F-Open: cartridge choice.

[Quick]

G'day all,

I'm considering building an F-Open rifle off my Omark. What's the main considerations that you guys look for when choosing a cartridge/calibre combo? It's going to be either 6mm, 6.5mm or 7mm. Some cartridges like the 284 win, 6.5 super LR, 6.5x47 Lapua, 243, 243AI, have got my interest but then its deciding what would be best for me. I mainly shoot 308 Win in my R700 in F-Std but want something different and interesting to shoot aswell.

Any advice F-Open gents?

[Gadget]

Hi Quick,
That's a hell of a question, and I don't think it has one answer.
We are all different and so chose for different reasons, I also think most of us have probably used them all at one time or another, and you will probably change as well, it's the nature of the beast.

If I recommend ONE caliber to new guys at my club its 6BR or variants cheap to run easy to tune and dang competitive even to 1200y.
Just as an idea about cheap to feed, I just loaded 60+ BR's, the powder used would only load 26 rounds for my 7mm (ouch!! )

Graham

[Aubrey]

Go 6XC.

[RAVEN]

6.5X47 Lap is an option as well brass isn’t cheap very accurate easy to tune

[Quick]

Raven,

The 6.5x47 Lapua and 6.5 Super LR are really appealing to me. This would also be a rifle I use to get my missus shooting F-Class and alike as shes a tad recoil sensitive.

From everything I'm reading about Reloader 17, It seems to be a good powder to try in a 6.5mm aswell.

Anyone got any advice as to why one would go for a 7mm over 6.5mm? Everytime I look at wind drift, etc at 1000yds, there just seems to be maybe 0.25MOA to 0.5MOA between them. Do guys find the difference matters in competition at the longs?

[DaveMc]

First of all it is great to see someone else considering Fopen in the west. Great news. Second if you talk to the guys locally over there they all shoot (or did) 6mm and 6.5mm.

[RAVEN]

Quick I can give you the old reason
6.5X284 would burn out barrels in 1000 rounds
6.5 X 47 would give you more like 1800 - 2000 rounds before a re-chamber was required it also depend on throat length I prefer shorter giving that set up a longer competitive life span.

Quick what velocity did you use to calculate the 6.5

You may to re evaluate your wind drift between 6.5mm 130Gr VLD @2830fps and 7mm 180GrVLD @2830fps
The difference is about 1.5MOA this is 15"@1000yrd
The 6.5 built on a 10kg rifle would be very easy to shoot recoil wise
RB

[Quick]

DaveMc,

The guys I've met all shoot 6mm or 6.5mm. Two top FS blokes also have 6BRX in F-Open rifles I think aswell. There are stuff all FO guys over here from what I know.

Raven,

I used 2950fps with the Berger 140 LRBTHP and 2950fps with the 180gr VLD. From what I've currently read about the 284, it can do those velocities with certain powders like RE 17 which is what I think id be trialling first with whatever cartridge I go with.

Gents,

Im sorta leaning towards the 6.5mm for the recoil issues, and ease of loading from what Ive seen of the 6.5x47 Lapua but as I like tinkering and alike, the 6.5 Super LR seems very interesting to me aswell. Barrel life of 1500 - 2000rds is appealing aswell. I dont wanna have to change barrels within a shooting season like I would have to do with a 6.5-284.

There seems to be alot of emphesis of wind drift and alike, which you only have maybe 1MOA difference, does it matter that much or is it more personal perference for the most experienced FO guys. 7mm seems to be the rage these days from what I can tell.

Keep the info coming guys!!

[IanP]

Quick, lets say the 7mm picks up a 1 moa wind drift advantage, thats 10" less drift at 1000 yards. If you make a 1 moa wind reading mistake with the 6.5mm then you are 10" further away from where you intended than if you used a 7mm high BC round. Thats a lot to give away unless you dont make wind reading errors of course. If like the rest of us and you get caught out occassionally, (too often in my case) then the 7mm shooter may score a point higher than the 6.5mm shooter every time it happens.

