Lapua Match .223 Weight Variation... Meaningful?

[WindSurgeon]

I looked for this topic in the forum and could not find it so thought I would try posting. I recently purchased some Lapua .223 Match brass and went through the process of weight sorting after the first firing. My question is what weight variation should I expect cases. My brass varied from 92.7 to 96.7 grains with clustering around 93, 94 and 96 grains (+/- .2 grains). Around these three clusters, the number of cases was evenly distributed.

I am also wondering how much variation in .223 case weight does there need to be to have a meaningful impact on 10 ring accuracy at 600 meters. What tollerance for variation should I allow in my sorting efforts. Is my 4 grain spread nothing to worry about?

For reference, the 10 ring at 600 meter is about 12 inches and the X ring is about 3 inches. I am shooting with a scope in F class target.

Any thoughts or information would be helpful and appreciated.

 

[HPMike800]

I hold little value in sorting by case weight. Take the extremes of your lot and shot them for group over a chrono. If I have any real oddballs, I will cull them out just incase. I sort by casewall thickness and that has helped for long-range stuff.

Mike

 

[mikecr]

Why do you go through the effort to weigh AND THEN ask for meaning in that action, instead of just measuring h20 capacity to know?
Seems backwards to me.

 

[Steve Blair]

Mike is right about case wall thickness, it is a more significant determinant than weight. I weight sort to eliminate unusual cases and to reduce variation. My results indicate a statistical relationship between case weight and velocity but not a direct relationship. How much does it reduce velocity variation? A few percent. That may influence long strings and tight vertical requirements at long range. I ran a test with two hundred Lapua .223 cases sorted into two groups whose medians were two grains apart and loaded with a proven match load. The heavier cases' median was slightly faster. If you do not want to sort, I would not call it a problem.

BTW, the 600 yard F-Class target has a 12" 9-ring, 6" 10-ring and 3" X-ring.

 

[WindSurgeon]

Mikecr - Sorry about the question's placement in my process. I asked after sorting because I was surprised by the Lapua spread.

I weigh brass because it seemed to help me previously with a different brand and a lot of shooters I speek with have talk about the need for sorting brass in some way. Most seem to do this by weight because it is fast and does not require special equipment. I do not have the time to measure wall thicknesses and filling them with liquid to measue case volume, etc. The most I do is neck turn off the high points (once), trim length (every 4th), and resize.

Previously, I tried sorting my LC brass first by headstamp then by weight. That helped LC brass round consistency but I had to sort through a lot of brass to get a couple of hundred all the same (+/- .2 grains). The Lapua is supposed to be much better than LC in this respect with a smaller weight spread right out of the box (so I hear and so I was hoping for less work). I did have some fliers on my first trip to the range with the new Lapua and thought that perhaps sorting by weight might help the next time out. Weighing them, I was surprised at the variability accross the lot. Just trying for the most consistency I can and asking the question to see if I am waisting my time worying about it and to see what others do.

 

[Cheechako]

Plus or Minus 1% is considered very good brass by most Benchrest standards. Plus or Minus 2% is still good.

Ray

 

[WindSurgeon]

Thanks Ray. That's a benchmark I can use to help out the sort process. I can use the 93 and 94 grainers and be within that tollerance and have enough to practice and shoot matches. I'll use the rest for practice and prairie dogs.

 

[mikecr]

Ok put another way,,

Just trying for the most consistency I can

And yet,,

I was hoping for less work

As,,

Most seem to do this by weight because it is fast

Shortcuts, benchrest or otherwise, hold the least probability of reward.
That is, unless shortcuts ARE the reward for you(and it's kinda lookin that way).
But when you really do care for most consistency, consider that case weight is not a capacity standard at all.
Seriously, For all you know, perfectly matched case weights(in your lot) might hold higher capacity spread than mixed weight cases..
Neither you, nor anyone else, will ever know until the capacities are actually measured.
So,,,,,
If not worth the efforts to do it right, then what worth are efforts in doing it wrong?

 

[Laurie]

I'm very surprised by a 4gn weight variation. Were the cases all from the same manufacturing lot? My current .223 Rem Lapua brass is from three lots (all pre blue box) and I weigh them after sorting by neck thickness / light neck-turn; trimming (if needed - hardly ever); mouth chamfer and flash-hole ream (worth the effort in some batches as maybe 3% have markedly smaller flash-holes than the norm, but not applying to all lots I've found). Cases are always kept separate by lot in use.

Within recent lots, I haven't found a 1gn maximum variation as yet and all bar a handful fall within a 0.6gn range. You can get 1gn or more variations between the modal weights of different lots. However, 96gn is VERY heavy by the standards of .223R Match - I haven't seen any weigh up there since Lapua moved to its current thinner 'Match' type and that weight falls between the current 'Match' 93-94gn weights and the old thick-walled low capacity stuff that weighed around 97-99gn and generated much higher pressures. I've been buying Lapua .223R brass a few boxes at a time on an annual basis for over 10 years now, so have seen enough of these cases to be surprised by this.

Laurie,
York, England

 

[WindSurgeon]

Thanks Mike. Like many shooters, I don't have the time to do everything perfectly and I don't think I was arguing against your point that there is more relavant ways to get to consistency. I wish I did have the time to do everything. It was really a very simple question and you have accomplished answering it by pointing out laziness and ignorance. As I think I stated, time is limited, but I still want to compete and shoot. Church, family, and work take up the vast majority of my time and I get a few precious hours to pursue shooting each month. For your sake, I will simply stop weighing and wasting my time doing so at the loading bench and shoot more.

YOU ARE RIGHT!!!

 

[fl3gun]

I think if you found a 4 grain variation in Lapua brass you need a new scale

 

[WindSurgeon]

Using the digital scale on an RCBS ChargeMaster

 

[WindSurgeon]

Here's the plan. I will be culling everything above 94.5 grains and calling it a day. The remainder will go into my coyote and prairie dog shooting stash. I'll report back on how that batch works after going out for practice next week. Thanks for all the replies and thoughts.

 

[fl3gun]

Using the digital scale on an RCBS ChargeMaster

IMHO That is your problem. I had an RCBS electronic scale. When I finaly broke down and bought an Acculab 123 I found out how bad my RCBS was.

Someone you know must have a lab quality scale. I would double check the brass on it before i culled any

 

[HPMike800]

I had a batch of LC 308 that I fully prepped and weight sorted. I shot them and measured case capacity. Of the ones with abnormal capacities, the weights were right around the middle of the spread. There was no correlation at all. I say get a tool to measure case wall thickness.

Mike

 

[ronemus]

I did an experiment several years ago to determine just how much effect brass weight has on .223 loads. I used WW brass (sized, trimmed and deburred, primer pockets uniformed, flash holes deburred, and neck turned) , WSR primers, charges of RL-15 or N-550 powder weighed to 0.1 gr, and 75 gr A-Max bullets. Using the lightest and heaviest cases (sorted from 1000 once-fired I had on hand), I had two lots of 10 cases with a 3 gr difference in weight. The average muzzle velocity difference was 16 fps, just a bit more than the 12 fps due to 0.1 gr of powder. I choose to sort 0.5 gr lots of brass for my long range loads, but the effect will only matter at 800-1000 yards - the vertical displacement on the target from such a small velocity change is negligible at shorter distances. Unless you control all other sources of variation, the effect of brass weight is negligible.