Reducing SD by trying different powders and primers in 223AI

[DHD]

How many places do they pay out for best chrono numbers at your local matches?

It should be a side match. The bullet has to hit the target, 10 shots, with extra points if you have receipts for all of the equipment you bought to get there, and group size as the last and lowest points added.

Not being serious!

 

[Dwubyd]

Update: The bedding did not make an apparent difference.

Paying attention to bushing and mandrel sizes seems to have reduced ES to 25-30 for 5 shot groups. That is actually quite an improvement. I am sizing the necks in two steps: 249 then 245 followed by a 2215 mandrel. I found that if I sized a fired case down to 245, the neck came out flared. Out of a 245 bushing it would be 242 in the narrowest part of the neck (the middle) and 244 at the flared end. Weird. I did some research and this occasionally happens when you size the neck down too far in one step. I am starting at 255, so sizing to 245 is 0.010" and apparently that is too far. I don't know whether the flaring was happening before - I never noticed it.

Next I am trying a hotter load: 26.0 grains 2206H for 2980fps. I will test seating depth and see if I can get some good groups.

At some stage I will give up and get a new barrel. Not sure whether to stay with 223 Ackley or move to 6 Dasher. The move would mean new dies, brass and bolt. At this stage I am leaning towards staying with 223AI even though 6 Dasher is the go to calibre for PRS, and for good reason.

 

[Dwubyd]

The seating depth test worked okay, but it looks like there are more significant factors than seating depth that are affecting accuracy.

I did have some success with reducing SDs. SDs for 4-5 shot groups are mostly in the 10-15 range with some well below 10.

The steps that helped were:
1. Sort out the right bushing sizes, mandrel sizes and sizing process
2. I weight sorted cases, but after testing I have concluded that it is sufficient to eliminate very heavy or very light cases.
3. My testing suggests that having a long case length such that the neck comes too close to where the carbon ring would form increases SD. Slightly shorter cases gave lower SDs. I am not convinced on this one. Just a suspicion.

My other conclusion is that the barrel is done. I am never going to get good accuracy out of it. Off to the gunsmith it goes!