High extreme spread with h335

I know a lot of people say use Mag primers for 335. Personally I have not noticed any difference between CCI reg and CCI mag. If anything the Reg primers are a bit more consistent. I have noticed quite a bit of variance in velocity using 25.0gr of H335. I have tried mixed brass, single manufacturer brass. Very little difference. One thing I have noticed is that even with a full crimp I get slight bullet movement within the case when the cartridge goes into battery. I suspect that this movement is my biggest source of variability plus the fact that a 556 chamber has a looonnnngggg lead. Mine measures a Max OAL of about 2.37" (using 55gr campro) compared with the max for my mags of 2.27". That is a pretty big jump before the rifling. Still trying options to improve accuracy. Currently the best I seem to be able to get is about 3-4 MOA with this combination. I have tried other powders and the results have been more or less the same with most slightly worse so I really don't think the powder is the issue. Also recently tried cartridges at 2.27 OAL and 24.0gr H335. Very slight improvement in accuracy over 2.235 OAL. In the process of working up the powder charge on the longer OAL. So will see what happens. I don't really want to go above 25gr as the gun is already a bit overgassed, typical, and it gives more bullet movement at higher loads due to the higher recoil energy.
 
Questions:

1. Are you using mixed brass?
2. What type and make resizing die.
3. What is the diameter of the dies expander?
4. How much are you bumping the shoulder back?
5. Iron sights, red dot or scope?
6. Are you wet tumbling with SS media? This scrubs the inside of the case neck free of carbon/powder residue and can cause seating problems.

Below many reloaders use a Lyman type "M" expander and taper crimp their AR15 loads. Notice the expander is .003 smaller than bullet diameter and the case mouth is just bumped on to the .226 step. This allows the bullet to be seated straighter and reduces neck runout.

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The expander in my RCBS .223/5.56 dies have been polished and are .0025 smaller than bullet diameter. The smaller expanders give more bullet grip and you only need a light taper crimp to streamline the case mouth for feeding.

NOTE, Using Quickload the chamber pressure of my same load using Hornady 55 grain fmj is below 50,000 psi. Meaning you could increase the load and "may" get better groups and lower ES. I use Lake City brass and Remington 7 1/2 primers, 25 grains of H335 and my groups are smaller than yours using a red dot sight.
 
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I am using remington brass only, not mixed.

I am just using a set of lee dies. I am thinking about getting a redding but honesty I think I can get more out of the lee.

I have no idea what is the diameter of the neck expander or how much I am bumping the shoulder back. I just full length resize after every firing.

I am using a red dot as well, an eotech. Honesty I just want to have a consistent 2" group at 100 m, I am not really interested in sub moa with 55grs, I think my match kings is for that job.
 
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