7MM long-range rifle project

[tazzman]

Hi everyone,

I am planning on building a LR rifle in 7MM Rem Mag. Before anyone blows this away, it is what I've got, action and dies, and it is what suits my requirements, caliber-wise. My action is a Remington long action, in a Classic stock profile, barely-fired(50-75 rds). I bought this rifle new(mid 80s). Due to my negligence(I guess, I never had the rifle bore-scoped when new), it has a rust blister approx. 12 inches into the bore at 10 o'clock. My bad, and I have to live with it. I'd like to build up on this platform. I live in Canada, so a lot of the best parts wil be off-limits to me but there are some options. We have a barrel manufacturer in Saskatchewan name of Gaillard that produces a high-quality product, so the barrel source is dealt with, but... Barrel profile. I'd like to think that a barrel length of 26-28 inches is suitable, if something that measures 30 or so inches does not provide an appreciable improvement. We also have Robertson Composites that manufactures stocks and stock accessories, in Ontario. I am asking your opinion on barrel profile and stock type selection. Like I said above, this rifle will be a paper-puncher, but will be occasionally used on hunts using blinds. I am not worried about scope and scope base selection, it will probably be 20 MOA picatinny and an 8-32 scope(TBD) My action has Redfield side-action mount bases, so Palma-style peep sights are not to be discounted(does barrel length affect sight radius?).

Long-winded and hopeful,

Phil

 

[canderson]

I think that will be a great rifle. A gunsmith near me uses a lot of robertson composite stocks. I believe the one that he uses for a multifunction rifle is callled the ranger. It has a fairly wide front end (not 3" maybe 2+") and a good back end for riding a bag. All of the ones that he has in stock have adjustable cheek pieces. Very good looking stock. Depending on your total weight goal, I would go with as heavy a contour as possible. 28" finished should be plenty on barrel. You could probably gain 50 fps per inch if you went longer. As a side note, 1-9 twist for the heavy bullets. I am stabilizing 180 @ 2880 with a 284 win. I have one base from NEAR mfg. in Canada. That is a great product. I will buy some more if I ever build another remington.

 

[tazzman]

This project of mine has grown to be quite the headache. I often wonder what I've possibly missed. Does anyone on this forum have advice, ideas, suggestions? I am now wrestling with the type of reamer to order. How tight do I want this to be? Do I want a no-turn neck? Is wanting a SAAMI spec chamber a good thing? I am also considering playing around with a barrel tuner...

???
Phil

 

[k80skeet]

You and I are on the same line. I just finished building a 7mm Remington Mag on a 700 action. It started life as a 264 Win Mag. in 1962 I have had it rebarreled (4) times in 264 Win Mag a caliber that has served me well for the past 45 years. I just didn't like the short barrel life (500-700) rounds of peak performance then down hill from there. So this summer I decieded to try the 7mm Remington Mag. I sent the whole gun to Brian Volker of Iowa to build me a long range hunter / target . I have had great seccuess with Broughton 5C barrels so that was my pick for this project with a 1 in 9 twist Tim North owner of Broughton Barrels said this twist would handle everything from 140gr to 180gr. I used a barrel that was 26" finished and was .650 at the muzzle this kept the rifle under 9lbs with a 4.5X14X40 Leupold scope with target knobs. I am very pleased the rifle shoots 2'' to 2 1/2" 5shot groups at 600yards with 168 and 175 gr Sierra Matchkings. I couldn't ask for anyting better with a good barrel life and light enought to hunt with.

 

[Clark]

I have built (3) 7mmRemMag rifles over the last couple months.

90% of the belted magnum cartridges the have the same SAAMI spec as the 7mmRemMag:
.220 - .008" for cartridge
.220 + .007" for chamber

The best job would NOT be done with a Go-gauge to set the headspace.

That is because...
All the 7mmRemMag brass I can find is between .213 to .215".
All the 300WinMag brass I can find is between .210 and .217".
All the 338WinMag brass I can find is between .211 and .215".

What does it all mean?
The best job would be to headspace to just close on the longest measuring piece of brass you intend to use.

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Likewise, you will be happier with an expensive custom reamer that has a neck barely larger than that of your largest loaded cartridge.

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Why have a smaller chamber that SAAMI specs?
The brass will last longer and be more accurate.

 

[Nodak7mm]

Clark,

I am prob missing the obvious or am just under edgumacated, but without a print to ref, what do those measurements represent? ???

Thanks,

Rod

 

[Clark]

That is the distance from the bolt face to the front of the magnum case belt relief cut in the chamber.

