7mm Backcountry anyone?

[ismith]

No idea. Is that what Federal recommends or is this satire?

Is it reloadable or not?

 

[Alpine01]

That’s poor physics. You didn’t account for the mass and velocity of the powder. I don’t know what velocity they use for burned powder in recoil calculators, but it exits the muzzle at a much higher velocity than the bullet does, and thus 1gr of powder increases recoil more than 1gr of bullet. The decreased powder charge of the 7BC compared to the magnums results in it having very similar recoil despite the increase in performance.

Fair point - in my example I was assuming same powder charges. But your right, the 7mm BC is probably running something in the neighborhood of 50 gr vs a 7mm RM at roughly 65 gr. But this is partially offset by the higher pressures generated in the BC.

 

[yakimanoob]

More slightly off physics.

Momentum is always conserved.

Fair enough - I was playing too fast and loose between momentum and total kinetic energy.

 

[ImBillT]

Fair point - in my example I was assuming same powder charges. But your right, the 7mm BC is probably running something in the neighborhood of 50 gr vs a 7mm RM at roughly 65 gr. But this is partially offset by the higher pressures generated in the BC.

My guess is that the 7BC is closer to 60-63gr. IIRC I’m shooting 61.5 in my 280AI. I’d have to look. The 7BC would likely use a similar powder charge of a slightly faster powder. I was originally thinking the 7mag tended to use more powder than most load data suggests. It isn’t as much larger than a 280AI as I thought it was.

 

[ImBillT]

Is it reloadable or not?

Last I heard Federal said something along the lines “yes if you follow our method”, but I’m not aware of them publishing any methods. So unless someone has new information, then would lean toward saying that it is not currently reloadable.

 

[Alpine01]

My guess is that the 7BC is closer to 60-63gr. IIRC I’m shooting 61.5 in my 280AI. I’d have to look. The 7BC would likely use a similar powder charge of a slightly faster powder. I was originally thinking the 7mag tended to use more powder than most load data suggests. It isn’t as much larger than a 280AI as I thought it was.

I load a 7mm RM with 65 gr of powder and push a 150-gr copper bullet to 3172 fps. With sub-0.6 MOA performance over 100+ rounds fired, I don't see much of a reason to make the switch for a few gr of powder savings and a few percent gain in velocity. Maybe handloads will show themselves to gain a bigger bang for the buck if reloading dies and the right powders start to come to market.

 

[kodiakisland]

Is it reloadable or not?

I think the official answer is still yes, but just not yet. It's designed to be reloaded and Federal wants it reloadable, but the dies and process have still not been perfected to roll out to the masses.

 

[ismith]

I think the official answer is still yes, but just not yet. It's designed to be reloaded and Federal wants it reloadable, but the dies and process have still not been perfected to roll out to the masses.

So kinda like living on Mars then, cool.

 

[kodiakisland]

So kinda like living on Mars then, cool.

It's 50/50 as to which we do first.

My guess when they do get it going, it will be only for presses that can handle the 50BMG size cases.

 

[brockel]

Last I heard Federal said something along the lines “yes if you follow our method”, but I’m not aware of them publishing any methods. So unless someone has new information, then would lean toward saying that it is not currently reloadable.

I believe their method is running into a sizer half a dozen times for it to fully size it. Pass.

 

[Jnasa]

My initial thought is it seemed like a gimmick. Reading more on it J could see why someone wanting a shorter barrel to shoot surprised May like it.

I’m not interested in it for me. First I don’t have the need. Second I like reloading and wouldn’t want a cartridge I couldn’t reload for. Finally I am also not an early adopter when it comes to new cartridges.

I understand why someone would be interested. It just isn’t for me.

 

[7's-and-30's]

Wish we could use the same technology to increase pressures in other cartridges. 7mm-08 at 80,000psi would be a sweet little cartridge probably a bit better than the 7mm rem mag.

 

[ImBillT]

I believe their method is running into a sizer half a dozen times for it to fully size it. Pass.

While not exciting, st lesst that doesn’t require extreme equipment.

If a single sizing doesn’t size it down all the way, why not reduce sizing due dimensions slightly?

 

[ImBillT]

Wish we could use the same technology to increase pressures in other cartridges. 7mm-08 at 80,000psi would be a sweet little cartridge probably a bit better than the 7mm rem mag.

I don’t know why we can’t as soon as someone offers brass. My guess is that manufacturers will be reluctant to offer brass for other cartridges based on that giving the loader the ability to raise pressures regardless of whether or not the rifle manufacturer has given their stamp of approval. I think some reasonable common sense could make it doable safely, but that doesn’t mean Federal wants to risk it.

 

[brockel]

While not exciting, st lesst that doesn’t require extreme equipment.

If a single sizing doesn’t size it down all the way, why not reduce sizing due dimensions slightly?

I believe it has to do more with the cases slightly springing back. Reducing the sizing die dimensions might make it even tougher to size on first pass

 

[ImBillT]

I believe it has to do more with the cases slightly springing back. Reducing the sizing die dimensions might make it even tougher to size on first pass

Cases springing back is exactly why you would reduce the sizing die dimensions. You don’t get any plastic deformation until you go past the elastic region. An over simplification would be to say that if you had a bar that could be bent 1” and fully return, but you needed a .5” bend in the bar, then you would have to bend it 1.5”. It would then return 1” and maintain a .5” bend.

The reason a fired case is sticky in a chamber if it’s overpressure is based on exactly that. The chamber expands during firing, and the case expands inside it. The barrel can tolerate a certain amount of expansion before deforming permanently, and the case can tolerate less expansion before it deforms permanently. When pressure reaches a level that the chamber expands beyond the case’s elastic region, the case becomes larger than the chamber, but once the pressure is gone, the chamber clamps down on the now larger case and it becomes difficult to extract.

A sizing die has to deal with that issue. When you remove the case from the die, the case is larger than the inside of the die. Also, it does get easier to run through the die for a few iterations if you keep running it through. This is because the die expands ever so slightly when you run a fired case into it. After the case was sized, even though it remains a little larger than the die, it puts less force on the die the second pass through, thus expanding less and sizing the brass down a little further. The softer to the brass is, the less pronounced this effect is.

A slightly smaller sizer should be able to return the 7BC cases to the proper dimension in a single pass, BUT that only solves one problem. Case size. Force could absolutely be a consideration. I don’t know how hard it is to size a 7BC. Friction could be another issue. It’s possible that with steel dies, normal presse and conventional lines that a smaller die isn’t a good option. I don’t know. I will be interested to see how it fares as time goes on.