7 Mashburn Form Questions

J

joelkdouglas

Handloader
Jun 5, 2011
1,310
3
Alright. Didn't want to text Scotty too late--it's 1130 EST.

My wife loaned me a corner of the entryway near the garage to set up a bench. It will work! We got our new loaner (base) house on Thursday, and have been steadily unpacking since Friday when our goods arrived. We still have some pictures to hang, final resting place for some items, clean the house, etc., but I took some time to start 7 Mashburn loading.

Here's the bench:


Let me know if I'm doing this correctly. I take one of these:


Put this on, except the neck and shoulder:


Screw the RCBS Form Die down until it touches the shellholder, then lock it down. Run the lubed case into the die until the shellholder touches the die? Will it stop first? What's the OAL I should trim the brass to?


Then put 13 grains of Bullseye, Large Pistol primer, fill with cream of wheat, and seal the neck with either tissue paper or paraffin wax. OR load with 45ish grains IMR4350, LR Mag Primers, and 139 SSTs to fireform a low recoil round.


Then load up to 3200 fps with H1000 and these:


Scotty how much H1000 does it take you to get to ~3200 fps with 160 ABs? I forgot how much you said. I wish my phone had a search feature!

Is that right?

Thanks all!
v/r
Joel
 
Joel: Skip the lube. No needed for the form/trim dies.

1) run the 300 win mag case into the form die,which forms the new shoulder;

2) then the case into trim die which reduces neck diameter.No need to trim anything.

3) This is a wildcat.Reamers and chambers may vary slightly. As a next step,You may find you need to run the newly formed cases into a FL die in order for them to chamber.

4) Once you know they will chamber, for COW FORMING, prime with LARGE PISTOL PRIMER. I use 13 gr Bullseye and RCBS Corn Husk tumbling media. Top with a wad of tissue. Fire form.Or,

5) I use 65 gr IMR 4350-139 Hornady for live fire forming.

If you want, you can skip steps #1 and #2 above by running 300 WM cases into a Mashburn FL sizing die. But I have found FF loads shoot better using the Form/Trim die.


Possibly you have already asked Scotty about this. He has likely told you the same stuff.
 
Damn. I have a form die and an FL die. That would probably work to form five or so?

But Midway had a trim die on clearance...

I will fire form some cases and send them to Lee also to try out a collet die. I use them for my other cartridges. And Redding says they will make a body die for me.
 
OK. Then just lube the 300 WM cases and run them into the FL Mashburn die. This should form the new shoulder and reduce neck diameter in one step.

Then FF the case using either method you want.

If they don't chamber after a trip through the FL die, screw the die down more and feel the press "cam over" a bit to "bump" the shoulder some more. Play with it. Pretty easy.

Once you get good brass from your rifle use it to order the dies. But I know your rifle and you should be GTG just ordering Redding or RCBS.

Remember.....the Form/Trim dies are NOT required to form Masburn brass from 300 WM. You can do it with just the FL Mashburn die.But I still use them because my rifle seems to shoot a bit better with new formed brass that way.
 
Bob gave you the good scoop Joel. I run mine directly into a FL die, put 65 grains of IMR4350 under just about any 139-145 grain Bullet I have laying around and Fire em! I've done some with COW but honestly 50 cases last forever.

As for the 160 ABs and H1000, my old lot required 75.5 to get 3200. I haven't tried the 160's with my new lot but the 175 Partitions went from 73 to 75 with the new lot to get the same speed. If I were you, I'd load from 75 up to 77-78 and chrono and shoot for some groups. You'll see if you need some seating adjustments and get a great idea of speeds.

Don't ever be shy to text me. I keep it on vibrate and if I don't see it at night I'll get you first thing in the morning.
 
Oh, I have NEVER had to trim a Mashburn case. Fired a bunch over 10X. They don't grow enough to matter.
 
joelkdouglas":1vuaw7c6 said:
Thanks Bob and Scotty!


Sent from my iPhone using Tapatalk
Click to expand...

No problem. I bet you'll be done with your load work pretty quick once you get some formed cases. It's EASY!
 
Joel no like this..... :grin:



IMG_0325.jpg
 
wayno945":wg6qdphw said:
Did you remove the decapping rod from the FL die?
Click to expand...

I did now! Things haven't improved much yet. Case #1 pictured above. Case #2 has the expander button stuck in it, as I had to unscrew the expander button to get the brass out of the die. Case #3 I went back to the form die only, but I didn't push it enough in. Case #4 form die only, crumpled the shoulder (too much lube?). Case #5 I tried graphite on the neck and wax on the lower body, couldn't even get the case into the die half way.

Then it was dinner time. Then kids to the playground, bath time, bed time stories, you get the idea.

There's some debate whether these dies are for a 7 Mashburn Short instead of a 7 Mashburn Super. I don't really know. I have an RCBS Form / Trim die set coming Friday. I'll try again with those! And I'll update here.
 
After FF. They don't look a WHOLE lot different after a trip through the form dies.

Lets go from the beginning.

I just formed these cases with new Hornady brass to illustrate this post.


Left to right:

1) 300 Win Mag case.

2) 300 win Mag case after trip through Form Die.(This forms the new shoulder and reduces neck diameter slightly).

3) 300 Win Mag Case after trip through Form Die AND Trim Die. (Te trim die tells you case length and reduces the neck diameter further).



IMG_0326.jpg
 
Here are the dies you need,or that I use.

Keep in mind that the RCBS Full length die and seater die are referred to as 7 Mashburn "Short". It's actually the "super". Where short came from I have no idea. I will try to find the right dies at Huntington Die Specialties and post them.

Joel I want to guess the Form die you have is for forming Mashburn cases from 300 H&H and NOT from 300 Win Mag. Speculation on my part but since they are used dies,that could be the case. Remember,,,,the Mashburn was originally formed from 300 H&H cases.


This is the RCBS Form/Trim set, and the Redding FL die and seater.Nothing complex here.


IMG_0327-2.jpg






Top view of the Trim die on the left;and Form Die on the right:


IMG_0329.jpg
 
The FL/seater dies from RCBS can be purchased from Huntington Die Specialties.

They are called "7mm Super Mashburn Mag Short", Part # 10-56234,Group G.

They are special order as we'd expect.
 
You may also just wanna order a FL sizer from Redding or RCBS. Just to have one on hand.

On the dies you have, they did work for Jake but I'll be darned if I can remember what he did. I'm thinking he used the form die for most of it though. I never got to monkey with them as they went to Jake, then onto you.
 
Thanks Scotty! I may use this FL die just to neck size, and touch the shoulder once I get fire formed brass. I ordered a 7 mm expander mandrel from PMA Tool yesterday, I can run the brass into the sizer and then expand with the expander mandrel. I already have an expander die, the new mandrel just sits in the die. I'll find an FL sizer too.
 
Bob thinks those dies might be to form 7 Mashburn from 300 H&H (the original design). Midway earlier this week had 1 set of 7 Mashburn Super Mag from 300 Win Mag Form and Trim dies. Luck I guess that I got their last one in stock (that they had one in stock at all!).



Here's the Form die:


Trim die:


3 pieces of brass. Left is 300 Win Mag. Middle is after the Form die. Right is after both the Form die and the Trim die.


It is easy peasy. Just screw the die in until it touches the shellholder, then about 1/8th turn more, put some lube on the case (might not even be needed), up into the Form die, up into the Trim die. The brass chambers in the rifle no problem out of the Trim die.
 
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