6 creedmoor reloading questions

[jimbob_walker]

I recently purchased a 6 creedmoor. I messed up when I ordered brass and got 6.5 creedmoor. ( I still have no idea how) so I necked them to 6 using a bushing did. I know that's not the best way but that's what I had. I was just trying to shoot my new rifle. It shot really well for all the better I am. .445 at 125 yrds off a bag. I've been shooting these cases while I waited for 6 creedmoor brass to come in.

Here is where I'm kinda stumped. Recieved the 6 creedmoor brass( both lapua) and loaded straight out of the box with the exact same load data. The difference was

Lapua 6.5 necked to 6 (new)
Coal 1.917
Neck tension loaded .003
Avg mv 3136
SD 9. ten rnds

Lapua 6 creedmoor (new)
Coal 1.911
Neck tension when loaded .002
Avg mv 3175
SD 6 ten rnds

So what has me baffled is how can I have .005 less surface holding the bullet and .001 less neck tension and be shooting a higher mv with the exact same of everything else? Or am I looking at it backwards? I don't usually have brass for a rifle that isn't all as exactly the same as I can make them so I just figured I'd try to shoot these and see the affects it would have. I was expecting a lower mv so now I need to know why it isn't. Thanks

 

[Redfoot Ranch]

It sounds like both of these sets of numbers came from 2 different 'types' of virgin brass, it is now fireformed to your chamber.

If this was the case, now prep both type to identical specs and re-run your test. I never expect much from brass until it's fireformed. Myself, I would also water weigh internal capacity of each type to look for a difference there as well. I would only test using same lot brass. I hope this makes sense and helps.

 

[jimbob_walker]

Yes, makes perfect sense. The plan was to get true data once they are fire formed, but I was surprised at the data I came up with between the two virgin.

 

[Redfoot Ranch]

To make the initial 'test' a bit more fair, I would have tried to seat to the same COAL and run like neck tension in both.

Curiously, what was the ES in both loadings?

 

[jimbob_walker]

I didn't document es. I wasn't wanting the test to be fair. I try to do as precise reloading as I can and was trying something with a pretty big difference just to see the results. Sometimes I wonder if everything I do makes that big of a difference. I guess when you add all the little things up it ends up being pretty important. I was just wanting to see how much difference the two would perform with the differences I left be. I am just surprised that it came out opposite of what I was expecting. I figured the 6 creedmoor brass being less coal and .001 less neck tension would have less mv.

 

[TheOfficeT-Rex]

Too many compounding factors - I would think the brass change and differing internal volumes could account for the speed.

You also changed OAL - I've seen an increase of 25fps just by seating the bullet 15k deeper. Everything else identical (loaded same day and shot in subsequent strings).

 

[Redfoot Ranch]

In looking back and scrutinizing your "Coal" I am a bit confused. It appears you are referring to this as your case length and not the Cartridge Overall Length of a loaded round. Hence my comment about seating to different lengths (.006").

Were these rounds loaded to the same COAL by measuring case base to bullet tip or CBTO, from case base to bullet ogive with a comparator? A loaded round should be somewhere in the 2.5-2.800" OAL range. Even my 22CM runs 2.1+" CBTO lengths. The only time I use COAL is for the conversion into QuickLoad which has no input field for CBTO parameters.

 

[jimbob_walker]

I'm sorry. I got the coal definition wrong, but you are correct. I was referring to case length not cartridge length.

 

[Rocketmandb]

A couple notes:

- Assuming 50 rounds went through the rifle with the 6.5 brass.
- Your barrel will speed up over the first 100-150 or so rounds. Not at all surprised to see the second set of brass fire faster.
- How much did the neck thickness vary between the necked down 6.5 and the new 6 brass?