Which 7mm for F Class?

[AndyMass]

Relatively new here, so please be gentle with me.

I am planning a new build F Class rifle for the 2008 season in the UK and have settled on 7mm as my chosen calibre for the primary reason that they,7mm bullets) have better B.C. over 6.5mm and in our countries "changeable" climate, I think this will be a distinct advantage.

My question to the "panel" is, what parent case to use?

I would like, if this is possible, to drive 170 - 180 grain ULD bullets in the region of 2900 - 3200 fps,MV) out to 1000 yards.

At the moment i'm mooching over the following;

,in no order of preferance)

7mm WSM

7mm / 300 WSM -,I already have this calibre in a hunting rifle - so dies / case forming no probs)

7mm Dakota

7mm Boo Boo,wildcat 8x68 RWS)

7mm/338 LM,necked down 338 Lapua Magnum)

284 Win AI

280 AI

7mm-08 AI

Obviously powder capacity is an issue in the 7-08 case, so it may be a non starter.

The rifle is basically going to be specced like this:

BAT 8.5" action, Kreiger 30" tube, Jewel, Macmillan F Class or Robertson F Class stock.

Oh, barrel life not in the equation providing I get circa 1200 rounds.

Thanks in advance.

Andy

 

[Bobs243Ackley]

Hello Andy,

FWIW, I have talked to some of the members of the British F-Class team. From what they are indicating to me, they will be using the 7 WSM for the upcoming season. The one area that I am not certain of is if they will be using the standard version of the 7 WSM or the 7/300 WSM. They did indicate that the quality of the std. 7 WSM Winchester brass did leave a lot to be desired, but we did touch upon the superior quality of the Norma .300 WSM and then neck it down to make a slightly longer neck for better holding of the long 7mm bullets. So, I guess we will find out later as to the actual version of the 7 WSM that the British team will be using. I hope this information will help you with your project.

Cordially,
Bob Blaine

 

[2RECON]

Hi Andy,

the 7mm/.338Lapua,aka 7mmKM) is way too mutch....

But mayby have a look at a 7x66SE vom Hofe....

Best

 

[AckleymanII]

One thing that you can count on in Norma brass is soft case heads. The extreme pressures can and will leade to premature primer pocket failure if you do use Norma brass.

 

[JoeDuke]

Will the 6.5 - 284 case necked back up to 284 push a 180 grain bullet to 2900 fps? If so, does anyone have any workable loads?

Thanks, Joe

 

[JERRYHM]

Lapua 6.5-284 brass necked up to 7mm.
Head space new = -0.0005”, fired = +0.0005”
Rear Base dia. New = 0.4975”, fired = 0.4985”
Neck dia. New = 0.3115”, loaded = 0.3125”, fired = 0.3130”

Does require neck turning about 0.003”

The necks were turned so the loaded round neck diameter is 0.310”
The cases are resized to 0.308” giving a neck tension of 0.002”

Brass average weight is 195.8 gr.
The loaded round average weight is 428.4 gr.

The OAL to touch the lands is 3.141”
The Sierra 175’s OAL is 3.126”, jumping 0.015”

Load Testing

H4350 50.0 MV = 2743 fps
50.5 MV = 2793 fps
51.0 MV = 2822 fps
51.5 MV = 2867 fps
52.0 MV = 2897 fps, ES = 22 fps, SD = 9

 

[JoeDuke]

Thank you Jerry, That look very good.
Joe

 

[jb1000br]

Joe -- 2900 is abolute max for my 30" krieger and h4831sc/180 berger...

JB

 

[AndyMass]

Thankyou for the replies so far, I must admit I hadn't considered the 284 case, but even with the load data, it still appears a little "slow".

I accept that the 7mm / 338,Allen Magnum) may be a bit overbore for competition use.

As i am already set up for 7mm/300WSM, this may be the way forward, I use it as a hunting round, but it has proven excellent accuracy,the curent UK BRA tightest group was shot with a rifle in this calibre recently)

I was rather hoping for opinion on the other calibres I mentioned particually the 7mm Boo Boo - is there anyone here with any experience of it in competition - loading, is it a fickle cartridge?

