Need help me with my F-Class build, which 7mm cal to use????

[elmerdeer]

Hi guys I am going ahead with an F-Class build, and my main problem is which 7mm caliber should I use? Has anyone used a 280AI for F-Class as I have the reamer and my gunsmith can throat it for the 180 Berger hybrid or another bullet with extremely high b.c, like the new Sierra's? I would like to be able to get speeds of 2950 to 3100 maybe, can I achieve that with the 280AI? Or do I have to go bigger?
Anyway I am just looking for the best option, that expierenced F-Class shooters are using.
Thank you
Elmer

 

[Laurie]

Elmer,

hardly anybody, perhaps even nobody, uses the 280 or 280AI at top level F-Class. It's not a cartridge design / ballistic performance issue, rather that there are alternatives giving similar or higher performance with better quality brass available.

The base 7mm now to be competitive in long-range F (800yd and upwards) is .284 Win but throated long to allow 175 and 180gn bullets to be seated right out. Most people use Lapua 6.5-284 brass necked up, although Winchester brass has many adherents too on your side of the Atlantic. The next step up from there is the Shehane (improved) version, like all improved cartridges simply a fireforming operation. Its downside is that nobody seems to make off the shelf dies for it at the moment - not even the CH4 Tool and 4D Die Co. which seems to have almost everything else, so it's an expensive custom die set (or the gunsmith 'rechambers' the sleeves on a .284W Redding Competition set).

The 'straight' .284W tops out at 2,800-2,850 fps with 180s with all powders except Re17 that has been found to add another 100 fps on with 30-32" barrels. The Shehane version adds another 3gn powder capacity and can produce 2,950 fps with a range of powders and break the 3,000 fps barrier with Re17.

To get higher MVs, you need the next sizes up in case, which in terms of 'overflow water capacity' are:

Rem SAUM: 72.6gn
280R AI: 74.0gn
7mmWSM: 77.9gn
(source: QuickLOAD cartridge database)

The WSM has been the main F-Open cartridge here in the UK for some years now, or to be precise, a wildcat that uses the .300WSM necked down to get a longer neck than the factory 7mm version. Norma brass is available (at a price).

7mm/300WSM is quite a performer at long-range both in ballistics and accuracy and helped the GB F-Class squad to wipe out the rest of the world in the last F-Class World Championship meeting at Bisley the year before last. There is a price though - barrel life - and it's not a poor man's cartridge. As a result there has been some interest in the 'straight' .284W and Rem SAUM versions here with a little reduced performance but much better barrel life. Scotsman Grant Taylor has won the GB F-Class League Championship two years in a row with .284 Shehane up against a big raft of guys with WSMs, so it works for some! The SAUM falls between the .284 Shehane and WSM and has Norma brass available. It is a very efficient short cartridge with a good length neck that appeals to many people.

Your .280AI has slightly more case capacity than the SAUM so will give similar performance, 3,100 fps maybe even more with 180s and falls between the .284s and WSMs. As you're thinking of this cartridge, I assume that your bolt is dimensioned for cases with 0.473" dia case-heads as per .30-06, .308W etc, while the WSM and SAUM families are 0.550" and need a magnum bolt-face.

So it looks like a choice between the 'straight' .284W, Shehane version of same, .280 Rem. .280 Rem AI. The last will give the highest performance potential, but if you use it all, you WILL get a much reduced barrel life. If it were me I'd have a 'straight' .284W, but I'm a born and bred Scot who lives in Yorkshire, two parts of the UK where it is said that moths are seen fluttering out of wallets on the rare occasions that their owners take them out!

Laurie,
York, England

 

[Forum Boss]

Laurie,

That's the best summary of the current 7mm choices for F-Open Class shooting I've ever read. Thanks for contributing your thoughts to the question.

There is growing interest in the RSAUM among USA F-Open shooters now, based on the success Danny Biggs has had with the round. Personally, I think the .284 Shehane may be the "goldilocks" cartridge for the 180s (not too big, not too small), and I'm glad to see Grant Taylor do so well with it. But the RSAUM gets you to 2950 fps without pressure issues.

 

[1000yardstare]

The 2010 Canadian Championship F Class Grand Agg was won by a .284 Shehane. Second place in the Governor General Final was a straight .284Win.

A 7mm/270WSM won the 2010 Ontario F Class Championship.

I believe all three chaps were shooting 180 Bergers.

 

[DBailey]

Hi Elmer

The trend of the moment is short mags. However, the 280 AI with a 30 or 32" barrel will push the 180's to 2950 fps without any problems.
A few people are running 2950 fps with the standard 280 Remington.

If I already had the stuff to build a 280 AI, I wouldn't hesitate to use it.
I don't like fire forming brass at all, but there is decent brass available for the 280 AI.

David

 

[elmerdeer]

Thank you guys, you are a wealth of information! I tried the sport with my custom hunting rifle 7mm Dakota 24.5" #4 contour barrel and 180 bergers doing 2980fps , it was a mock competion 3 targets 700,800,900meters, 2 sighters and 15 rnds for score,and in the open class I came in 2nd, on my 2nd time shooting. So I am hooked as It was lots of fun and great sport. The one thing I noticed was when that wind changed is some of the .308 guys who missed the wind, missed the whole target. Anyways thanks.
Elmer

 

[flatlander]

Elmer, I've only worked with the 280AI in one rifle - it had a fine quality custom handlapped bbl. on a trued Howa action. Accuracy wasn't what I'd hoped for, nor was velocity. I know a couple of local guys who've got 280AI hunting rifles, and they're both happy with them, so I'd expected much better results, but am informed by the barrel maker that they dropped this chambering because of accuracy issues. That'd be enough to spook me away from this chambering for a target rifle.

OTOH, I've chambered three barrels for the straight 284 - 30" Bartlein & Krieger, and a 28" PacNor. They all three shoot great at 1000yds with S175MKs or any of the Berger or JLK 180s. I had my reamer ground for use with WW brass, and haven't had any reason to regret going that route. I load H4831 (tried the SC version, but prefer std. 4831), N165, and RL17. Concur with Laurie's velocities; haven't shot enough at 1000 with RL17 to have a lot of confidence in it, while 4831 has always worked well.

I do my own barrel work, so barrel life isn't a huge issue with me. However, I shoot prone, not F-class, so recoil is an issue. My 284s weigh 15.25-15.5lbs., and I feel the recoil with 180s is about the top end of my personal tolorance level. So for my purposes, the 7mm mags are out.