7x57 Spanish Mauser chamber cast

[Brettitt41]

Well I recently acquired a nice Spanish Mauser dated 1921 in 7x57 for a nice price. The bore was in less than stellar shape but I could see rifling (barely) with the naked eye. A lot of cleaning and scrubbing and I now have at least a little more rifling. There is still some sort of gunk coming out of it that I am not sure what it is but maybe a few rounds will help clear it up. Anyways I drove a lead slug from the muzzle and got .287 grooves then did the same with a different slug from the chamber and got .287. So not to bad. I tried to make a chamber cast twice with cerro safe and both times had to melt it back out as I couldn't get it to pound out. I know the bore is kind of rough but the chamber looked ok with my borecam. Is there another way to get a good chamber cast that will come out, do I need a chamber cast since I know the groove size? My intention is to shoot PPB in her so I'll need to find the bore diameter somehow. I did check headspace, with a go and no go gauge, and its good.

[leadhead]

Buy a can of that foam stuff in a spray can and shoot it down the barrel.
Let sit for 30 min and run some clean patches thru it. You won't believe
what comes out of that barrel. Great stuff.
leadhead

[Larry Gibson]

How long did you leave the cerrosafe in the chamber after pouring in did you leave it?

[Brettitt41]

How long did you leave the cerrosafe in the chamber after pouring in did you leave it?

I tried tapping it out as soon as it frosted over, 3-5 seconds maybe. Then spent the next 20-30 minutes trying to drive it out with a steel rod then eventually getting the torch back out and lightly heating the area to melt it out. I half way expected it because even trying to push a doubled patch through was hard. Not squeeky clean hard but dang this bore is rough hard. Looking through my borescope I can see the chatter marks from the rifling process in the grooves in places but the lands look like they have small pimples, probably from corrosive ammo and not cleaned properly years ago. Just hoping to get it shooting well and use it as a learning tool. I've already learned how to turn my excess garand brass into 7x57 brass so it's working. I would like to PP it though since the bore is so bad.

[swheeler]

Brett let the cerrosafe set for 25-30 minutes and that will be the smallest size it will shrink to and will tap right out, then at one hour take your measurements. I have used 9.5 sulfur to .5 artist charcoal, it too works but is delicate, so much so I have eventualy broken every cast made with it, sad to say.

[Larry Gibson]

What swheeler said^^^^^

If the cerrosafe still sticks then try a casting of paraffin wax. pour it then put the rifle in a cool place for an hour to "harden" the paraffin. It will push out easily and some decent measurements can be made handling it in the cold. Perhaps not exactly precise but close enough. Probably small pitting in the chamber you can't see.

[DonHowe]

A while back a friend wanted help identifying the chambering of a rifle. First I slugged the bore to verify caliber. Having determined it was .30 cal, I chose a soft .38/.357 bullet and slugged the chamber neck. Then a soft .45 cal tapped into the shoulder area got me the diameter at the shoulder. A .50 RB gave diameter at chamber mouth (cartridge base). Those gimensions plus a quick check with fired plus resized cases verified it was .30-06, which I suspected since it was an older sporterized 1917 Enfield.
Just another possible method if you are a hoarder of leftover stuff, just doesn't give the visual of a chamber cast.

[atr]

you might also try spraying the chamber with silicone. that might help when it comes to removing the cerrosafe.
also, I believe the rim/base dimension of the 7x57 case is different from a 30-06 case....

[Soundguy]

I wonder if someone tried to polish the chamber and oversized it at the top.. making a chamber cast essentially.. stuck.