.223/.6.5CM what difference in length make a p.o.i difference

[chaz]

Hi folks,

I was wondering what the difference in total brass length makes to the point of impact. Say at a 1" group.

For instance I try and get my .223 Rem brass to as close as i can to 1.750". And allow 2 thou difference. And my 6.5CM to 1.910" but again with 2 to 3 though thou max difference, longer or shorter.

At what difference in length of brass in both calibers will it make a difference to a 1" group??

At the moment i allow a 2 to 3 thou difference to be OK. But i would appreciate some more CONSTRUCTIVE accurate feedback as to how much difference in brass length would it matter to a 1" group at 200-300 yards for argument sake, in .223 Rem, and 6.5CM.

Constructive replies very much appreciated...

Thanks

[Catch-22]

Doesn't bullet jump to lands have a greater effect on group size than brass length?

Length of brass is important to 1. Permit reliable feeding (if too long, it won't chamber/extract properly), 2. Minimise the amount the brass must stretch to properly seal the chamber and develop the right pressure to release the bullet and 3. Prevent overpressure by ensuring brass isn't tight in the chamber.

But imo, shrinking group size has more to do with other variables; such as bullet type, jump to lands, powder type, charge weight, primer type etc...

??

[chaz]

Thanks for the info.

I'd appreciate further opinions on the subject to get a more opinions.

Thanks.

[TJC]

Catch is spot on. 

[chaz]

I appreciate and agree with your comments Catch-22. I suppose i'm asking if there is a maximum difference in length between brass when it gets to a point where it affects accuracy.

I know there's a maximum length for my brass and keep it well under max. I also personally do my best to keep my brass to be within 2 to 4 though difference in length. Is that going too far? And what is too far? There must be a point where it becomes a factor?

Cheers. 

[Catch-22]

1 hour ago, chaz said:

I appreciate and agree with your comments Catch-22. I suppose i'm asking if there is a maximum difference in length between brass when it gets to a point where it affects accuracy.

I know there's a maximum length for my brass and keep it well under max. I also personally do my best to keep my brass to be within 2 to 4 though difference in length. Is that going too far? And what is too far? There must be a point where it becomes a factor?

Cheers. 

I think the goal  is to trim all your brass to the same length, and to not exceed either SAMMI/CIP max and min lengths. Trimmed too far (so too short) will force the brass to stretch too much, possibly leading to split necks or a case head separation over time (also induced if you size the brass, e.g. push the shoulder back, too far).

[chaz]

So as long as my brass stays in Sammi/CIP spec. I'm not being OTT by making sure my brass is no more than a maximum difference of 3 thou?

[Catch-22]

2 hours ago, chaz said:

So as long as my brass stays in Sammi/CIP spec. I'm not being OTT by making sure my brass is no more than a maximum difference of 3 thou?

 Think we can all go a little OTT & OCD with all the small aspects of reloading. But personally I don't think you need worry about it. Just ensure you arent exceeding max length (or trimming beyond min length) and just try to keep all brass trimmed to same length. 3 thou is more than good enough imo! 

I think your time, energy and focus is perhaps best spent looking at things like seating depth, tension on bullet, component choice (e.g. bullets, primers, powders) using the OCW method, to shrink groups.

If you haven't already run an OCW test (selecting powder, bullet & primer combo then shooting different charge weights in a round robin style) I suggest you do so. That will give you an idea of how those components perform in your rifle. Once you find a good, stable and consistent node ( per OCW rules) then play with seating depth and neck tension to tighten the group up. If the OCW fails to show groups as you would like, try again but change one core variable, such as bullet type or weight. Repeat OCW process again to see if groups improve.repeat process (but only change one core variable each time otherwise you'll chase your tail) until you arrive at groups that satisfy. If nothing is working, it's a good time to then look at other factors, such as bedding etc...but it's more than likely you'll find a group to satisfy by OCW.

As ever, it's all learning and good fun (if frustrating at times). Good luck!

[chaz]

Cheers Catch-22.

[Catch-22]

4 hours ago, chaz said:

Cheers Catch-22.

Most welcome!

👍

[VarmLR]

I wouldn't lose sleep over case length variations of 5 or 6 thou.  Much more and there's always the old argument about neck tension variance but you're likely to get this from badly inconsistently annealed brass too.  My 6.5 cases show little signs of growth and I haven't had to trim any in the last 4 reloads.  When new, I checked and trimmed all to be uniform +/- 2 thou then forgot about them.

Do yourself a favour and buy a Lee factory crimp die.  Size your brass, don't worry about small case length variations,  load your rounds, add a consistent crimp and watch your ES figures drop...it works.