So a while back I picked up a 300PRC modified case as I was planning on building one for long range. When I ordered the build I was convinced to go with the 30 Sherman Magnum as it’s basically an improved 300PRC. It will shoot the 300PRC factory ammo. Does that mean the modified case I have will work as is? I wasn’t looking forward to wasting brass making my own case but now I can’t think of why the 300PRC case wouldn’t work. It’ll chamber and give me a usable measurement. Am I missing something?
300PRC modified case in 30 Sherman Magnum
- Thread starter DOA357
- Start date
What do you mean that you have "a 300PRC modified case"?
Like you have one case that someone has modified? What good does that do? What kind of modifications does it have?
If this 30 Sherman Mag is a fire form wildcat of 300PRC, then the normal technique is to shoot your 300PRC ammo in your 30 Sherman Mag barrel. The brass will conform to the chamber. Then you use a 30 Sherman Mag sizing die and reload it with 30 Sherman Mag load data.
Like you have one case that someone has modified? What good does that do? What kind of modifications does it have?
If this 30 Sherman Mag is a fire form wildcat of 300PRC, then the normal technique is to shoot your 300PRC ammo in your 30 Sherman Mag barrel. The brass will conform to the chamber. Then you use a 30 Sherman Mag sizing die and reload it with 30 Sherman Mag load data.
A modified case is threaded to use the Hornady tool for checking bullet seating depth. So I bought the Hornady virgin modified 300PRC when I came across it one day with the intent of building the rifle. It’s the only way I was taught to determine seating depth. How else does one do so? I have virgin brass for the 30SM coming so I’m eliminating the fire forming step.
Ah.
You can use the 300PRC case to find jam length, even an unmodified one.
I use this method:
Another way is to use a micrometer seating die and start too long. Insert into chamber with the bolt closed and feel if it resists (sets back the bullet) on close. If it resists, keep going .010" shorter until it doesn't resist. Measure this length and it's your jam length within 0.010", which is close enough.
You can use the 300PRC case to find jam length, even an unmodified one.
I use this method:
Another way is to use a micrometer seating die and start too long. Insert into chamber with the bolt closed and feel if it resists (sets back the bullet) on close. If it resists, keep going .010" shorter until it doesn't resist. Measure this length and it's your jam length within 0.010", which is close enough.
Base to shoulder will be different when using the 300 PRC modified case, since that case has not been fireformed to the Sherman chamber. When you measure base to bullet ogive using the PRC case, pushed tight against the Sherman chamber, and later compare that measurement with a bullet seated in a fireformed piece of brass, you wouldn’t be able to use the same measurement to determine distance from lands in your rifle. The shoulder is pushed forward in the Sherman chamber.
I have a Sherman chambered rifle, I just took a piece of my fireformed brass and had a guy thread it for the Hornady tool.
I have a Sherman chambered rifle, I just took a piece of my fireformed brass and had a guy thread it for the Hornady tool.
358Rooster
CGN Regular
- Location
- Central Saskatchewan
You absolutely can use the PRC case to find the max loaded length. It does not have to be formed to your chamber, and as long as that case doesn't present any interference, you're good. You're looking for a linear measurement from (essentially) the bolt face to some point along a given bullet's nose profile (won't recommend measuring to the tip, as we all should know by now).
No other critical dimension will be possible without a formed case, but finding max seated length certainly is with the raw modified case that you have.
No other critical dimension will be possible without a formed case, but finding max seated length certainly is with the raw modified case that you have.
