COW fireforming and throat erosion

[tooter]

First off, I'm newly registered to this wonderful site and have learned so much in the past few months thanks to all of you.

I'm returning to shooting after sixteen years of a attending to a career priority. My past shooting experience was with factory rifles so I'm new to this precision shooting game.

I have a 6mm Dasher build underway and am concerned with the fireforming process and throat erosion. I've checked through many threads but haven't picked up any discussion on the abrasive effect of COW on the throat of a virgin chamber. Any experiences, thoughts or advice to share will be much appreciated.

 

[dmickey]

Just do as I do. Shoot it and don't worry about erosion!! That's why replacement barrels are made!

 

[tooter]

Dennis,

Sounds like sage advice ---- all things in perspective now that I'm looking at retirement, it's time to enjoy the toys not preserve them for someone else!

 

[ChuckMiller]

I do it in my garage and see no effect on the throat. It's expecially handy on big 6's or extreme case forming and saves on powder and bullets. I especially like the fact that I can do it at home at my leisure and it's easier to customize the load one at a time. If your an accuracy buff it's no fun blowing barrel steel down range and the variances in load performance when fireforming make load workup useless. Flip side is that On small case's such as 223 family on down or someone that's putting together a hunting load just shoot them. I only see big differences in the larger cases, smaller cases usually shoot pretty well.

 

[tooter]

Chuck,

Thanks for sharing your experiences. I also have an additional 223 BAT bolt on order and will eventually do a 223AI switch barrel. For this one I'll likely go with a slightly lighter than full charge and some bullets still hanging around after sixteen years.

 

[drano38]

tooter

Another option is the Hornady hydraulic form die. A search here will find a few hits. I got mine last year when I made a Dasher barrel for my Savage.
Best way is buy your own reamer, then send the prints to Hornady, and they will cut the die to match your chamber. If you aren't buying your own reamer, maybe you can get the print from your gunsmith.
Hydro forming takes some time and swinging a 3-4 lb dead blow hammer gives the arms quite a workout--I did no more than 20-30 cases a night.
Also, I'd recommend not hydro forming on your good press. Go find a used one at a gun show. I picked up an old Pacific from a friend. I hit the ram rod 2-3 times per case for the 200 cases I formed. I don't want to beat on my Redding Big Boss w/ a big hammer that I expect to load very high quality ammo.
Call Hornady and ask for Lonnie Hummel of the custom die dept for more info. The die was about $140.

Just another idea.
good luck
drano

 

[tooter]

Drano,

I've been intrigued by this forming process. Without understanding the whole process in detail, I assume you screw the die in a press, partially fill a case, lift the press ram and then beat on a small dia. precision plunger. Have you seen any plunger deformation or bending? I would guess there is some water spray as well.

I'm glad to hear this is an effective forming method. Do you think this would also be suitable for the 223AI?

I much appreciate your comments.

 

[WayneShaw]

Using COW can do a fine job without barrel wear, but it has to be done right. The trick is getting the case to hold in the oversize chamber so it will fill out properly and the shoulder be in the right place.

Jamming a bullet hard and shooting is fine and will achieve the same thing, but there is the wear factor.

My method is to expand the neck up one caliber, then size down the neck only enough to 'wedge' the case between the boltface and the neck, which means running the case into the die about the .100' less than a normal BR case. What you create is a 'step' in the neck that will wedge in place closing the bolt.

I use 12 grains of Bullseye, fill with COW on top of powder up into the neck, then a piece of paper towel stuffed in to keep it all in place. The COW acts as an inert filler that will push the shoulder out and forward.

I'm sure other methods work too, this is just the method I've used successfully.

 

[1000yardstare]

I share 'dmickey'`s philosophy. I just fireformed 150 6AI cases by zeroing and shooting different bullets for group on my club`s 300 metre benchrest range and by obtaining 500 and 900 yard elevations at F Class practise on a Canadian Army base. The higher velocity of the fully fireformed cases will change the elevations slightly but I have a starting point and had a lot of fun doing it. I have also determined which bullets my barrel prefers. In two years MacLennon can build me another barrel.

 

[tooter]

Wayne, thanks for the input.

I've started experimenting on doing this with some Lapua brass and a 25 cal. Hornady elliptical expander. I've begun to partial size the necks back down but can't bring them all the way to fit the chamber since the rifle is still being built by Mike Bryant.

I've tried partial neck re-sizing using a .270 Redding TN bushing in a Wilson die,the chamber will be finished at .272). So far this seems to work OK but until I get the rifle, I can't go the full route.

Is there any need for a retainer/separator barrier between the powder and the COW? Cotton? Paper towel?

 

[WayneShaw]

I never have, I just dumped the COW right on the powder. I doubt you'll giggle them around much to stir it up between loading and fireforming.

 

[drano38]

tooter
Read this thread.
http://6mmbr.websitetoolbox.com/post?id=2327659
Yes, screw die into press, use special,included) shell holder that does not have a hole in it. Put spent primer in case, completely fill w/ water, put in press and run ram up. Slowly insert plunger until it touches water. Then smack hard w/ 3-4 lb deadblow hammer. Make sure you hit square, or you will bend the plunger rod--if you bend it, Hornady will have a new plunger rod in your mail box in about 4 days,don't ask why I know this). My second plunger rod is bent just a bit now. There is almost no clearance on the rod to the die, so any bending will show fast.
You don't really get much spray because of the tight plunger fit--but wear glasses just in case.
I hit the plunger, remove case, add a few drops of water to re-fill the case,some water sprayed out, and I just blew the shoulder .1' up and to 40 deg), then hit it 2 more times.
Pour the water out, knock out the primer, then if you want, blow dry w/ air compressor.
I have a Stony Point,Hornady now) headspace gauge. So I set the forming die so the shoulder was about .005' longer than my chamber. Then I resized the case to push the shoulder back, which formed it a little better. My first match was 1000 yd IBS using virgin hydro formed brass. First group was 7.9', so I believe it works.
Should work great for a 223AI. But since an AI can be shot in a regular chamber,assuming its been chambered correct), I'd just shoot 223 in your AI gun--more fun than hydro forming!
good luck
drano

 

[tooter]

Thanks DRANO!