Cerrosafe chamber casting numbers. Now what.

[Colorado4wheel]

I did a Cerrosafe Chamber casting of my M1A. Essentially, the biggest number is .309+ a little. I can't measure the small number (what a bullet would get stuck into the bore by). I don't have the right tools. I did manage to cast a .305" bullet and it left a impression of the rifling that measure at .303". But that is hard to measure.

I am thinking of ordering a .302 or maybe a .303" bore riding section of the mold from Tom. I have a .311 sizing die. Thinking of ordering the bullet size at .312" at the base. Any suggestions before I pull the trigger. I really do think I measured it right at .303" but I don't want to get bullets stuck.

[Colorado4wheel]

I would have to adjust the numbers on the bullet just a little of course. Don't know why I would pick one of the other.

http://www.accuratemolds.com/bullet_detail.php?bullet=31-200L-D.png

http://www.accuratemolds.com/bullet_detail.php?bullet=31-200M-D.png

[Calamity Jake]

.302-.303 bore ride nose is to big for that M1A you need more like .2995-.301

On your chamber cast see if you can measure between the lands, that is the bore diameter.

[Colorado4wheel]

.300" goes in with room to spare. Do I want to go that much smaller? I did measure the between the lands # on the lead bullet I jammed into the lands and it is .303". But like I said. It is hard to measure.

[Wayne S]

With all auto loaders you are limited to OAL to clear the Mag. and bullet depth to allow FREE chambering.
One way to check bore Dia. in weapons W/O a flash hider is to take a bullet ,stick in in the muzzle and slowly turn it letting the lands cut off excess material.
You say that a .300 just goes in w/o any problem sounds like a long throat used on military rifles.
Unfortunately the M1's & M1A's don't allow a straight line access to the chamber.
One of those Stony Point bullet seating depth tools that is made for auto-loaders may help with the lands ID

[Calamity Jake]

Then go with a .303 nose

[45 2.1]

It depends greatly just how far those measurements are from the case mouth. The throat in these rifles taper somewhat and are bigger than what most people here realize.

[Colorado4wheel]

So I took some time to remeasure. Cerrosafe grows over time so I had to do some math to get things figured out. It is hard to actually measure the smaller number created by the lands. I think Calamity Jake is right. .303 might be too large. I was able to get my Dial calipers into the groove created by the casting and after all the math is done I think a tight fit would be under .303. More like .302" I don't want to order a mold so totally specific that it may not work. If it or my allow is off just a little. I am thinking .301" is a better/safer bet. Even Tom at accurate said to not order it too tight. Neo makes a 311284 copy and Tom has the 314299 copy that I can size to my own specs. So I am thinking .312 bullet and .301 nose. Leaning towards the Accurate mold because he treated e right with two other molds. Neo is in stock ready to go.

[Colorado4wheel]

The leade is .310" and is very long and the rifling doesn't even begin to touch a severely oversized bullet till .215" and not any serious contact till about .250". Your right.

[Colorado4wheel]

Ordered a Accurate Mold in .312 for the base and .301 for the Nose. Thanks everyone for their help.

[45 2.1]

If you taper the nose some, you'll have a lot more room to get better accuracy than having a nose too small.

[Colorado4wheel]

The nose is tapered.