The Great 7mm Rem Mag Ballistic Experiment.

Pathfinder76 · #1 09-05-2016, 09:56 AM

Well maybe great is a bit of a stretch.

A few months ago I picked up a 375 Ruger (subsequently replacing it with a H&H) so decided I didn't need a 338 WM. I've always had a soft spot for the 7mm Rem Mag. My dad used one, in a Remington 700 ADL, as his only big game rifle for over 30 years. I've owned them and have had custom rifles chambered for the round.

A year or so ago my dad drug a Model 70 take off barrel out of his basement. He figured it was mine, it was, and it turned out to be an unfired 7mm RM barrel that I had pulled for the action and a custom Leeper build 15 years ago. So with that barrel handy I figured a 338 to a 7mm of some sort was in the cards. Because of magazine restraints and this particular receiver not ejecting cartridges properly with the longer box the long 7's were out. That left the WBY and RM and the RM won out. I'm getting to a stage in life where the ability to buy cartridges in town is a comforting option if needed.

Now we all know the horror stories associated with the RM and pressure. Things like pressure spikes, difficulty getting published velocities etc. All factory rifles, including my dad's that I have worked with seem to suffer this malady. At least in my experience. With customs some seem to side step the issue. Then there is the extra velocity the WBY gets. This despite a case capacity difference that is negligible. The throat has to be the culprit.

The great Remington Magnum has a very short SAAMI throat. I have always thought this odd as the rifle it was introduced in has a magazine box longer than the current male presidential candidates comb over. The last fifteen years have also seen short throats become absolutely necessary in custom rifles. Especially if you are going to showcase these builds on the Internet. In my experience, with custom chambers and good minimal diameter throats this is a bit of a tidal wave in a tin cup scenario. But whatever.

With this in mind, I called Bill Leeper, begged him out of retirement and sent him the pieces asking him to install the barrel, and cut a throat longer than bullet diameter. I think .288 ish. With this throat, I could reach the lands with some bullets and others would need binoculars to locate them. It turns out the barrel needed to be set back enough that the chamber needed a complete recut. Excellent. The Barnes 145 LRX is diminutive in ogive so would need to jump a country mile. Perfect. I have found that this bullet likes being away from the lands. A long way away. I also find, with it's long bearing surface, it compares pressure wise to most 150 gr bullets.

As a happy fluke, this barrel fouls less than any barrel I think I have owned. And that has been a lot. Most of them custom barrels.

Here are the results. And by all indications is not breaking a sweat yet.

Deer Hunter · #2 09-05-2016, 10:03 AM

Nice groups. 100 yrds? I like the 7 rem mag a lot and never found it necessary to have a long throat shooting the lighter for calibre bullets.
I surprised given your almost identical 280 rem, that you just didn't step up to a 300 win mag. Not sentimental i guess.

Pathfinder76 · #3 09-05-2016, 10:14 AM

It definitely has a bunch of overlap with the 280. Almost intentional as this one will get beat up a bit more.

Yes 100 yds. The beauty is these groups represent less than 20 rounds down the barrel!

ROA · #4 09-05-2016, 10:22 AM

So you took a 7 mag apart then 15 years later made a 7 mag because you had the bbl? Sounds like somthing I would do.

Deer Hunter · #5 09-05-2016, 10:22 AM

Nice. It wouldn't be an overlap if you put on a bigger scope and did some turret twisting.
Great gun none the less
Thanks for posting

Pathfinder76 · #6 09-05-2016, 10:44 AM

Quote:

Originally Posted by ROA

So you took a 7 mag apart then 15 years later made a 7 mag because you had the bbl? Sounds like somthing I would do.

