So, F Class, what's it all about then?

[Dougan]

The principle is similar for both the 22C and 7mm

The simplified version:

For the 7mm I use 300 SAUM brass so first stage is run it through a die that had been cut to size with the rifle chamber reamer, this gives brass that fits the chamber but the internal diameter of the neck is too small and it is not parallel so I run a floating mandrel through it which takes it to .284" ID, then neck turn it to .0125" with a SInclair neck turning tool and a powered drive or alternatively on a small lathe with a sacrificial mandrel. Then trim to length and chamfer the inside and outside of the mouth. Then gently ream the inside to remove any doughnuts and then weigh them to weed out any significant variations. Finally I neck size them to give the correct neck tension.

I build my first load with the bullet jammed into the lands by .020" so the case does not move forward when it is hit by the firing pin and this blows the case to the shape of the chamber.

I need to post some pictures don't I

I am halfway through a batch of new cases and if I get a chance to continue with them this weekend I will take some pictures.

Very interesting :geek:

So you modify the dies - and interesting that the chamber does the final touch

Still got a bit 'lost' in the middle...a 'floating mandrel'?...sounds like some sort of swimming monkey :?

Pictures would be excellent

[Sim G]

F-class....... think "benchrest shooters who like to lie on the ground and get wet...." :lol: :lol: :lol:

[20series]

F-class....... think "benchrest shooters who like to lie on the ground and get wet...." :lol: :lol: :lol:

Sim, or in the case of this last weekend sunburn!!

I fairness it's not a bad description certainly for the F-Open,

Alan

[ovenpaa]

Still got a bit 'lost' in the middle...a 'floating mandrel'?...sounds like some sort of swimming monkey :?

Pictures would be excellent

I recently wrote something on the principle of necking down .308 to 7mm08 which is a .308 case with a reduced diamater neck so you can use 7mm bullets, I will dig it out in a bit so you can see what I mean.

[ovenpaa]

This is the Sinclair expander die I use plus an assortment of mandrels some purchased and some made. You should just see an O ring under the locking ring, I use this so that when tightened into the vice the die can still move slightly, this should reduce neck run-out. I also leave the top cap slightly loose so the mandrel will move up and down for the same reason.



This is an example of a very quick 7mm08 job, I don't actually shoot this so I had to improvise but you should see the differences.

Left is a .308 case fired and cleaned
Middle is a .308 necked down to 7mm - this one went quite well but you should be able to make out a slight buckling top left
Right is a.308 necked down to 7mm and the opened slightly with a mandrel

These are all scrap brass with no preparation but hopefully show what I mean, apologies for the crap picture.



I will post some pictures of my 7mm SAUM cases when I finish them off.

[ovenpaa]

If you get a chance check out Spud's Youtube clips on this, he explains things well and it is always good to be able to see the stages as opposed to having them explained in writing.

[Dougan]

This is the Sinclair expander die I use plus an assortment of mandrels some purchased and some made. You should just see an O ring under the locking ring, I use this so that when tightened into the vice the die can still move slightly, this should reduce neck run-out. I also leave the top cap slightly loose so the mandrel will move up and down for the same reason.



This is an example of a very quick 7mm08 job, I don't actually shoot this so I had to improvise but you should see the differences.

Left is a .308 case fired and cleaned
Middle is a .308 necked down to 7mm - this one went quite well but you should be able to make out a slight buckling top left
Right is a.308 necked down to 7mm and the opened slightly with a mandrel

These are all scrap brass with no preparation but hopefully show what I mean, apologies for the crap picture.



I will post some pictures of my 7mm SAUM cases when I finish them off.

Hi Ovenpaa,

I very much appreciate you taking the time to do that

That does make more sense now - I didn't realise you could change a case that much using a die! It's also making more sense of some of the other threds I've read on here - You guys were talking about cases getting stiff, and 'annealing' (is that right?) - I couldn't figure out why you were trying to get so many shots out of each case...but now I realise that it's not just about cost, but also the effort required to produce a 'self built' case for a bespoke rifle....

I understand enough now to read more about the 'whys?' (rather than incesant questions :) ) I will also watch Spud's videos - If I'm being totally honest (sorry Spud ) I saw that the second vid was 20mins long, and at the time thought I'd watch it later...and havn't got round to it yet.

Just one more question ( :roll: :lol: ) In your opinion - After how many uses (generally) is a case at it's best for accuaracy...both for F class home-builds, and for standard rounds?

Cheers,

Dougan.

[ovenpaa]

Just one more question ( :roll: :lol: ) In your opinion - After how many uses (generally) is a case at it's best for accuaracy...both for F class home-builds, and for standard rounds?

Well taking my 7mm case as an example, it will not shoot when first built as the case moves forward when struck by the firing pin so I have two choices, I either leave a false neck as a register to hold the case in place or I build longer so the bullet is jammed in the lands and holds the case in the right place. So that is one firing

It took a while to find this out.

Add the stages of necking down, passing a mandrel through, neck turning to reduce and uniform the neck wall thickness and then sizing again and firing and it is ready to be annealed and will then be perfect for a 1-2 firings whereas I have some Lapua .308 brass that has been shot 12-14 times and is still going strong albeit annealing would help the neck tension. Really it is down to what you are looking for and how hot you load, average brass will probably benefit from annealing after 5 shots so probably the second and third shots will be as good as it gets. This is just my opinion.