Andy

 

[TonyZ]

In regards to the 7 mm, i have 5 barrels in 4 twists, 1 in 9, 2 in 9.5, 1 in 10 and 1 in 11. Not one of these barrels with multiple chamberings in different rifles in a number of cartridges will produce an acceptable grouping capability,repeatability) using the 175 SMK. Yet all the barrels will shoot the 168 SMK and the 162 Amax to a very good level. ?????
Tony Z.

 

[RAVEN]

Hi Andy
I use 284W .311 neck in F-Class,Aust)
max velocity out of my Krieger 30" is 3000fps but every barrel is different.the loads below are from 2 different rifles
The node at were it like to shoot is around 53-54Gr of 2213SC 2850fps - 2900fps barrel life seems to be good have had 1900 down the tube still shooting great re chambered @1600 rounds still using the same 150 pce of Lapua brass with no flow
Put a group down the other day @ 900mtrs 6.2"wide X 3.8"high
I also get good results with 168Gr VLD Berger's @ 2930fps
Test loads 89mtrs ASL,291feet above sea level)
180Gr BERGER VLD 2213SC Lot# 4216 FED210GM LAPUA CASES 30" Krieger Bullet seated into lands
POWDER
2213sc 180Gr VLD

Shot Charge Velocity
1 52.3 2765
2 52.6 2823
3 52.9 2801
4 53.2 2829
5 53.5 2836
6 53.8 2870
7 54.1 2898
8 54.4 2880
9 54.7 2919
10 55 2954
11 55.3 2955
12 55.6 2975
13 55.9 2993
14 56.2 2987
15 56.5 3015
16 56.8 3029 Pressure
17 MAX 57.1 not fired

284Cal 180 Grain Berger VLD ADI 2213SC Lot# 3919 CCI BR2 LR Primer LAPUA CASES 30" Krieger Bullet seated 15th into lands
DATE

Shot Charge VEL


1 52.3 2781
2 52.6 2812
3 52.9 2824
4 53.2 2845
5 53.5 2870
6 53.8 2870
7 54.1 2873
8 54.4 2881
9 54.7 2886
10 55 2909
11 55.3 2927
12 55.6 2937
13 55.9 2960
14 56.2 2969
15 56.5 2988
16 56.8 2998
17 MAX 57.1 not fired
If y are using 18lbs - 22lbs rifle the recoil is mild
Cheers
RB
BTW I started with a 7mm Rem Mag and this is not a very effecient cartrige the .284W is a far better cartrige less recoil less powder better barrel life.
Also a magnum bolt face will limit your options if switch barrel,cal)

 

[mysticplayer]

Any real world BC estimates on the 180gr Bergers?

I have been shooting a version of the 280AI which I call the 7 Mystic. Accuracy has been very good with high load densities. Right now shooting the 162gr Amax and will test the 180gr Bergers after hunting season.

1000m results have been excellent with the Amax.

Case volume is very similar to the 7RSAUM,where I got load data from). I start with '-06 brass and neck down, form a new forward shoulder. Case can easily hold 60gr of H4831SC,not a load just for comparison) with the 162gr seated short enough to feed from a mag. I would be seating the 180's long so case capacity will increase a few grains.

From my 24" Shilen, I get 2950fps using moly 162gr Amax and H4350/Fed 210M in Fed GM brass. In a 30" tube, shouldn't see a problem pushing the 180gr to 3000+fps as there is a significant volume increase over the 284W.

Wildcating a bunch of different cals and cases, I have not found the 'short/fat' case to be any better then a 'long/skinny' case as long as there is a proper matching of powder vs bullet weight vs bore size. At least from the perspective of LR shooting.

With the loads listed for the 7WSM, there is still quite a bit of room left in that case. The RSAUM or some version of the 280AI would lead to better load density. Would also run lower pressures then the 284W.

Jerry

 

[AndyMass]

Raven, Mystic,

thanks for the information, the 284 Win case certainly seems to be a realistic proporsition, as does the 280Ai Remington.

I wonder if there would be any merit in Improving the 284 case to a 40 degree shoulder?

With regards to real world BC figures of the 180 Bergers, I cannot comment. I will say that their 140 grain VLD's would seem to be very close to the factory "estimate" of .627.

I have run this figure in conjunction with Exbal and found the actual recorded point of impact down range to very, very close to the estimates in the programm out of my 6.5x284 out to 1000 yards.