 

[lelongcarabine]

Tazzman, If you are going to do this, have the action and bolt trued, blueprinted, etc. . Replace the factory recoil lug with a thicker offering (I have used the Tubb lug and am presently using Chandler lugs made by Badger Ordinance). What ever lug you use, make sure it is flat/parallel (Plus/Minus .0001" parallelism) and the surface is square with the bore in the lug. The foundation is good, it just needs a tune-up ;D. I have built rifles on Remington 700's, both short and long. I am presently using/shooting a .30/338 I built on the same action you are using. This is the same base case as the 7MM remington Magnum. I would use a 30" heavy palma taper (app; 6# weight) to get the maximum velocity out of your case and stiff. With a fully freefloated barrel, there should not be an issue finding the node using statistical load developement. If everything is square and trued, you will eliminate any harmonic issues. Your reloads will then be the limiting factor.
Bedding is another concern! There is no such thing as a drop-in that will provide a correct fit. The action on my .30/338 is .009"TIR out of round. It is fitted to an H-S precision sniper stock. I scraped the high spots off the aluminum chassis in the stock and skimmed the bedding block with Acra Glass Gel. That was in 1993. There are better bedding epoxies out there like Marine Tex and Devcon Titanium Gel. I have used these recently on a Remington 700 S.A. project!
Watch the scope base holes as drilled by the factory. They are not always parallel to the axis of the action. Talk to Dave Kiff from Pacific Tool and Gage about your reamer needs. I like a minimum chamber, no bulges in the fired case. Neck sized cases. Once the case is fired in your chamber, it is a perfect fit and headspaces on the shoulder, as it should. Neck size and your cases will last a very long time. I am still using the original Federal brass in the .30/338 for 800+ rounds, neck sized only. These are V E R Y HOT loads. Excellent accuracy!, 3 Elk! I would like to field this rifle (2010) in a 1000 yard match, just to see how well I can do .
Summary; Pay attention to the fine details as you pursue this project! Hope you do well and have a shootin' fool! lelongcarabine

 

[tazzman]

I have built (3) 7mmRemMag rifles over the last couple months.

90% of the belted magnum cartridges the have the same SAAMI spec as the 7mmRemMag:
.220 - .008" for cartridge
.220 + .007" for chamber

The best job would NOT be done with a Go-gauge to set the headspace.

That is because...
All the 7mmRemMag brass I can find is between .213 to .215".
All the 300WinMag brass I can find is between .210 and .217".
All the 338WinMag brass I can find is between .211 and .215".

What does it all mean?
The best job would be to headspace to just close on the longest measuring piece of brass you intend to use.

-----------------------------------------------------

Likewise, you will be happier with an expensive custom reamer that has a neck barely larger than that of your largest loaded cartridge.

---------------------------------------

Why have a smaller chamber that SAAMI specs?
The brass will last longer and be more accurate.

Hi Clark,

This is interesting. If what you say is true for most brass, then if you cut your chamber to spec, you would have a space between the front of the band and the edge of the chamber when the cartridge is fired, and you would get the resulting bulge common to belted brass? Am I understanding this correctly?

Phil

 

[Clark]

I don't think .005" length wise change in chamber support is a big deal to the bulge phenomena.
I don't know for sure, I have not suffered from bulges there.
That is probably for people who reload the same brass many times with hot loads.
I think that has to do with the web expanding and the sizing die not being able to change it.

What motivated me to do tighter headspace was that best accuracy and longer brass life are when the firing pin only pushes the cartridge forward 0.001".
If the brass is .215" and the chamber is .220", then the firing pin will push the cartridge .005" forward, the case will expand ahead of the belt, the case will grab the wall ahead of the belt, the pressure will push the case head back to the bolt face by stretching the brass. The brass may have an elastic limit of .001" longitudinally, and thus get .004" of plastic deformation. That permanent stretch is going to be taken out with the die, or the case will have to headspace, next time, off the shoulder instead of the belt.

 

[tazzman]

Hi Clark,

You mention that it is a firing pin that pushes the case forward, .005 in. I believe, in a standard cut chamber. I believe that an ejector would pretty well guarantee that the case is as forward as can be in a chamber once the bolt is closed. How deep have you cut your chamber, rear edge of barrel to front of belt relief, to obtain as you say "...when the firing pin only pushes the cartridge forward 0.001". ..." ?
Did you have to order a custom reamer? Did you order a reamer for a specific bullet type, VLDs perhaps?
Sorry for the questions, I am still in the planning stage, getting my ducks in a row, as they say.

Phil

 

[Clark]

I am using a standard 7mmRemMag reamer, I just use the longest 7mmRemMag case as my headspace gauge.