7mm Backcountry anyone?

[ImBillT]

I was initially of the opinion that it was a great way to ruin a barrel and pierce my eardrums, but I have changed my mind. Looking at recoil calculations, powder mass is a huge factor. The powder mass doesn’t really increase compared to a 280AI. In terms of barrel life, heat is the main factory, and that’s primarily powder mass and bore area. Again, same as a 280AI. For muzzle blast, that’s pressure at the muzzle. Chamber pressure has a lot to do with powder burn rate, and bullet mass, but pressure at the muzzle is primarily based on powder mass and bore volume. Yet again, basically the same as a 280AI. Recoil, muzzle blast, and barrel life will probably all be slightly worse than a 280AI, but I suspect they will all be much better than a 7mag. I’m interested!!!!


I would like some once fired brass for experimentation. I’m considering just buying a box of loaded ammo.

 

[Robert N]

Federal 7mm Backcountry

I just read this article on it. Pretty cool if the claims turn out to be legit. https://www.fieldandstream.com/guns/federal-7mm-backcountry-ammo-review

www.hunttalk.com

 

[ImBillT]

Federal 7mm Backcountry

I just read this article on it. Pretty cool if the claims turn out to be legit. https://www.fieldandstream.com/guns/federal-7mm-backcountry-ammo-review

www.hunttalk.com

I skimmed, but I guess I should have used the search function!

 

[ismith]

Is it reloadable without a hydraulic press yet?

 

[VMHunter]

I think just with the bullet speed and grain weight the recoil will be on par or worse than a 7 RM/7 PRC.

You can’t gain extra velocity without giving something up. Can’t beat physics.

 

[Big Sky Guy]

I think just with the bullet speed and grain weight the recoil will be on par or worse than a 7 RM/7 PRC.

You can’t gain extra velocity without giving something up. Can’t beat physics.

True, but the explanation I’ve heard is the grain weight of powder contributes to recoil in addition to bullet weight. Less powder in 7BC than 7PRC/RM. my guess is somewhere a bit above .280ai but below the “magnum” recoil.

 

[ismith]

True, but the explanation I’ve heard is the grain weight of powder contributes to recoil in addition to bullet weight. Less powder in 7BC than 7PRC/RM. my guess is somewhere a bit above .280ai but below the “magnum” recoil.

Sounds like marketing to me, but what do I know?

 

[VMHunter]

Depends on the powder and the energy contained in that powder. I’d imagine to get to the 7 BC pressure there will be a lot more energy in that powder than what’s used in the 7 RM/PRC especially if there’s less powder.

 

[Alpine01]

Basic physics - Taking Federal published data for the 7mm BC vs a 7mm RM, for the same bullet mass (155 gr), you get 3300 fps vs 3000 fps. That's a 10% increase in velocity (3300/3000 = 1.10). Energy goes as velocity squared so the energy increase is 1.1 x 1.1 = 1.21 or a 21% increase in muzzle energy. For the same barrel length noted (24 inches) for both sets of data, the resulting force is increased by that same percentage. Thus a 21% increase in recoil for the BC over a RM all other things held constant.

For a 7mm-08 with a 150 gr bullet, Federal shows a velocity of 2650 fps. Compared to the same BC numbers above, the recoil in the BC will be 60% greater assuming a 24-in barrel.

 

[KingOfTagSoup]

I'm definitely watching it closely but as with any new cartridge, my approach is to not touch it until it's been around a few years and has worked out it's bugs (cuz there are ALWAYS bugs) and has proven it has the support to survive. In theory it sounds great but seeing is believing. A buddy of mine is all on board and has a rifle on order so hopefully I'll be able to get some hands on testing with him when it comes in. I'll be sure to report back once I get the chance to shoot it.

 

[ImBillT]

Is it reloadable without a hydraulic press yet?

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

 

[ImBillT]

I think just with the bullet speed and grain weight the recoil will be on par or worse than a 7 RM/7 PRC.

You can’t gain extra velocity without giving something up. Can’t beat physics.

Run it through a recoil calculator.

A 7mmBC pushing a 175gr at 3000fps is very similar in recoil to a 7PRC pushing a 175 at 2800fps.

The reason it isn’t a direct correlation to bullet mass and velocity is that powder mass also contributes to recoil, and once the bullet unplugs the barrel, the burned powder is escaping faster than the bullet did. So adding 200fps by using less powder in the 7BC doesn’t increase recoil as much as you might expect.

