Brass of varying length question

[gomeybear]

Hope all is well Gents.

Evident by some of latest posts, Im trying to squeeze as much accuracy out of reloading the 300 blackout as possible and so I have a question regarding loading up some brass of varying length (all Lake City brass). Ive ran some of the 1x fired LC cases through the sizing die and they are at times varying in length; some by as much as .007” from each other.

Would not trimming these all up to a similar/exacting case dimension from case to case cause accuracy to degrade? Some extra info, after sizing, Im getting a max variance of .007” between the cases. The shortest case lengths are very close to minimum SAAMI spec at 1.346” - 1.347” or so - the max case length Im seeing are coming in at 1.354” - 1.355”

Any help is much appreciated!

[dellet]

What’s the length difference at the shoulder?

[wildfowler]

I try and keep my brass neck all trimmed to below a specific number. But I’ll admit I do make mistakes in trimming, I might have a brass shaving under the case head and didn’t notice it causing me to trim too short or for whatever reason wind up with cases that are shorter than my minimum objective.

I go ahead and load and shoot those anyway because I don’t think I have my loading process refined to the point where I could ever test 1000th incremental difference in neck length to see if it will show up on paper.

I feel like I have squeezed out all the accuracy potential from a rifle that I’m currently capable of.

But maybe since I’m talking about it I should mark the ones that are noticeably shorter than the majority of my batch and shoot them separately to see if they print any differently?

[gomeybear]

Harder to get that measurement with my caliper. But from what I can tell by rough measurements, all the variance is coming from the shoulder to the case mouth.

[gomeybear]

But maybe since I’m talking about it I should mark the ones that are noticeably shorter than the majority of my batch and shoot them separately to see if they print any differently?

Good point - put it to the test!

[dellet]

You will want something like this, a comparator. It doesn’t make any sense to worry about overall length until the case body is the same length. I can form 4 pieces of brass with all having the same length, but powder capacity may vary as much as 2 grains.



https://www.hornady.com/headspace-bushings#!/

Having a longer neck will not have as much effect, but it will be noticeable if you pay enough attention.

[gomeybear]

Groups definitely opened up by not having consistent brass lengths. Just tested it over the weekend. Maybe a 1/3” difference at 100 yards or so....

[TRshootem]

I finally settled on just checking the sized brass in the Dillon case gauge. I'm OK with .003-.005 difference in base to shoulder with most BLK brass. More than that I start paying close attention to what kind and how much lube is applied. If shooting in the AR platform and not looking for bench rest groups, this has worked out fine. Body shoulder/thickness at that juncture can vary by at least the above numbers in converted brass.

I Size and load BLK and others on a Dillon 550B, perhaps a bit of this variable in induced there. All this to say, I get pretty fine results without much more than basic quality measures. LC brass from a number of different worn tools in the same head stamp date can vary this much. Heck, even places like Starline have body thickness issues from some of the processes involved. *Note* Any misstated info here has not yet been fact checked by any of the resident pros* Correct as needed.