Any ideas

[hornady]

I posted this on another forum. I have a Chilean Mauser in 7X57 Mauser I wanted too shoot cast Bullets in.
The mold I used is the Lyman 287346 135 Gr, A little light for this rifle.
Barrel slug is .284 I sized and checked my cast bullet diameter they are .285
I seated bullets per the Lyman cast bullet manual.
Bullets hardness per my Saeco tester are a little harder than Lyman #2.
I am using Hornady GC and BAC special blend lube.
I have loaded test rounds with three different loads of Red dot with a max of 13 Gr,
No matter what I have done so far about half the bullets key hole. At first I thought it may be the crown. How ever I bought a box of Hornady 154 Grain Jacketed Bullets pushed with 36.0 of Varget, At 50 yards off hand I am getting two inch groups without any key holes.
On the other forums ideas I have gotten were Alloy too hard or soft, seating depth, powder used, and the bullet too light for the rifle.
How ever one guy said he had a Turkish Mauser no matter what he tried no cast bullets shot well in it. I cast for 3 different 30 cal rifles and several hand guns as well, but this is a new one on me. I may start playing with bullet seating depth. But anyone else have any ideas. This may just be the odd ball that don’t like cast bullets. 

[SHOOTALL]

could it be depth of rifling ?  or rate of twist for bullet used ?
 

[hornady]

It has me stumped I am thinking about adjusting bullet position off the leade.
What has me puzzled is the Key holing . Jacketed bullets shoot fine. If bad riffling you would think accuracy would be bad with jacketed bullets as well. But that is not the case. I could see poor accuracy with the wrong bullet weight but not going from good accuracy with jacketed to key holing with cast.

[SHOOTALL]

It may be bullet shape . the bearning surface that meets the rifling may be short OR when you seat the bullet you may be reducing the dia of the bullet thus creating a lose fit .

[Nobade]

Throats on military 7X57 rifles are quite long, with a very gentle taper. First thing, make a cerrosafe cast or an impact impression of the throat. Size the bullet to that, not the groove diameter. What is causing your headaches is gas cutting while the unsupported bullet flies through the throat area without some way to get a gas seal. If you have some way to recover bullets without damaging them you will see cut marks on the sides where they were torched away. You may find you have to invest in a custom mould designed to properly fit your own rifle. Veral in the other room below is a great source for those.

BUT...

Likely you will be able to shoot that bullet if you use some kind of granular filler. I like cream 'o' wheat, but I live where the humidity is very low. Other people warn against it because it turns into a rock when moisture is present. A good alternative is plastic shotshell buffer, which doesn't absorb moisture. If you have some slow powder like 4350 or slower, try about 25 grains of it and enough filler to make a lightly compressed load. Seat the bullet out as far as you can. Likely it will barely be in the case and still not touch the rifling. If you can get it to engrave all the better. Try a couple and I think you will be pleasantly surprised. You won't even need gaschecks because the filler completely seals the gas.

Be careful with this. Only use slow rifle powder, never anything faster than 3031 with filler. It will raise pressures considerably, so use only half the powder you would use for a full load. Used intelligently, it works wonders to make cast bullets perform. Paper patching will also solve your problem, as well as allow you to load cast bullet to full military ammo performance.  But that is a subject for another time.

[hitman54]

+1 Nobade, Easiest solution to your problem.

[kbstenberg]

+2 for Nobade. He is a good gunsmith and very knowlegeable of firearms.

[hornady]

Thank you No blade very good explanation. A friend has the mold now, I told him he could try it in his rifle and if he liked it he could buy it. If not I would take it back, If I get it back I will try your suggestions. I cast for modern rifles with no problem. And a few years back I Had a Spanish Mauser in .308 that loved cast. I still can not remember why I sold it. Guess I needed a new project a thought the 7X57 looked like a good one.

[jhalcott]

 Hornady, you do realize the MILITARY 7x57 load used a LONG 175 grain slug. YOUR bullet has a long way to fly before it hits the grooves. This gives the gas plenty of time to blow by it and do a lot of damage. Try a longer bullet if you can . Doing what NOBADE says should work also.

[hornady]

Up date I still don’t have the mold back, but I had some of the bullets I had cast on hand. I loaded them at various COL with 2.900 being the magic number with 12.0 Gr, of Red Dot. The bullet is set out of the case past the first grease ring. I tried 4 rounds at 2.950 but I started loosing accuracy. The groups at 2.900 were not great but no key holing and in reason. If I get the mold back I think I will loose the GC and try different buffers and powders. I think with some work I could get this bullet too work.

[ventura guy]

Red dot never worked for me too good. I'd try something like 4198 or RL7 or even 4895. Seat the bullet as far out as possible. Keep the gas check. Up the velocity. You should be fine.

[Nobade]

Or 4350 or 4831......

Something to get that bullet up to speed gently. Use filler behind it and it'll most likely shoot well at good speed.