Case Capacity and grouping.

[Treeman]

I have been really battling with grouping on 2 calibres I am do load development for. Now I am one of those guys that always ends up paying more because I tried to save money, doing twice because i rushed first time. Not getting it right because I hate wasting and recycle and reuse.

So I have brand new brass and I have in use brass and some left over brass that came from seller with the rifle. Now I do not want to get uneven or mismatched number of firings on my good brass and also do not want to waste my hunting ammo cases on paper, so I turn to the 30 - 40 cases that came with the rifle, same brand, full length size, anneal, trim - reload.
I am really battling to get groups, I do not usually battle.

I thought a few moments ago to weigh the cases, because the guy I bought from was shooting like 5 different brands and mixed bullets because they were all the same weight kinda reloader. I thought perhaps case are 3 x to 5 x shot mixed, let me weigh them.
Below is the 3 groups of weights I ended up with....
178 gr give or take 0.3 +-
182 gr .....................
183 gr .....................

Quick load tells me that that kind of difference in case capacity will give at least 80 fps spread.
I only chronied like 2 shots per load and got a 30 fps spread, like had the more like cases over the chroni.
Question one : will the 82 gr to 83 gr difference affect group size ?
How badly will the 78 gr to 83 gr difference affect group size ?

Can I shoot under a inch, more like half inch with these cases ?

[big5ifty]

For practical purposes, your weight distribution is excellent.

Weight is not case capacity.

The variation in case weight is from variation in the cut of the rim between production runs.

There is a variation in volume between cases, it's always small, not exactly repeatable, and never directly related to case weight. By not repeatable, I mean if you measure the volume of a fired case, reload it, fire it, measure again, it won't have the same volume. That's why I never bother trying to sort cases by weight or volume.

You can ignore case volume differences if the brass is all one headstamp.

There is a material difference in case volume from one brand to the next, and that is due to the case wall thickness. PMP has the smallest case volume relative to others in most calibers, for example.

If you're confident there is nothing wrong with anything on the rifle, I suggest an OCW test. 15 rounds is all it takes to see which load is best for the bullet.

[Treeman]

Did a case volume test in mean time, total volume spread is 0.6 grains H2O.

[Treeman]

If you're confident there is nothing wrong with anything on the rifle, I suggest an OCW test. 15 rounds is all it takes to see which load is best for the bullet.

>>>>>>>>>>>>>>>>>>>>>>>>
I really need to try learn, understand this OCW test, never took  much notice of it.

[Treeman]

Just looked up this OCW, it stands for Obsessive Compulsive Worker. Gees, a day at the range, I love reloading yet hate being at the range, half my trouble is I rush the range time.

I guess it comes down to my main issue again - finding time and the willingness to sit and do it slowly (waste time), hate slowly, can not do things slowly.

Perhaps i must find a day to do this whole OCD thing   

[Tripodmvr]

I have a strong belief in QL to get me close to an accuracy node. From there you can move up and down in small increments to refine the load. I have offered to help big5ifty but have not received figures to work with.

I got an excellent group with Kriek 48gr bullets in my 223. The figures below from a QL calc showed that I was close to a node. That is not a coincidence as I have tested and got good results in other calibres as well.

5 Mar 2021        Vliegveld    Fed Match    Sako    Riflex RFL            QL prediction for node           
        57mm    Speer 55        25        3134                                          25,9    3255
        57mm    Hornady 55        25        3142                                      25,8    3244
        56mm    Kriek 48        25        3234    Skote sny amper              25,2    3266

[Ds J]

I once measured 100+ PMP 308 cases, probably closer to 150 pieces. There was a correlation between case weight and case capacity, but it was small enough that my own shooting ability would have had a larger impact.

[Treeman]

Your QL load work and understanding is phenomenal, I have found your helps to be within 20 -30 fps on occasion. I would rule out coincidence, total faith in your work to date. 

[Treeman]

I once measured 100+ PMP 308 cases, probably closer to 150 pieces. There was a correlation between case weight and case capacity, but it was small enough that my own shooting ability would have had a larger impact.

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I have just found that a rather large case weight difference delivered a rather small H2O capacity difference. nearly 5 gr weight dispersion in cases had a 0.7 gr case capacity difference.

[Ds J]

The worst differences in case weight vs case capacity was with 303 cases.

[big5ifty]

I have offered to help big5ifty but have not received figures to work with.

Not because I don't trust your method. I intend to make use of your expertise when I do load development for the new bullets I have coming on order. The rifle is in for a bit of work, and the scope mount will change, so when ready, you'll hear from me.

[big5ifty]

I have just found that a rather large case weight difference delivered a rather small H2O capacity difference. nearly 5 gr weight dispersion in cases had a 0.7 gr case capacity difference.

 0.7 grains is the weight of one drop of water.

[Tripodmvr]

Had a look on QL and with 223 (30,3 H2O) 1gr volume = 46fps speed difference. With 7x64 (66,9 H2O) it is only 23fps. It is a known fact that ES is larger with smaller calibres, but decent grouping is still achieved. 

[Ds J]

Had a look on QL and with 223 (30,3 H2O) 1gr volume = 46fps speed difference. With 7x64 (66,9 H2O) it is only 23fps. It is a known fact that ES is larger with smaller calibres, but decent grouping is still achieved. 

In "The Houston Warehouse" article, the writer mentions that .22 calibre cartridges give the best accuracy?

I think that most of us still have much to learn.

[big5ifty]

In "The Houston Warehouse" article, the writer mentions that .22 calibre cartridges give the best accuracy?

I think that most of us still have much to learn.

I think that is due to the small powder charges providing reduced shock waves with which to vibrate the barrel.

It remains to be seen if structured barrels can invalidate that observation.