:-)

Pathfinder76 · #7 09-05-2016, 10:45 AM

Quote:

Originally Posted by Deer Hunter

Nice. It wouldn't be an overlap if you put on a bigger scope and did some turret twisting.
Great gun none the less
Thanks for posting

That may happen.

brimmer · #8 09-05-2016, 10:52 AM

Great build as always thanks for the great write up. Let me know if you get bored of either the 7 or the 280 and I will take it off your hands. 😀

Pathfinder76 · #9 09-05-2016, 10:54 AM

Slicktricker · #10 09-05-2016, 11:11 AM

Wish my 7mm rem shot that tight of groups in around a 1-1 1/2 at 100 yards never could find a bullet other then the Hornady interlock to shoot great in my rifle

RickF · #11 09-05-2016, 08:51 PM

That 7 Rem makes a ton of sense Chuck.

With a pet 280 as nice as yours, having a very similar 7mm to use as a spare and hard use rifle is a brilliant idea.

JD848 · #12 09-05-2016, 10:21 PM

Very nice CHUCK my heart has always been the 7mm rem,and tight groups with the right shooters is a breeze with this cartridge ,very good post.

TangoKilo · #13 09-05-2016, 10:56 PM

Great rifle chuck!

Only thing better would be a 7 WSM

Pathfinder76 · #14 09-06-2016, 07:37 AM

Quote:

Originally Posted by RickF

That 7 Rem makes a ton of sense Chuck.

With a pet 280 as nice as yours, having a very similar 7mm to use as a spare and hard use rifle is a brilliant idea.

It makes a lot of sense Rick.

Pathfinder76 · #15 09-06-2016, 07:38 AM

Quote:

Originally Posted by JD848

Very nice CHUCK my heart has always been the 7mm rem,and tight groups with the right shooters is a breeze with this cartridge ,very good post.

Thanks.

Pathfinder76 · #16 09-06-2016, 07:38 AM

Quote:

Originally Posted by TangoKilo

Great rifle chuck!

Only thing better would be a 7 WSM

rembo · #17 09-06-2016, 08:26 PM

Quote:

Originally Posted by RickF

That 7 Rem makes a ton of sense Chuck.

With a pet 280 as nice as yours, having a very similar 7mm to use as a spare and hard use rifle is a brilliant idea.

Well this makes me feel better...:-)

I've always though I was breaking some kind of unwritten rule because I have a 280AI AND a 7 Rem Mag....so I picked up a 7 RUM to boost the top end a bit, but I'm thinking I should have another 7-08.....:-)

Dick284 · #18 09-06-2016, 08:32 PM

Quote:

Originally Posted by rembo

Well this makes me feel better...:-)

I've always though I was breaking some kind of unwritten rule because I have a 280AI AND a 7 Rem Mag....so I picked up a 7 RUM to boost the top end a bit, but I'm thinking I should have another 7-08.....:-)

Get a .284 Win.....

rembo · #19 09-06-2016, 09:27 PM

Quote:

Originally Posted by Dick284

Get a .284 Win.....

Had one, have the reamer. Should build another one. Did the 7-08AI too but I won't do fireforming. I like 7's.

Nice rifle chuck, good writeup. I have the same barrel sitting here from my left handed son's 416 Rem project.

RickF · #20 09-06-2016, 09:50 PM

Quote:

Originally Posted by rembo

Well this makes me feel better...:-)

I've always though I was breaking some kind of unwritten rule because I have a 280AI AND a 7 Rem Mag....so I picked up a 7 RUM to boost the top end a bit, but I'm thinking I should have another 7-08.....:-)

Chuck notwithstanding, only an idiot would have a pet 280 and a 7 Rem as a backup rifle.

... wait a minute!

Pathfinder76 · #21 09-07-2016, 07:47 AM

Laughing.

Deer Hunter · #22 09-08-2016, 07:36 AM

Have you tried RL 17 in this calibre?
My experience has been good accuracy and an increase of nearly 100 fps compared to 4350 type loads. It also seems to give the best accuracy when bullets get a lot more jump than usual.

http://www.alliantpowder.com/reloade...px?powderid=25