OAL for 7SPRC Wildcat

[Rockdoc173]

I'm attempting to rework the 6.5 PRC modified case I bought to work in my 7 PRC (6.5 PRC necked up, not the new SAAMI cartridge). I ran the case over a 0.284 mandrel but it's still too tight to move freely. Anybody know how far over caliber the mandrel needs to be to account for spring back and get the bullet to slide easily in a modified case?

 

[IHFarmer07]

I'm attempting to rework the 6.5 PRC modified case I bought to work in my 7 PRC (6.5 PRC necked up, not the new SAAMI cartridge). I ran the case over a 0.284 mandrel but it's still too tight to move freely. Anybody know how far over caliber the mandrel needs to be to account for spring back and get the bullet to slide easily in a modified case?

Usually rule of thumb is .001” spring back but that depends on if it’s been annealed of multiple times fired. More time it’s been fired the harder it is t on overcome spring back.
I would go .285 or .286 for the bullet to slide. May have to do a trial and error deal.

 

[Mike Casselton]

I'm attempting to rework the 6.5 PRC modified case I bought to work in my 7 PRC (6.5 PRC necked up, not the new SAAMI cartridge). I ran the case over a 0.284 mandrel but it's still too tight to move freely. Anybody know how far over caliber the mandrel needs to be to account for spring back and get the bullet to slide easily in a modified case?

Probably .287 to give enough room for spring back, and allow the bullet to slide freely.
I've got some Hornady brass here if you want to make 7/6.5 PRC. Shoot a couple and then I can make a modified case for you. It takes less than 5 minutes on the lathe.

Hell, we can even use some scrap bullets so you don't have to shoot good ones making the case.

Or, I can take a bolt and turn it down to .287 and make a mandrel...

BTW, we're probably shooting two days next week if you can make it.

 

[Rockdoc173]

Probably .287 to give enough room for spring back, and allow the bullet to slide freely.
I've got some Hornady brass here if you want to make 7/6.5 PRC. Shoot a couple and then I can make a modified case for you. It takes less than 5 minutes on the lathe.

Hell, we can even use some scrap bullets so you don't have to shoot good ones making the case.

Or, I can take a bolt and turn it down to .287 and make a mandrel...

BTW, we're probably shooting two days next week if you can make it.

I would like that very much. I'm right at the end of the semester and should have some free time so I'll try to link up with you guys. When do you plan to be out there?

I have both a 21st Century expander die with a 0.284 mandrel and an LE Wilson expander measuring whatever their standard is, maybe 0.283. I bought two Hornady 6.5 PRC modified cases and ran one over the 0.284, it wasn't enough. I cut two slits in the neck and it's still hanging up right at the neck/shoulder junction. I think what's happening is as I run the brass into the die, the die puts all the pressure right on that neck/shoulder junction and it may protrude ever so slightly, though not enough that I can see anything. I think I'll get like a 0.274 mandrel and run it over that first (for normal brass that I'm going to shoot), then the 0.283 so that the expansion is a little less abrupt. That said, it doesn't seem like 0.264 to 0.284 should be that bad. I don't know, I've never done this. Do I need that step?

 

[Mike Casselton]

Probably Tuesday for sure and maybe Friday.

Give me a shout over the weekend and I'll know for sure.



A single mandrel should be just fine, you are only going up .5mm.

I've taken 223 cases and gone straight to 7mm/.284 in a single pass without issue.

The issue you're running into necking up is sometimes it creates a donut at the base of the inside of the neck. It's pretty normal because the shoulder of the brass is thicker than the neck. When you expand, that thicker shoulder portion is now part of the neck. It ends up on the inside because the resizing die pushes it there.

If your bullet base (full diameter portion) doesn't go below the bottom of the neck, it's no issue.
If it does go below, an inside neck reamer will fix it.

Otherwise you'd have to mandrel it up and skim cut the neck/ shoulder junction with a neck turning tool.


For the purpose of a modified case, you could literally just buzz it out of there with the correct diameter drill bit.

It doesn't matter how thin the neck gets because you're only using it to keep the bullet pointed forward.

I'll head out to the garage and see what I can scrounge up and turn into a mandrel.

My K&M expander looks like a modified shoulder bolt turned into a mandrel...

 

[Rockdoc173]

I chucked a bullet in the drill and lightly "reamed" it which actually worked but since it has the slits in it it's not very stable. I think running it over a 0.287 mandrel will be enough to account for the spring back, then if I need to I'll ream the necks.

 

[Mike Casselton]

Success!!
Turned a Mandel to .287 and tried it on a 6.5 necked to 7mm.
The bullet slides in and out perfectly.

Broke the 8-32 tap because I'm impatient.
Oh well, it'll still do the job.

 

[Rockdoc173]

Ahh sweet. what kind of die does it fit?

 

[Mike Casselton]

It fits that K&M in the pic.
If you need one made to fit the Sinclair with the flat, I can make a different one and add it. I'd just need to take some measurements off of it, unless I can find mine.

 

[Mike Casselton]

When I tested it, I just lubed it and pressed it into place.
I then put it in the press and pulled it out like I was pulling a bullet.

You should only need it once, so gripping the fatter end with pliers won't make any difference.

 

[Rockdoc173]

Awesome. Man I so tempted to log in to the shade tree machinist thing when I move back to Texas and have the room. That's so cool...and convenient

 

[Mike Casselton]

Yeah, I'd love to own a full sized lathe and mill.

Instead, I have that little Grizzly 7x12 and an X-Y vise on my bench top drill press.

They've done a lot of work and paid for themselves over and over.