7mm Rem Mag Memorial Build

[lancetkenyon]

I would think a combination of a few variables.

 

Probably a fast barrel with a tight chamber and long throat for the 168-180 VLDs. Tighter chambers allow less case expansion upon firing. Hand lapped barrels (like Bartlein, Rock Creek, Brux, etc.) have less initial resistance since they are smoothed out a bit too. My other Bartlein actually sped up after 100 rounds too. It is about 70fps faster than my initial load development when it was new.

 

5R rifling is SUPPPOSED to not cause as much bullet constriction/distortion since the lands and grooves are opposite from each other, not lands that are across from each other, meaning a little less resistance. Not sure on that one though, just what I have read from barrel makers that use 5R.

 

The bullet seated long allowing more usable case capacity, meaning higher charge weights, meaning more velocity at lower pressures.

 

Cases with less brass content meaning more case capacity. See above.

 

The Berger Hybrids have a longer boat tail, and ogive to tip, meaning a shorter bearing surface than the VLDs or most other bullets of similar weights, meaning less friction and resistance travelling down the barrel.

 

Longer barrel than most stock rifles. The factory barrel was 24" before, and I know all the Ruger M77 7RM barrels I have worked up loads for were 24" too.

 

Magnum primers.

 

Good burn ratio to barrel length? Maybe I got lucky.

 

I was realistically expecting 2900fps, was HOPING for 2950fps, which I thought should be attainable. I just got lucky with the best node being a hot one, up in the 3000-3050fps range across 4 charge weights that are at least 1.0 to 1.5 grains lower than my rifle's max load. Should give some flexibility in conditions and pressure changes. I could go down to the 2900fps node and extend barrel life a bit, but this is a hunting rifle, not a target rifle that will see hundreds or thousands of rounds per year on it. This should last a lifetime now.

[Hoss50]

Pretty awesome lance.

[azbow]

Lance do those long oal loads fit in the magazine box?

[lancetkenyon]

The cartridges fit in the magazine easily. Magazine length in the Rem 700 LA is 3.685". My COAL is 3.472" with a .0200" jump.

 

Which is weird, because a Ruger M77 LA magazine is only 3.370". So a lot of the other loads I have worked up have been around 3.355" max COAL to fit in those rifles. And with a chamber length of about 3.435" to the lands in the Ruger M77, there is a big jump to lands of .090" or so without even adjusting seating depth for the sweet spot. So the bullets are seated really deep if you want to be able to load them for mag length.

[azbow]

My Win mod 70 has a short box and dictates how deep the bullets are seated. I seat them out as far as I can to still fit in the box without getting jammed, but it causes a pretty good jump to the lands with 180 VLD's. Wish the box was longer.

[lancetkenyon]

Azbow, What is your blind magazine length, for reference? It would be good info to have.

And your COAL, length to ogive, chamber length to lands, etc.?

[azbow]

The magazine box is 3.40". I am loading the 180vld hunting to 3.385 oal and the ogive is 3.685 with the Hornady comparator. That is max length for them to cycle through with the bolt to smoothly pick them up and chamber them. I can't find the chamber length to lands measurement, ( have it somewhere) but with the longer and bigger bullets in this gun it isn't much of a factor since I can't seat them out any longer.

You built a great rifle!!

[lancetkenyon]

The magazine box is 3.40". I am loading the 180vld hunting to 3.385 oal and the ogive is 2.685 with the Hornady comparator. That is max length for them to cycle through with the bolt to smoothly pick them up and chamber them. I can't find the chamber length to lands measurement, ( have it somewhere) but with the longer and bigger bullets in this gun it isn't much of a factor since I can't seat them out any longer.

You built a great rifle!!

Must have meant 2.685" to ogive. I do the same thing all the time. I write it down, and then go back for reference and think, "No way. Must mean 2.xxx", not 3.xxx?"

 

Thanks for the info. Glad I have a longer magazine box to start with.

 

Here is the real question...how does it shoot? Most important factor. Accuracy over speed. But getting both is a plus.

[azbow]

With the Hornady comp on the caliper it does measure 3.685 at the ogive.

68.3 gr of Retumbo with Fed 215 primer, 2920 fps.

