Velocity seems a bit high

[Hook'N'Bullet]

What is the brass telling you post picture of the hot case , my Sako 85 with a standard barrel ran at 2870 very happy with a 150 Pro hunter.

I dont have one to hand as I'm in work at the moment (great getting paid for this ) but theres no obvious signs of anything untoward. None or a very small bit of sooting but thats it

 

[paul o']

If there is nothing more than high FPS and you can see no Pressure signs! no sticky bolt, no case marks then one of two is what i would take from it. Your good to go or the reading on the fps is off a tad lol .The only time I reached 3k fps was with Vmax 110 gr bullets and I was pushing the rifle to see what it would give ! As it turned out the 150 pro hunter gave the best results both low recoil and good results down range . Another thing Sako prob did there test in a still air range with all the real world environments removed Speed kills but accuracy tells you more .
Good luck mty

 

[Hook'N'Bullet]

If there is nothing more than high FPS and you can see no Pressure signs! no sticky bolt, no case marks then one of two is what i would take from it. Your good to go or the reading on the fps is off a tad lol .The only time I reached 3k fps was with Vmax 110 gr bullets and I was pushing the rifle to see what it would give ! As it turned out the 150 pro hunter gave the best results both low recoil and good results down range . Another thing Sako prob did there test in a still air range with all the real world environments removed Speed kills but accuracy tells you more .
Good luck mty

No nothing like that was noticed. I'm a bit baffled at the supposed velocity. I've bought a chrony anyway that will be at my door next Wednesday so I'll update the thread with the accurate velocities then.

 

[Smellydog]

What? Am I not allowed to be curious?

Of course but it doesn't really matter does it. Sounds like a great load to me.
I use to get 3150fps from a 20" barreled 308 with 110gn v max and 2650 with a 170. All on h4895. The light bullet load was getting up there pressure wise but the heavy load was sedate.
Without a chrony is all speculation.
I mean everyone assumes the scope tube is pararell to the bore but it may not be, and it would only take a fraction to throw out the theorising.

 

[Heym SR20]

Take two identical rifles in the same calibre with the same barrel length.

Take one brand of ammo.

One rifle will group it well, the other rifle probably will not. Neither will shoot to advertised velocities one will be lower, the other 100 fps higher.

Now take another brand of bullet or ammo of the same bullet weight and the reverse will be true.

Slight differences in bore diameter, internal surface finish, chamber dimensions etc can all have quite a big effect on velocity.

And bear in mind that 100fps at 3,000fps is only a 3% variation.

And cheap end of chronograph market - quite how accurate and calibrated they are is a matter for debate. They probably very good at telling you variations in velocity, but is it actually 2750 or 2780 fps. (A bit like police radar guns and having to be regularly calibrated).

 

[Muir]

Or..... you could write to SAKO with the LOT Number of the ammo and ask whatr they got for velocity. You might get an answer; though it may take so long to come back that you'll lose interest in the answer while waiting~Muir

 

[Drum123]

Are you sure your group at 100 was exactly bang on in the centre at 100 and not say .25 high? Easy to do and it gives you a zero at 125 and not 100 .

 

[Hook'N'Bullet]

Are you sure your group at 100 was exactly bang on in the centre at 100 and not say .25 high? Easy to do and it gives you a zero at 125 and not 100 .

Well, I had a 100 meter zero target with a large diamond on it. At 100 meters, I aimed at the tip of the diamond and all three impacts hit it. I was able to cover them with my thumb. So it's as zeroed at 100 as it can be IMO. As I mentioned in a previous post. Somebody was shooting a 20" .308 (same as me) with 130grn copper at 3000fps. So maybe my 150grn is close-ish to the 2900 the app is suggesting.

Either way, I've ended up buying a chrony to take the guess work out

 

[ofbiro]

Everybody is anxious to learn the chrony measurements. Let us know.

 

[Hook'N'Bullet]

Everybody is anxious to learn the chrony measurements. Let us know.

Haha I sensed an air of anticipation. It will be delivered on Wednesday 30th, so will try get out over the weekend to chrony it

 

[Muntybuck5803]

I use the same 150gr Sako Super Hammerhead in my 308. 22inch barrel.
Chronographed at an average of 2790fps over 3 five shot groups.

 

[Selous]

I think extrapolating velocity from drop at two short ranges based on two groups and a manufacturers reported BC is about as inaccurate a way to determine velocity as you could get because so much is being assumed. Far better to get a chronograph, get a series of accurate velocity readings and map out the trajectory over much longer distances.

 

[25 Sharps]

To start off, I'm shooting a 20" .308win using 150grn Sako Super Hammerheads (I love them)

I was curious as to what speed my bullets were scooting along at. Without access to a chrony, I decided to do the old, shoot a group at 100 (zeroed range), then shoot a group at 200 and fiddle the speed in the ballistic calculator to match the drop. Unfortunately, my max range I could get in the area was 186 meters. It will have to do. First group at 100 was bang on the money. Couldn't have been happier. I actually surprised myself. Next group at 186 meters was good too. Drop between the two groups was 3 inches.

I went into my Sako Balistics App, input my barrel length, cartridge info, scope height etc and fiddled the velocity to match the drop. To mimic a 3 inch drop between 100 and 186, the velocity would have to be running at around 2900fps.
Now to me that seems way too fast. The advertised velocity on the box is 2805fps which I assume is from a 24" barrel. I was expecting a number more towards 2600 - 2700.

Anybody have an ideas? Have I missed something?

Your BC will vary with the speed you are getting. You need velocity and distance to calculate BC, you can’t reverse engineer it as manufacturer BCs are often over stated.

Buy, beg or borrow a chrono

 

[25 Sharps]

Does it matter

Only if you want to push ranges further in wind

 

[Smellydog]

Only if you want to push ranges further in wind

I guess so but being a hunter my view is limited as in I would not push range on a live animal in a wind beyond any reasonable expectations of the cartridge. Others may do and that's fine by me. To be honest, in the past I have done just so.
Did the op indicate he desired to push the range? If so I missed that and if so I apologize.

 

[HandB]

The ballistic apps you have seem over generous with velocity by approx 100fps. If you check the drop for standard NATO ball ammo in 7.62 (mv 2800fps) it is 3 inches drop at 190yds using this online calculator Ballistic Calculator GunData.org

 

[Dunwaters]

Thanks for your help, I've replicated it in strelock too and get 2890/2900 to mimic the drop give or take a centimeter. The 3 inch drop is correct, I was out with the tape measure and everything . I'm using a vortex rangefinder ranging the target and surroundings a couple of times to check give or take a meter. Nothing which would drastically affect the shot

It’d be a big help if you standardised your measurement units. Pick either imperial or metric and stick with it, you’ll drive yourself, your ballistics app and most of the rest of us batsh1t crazy if you don’t.
You’re currently trying to work out a muzzle velocity using 3” ( imperial) drop at 186M ( metric) from a 20” barrel, with corrections from 24” ( imperial again).
If you go imperial your 186M range becomes 204Yds or thereabouts, you can easily shift a bit to 100 and 200yds and shoot again.

 

[wag]

The measurement in drop would need to be so precise to get an accurate speed it's just not worth it.

 

[Hook'N'Bullet]

Everybody is anxious to learn the chrony measurements. Let us know.

So I chronied it - average velocity was 2741fps over 5 shots. Did it a while ago but completely forgot about this thread

 

[long_range_rob]

Sounds right. I’m using 162gn Sako Blade and that chronos at 2600fps at the muzzle (using a magnetospeed)