 

[mysticplayer]

I see little benefit to improving the 284W since it already has a sharp shoulder,30 something degrees). With the bullet seated long and pressures ramped up, it most certainly works as is.

I just think having a bit more boiler room for the 180gr bullets will make the rifle more docile. There will be barrels that will not tolerate the elevated pressures of the 284W/180gr combo.

There would be little to gain if you could only get the 180gr bullets to 2700 to 2800fps vs the 6.5 140gr class going 2850 - 2950fps. Certainly not worth the extra recoil.

The ideal case volume in longer barrels would be 58 to 60gr of H4831SC at 100% load density with the 180gr seated with the boattail just below the neck/shoulder junction. This would be run at magnum pressures not 'BR' pressures.

This is a 280AI/7Mystic or shorterned WSM.

Jerry

 

[coupalr]

How about a 7mm-300 win mag? Lots of great brass choices and enough power to get that 180 moving along above 3000fps. I will be shooting the 180's out of my 7STW in a few weeks. I will let you what I find out about there BC.

 

[mysticplayer]

coupair, I have a couple of 7RM's. One a custom LR rifle with a Kreiger barrel. The other a factory Savage. I see no benefit to use the 7-300WM over the standard 7RM.

Both rifles are very impressive for velocity AND accuracy. I use the Lee collet neck die and have had no issues with the belt. The reamer that cut the Kreiger has a very tight dimension around the belt so no bulging there.

The Savage bulges a smidge but as a hunting rifle, I just pitch the brass when it grows too much.

The case capacity will have no issue pushing the 180's to as high as they are likely to tolerate. With powders like Retumbo, Re25, US869 and H50BMG. There will be something to work.

However, when burning that much powder, I fear that barrels are going to wear quickly and overheat during long relays.

I had to put a dozen rds through my heavy barreled Kreiger on a hot day to finish a 1000m fun shoot. The barrel was screaming hot. Still shot well but I just don't know how many barrels can take that type of heat and not open up their groups.

Loads are likely to approach 70+gr. Even the 7 WSM at around 65gr is going to heat up barrels in a big hurry.

For F class needing 20+2, that is going to cook alot of pipes.

Jerry

 

[JoeDuke]

Jerry, Is the print for your cartridge available? Thanks in advance,

Joe

 

[mysticplayer]

The 7 Mystic is my version of the 280AI and came about because of having a set of 7RM dies.

If you know what a 280AI looks like, the 7 mystic is similar except the shoulder is moved forward. 40deg shoulder

To form the false shoulder, you put a 30-06 brass into a 7RM FL sizer. The die forms the secondary shoulder on the neck. I fireform using the cream of wheat method. Trim, neck turn to clean up the necks, deburr and you are ready for full pressure loads.

I also seat the bullets using a 7RM seating die and runout has been zippo. After firing, the necks are sized and the cases deprimed using a Lee 7RM collet neck die.

This way I get a wildcat but don't need to use custom dies. If the shoulder moves after firings to make the chambering stiff, you can bump the shoulder with a 280AI FL sizer from Lee or body die from Redding. Just back off the die.

A 7-08AI die will also work if you have a 280AI reamer with a .460" diameter shoulder. My 7 Mystic has a .455" shoulder.

The 7 Mystic has the shoulder between the reg AI and the Gibbs.

In my 24" Shilen, I can push 162gr Amax to 2950fps using H4350 and Fed 210M. Case volume is almost identical to the RSAUM and that is the load data I used to work up. A magnum pressure load. Still brass life has been excellent with around 6 reloads before a shoulder bump is needed. Primer pockets stay nice and tight.

I used a 280AI chambering reamer to cut my barrel. Just moved deeper and used the formed brass to index off for headspace guage.

Jerry

 

[JoeDuke]

Jerry, Thanks for the info. Very interesting. This way you get to use good lapua 30-06 brass huh? How much larger in capacity is your cartridge than a standard 284 Winchester?

 

[mysticplayer]

I have tried the 'Euro' brass and have not found it to offer any benefit over well prepped commercial brass. Plus, Norma is not all that durable. Really had good luck with Win, Rem and Fed GM. With sorting, I have also used surplus LC brass with excellent results.

Don't have any 284 brass but from the Lee reloading manual, effective case capacity of 284W brass is 3.97CC, RSAUM is 4.67CC, 280 is 4.39CC.

Jerry