Bartlein 25" barrel, Mcmillan stock, Zeiss Conquest 5-25

Accuracy has been a work in progress but this load showed a lot of promise going into the hunting season so that is what I used. Elk, Antelope and Coues all drt, but all were taken at about 300 yds. Shot out to 700 with pretty good results. Will start again with it soon out to 900 or so.

You set the bar pretty high with your effort and results. Thankyou for sharing and showing what is possible.

[lancetkenyon]

With the Hornady comp on the caliper it does measure 3.685 at the ogive.

68.3 gr of Retumbo with Fed 215 primer, 2920 fps.

Bartlein 25" barrel, Mcmillan stock, Zeiss Conquest 5-25

Accuracy has been a work in progress but this load showed a lot of promise going into the hunting season so that is what I used. Elk, Antelope and Coues all drt, but all were taken at about 300 yds. Shot out to 700 with pretty good results. Will start again with it soon out to 900 or so.

You set the bar pretty high with your effort and results. Thankyou for sharing and showing what is possible.

Digital caliper or dial? Did you re-zero the caliper up against the comparator, and not fully closed? I know my Hornady comparator with bushing is 1.004" long, making that much of a difference if I don't re-zero it. Because you are not measuring the full COAL to the tip, only to where the ogive stops at the bearing surface of the bullet from the case head. So it can't be longer than COAL (Combined OverAll Length). To fit your mag length of 3.40", you have to be forgetting to re-zero your caliper when you install the comparator and bushing. Should be around 2.647"+/-. I am at 2.734" to ogive, with a COAL of 3.472". And a max mag length of 3.685". The bullet length is only .004" between the 180 Hybrid and VLD, but the bearing surface to ogive placement is probably a bit further back on he Hybrid.

 

That is good velocity from a 25" barrel. The Retumbo is supposed to give better velocity than H1000, but a lot of people say H1000 is a bit more accurate. Your load is a good example of why you take book loads with a grain of salt. Berger book lists Retumbo with a max charge weight of 69.2 @ 2881fps from a 26" barrel. You are at a grain less charge weight, with 1" shorter barrel, and getting 40fps faster velocity. Berger COAL is 3.290" and you are at 3.385" COAL, meaning even though you are seated deeper than I am running, you are still longer than the Berger spec., meaning more case capacity available. The Hodgdon book states Retumbo starting load for the 180 VLD @ 64.4 @ 2638, and max load @ 70.8 @ 2914 in a 24" barrel. So you see an even bigger difference. 1" of barrel length should be around 30fps for the 7RM.

[azbow]

I am using dial calipers now. The digital was frustrating as it would turn itself off and other annoying tricks. You are correct, the comp is 1.004 " long, I just add that to my ogive length and record that measurement instead of rezeroing. Sorry for the confusion.

I have tried a lot of powder and bullets through this gun and it seems to like Retumbo with the 180's the best so far. It didn't do as well with the 168 VLD' s or classic hunters. The 1 in 9 twist might be the reason...

[Okbow87]

Great rifle build thread Lance. I am always looking for the same scope, but can never find one that fits the perfect specs. The 4-16x42 f1 is the closest I can come up with. Just ordered a 3-18 gen 2 razor to run on my match rifle this year. It is a little chunky for a light hunting gun, as I'm sure you know.

[lancetkenyon]

After weighing approximately 100 Winchester brand brass, I was so disgusted to find 10 grains of overall weight difference with only 51 within 3 grains of each other, I ordered up some new Remington stuff. My brass finally came in last night. 250 pieces of Remington brass. After weight sorting, I culled 23 that were over/under 1.5 grains from my target weight of 235.0 grains. I kept 227 from 233.5 to 236.5 grains. I was going to keep from 233.0 to 236.9, but I only had to cull an extra 8 from 235 pieces to get it to within 3 total grains of brass content. That should last me a while.

 

 

Now to resize it all and fully prep it.

[4Falls]

Lance, you should open a reloading university. Im amazed at your technical knowledge. I have no idea what your even talking about most of the time, yet I'm completely interested and always waiting for you to add to your posts. Thanks for sharing this stuff.

[Big or Bust]

Why not Nosler 7 mag brass Lance? My nosler 280 Ackley and .243 stuff is really good...