fireforming 6.5 grendel brass from 762x39

[chas442]

I plan on fireforming 7.62x39 into 6. grendel. I know this is not optimal but gonna do it anyway. I have 123 gr. projectiles and plan on using IMR 4895 for fireforming. I already have resized the 7.62x39 brass. I would like to know how much powder is needed to fully fireform. I have fireformed 12 pieces already with 20 grains of IMR 4895 and it appears to have done the job. Ihave no aversions from using pistol powders I would prefer to use the least amount as this is a wasteful operation.
Any help would be greatly appreciated

TIA

 

[adcoch1]

I'd use a starting charge of your favorite powder. Worked when I fireformed 6.5 grendel. Check your neck thickness though...

 

[chas442]

The PPU cases that I'm using are at 0.014" thickness. So that equates to 0.292"dia. neck thickness. That is less than SAMMI specs of 0.300" for neck diameter of the chamber.

 

[chas442]

The problem is that Hodgdon does not list data for the 6.5 Grendel using IMR 4895.

 

[Swampman]

What weapon are you using to fireform?

I've used Red Dot and a case full of Cream of Wheat to form various cases, but only in bolt guns or single shots. I'd be leery of trying it in a gas gun.

 

[troy fairweather]

Fine to form using cow method in a gas gun, id pull the gas block off tho. Make sure there is no muzzle device on the barrel of you use the cow.

 

[Bfh_auto]

Are you annealing you brass after such a big step? You're liable to get splits soon if you don't.

 

[chas442]

I'm doing this in a gas gun. I plan on annealing after fireforming before sizing.

 

[Laphroaig]

Nosler has IMR4895 data for 123/125 gr. projectiles:

https://www.nosler.com/65-grendel

Just be aware that 20 grs. is below their minimum.

 

[chas442]

Thanks for the info. 20 grs. appears to fireform compared to a starline new piece of brass.

 

[berettaprofessor]

Am confused. I thought 6.5 Grendel dies would resize a 7.62X39...and then a neck trim?

 

[Swampman]

Am confused. I thought 6.5 Grendel dies would resize a 7.62X39...and then a neck trim?

True, but the case shoulder/body on the Grendel is wider so case capacity is greater.

Until you fireform to blow out the shoulder and reduce case taper, you're not going to have the case capacity to load the Grendel up to it's full capabilities.

 

[rdnktrkr]

I worked with a friend making 6mm ARC, we used 6.5 Grendel as a parent case and used LVR as the powder, we also tried using 7.62x39 but wound up with split cases. We had to turn the necks to remove ridges.
I've been fortunate enough recently to find fired Grendel brass locally, at GA Arms, you might try some online resources also.

 

[Warpiece]

I did this for 6mm arc cases as well. I suggest anything you try, only do small batches to ensure you don't waste too much. Everyone seems to get wildly different results depending on their methods of sizing, annealing and loading. If you get too many splits, try changing things up, like annealing after sizing but before firing.
Also suggest stopping to clean the chamber well if a case does split, don't just shrug it off and keep going. It'll just make the process go a bit smoother for you and the gun.

It helped me get past the wasteful feeling to think of it as cheap, plinking factory ammo. It'll still be on target for the most part.