Fire forming Lapua 243 to 22 CHeetah
Yesterday I decided to fire form my new Lapua 243 brass to 22 CHeetah. After conforming 20 cases in the Neil Jones forming die, loading 41 gr's of IMR4895 under a 55 gr. Hornady FMJ.
Everything went well, however I only fire formed 2 cases. The first case came out easily, the second was a problem. Tapping the bolt handle to remove the case with a rubber mallet is not my idea of something going right.
Seems the Lapua brass is a bit larger in the web area, and even though I resized it in a 243 FL die, this brass is not going to work for the CHeetah. I called an old friend and told him of my trouble. He indicated the same thing, Lapua brass is really great brass, but not for what I am doing. He suggested Winchester brass as that is thinner overall from the rest of the brand names.
So, I am prepping Winchester cases today and fire forming in a different manner.
Running bullets down a barrel to fire form wears the barrel, so I am going to change to 19 gr's of Green Dot, then fill the case full of corn meal to the bottom of the neck and then topped with a dab of Crisco to hold the corn meal in. I may have to increase my charge weight to get the desired results. Will post later on what happened.
Also, having a wildcat is a lot of trouble, if I had known the problems I would be encountering, I might of thought twice before buying this rifle. I have spent hours and hours on case forming, just something I didn't expect.
05-21-2009 08:01 AM
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> The first case came out easily, the second was a problem.
> Tapping the bolt handle to remove the case with a rubber
> mallet is not my idea of something going right. Seems the
> Lapua brass is a bit larger in the web area, and even though
> I resized it in a 243 FL die, this brass is not going to work
> for the CHeetah.
I'm surprised. Would the unfired cartridge chamber and then extract (unfired) without problem? If the cartridge could do that w/o sticking, the very thickness of the web should never cause a problem in that area unless unusually high pressures are involved (i.e, the kind that causes head expansion.)
NOTE: QL shows that 41gr/4895 under a 55gr bullet in a Cheetah MkI to produce ~57,000psi ... 7,000psi over max for the cartridge (as listed), and that's for "normal" brass volumes. Three things may be happening:
- You have a high pressure load to start with
- If I drop the "normal" case volume by 3% to account for Lapua thickness, QL pressure jumps to 60,000psi; Drop it by 5% and it hits 66,000(+)psi
- Did you turn the necks in case the .243 -> .224 resizing might induce neck constriction?
Last edited by MEHavey; 05-21-2009 at 08:41 AM.
Yes, that load was very hot, too hot! The data I received from the previous owner was totally incorrect and extremely dangerous. Now I understand why he gave up!
I'm starting over, fire forming without bullets using green dot.
Using the Lapua 243 brass, the procedure to reform for fire forming is rather simple. There is no neck turning required.
First, I full length size then use the Jones forming die with the .250 neck diameter bushing, forming the neck and bumping the shoulder near the neck down .050. The shoulder now is not straight, it's convex to the naked eye. I then use the Sinclair neck turning mandrel and run the neck through it which straightens out the neck. I then trim to 2.012. I check to make sure it chambers and it's ready for fireforming.
As far as the QL data, I checked it and was astounded! Never, never trust anyone's loading data, NEVER!
I'm 60 and still learning, boy that sure was a lesson learned!
I'm tempted to say that all's well that ends well,
but somebody already used that story title. :-)
Well, as it turns out there seems to be a qlich in the Quick Load program. The program shows the 22 CHeetah at 50,763 psi and the 22-243 at 65,000 psi.
As it turns out, that load really isn't that hot for a 65,000 psi max. Anyway, since I made my brass out of Winchester 243, I simply used starting loads for the 22-243 AI which is close to the CHeetah.
I have shot three different loads using IMR 4064, 4350 and 4895. All of these are starting loads and are in the 3,900 fps range, but not over 4,000 fps using 55 grain Hornady bullets.
The rifle is remarkable, a 5 shot group at 100 is a hole measuring .385 and at 200 with no wind, grouping is at .520 using a 36 power Weaver.
There really is no reason to continue with load development, I'm happy with the velocity and accuracy.
I sure learned alot in these last 3 weeks, and this will be my only wildcat!