7mm Backcountry: Skeptic to Interested?

Nathan P.
Sep 29
6 min read

Updated: Nov 23

Skeptic

Like many people I was skeptical of not only the claims of the 7mm Backcountry but also the need. With cartridges such as the 7mm Rem Mag, 28 Nosler, the 7mm PRC, and last but not least the 7-300 PRC did the 7mm Backcountry bring anything new to the table? I couldn’t help but also consider the 6.5mm and 30Cal magnum cartridges around their 7mm brothers. You could say I’m suffering from a bit of magnum fatigue.

Curiosity

As time passed after the initial release discussions around the shop about the 7mm Backcountry increased, until my curiosity was peaked. I couldn’t help myself and I had to buy my own rifle in 7mm Backcountry to start experimenting with. When I say my curiosity was peaked, I do not mean peaked enough to spend a couple grand on a nicely built rifle let alone even half that. My interest was peaked just enough for the Savage 110 Trail Hunter Lite with the 20-inch barrel I purchased. After all, any side-by-side comparisons with different bore and groove configurations only requires keeping everything else on the rifle consistent and controlling the variables we want to evaluate. Plus, if the 7mm Backcountry turned out to be just as underwhelming as some say it is the price tag would be easier to live with.

For testing the rifle was set up with a non-traditional optic for a rifle designed for packing into the backcountry. But for the purpose of our testing offers enough magnification to get the job done. Everything else on the rifle was left factory original.

Initial Inspection

As you might expect nearly immediately after receiving the rifle we just had to inspect the barrel, a hazard of making barrels for a living I suppose. The borescope showed what you would expect; reamer marks running the whole length of the lands, not entirely perpendicular sides of the lands, and normal roughness in the grooves for a button rifles barrel. The dial bore gauge while picking up the highs and lows of the reamer marks was relatively consistent along the length of the barrel. The mean bore diameter was determined to be 0.2777-inches which is above specification per SAAMI but for reasons that would be revealed very soon the oversize bore is kind of a necessity.

Everything up until this point was as expected for any mass production rifle, The next step in our inspection was to measure the groove diameter and sweep from land to land in the groove. We were surprised to see the mean groove diameter was 0.2825-inches and yes, you read that correctly 0.2825-inches. Nominal groove diameter for a 7mm barrel is 0.284-inches and being 0.0015” under diameter was a huge surprise to us. So much of a surprise in fact that after I got this measurement I had someone else do their own independent measurements and they got the same value.

At this point we were concerned about the safety of the rifle. In past testing we know you will see a statistically significant change in velocity with as a little as a 0.0003-inch change in groove diameter due to the change in resistance to the bullet moving along the bore causing a change in the burn rate of the powder. That being said bore and groove diameter are not the whole story but are only two of the three critical characteristics. The final characteristic is the land to groove ratio and from this we can determine the bore and groove area. To determine the land to groove ratio we need to know either the land width or the groove width. To determine this, we swaged a lead slug in the bore and performed physical measurements to determine the width of the lands. On this barrel we determined the land width to be 0.0048-inch and calculated the groove width to be 0.1003-inch. From the swaged slug we also took another measurement for the bore and groove diameters. The bore diameter was no different, but the groove diameter as measured by the lead slug varied from groove to groove from 0.2827-0.2833-inch. It is normal to see a difference between the dial bore gauge and a swaged slug if the grooves are rough as the dial bore gauge is measuring the peaks of the groove and the micrometer on the lead slug is measuring the valleys of the grooves. With this information we can calculate the bore and groove area to be at most, taking the 0.2833-inch groove diameter, 0.0622 in² and at least, taking the 0.2825-inch groove diameter, 0.0620in².

SAAMI Specification

For those who haven’t spent much time looking at SAAMI specifications there are a few specifications that as a barrel maker we pay close attention to. Below is a portion of the SAAMI specification for the 7mm Backcountry and specifically the chamber dimensions which do include the bore and groove as well as other critical specifications.

Outlined in green you can see the bore diameter given as 0.277 and the groove diameter given as 0.284 as well as the minimum bore and groove area of 0.0622in². To try and keep everything as simple as possible every specification we’re evaluating for this barrel is in a table below. Keep an eye out for a future article that goes more in depth into barrel design and the part SAAMI specifications play.

Description	SAAMI	The Rifle	In Spec?
Bore Diameter	0.277-0.279 inch	0.2777 inch	Yes
Groove Diameter	0.284-0.286 inch	0.2825-0.2833 inch	No
Bore and Groove Area	0.0622in² min	0.0620-0.0622 in²	Yes (ish)

First Test Firing

Knowing that the bore and groove area is at the minimum, if we give the barrel the benefit of the doubt, we were not concerned about the barrel being safe to shoot but were expecting to see very stiff bolt lift and other pressure signs. The first ammunition we tested with was the 175gr Fusion Tip with an advertised velocity out of a 20-inch barrel of 2,975-fps. After a few shots to zero the rifle we chronographed a 3-shot group and achieved an average velocity of 3,119-fps, 144-fps over the advertised velocity on the box. The 170gr Terminal Ascents and 168 Barnes which advertised at 3,000-fps were both significantly above the advertised velocities at an average velocity of 3,043-fps and 3,079-fps respectively. To our surprise the Fusion Tip and Terminal Ascent ammunition did not cause any stiff bolt lift or extraction issues. The Barnes bullet being a solid copper bullet were not as forgiving with two of the three rounds taking significantly more force to open the bolt, but all fired casings extracted just fine. All things considered, the Savage 110 action took what must have been significantly higher pressures like a champ, and inspection of the action after the test firing showed no signs of stress or extraneous wear.

Description	175 Fusion Tip	170 Terminal Ascent	168 Barnes
Advertised Velocity	2,975	3,000	3,000

Average Velocity	3,119	3,043	3,079*, 3,055

Velocities	3,127	3,005	3,077
	3,107	3,061	3,084
	3,123	3,064	3,077
			2,982*

Extreme Spread	20	59	7 , 102*

*Includes the 4^th shot which opened the group up from 6-inch to 12-inch

Groups

We were not expecting great accuracy given the very tight groove and that is exactly what we got. The best group was with the 175 Fusion Tip coming in at 1.75-inch. The 168 Barnes was by far the least happy with the tight groove coming in at roughly 6-inch group if you throw out the worst of 4. If you include the 4^th shot you’re looking at roughly one foot at 100-yrds.

Manufacture Contacted

Savage was contacted based on these results and I offered to send the barrel itself back for evaluation. I was informed I would need to send the whole rifle back but at that point we had a new barrel on the rifle and were in the middle of more testing. I made the decision that sending the rifle back at this point wasn’t ideal to ensure we would continue testing.

Conclusion

Even though I was initially skeptical of the 7mm Backcountry through this process I have become genuinely impressed by the ability of the cartridge to handle pressure. Obviously, a steel case has a huge advantage over a traditional brass case to handle pressure. But to shoot a round averaging 144-fps over the advertised velocity with no significant signs of pressure in either the rifle or on the cases shows me there is some potential in this steel case design for something very interesting. I believe there is more to be extracted from this cartridge in terms of accuracy with a dimensionally correct for cartridge barrel and maybe some load development. The only roadblock as far as load development is concerned for this will be the lack of commercially available reloading dies, but I doubt we will let this stand in our way. The next step, however, was to get one of our barrels on this rifle and start evaluating bore and groove dimensions to compare the performance.

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