Making your own 7LRM brass

[P7M13]

A fellow member here, outside the US, contacted me asking how I made 7LRM brass. He stated that Gunwerks wouldn't ship him their ADG made 7 Long Range Magnum brass. While I don't know the truth of that, I said I was happy to supply info on how to convert brass to make your own. Here we go... Comments, suggestions and criticism invited!

Procedure for necking down 375 Ruger to 7mm LRM
Pictures for reference

Dimensional Information:

Cartridge​	OAL​	Neck Length​	Shoulder Length​	Shoulder Diameter​	Shoulder Angle​	Shoulder Δ Length​	CW Die Turns for Setback​
7LRM	2.514​	0.382​	1.965​	0.511​	30°​	0.000​	​
300 PRC	2.580​	0.308​	2.127​	0.515​	30°​	0.162​	6 + 209°​
375 Rug	2.580​	0.305​	2.179​	0.515​	30°​	0.214​	7 + 96°​

Parts Needed for reforming 375 Ruger

• 338 RCM FL die
• 300RCM FL die
• 7mm SAUM FL die
• Neck Turning tool (currently use Forster)

Parts Needed for reforming 300 PRC

• 300PRC FL die
• 7mm SAUM FL die
• Neck Turning tool (currently use Forster)

Steps to Convert 375 Ruger (haven't done from 300 PRC)

Remove mandrel/decap pin from 338 RCM
Install 338 RCM die into single stage press (RCBS Rock Chucker or equivalent), back die out as much as possible.
Think of the press lever as a protractor with vertical being 0° and the full stroke being ~140°. On my Lee Classic Cast, home position is -7°, full stroke is 133°. Since I desire to move the shoulder down 214 mils (0.214"), I want to set my die in the press so my ram movement from the point of the shoulder engaging the die to the setback desired is 214 mils. On my press, that starts at 107° of lever angle.
Why? Setting the shoulder back must be done at an extremely slow ram speed or you will collapse the case. Also, the best way to achieve accurate size conversion is when your travel is limited by hard stops.
Set a case in your ram, move the lever to the proper angle of travel, and use something to hold it there. Then screw the die down until it just contacts the mouth of the case.
Return the ram to home position, then screw the die in further, the number of turns in the table on page 1.
Then lube your case. This is an instance where light lube does not help you. Don't be messy either. I will wipe on a 0W-20 Mobil 1 for this.
Run the ram up to the point of engagement, then VERY SLOWLY finish the stroke. By very slowly, this should take approximately 15 seconds from first contact, and move even slower for the last 10 seconds.
There is a reason you move extremely slowly. If you don't, this is what your cases will look like (fugly doesn't do it justice):

If they do turn out like this, you're moving too fast, and throw the case out.
Check your shoulder length against the 1.965" in the table above. Adjust your die accordingly. Too long, and it'll never fit in your chamber. A little short, and you'll just fireform the case. Your first firing is considered a fire-form anyway…
Housekeeping suggestion: be sure you set your locking ring on your die for when you form new cases. Hornady split ring cases are the best for this.
After you have taken the 375 Ruger case, necked it down to 338 and set the shoulder back, trim the case to 2.525" OAL.
Now neck turn the case to 13 mils thickness.
Anneal the cases.

1. Remove the decap and expander mandrel from your 300 RCM, then install the die on the press. Put one of your annealed cases, well lubed, into the ram and run it up to approximately 90°. Screw in the die so it is touching the case mouth.
2. VERY SLOWLY (e.g. 10 seconds) run the ram up until you feel the resisting pressure where the shoulder is contacting the die. This can be difficult to feel near full ram travel. Never force anything if your ram doesn't want to move with consistent pressure.
3. If need be, do this step near the top of the ram stroke so you have a better sense of when the case shoulder engages the die.
4. Remove and examine your case. You want to see FULL neck resizing, all the way down to the junction of the shoulder. Any bulges here, and your case will probably not chamber properly.
5. If you did your job, recheck your dimensions. As above, any folds and you're moving too fast (discard the case).
6. If all is good, neck turn the case back to 13 mils neck web thickness.
7. Back the die out. Put the case into the ram, run it all the way to full stroke and then turn the die down slowly until it's fully engaging the case. Set your locking ring on the die.
8. Set this case aside as a setup template.
9. Resize the necks on the remaining cases.
10. Trim to 2.515 OAL,
11. Neck trim to 13 mils.
12. Reize the necks again with the expander mandrel in place.
13. Anneal the batch.

Repeat steps 1-13 with your 7 SAUM FL die.
Fireform.
Here are finished loaded cases.
One is GW Hornady brass, one is my conversion.

Reloading
I have a set of the 7LRM Hornady Custom Dies from Gunwerks. I think they are crap. Seriously.
I took a set of 375 Ruger dies and shortened the die to do a FL when necessary. For the most part, I will just do a neck size with the 7 SAUM die.

 

[Magnus777]

Very interesting and informative! Thank you for this! That time of year for me to read up and catch up on the latest. So...suppose one wanted to further reduce that neck size down to .277...would one insert a finishing step with a bushing of appropriate diameter?

 

[can1010]

you will have less damaged shoulders if you first shorten a 375 ruger die to set the shoulder/ body measurement first then the 338, 300, and 7mm as neck dies. I have done this many of times.

 

[P7M13]

you will have less damaged shoulders if you first shorten a 375 ruger die to set the shoulder/ body measurement first then the 338, 300, and 7mm as neck dies.

