Need technical input: rifle project based on 7LRM cartridge necked to .277

[Magnus777]

Hello all! Long time member, lurker...posted a few comments and questions over the years. But this will be my first shot at initiating a real technical discussion. I'm a dry sponge, and intend to soak up every particle of knowledge offered by willing experts. Hopefully build something together that will contribute to the overall knowledge base for the group.
OK, so I finally dove in to reloading early last year, after gathering equipment for some time. Pleased overall with the results for the handful of cartridges I load for. But for a long time now I've had a burning desire to start a special (to me) project, and build a rifle. My full intention is actually to create a cartridge, and then build the rifle for it. But first things first...
The 7LRM intrigued me as a concept since it's introduction. I understand and appreciate what those guys did. But never had any affinity for a 7mm, myself. So the plan is to carry forward with the work they put in, and utilize the nifty, high-speed/low drag projectiles finally coming available in .277.
When asked, there was no plan from Gunwerks to enter such a project. A missed opportunity, I says! And apparently still no interest, even after Nosler fired first with their 27! And although there is occasional mutterings from the shooting community about the subject, it never goes anywhere! There is no follow through, or at least no published accounts that I have been able to dig up.
Apologies for the long winded introduction. Just trying to lay out the tape for the starting line. Now to get right to it, I'm open to any any all technical input carrying forward, starting with forming brass. And it's my understanding the first step is going to be trimming a 375 Ruger die to relocate the shoulder? If so, it can be chucked in the lathe most ricky-tick. But what brand of die to buy?

 

[Magnus777]

Guess I neglected to specify, but the intention is to utilise the overall cartridge dimensions of the 7LRM, keeping the shoulder where it is, and simply necking it down. But starting with choice, fresh 375 Ruger brass from the get-go. I think such a thing will be just the ticket!

 

[bigngreen]

Also a big fan of the .277 cal but not of the LRM which is a turd bucket BUT if I were to work of that I'd just start with ADG 7 LRM brass, get a bushing die made and single pass to .277, load and shoot.

 

[Magnus777]

Also a big fan of the .277 cal but not of the LRM which is a turd bucket BUT if I were to work of that I'd just start with ADG 7 LRM brass, get a bushing die made and single pass to .277, load and shoot.

Originally I had planned to do that. Have 100 once-fired cases I bought some years back, guess they're Hornady. Starting with the 375Ruger seemed like lots of extra work and problems at the time. But reading a post from another member here about doing just that has forced me to reconsider.
The ADG brass is Nosler, right? Which should certainly be of excellent quality. But carrying forward starting with the 375, doing the work now, will allow me to go either way...never have to be at the mercy of product availability from a proprietary source.
More than anything, I just really enjoy learning how to do things for myself. Always been of the "build it, don't buy" it mindset. And sure, often as not it takes five times as long, and costs three times as much to get to any particular destination...at least the first time through. Knowledge gained here is something that can never be taken away, and will pay dividends down the road. That's my belief, anyway.

 

[bigngreen]

ADG brass is ADG, WAY higher quality than the Hornady your working with, honestly using Hornady brass basically makes all the effort and work not worth it, it's a poor foundation and a large part of why the LRM is such a turd.
Properly done it's shouldn't matter if brass is from one source really as long as the quality is good and your design and subsequent dies are correctly made you should wear a barrel out with a 100 brass.

 

[gregsjt]

You should start with ADG 300 PRC Brass, maybe Lapua in the future. You would get better quality brass and it's less of a jump from .308 to .277.

 

[gregsjt]

Get a 300 RCM die and push the shoulder back on a 300 PRC case untill you get close to the desired shoulder position then neck down to .277 with bushings. Should be easy.

 

[Skimbleshanks]

I think starting with 375 brass is cool, but just more work than necessary. Reloading is fun but shooting is more fun and a better use of your time if you want to continue gaining skill. If the time comes that you HAVE TO use the 375 brass then do so. I say get some 7lrm brass, and bushing die with the appropriate bushing for a .277 bullet. 1 pass and you are done. No trimming, and necking and necking and necking and losing cases and neck turning, and once more through the press. Losing a case with that much work and time into it while hunting really sucks.

We will be more interested in the performance of the round than the effort you put into the brass anyway.

Oh and the ADG brass is not Nosler made to my knowledge.

 

[Magnus777]

ADG brass is ADG, WAY higher quality than the Hornady your working with, honestly using Hornady brass basically makes all the effort and work not worth it, it's a poor foundation and a large part of why the LRM is such a turd.
Properly done it's shouldn't matter if brass is from one source really as long as the quality is good and your design and subsequent dies are correctly made you should wear a barrel out with a 100 brass.

Roger roger! I just bought 100 count of once fired when they first started selling it. Had it in a box ever since. It was about that time when I first started mulling over this project. Initially was looking at some discontinued brass from Dakota, which iirc had a nonstandard size for the case head.

 

[Magnus777]

Get a 300 RCM die and push the shoulder back on a 300 PRC case untill you get close to the desired shoulder position then neck down to .277 with bushings. Should be easy.

Very interesting! Was not aware there was an alternate for a parent case.

 

[Magnus777]

I think starting with 375 brass is cool, but just more work than necessary...say get some 7lrm brass, and bushing die with the appropriate bushing for a .277 bullet...

We will be more interested in the performance of the round than the effort you put into the brass anyway.

Oh and the ADG brass is not Nosler made to my knowledge.

True enough. And looking forward to reporting results. Not sure why I thought Nosler owned ADG...

 

[gregsjt]

The 375 Ruger is the parent case for the 300 and 6.5 PRC and the 338 and 300 RCM as well as the 7 LRM.

 

[codyadams]

Your best bet is going to be what BIGNGREEN said. Just get a 7 LRM bushing die, and get the proper bushing for the .277, there is only .007" different the diameter of the 7 and your .277 LRM, this will not be an issue, and you will barely feel it pass through the bushing die. Then, get some of the ADG 7 LRM brass, and sell the hornady stuff. Lube, size, prime, dump powder, seat a bullet.

With a 26" barrel, I would bet you will see around 3000 fps or better with a 170 EOL. If you haven't already got a barrel/action, you may also want to look at the .270 Sherman, based off a standard .270 win., 40° shoulder and less taper, and with a 26" will also do around 3000+ fps. The only reason I suggest it is because you use .270 brass, which you will always be able to find, and also has tough precision American made brass available through Peterson. Absolutely nothing wrong with your idea, and it would be a cool cartridge, but if being able to readily find brass is a concern, or if you already have a long action standard bolt face action or something, this may also be a suitable option to propell a heavy .277 bullet. Whatever chamber you do, just make sure you get an 8 twist barrel if you want to shoot the best bc bullets! I know the .270 Sherman we put together is a Hammer, I didn't use to be a fan of the .277 cal until these new high bc heavy bullets came out, now it is a fantastic middle ground caliber!!

 

[Magnus777]

The 375 Ruger is the parent case for the 300 and 6.5 PRC and the 338 and 300 RCM as well as the 7 LRM.

Very well! I'm picking up what you're laying down!