Thread: 7mm mag 26" velocity

bought a 7mm mag sendero which has a 26 inch barrel, going to sight it in (if i ever get some spare time) using hornady super performance 154g SST rounds. Hornady states this round does 3100fps out of a 24 inch barrel so does anyone know how much faster it will be going in a 26 inch? dont have access to a chrony (nor a range for that matter) and what to get it sighted for 200m zero and set up for medium/long range shooting.

If you are going to shoot medium/long range you need to start with some real data, zero it at a measured 200m so you know that part at least is right (there are a lot of unkonwn variables in shooting, you dont want your zero to be one of them) If you have a range finder, find a spot you can shoot out to a bit of range, zero it at 200m then fire groups at a series of ranges out to your max shooting range, measure the real world drop (ideally you will also record air pressure, temperature etc here, I dont know what you consider to be long range so not sure how important this will be for you), plug that into shooter or a similar programme and it will spit out your velocity

Hornady is usually quite over stated. I would start at 3050 (from your barrel) and guess the dope, then measure it.

You got a rangefinder yet?

Chris

Just as an aside. I dunno about the 7mm RM Superformance but with 140gn SST, 270Win Superformance it's right on speed up at around 3080 or thereabouts. Pretty impressive from a 22.5" barrel

I agree with Aaron, 308 150 SST superformance chronoed at 2950 from a 24' barrel. The 7mm mag will probably be pretty close. I would guess 25 - 30 fps per inch so 50 - 60 fps more from a 26" barrel.
But like Horihunter said, if you don't have access to a chrono you are going to have to shoot at known ranges (the longer the better, minimum 600 yds) and work out your drops then back calculate the velocity, or play with a ballistic programme changing the velocity until it matches your drops.

I also have 7mmRM Sendero with a 26" barrel and a 7mmRM T3 with a 24 3/8" Barrel. With 162SST's, 168 VLD's, and 180 VLD's there is about a 2% increase in velocity for the same powder charge and projectile (bugger all). The difference with 150 Nosler BT's was more pronounced. Around 5% increase in the longer barrel. It is not a very scientific experiment as the Sendero has a much shorter throat than the T3. I guess the only sure way to figure out the actual velocity gain per inch is to start out with 26" and chop off an inch at a time and chronograph it (velocity loss really). I'm not recommending that!

For the record I have choreographed Hornady 308 Superformance 150SST's at 2965 fps Average, and 7mmRM Superformance 154 SST's at 3092 fps Average. Both out of T3's. The 308 only has a 22.5" barrel. I think most ammo makers now days are well aware of the availability of the internet and chronographs to shooter, and no longer put bullshit velocity figures on the boxes.

If you're shooting 2 diff weight proj with the same powder change then you will have more grunt behind the heavier proj - simple physics
Each weight pill needs to treated as a diff load

You need to be careful. Experience has taught me that ballistic programs are usually very accurate and if you don't get near to the results you expect it is usually data entry or a gear problem.

So, I had a problem recently with my 300wmag. It was shooting 7-10" high at 525 yards. Blamed the 'scope for not clicking properly so tore it off and replaced it. Same problem again. Soooo I chronographed the load.....75.5gr R22 & 180 grn Nosler BT I had estimated at 3000fps...real average velocity was 3155fps. So there was my 7" of elevation. Problem solved.

If we are going to shoot at long range (out to 600 yards for me), we owe it to the animals to get these things right.

Now I've got a good spare 'scope.

Ive chronied five different calibers in superformance they were all very close to stated velocities

Sent from my GT-I9300 using Tapatalk 2

its just siting there not being used? thats a bit unfair to that scope.

Originally Posted by Neckshot

its just siting there not being used? thats a bit unfair to that scope.

And its sulking, because I blamed it for something that wasn't its fault. Oh well, I 'spose I will have to get something to put it on now...

(2.5-12 Clearidge xp5)

Originally Posted by Spanners

If you're shooting 2 diff weight proj with the same powder change then you will have more grunt behind the heavier proj - simple physics
Each weight pill needs to treated as a diff load

The protectile and powder were the same in each test. Only the rifle and thus barrel length were different. Just an observation that the lighter 150's showed a more pronounced velocity gain in the longer barrel than the heavier 162 to 180 grain projectiles.