Dont get too excited about RL17 as the shooting world is almost over this powder now. The reason being that the velocity increase does come at a cost. Double based powders are more temperature sensitive and in the case of RL17 quite often the velocity increase comes with a loss of accuracy. Its also being said that this powder seems to burn out barrels quicker than others. I cant comment on the barrel burning but I can about the accuracy drop off in use with the loads I used for the 6.5x47L. I mention these loads on the thread for 6.5x47L loads elsewhere on this forum.

If you set your velocity ambition down a notch then 2900fps is readily achieved in 32" barrels for both the 6.5mm 140gr and 7mm 180gr projectiles. Good luck in your quest and weigh up the options then make your decision based on best bullet BC for long range that you can comfortably shoot. Use ballistic charts and do the comparisons based on G7 drag coefficients.

Ian

[johnk]

Quick, lets say the 7mm picks up a 1 moa wind drift advantage, thats 10" less drift at 1000 yards. If you make a 1 moa wind reading mistake with the 6.5mm then you are 10" further away from where you intended than if you used a 7mm high BC round.

Once that first sighter is shot, you're talking about relative effects of variations in wind conditions - unless you are shooting Bisley style where most shots are sighters. If there's a change at a thousand yards that's not allowed for that moves the little round 1 MOA (10 inches), then a 10% more efficient round will only be 1 inch better off - & that may or may not be relevant.

If I'm given my choices, I'll shoot with the gun that groups best at that distance.

[Quick]

Ian,

You put a very good case forward for the 7mm. Its given me a lot to think about mate. Mmmmmm........ Whats the barrel life like on the 7mm's?

Given that this is my first F-Open rifle, would a 6.5mm be better to learn with then the 7mm? Im also thinking about recoil considerations as I will be trying to get my missus shooting this rifle also when she lets me build it

Gagdet has suggested a 6BR as a first F-Open rifle, any reason not to go with this even though Im leaning toward a 6.5mm or 7mm?

Regards,

Shaun

[Quick]

John,

What considerations do you mean when you say shoots the "best groups at that distance"? I may know a few but if you could clear it up for me.

I see the SARA F-Class team uses 6.5x47 Lapua, any reason for this?

[RAVEN]

As a first FO Cal
6BR
6BRX
6.5X47

7mm great but allot more recoil
Expensive bullets
More powder
A tight grouping 6 or 6.5 in the right hands will out shoot anything

I use a 6X47Lap and 284W I like them both
And Quick dont believe everything you read
we are all using 300WSM's

RB FO Captain 2012 Mackay

[IanP]

Ian,

You put a very good case forward for the 7mm. Its given me a lot to think about mate. Mmmmmm........ Whats the barrel life like on the 7mm's?

Given that this is my first F-Open rifle, would a 6.5mm be better to learn with then the 7mm? Im also thinking about recoil considerations as I will be trying to get my missus shooting this rifle also when she lets me build it

Gagdet has suggested a 6BR as a first F-Open rifle, any reason not to go with this even though Im leaning toward a 6.5mm or 7mm?

Regards,

Shaun

I'm sympathetic to your cause because I went thru the same thought processes. Luckily some little known American shooter (Bryan Litz) advised me by email that I should re-think my 6.5mm bias and use BC and ballistic charts to steer me in the right direction. Bryan was the one that set me straight on using the 7mm high BC bullets.

The 6mm bullets are fantastic in low wind conditions and the 6.5m bullets offer low recoil with better BC bullets than the 6mm. The 7mm 180gr Hybrid or VLD from Berger is my choice for the perfect all rounder and use the other smaller calibres at short range in low wind conditions.

I have a host of smaller calibres and I prefer the 7mm over the lot of them. Bryan Litz could have saved me a lot of money if I would have come across him and his books earlier. The recoil from the 7mm 180 grainers is pretty mild in my 284 Shehane but everything is relative so its a good idea to borrow and try if possible before making your choice.

Ian

[Quick]

Raven and Ian,

You both bring up very good points. You have torn me between the 6.5mm and 7mm. The 6.5 is a tad more appealing due to lower running costs, recoil, etc. Mmmm, I must go away and have a think about this.

By all means keep the advice coming. I could see tjis helping others who are new to F-Open aswell.

Regards,

Shaun.