... good luck