Thread: 6mm cartridge comparison

Fellas

As you know I've always been a .243 kinda bloke. But the move towards higher BC, heavy and long for calibre bullets has got me interested in what else I can do with 6mm.

I ran through some of the options yesterday in Quickload, to see how they compared.

The assumptions I used was (a) the same bullet - 90gr ELD-X - so it would work in all rifles and not just fast twists, so 1:10" .243s are in the mix; (b) either a 100% case fill or maximum specified chamber pressure (Pmax), whichever occurred first. Obviously there's no accuracy component, what your rifle likes isn't quantifiable.

The results are really interesting. It shows that there's a couple of cartridges that are super efficient, with light powder charges for really decent velocity (6mm Dasher and 6 BR Norma), then the midfield is pretty much of a muchness, and as you'd expect the highest velocities belong to the highest charges (243 AI, 6mm Creedmoor and 6mm XC).

But what really stood out for me is the use of slower powders to get high velocity but low pressures. RL26 being the one I chose to look at... you can go on all day looking at dozens of powders. This is potentially a big positive for the throat erosion problem of fast 6mm rifles derived from the .308 parent case or similar.

However, we hear reports that not all rifles like RL26 and velocity and accuracy can be problematic. That said a good mate in the UK who I caught up with a couple of weeks ago (6mm Creedmoor) has nailed it using OBT and some very fine tuning of seating depth and is getting pretty much exactly what the model says he should.... plus one ragged hole. That's in a high end custom rifle however, but he's using it with great success in long range field sports - targets, hares, foxes and so on. He's a bit fussy about his deer shooting so no deer (yet).

Anyway, food for thought. I'll be adding to this spreadsheet and if anyone wants a copy that you can sort easily then flick me a PM.



By the way, those the say Quickload doesn't work.... I'd say 9 times out 10, once I get every single assumption 100% correct (particularly case capacity and consistent neck tension), my field outcome is pretty close to the model outcome. Batch-to-batch powder variability is a factor in differences of model vs actual, I've seen that with AR2209 when the only change to the velocity of 100 reloads is the powder batch number. But consistent neck tension is also a biggie (starting pressure).

@Flyblown, So for consistent neck tension, what do you do? Like, do you anneal every single time before you resize?

I've surgically implanted a gauge into my right bicep!

Nah... the highly unscientific process of "feel". I measure them inside and out a lot and find the dies do a damn good job in resizing the neck to the exact same size.

But still, its pretty darn close. Low ES / SD is a good indicator.

Yes interesting.
I like the 243W as well my go to load is a 95Gr Targex with a mid load of 2209. I would be interested if you added Win760 and RL-16 to the 243 data and see how that compares to the 6mm CM.

@Flyblown What length barrels was this assuming Dave?

24"

Interesting to see the high velocity's coming from the W760 and the significantly slower burning R26

Interesting - could you add the case capacity (in H2O) that you are using for each - I'm trying to figure the differences between 6mm Creedmore and 6x47 (SM or Lapua??) in Quickload

Thanks

you really need to run that comparison with 105-110g projectiles. That might show up a greater difference

What about the big boomers like 6-284, 6mmAI and 240 wheatherby magnum?

Those long heavy 243 pills are only the domain of the custom rifle as factory barrels will struggle with the new the VLD styles in 100gr or larger sizes.
NB I would love to see the comparision as well
Berger 105gr vld,
Hornady's 108gr eld-m
And R 26 powder amongst other things.
Z

Hey @Flyblown - any update or further thoughts on this ??

A cobber mentioned that there are a some new reamers about for some older cartridges with the leade/throat design updated for modern projectiles - be very interesting to know of this has been done for 6mm Rem. Supposedly Trueflite have a couple of the "updated" reamers.

@Flyblown have you heard about the new Black Jack 131gr .25 cal bullet? Made for them by Sierra I believe.

Very high bc bullet for its weight. Pushed out of a Creedmoor or '08 sized case it should have a decent ballistic advantage over anything in either 6mm or 6.5mm.

Something like a 25 Creedmoor with the 131gr BJ would make an awesome comp cartridge i would have thought, most likely a neat hunting cartridge too.

Ryan Pierce in the states is planning on building a 25 SAUM pushing the 131gr BJ to around 3,300 fps.

Ive got a 25 creedmoor reamer coming - will be interesting to see how it performs.

250 savage AI reinvented I guess :-) we are going full circle here