Anyone own a 7mm 300 Win Mag?


Well-Known Member
Feb 3, 2007
Townsend, Montana.
Yes, 7mm 300 Win Mag.

What do you think of it? I have a chance to aquire one. How does it differ from a 7mm Rem Mag?

28" custom barrel and I would want to shoot big BC bullets a long ways.

Any info would be appreciate about this caliber.


it will hold more it and just tell us what you think.I have been thinking of building one myself.would think it would make the 7mm bullets fly a little faster.but might be one for shooting out the barrel faster too.
I wouldn't buy it if it didn't come with dies as they could be expensive. Ought to be an easy round to form cases for and in a 28" barrel it should perform about like a 7 STW out of a 26" tube. 7 STW brass has been hard to come by recently but 300 WM brass ought to be available just about anywhere.
Well I own it. The owner says it is a tack driver with 168 gr SMK's. We will see. It s a 1 in 9 twist and I am hoping it will shoot a 180 Berger well too.

Should be interesting. I will report in after I shoot it.

Simply guessing based on additional powder capacity... but I expect you'll get about 100 fps more MV than a 7mm Rem Mag with the 180 VLDs. Let us know how it goes. Sounds pretty interesting. It must have come with reloading dies too?
Simply guessing based on additional powder capacity... but I expect you'll get about 100 fps more MV than a 7mm Rem Mag with the 180 VLDs. Let us know how it goes. Sounds pretty interesting. It must have come with reloading dies too?

Yes, it came with a set of Lee collet dies, a set of custom RCBS dies, a redding body die, and a few different bullet seating mandrels for seating different bullets.

If it shows promise I am going to restock it and I have some RWS 300 win brass I will feed it.

Broz, I have the numbers somewhere on exactly what you are gaining. I had considered having my .338 Win Mag reamed out to .338-300 Win Mag, but I was only going to get another 100 fps or so.

Running it through Quickload , real quick, I'm getting 3100-3150 with a 168 SMK with a 28" tube using RL22 & RL25. My guess is it will run 100-150 fps faster than a 7mm Rem Mag.

7mm RM with a 168gr SMK set at 3.4" has a usable case capacity of 75.645, using the .300 WM case at the same coal it shows 85.512
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So far the rifle has done ok with the 168 SMK's. It is easily holding under 1 moa but I have only shot it to 500 yards. It was in a wood stock and had been blessed with a Krylon Camo job, I have pulled it out of the stock and stripped off the paint. It looks great now. A new stock will be here any day. I purchased a BC stock off of a 700 XCR and I will bed it nice and tight.

Montananative sent me a few 180 Bergers to try. I hope the 28 1/2" nine twist will be enough to make them shoot. I will probably start with H-1000 and put them on the lands.

If anyone has any info for the 180's please fire away.

Yep, I am shooting 180's from a 1:9 (RUM) and wouldn't have it any other way. I think the 168 grain VLD is OK but its not quite as good on game compared to the 180 grain VLD as the wound from the heavier bullet is deeper and broader.

Did you say you are using RWS brass. RWS is heavy walled, not the best as far as case capacity goes. Can you get your hands on even a few Winchester cases?

You would be surprised how many people are interested in your cartridge. When I wear this RUM barrel out (6 months?), I will be going the same route. Please post all of your results as you obtain them as people will search this out months or even a couple of years from now.
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Nate, I have WW brass already fire formed for it. I also have RP ready to go. Plus I have a few Graff, some Lapua and RWS. I know the RWS has less capacity and I will only use it after I get the load close with the win brass. If the chosen charge will fit with the 180, I will feed some of the RWS to the project because it is tuff as nails.

So where are your 180's seated in the RUM?

Thanks for the reply.

My 7mm RUM is on an M70 action/box mag so this effects the COAL. Bullet jump is nearly half an inch, totally ridiculous. I can only acheive optimum accuracy with high SD/ bearing surface projectiles. If I use something like the 162gr SST, there is a moment apon firing, where the bullet is neither in the case mouth nor engaged in the rifling. The projectile is therefore prone to enter the rifling at non concentric angles. Both increased twist rate and increased velocity worsen yaw after the bullet leaves the barrel. In the M700 action, the results are not much better. Worse still, as the throat wears, starting at about 150 shots, bullet jump is increased beyond a half inch.

I have tried seating bullets out for single loading and while the accuracy is good, I am tired of the whole stupid design and excessive wear. I recently taught two newbie hunters how to shoot long range, one has a 7mm rem mag, the other, a .300 Winnie. Both guys are able to acheive the same long range performance as I am getting but without all the BS that goes with the RUM. Its sad when I am playing teacher and the guys I am teaching have a more common sense cartridge in hand.

I ran in a factory M700 medium contour barreled 7mm RUM a few weeks back, ran it in and wore out the throat over the space of two weeks. The rifle went from shooting fliers to run in and shooting nicely to worn out and groups wide open. I did try to keep the barrel cool etc, the usual no more than 12 rounds taken to the range at a time and rested the rifle between 3 shot groups. In due course, I will cut the barrel in half and publish the pics of the throat on the net. I should mention, some of the 7mm RUM barrels in circulation are showing signs of craze cracking (bore scope), something that takes about 50 years of continous shooting to acheive with an ex military M1917 or Lee Enfield etc.

Your cartridge on the other hand is a practical design. I get 3184fps with the 180gr VLD from the 26" barreled RUM, you will probably get 3050fps to 3100fps, an unnoticeable difference in the field.
Nate , I too have ventured away from the screamers. Just about the time I get one shooting to suit me then I start chasing the throat. :rolleyes:

I will do a report on how she shoots. I just bedded her in the XCR stock tonight and installed a tac bolt handle. Hope to be testing the 180's next week. All I am lacking is the bottom metal and it should be on its way.

Been a bit slow with this project. Had to get more bullets and in the middle of load development I had a scope start walking right. I changed scopes and imdediatly was sure the other had a windage problem. Sent it in for repair today.

Today I started over with some of the loads I thought should work but nixed due to the bad groups produced by the bad scope.

First load was H-1000 and a CCI 250 with a 180 VLD. It dropped 3 into a very small clover leaf at 100 yards. C/C on the group was .285" I was good with that and moved to the steel for some longer shots and to get mt Exbal program dialed in with this load.

Two shots at 500 yards were 2" apart and bored nice holes right through my 1/2" steel target.:rolleyes: So I moved back to 825 yards and shot from there. It was holding well under 1 moa but I need to get a bigger scope on. I put a 2.5 - 10 x 42 IOR Tactical on her and it is just too small at 800 yards to shoot small groups. If it were not for the MP-8 dot reticle I would not be doing as good as I am. That reticle is easy to place on a target.

The WW brass is looking pretty good with this load and there is no sign of pressure. My Chrony showed it at just under 3200. But I ain't buying that. I will see what exbal says when I get the tragectory right out to 1000.

Jeff gun)gun)

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