Point.
I have mine already marked for the cutting. Just haven't made the time to chuck it up in the drill press and attach a cut-off wheel to the die grinder.
I still have another 100 pcs of Hornady 375 Ruger to convert when I have worn out the 150+ cases I'm currently loading and shooting.
Finally got a hold of some H1000, looking forward to trying that.
[edit to add] Forgot I had already shortened the 375 Ruger, but don't think I've used it to push back the shoulder, which I have been doing with the 338 RCM.
It's been that long since I've converted brass. D'oh!

 

[can1010]

Point.
I have mine already marked for the cutting. Just haven't made the time to chuck it up in the drill press and attach a cut-off wheel to the die grinder.
I still have another 100 pcs of Hornady 375 Ruger to convert when I have worn out the 150+ cases I'm currently loading and shooting.
Finally got a hold of some H1000, looking forward to trying that.
[edit to add] Forgot I had already shortened the 375 Ruger, but don't think I've used it to push back the shoulder, which I have been doing with the 338 RCM.
It's been that long since I've converted brass. D'oh!
Do you know your fired case capacity of your converted brass? I have been tossing around the idea of an even shorter version something closer to the blaser case. my opinion is 85gr is about the best place for getting good velocities and not to over bored even with the heavier bullets

 

[Magnus777]

you will have less damaged shoulders if you first shorten a 375 ruger die to set the shoulder/ body measurement first then the 338, 300, and 7mm as neck dies. I have done this many of times.

That answers my question, as well. Just started reloading early last year, after many years of shooting, and believe I have a pretty good grasp of the fundamentals by now...well enough to produce very good results with the handful of cartridges I use. But I've had a burning desire for some time now to work on a special project. Ordered up 100 cases from Gunwerks awhile ago, and have been mulling over how to proceed, but just couldn't wrap my mind around how to get the desired result. I'm going for a ground up rifle build, you see, and will need dimensions for a reamer. But I've been working from the assumption that I had to start with the 7lrm brass! Been worrying over how to keep the shoulder angle and neck junction at the proper dimensions. Never entered my mind to look at the blueprint of the parent case! Now I see the print for the 375 Ruger, seems it's setting at 30 degrees from the start! Is that correct? So I just need a bushing die set for the 375, with a set of bushings of appropriate size, and I can churn out brass until I'm swimming in it! Am I right?
Sorry, not intending to hijack this thread. And please overlook my +10 enthusiasm... A little excited here! But I figured my project goes along with the subject matter, which is working over the 375Ruger case. Beauty! Thanks guys!

 

[can1010]

That answers my question, as well. Just started reloading early last year, after many years of shooting, and believe I have a pretty good grasp of the fundamentals by now...well enough to produce very good results with the handful of cartridges I use. But I've had a burning desire for some time now to work on a special project. Ordered up 100 cases from Gunwerks awhile ago, and have been mulling over how to proceed, but just couldn't wrap my mind around how to get the desired result. I'm going for a ground up rifle build, you see, and will need dimensions for a reamer. But I've been working from the assumption that I had to start with the 7lrm brass! Been worrying over how to keep the shoulder angle and neck junction at the proper dimensions. Never entered my mind to look at the blueprint of the parent case! Now I see the print for the 375 Ruger, seems it's setting at 30 degrees from the start! Is that correct? So I just need a bushing die set for the 375, with a set of bushings of appropriate size, and I can churn out brass until I'm swimming in it! Am I right?
Sorry, not intending to hijack this thread. And please overlook my +10 enthusiasm... A little excited here! But I figured my project goes along with the subject matter, which is working over the 375Ruger case. Beauty! Thanks guys!

bushing dies are for sizing finished brass not brass forming you need multiple non bushing dies trimmed and/or set to achieve desired outcome. what are the goals and desired dimensions of your project then we might be able to help

 

[Magnus777]

bushing dies are for sizing finished brass not brass forming you need multiple non bushing dies trimmed and/or set to achieve desired outcome. what are the goals and desired dimensions of your project then we might be able to help

Thanks much for the input! I'll start a new thread, so as not to completely derail this one.

 

[DMack]

Can you convert 7LRM brass to 7 PRC?

 

[P7M13]

Can you convert 7LRM brass to 7 PRC?

Looking at SAAMI specs for 7 PRC, I'd say yes.
Be sure to anneal the shoulder and neck first before attempting to shorten the case, or you'll crunch the body.
About a year ago, I tried to make 7 LRM out of Lapua 300 PRC brass. It was so tough, I ruined my first attempt, succeeded on a second, and ruined a third. Thought I'd stop while I wasn't too far behind.

 

[P7M13]

Update:
Had four more pieces of Gunwerks (Hornady) 7LRM brass fail after their third firing -- two neck splits, one start of case head separation, and one body split just below the shoulder/body junction. My Hornady pieces converted from 375 Ruger are lasting longer....

I recently bought some Peterson Cartridge 300 PRC brass and converted five to 7 LRM. Lost one in the conversion, which is why I'm posting.
I've always said, 'use lots of case lube', but need to strike that. In this batch of conversion, I started by cleaning out the die and mandrel and annealing the brass. Then I took clean brass, gently wiped on lube and then started the sizing process.
Peterson brass, though softer than Lapua, is much tougher than Hornady. It came out with dimple folds. Crap. What I noted was that the dimple folds showed lube like the classic "too much lube" shoulder dimples.
Responding to that input, I would advance the die a small amount, back it out and wipe any lube off the neck and shouylder, rotate ~60° then move it up again another few thousandths. I did this like five or six times to get a beautiful, finished piece. I then trimmed the case to length.
The finished piece fit in my chamber. What I didn't check was whether a loaded round did. Case in point, two of the four pieces didn't fit due to the neck web thickness needed to be turned to fit.