 

[ImBillT]

True, but the explanation I’ve heard is the grain weight of powder contributes to recoil in addition to bullet weight. Less powder in 7BC than 7PRC/RM. my guess is somewhere a bit above .280ai but below the “magnum” recoil.

I feel like I used an online calculator and came to this same conclusion earlier, but I just ran one, and the 7BC was right there with the 7PRC, but I was pushing the bullet faster in the 7BC. I may have used an excessively high velocity just now, which would drop the recoil a little.

 

[ImBillT]

Depends on the powder and the energy contained in that powder. I’d imagine to get to the 7 BC pressure there will be a lot more energy in that powder than what’s used in the 7 RM/PRC especially if there’s less powder.

It requires no special powder.

 

[ImBillT]

Basic physics - Taking Federal published data for the 7mm BC vs a 7mm RM, for the same bullet mass (155 gr), you get 3300 fps vs 3000 fps. That's a 10% increase in velocity (3300/3000 = 1.10). Energy goes as velocity squared so the energy increase is 1.1 x 1.1 = 1.21 or a 21% increase in muzzle energy. For the same barrel length noted (24 inches) for both sets of data, the resulting force is increased by that same percentage. Thus a 21% increase in recoil for the BC over a RM all other things held constant.

For a 7mm-08 with a 150 gr bullet, Federal shows a velocity of 2650 fps. Compared to the same BC numbers above, the recoil in the BC will be 60% greater assuming a 24-in barrel.

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.

 

[yakimanoob]

The total momentum transferred to the rifle will always be equal* to the momentum of the bullet as it leaves the muzzle plus the total momentum of the gas and unburnt powder leaving the muzzle. The momentum of the bullet is easy to find - weight of the bullet times velocity. The momentum of the gas and unburnt powder, however, is not so easy to find. But since the mass of powder exits the muzzle too (either in gaseous or solid form), yes, recoil depends on powder charge.


*ok technically it's not equal but ever-so-slightly less than the combined momentum of everything leaving the muzzle. A little bit of the energy goes into heat, elastic deformation in the barrel, etc etc. But these are very very small effects.

 

[yakimanoob]

ImBillT beat me to it

 

[jpc01101]

My Dad got a weatherby in 7 Backcountry that he topped with a Zeiss 5-25. He shot it for the first time last night. We zeroed it with 3 shots and he was stacking bullet holes at 200 yds. He loves the gun. I shot it once and it felt great. Were shooting it suppressed. 20” barrel will post chrono numbers when we get some.

 

[ImBillT]

The total momentum transferred to the rifle will always be equal* to the momentum of the bullet as it leaves the muzzle plus the total momentum of the gas and unburnt powder leaving the muzzle. The momentum of the bullet is easy to find - weight of the bullet times velocity. The momentum of the gas and unburnt powder, however, is not so easy to find. But since the mass of powder exits the muzzle too (either in gaseous or solid form), yes, recoil depends on powder charge.


*ok technically it's not equal but ever-so-slightly less than the combined momentum of everything leaving the muzzle. A little bit of the energy goes into heat, elastic deformation in the barrel, etc etc. But these are very very small effects.

More slightly off physics.

Momentum is always conserved. None is lost to heat or elastic deformation or anything else. The rifle started at 0 momentum, and in order for the total to remain at 0, the rifle must move rearward at the same MV(mass X velocity) that the bullet and propellant gases are moving forward. The main question is “how fast does the burned powder move once the bullet exits the barrel?”, but it’s rather unimportant for any of us, as we don’t have to figure any of it out! There are easy to use recoil calculators all over the internet! Also, I’ve only used momentum to evaluate collisions, so I’m wondering if there is a reason that I should not use it for recoil. I’m unsure.

For recoil energy, you need to know the mass of the powder and the velocity that it exits the barrel. The powder charge in a 7BC is likely 60-63gr. I don’t know how fast it exits, but I like recoil calculators are all over the internet. Recoil will be close to the magnums using a 62gr powder charge and a 175@ 3000fps compared to a 67gr powder charge and a 175@2800fps in a magnum. If comparing to the magnum, you pretty much get the extra 200fps with no recoil penalty due to gaining that velocity by increasing chamber pressure instead of by increasing muzzle pressure(powder charge).

 

[ImBillT]

My Dad got a weatherby in 7 Backcountry that he topped with a Zeiss 5-25. He shot it for the first time last night. We zeroed it with 3 shots and he was stacking bullet holes at 200 yds. He loves the gun. I shot it once and it felt great. Were shooting it suppressed. 20” barrel will post chrono numbers when we get some.

Now there’s a report that matters!