7mm rem mag "slow barrels"

[sundance1972]

Have heard and read about some of the 7mm rem mags (remington model 700's) having "slow barrels", and now it seems i'm the owner of one, also. The first one i owned had no problems whatsoever reaching published velocities (still kicking myself for selling it), but my latest is about 150 fps slower with the same factory and hand loads. My father has the identical rifle, and his is 150-175fps faster with the same loads.

Has anyone found a way to improve these barrels, or am i stuck with a "slow magnum?

I'm obviously not a gunsmith, but i just had an idea . If the barrel was cut with some what "worn out" tooling, is it possible to buy a finishing reamer and hone it out a little (if necessary), or would this just be a waste of time and money?
Any help would be greatly appreciated, thanks

 

[Blue Mountain Sports Inc.]

Bullet velocity is a direct result of the pressure beneath it as it travels down the barrel.A tight bore or a rough bore creates more resistance and hence higher resistance and higher pressure and higher velocity. A smooth bore creates less resistance and velocity will be lower because the pressure will be lower but the bore fouling will be minimal. An oversize bore would drop pressures back a bit , but in a high pressure cartridge like the 7mm Mag bullets would tend to swage up to bore size and you wouldn't see much velocity drop from this. Flat base bullets will seal the bore better than boat-tail designs. If a flat base gives you the velocity that you expect and a boat-tail does not then possibly the bore is at the larger size that is acceptable.

 

[dan belisle]

You can try the various barrel polishing/finishing products out there, that will help a little. Some rifles you just have to accept slower velocities. On the other hand, I've also had magnum rifles that would only achieve book velocities with certain powders and/or certain bullets. I have pretty good success in & Rem Mag with RL22 and 7828, somewhat less with H4831. AA3100 is a pretty good choice too, velocity wise. 160 gr partitions are my bullet of choice in this caliber. FWIW - dan

 

[Why not?]

When I first got my Oehler chronograph, more than 25 years ago, everyone at the range wanted to check out their loads. We got some real eye-openers.

One of the biggest was a guy who had used a 7mm Rem Mag for more than ten years for all his big game hunting. His favourite load was using the old 154 gr Hornady spitzer and he had killed a lot of game with the rifle; moose, caribou, black and grizzly bear, sheep.

The velocity was around 2800 fps, can't remember exactly. He was furious! "How can that be?" "That chronograph is wrong!" "No way that load is only 2800 fps!"

The animals were all dead, however.

Ted

 

[Why not?]

When I first got my Oehler chronograph, more than 25 years ago, everyone at the range wanted to check out their loads. We got some real eye-openers.

One of the biggest was a guy who had used a 7mm Rem Mag for more than ten years for all his big game hunting. His favourite load was using the old 154 gr Hornady spitzer and he had killed a lot of game with the rifle; moose, caribou, black and grizzly bear, sheep.

The velocity was around 2800 fps, can't remember exactly. He was furious! "How can that be?" "That chronograph is wrong!" "No way that load is only 2800 fps!" We checked again and got the same velocity, then shot some 22 rimfire to confirm, and checked the loads out again later.

The animals were all dead, however.

Ted

 

[blargon]

, but my latest is about 150 fps slower with the same factory and hand loads. My father has the identical rifle, and his is 150-175fps faster with the same loads.

I don't think you can really compare the same load in 2 different rifles. That particular charge/bullet may present 5000 psi less in your rifle than in your father's, due to the bore or chamber differences.

I would suggest that you work up the load again for your rifle and you may find that your max charge is now higher than it was in your old rifle...