Short barrel velocity

Guys i have a 7-08 cut to 18", i changed the sope on it last night and sighted it in again today im not reloading for it yet but used Winchester super x 140gn bullets today and found that it dropped 6" at 200m, 100m zero.
The ammo says 2800 muzzle velocity, my question since i dont have a chrony handy is, is a 400fps drop in velocity about right, JBS? agrees but Bullet flight has it at 300fps. I know some other distances would be good but no time today it was a quick test so a young girl can shoot a trophy buck tomorrow.

Cheers
Mal

400 fps less compared to what length? that sounds hilariously unrealistic, probably the factory ammo is slow anyway

You'll lose 35 - 45 fps per inch of barrel chopped off down to around 18" in a 708... if you were 24" thats around 240 lost... if you were 22 more likely to be 150/160....

I would be surprised if your factory load was a whole lot over 2600fps before you chopped it...

Give yourself 1.5" high @ 100 and you'll be 3-4 low at 200.... that sounds about right..

Factory Ammo wont be anywhere near what the manufacturer says ..... too many variables and too many law suits.

Change the brand of ammo and the POA will change with it.

Only way to tell MV with that brand of ammo now is to put it over a crony.

How much did you chop from the barrel?

Cheers
Pete

I brought it cut down, looks like they were 24'' from factory.
The factory web site says 2800fps at 100Y 2523@200y and 2268@300y i shot 0 at 100m and 6" low at 200m if i was to lose a max of 45fps per inch thts 270 fps lost which is close to Bullet flights program but still a bit off JBS and thats working from the higher limit lost per inch off.
Is that right, and then if you add in the factor of Winchester bullshit on their packets of ammo then it is really close?

If you are not dialling I would zero at 200 anyway. Shoot a group at your max intended range with the 200 yard zero. You can then work back and get pretty accurate velocity from there as long as atmospherics are not extreme.

I will when i reload for it, at the moment its just set up to get this young girl her buck, i normally just have it for a bush basher, her father has a .270 not dialed in and a 7mmrem mag which would put her off for life probably.
I was just a bit surprised at the drop when i shot it aye and wondered if the short barrel would change it as much as what i was seeing.

Cheers Guys.

Quote:

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Originally Posted by Malhunting

I will when i reload for it, at the moment its just set up to get this young girl her buck, i normally just have it for a bush basher, her father has a .270 not dialed in and a 7mmrem mag which would put her off for life probably.
I was just a bit surprised at the drop when i shot it aye and wondered if the short barrel would change it as much as what i was seeing.

Cheers Guys.

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Easily. The loss in velocity per inch is not that straight forward. It can be almost exponential once it get less that a certain length.

Read up on Point Blank Zero. Zero your rifle at PBZ distance for your pet load and intended target kill zone diameter and you'll find that a centre hold in the kill zone is good for any target within the min-max distance. KISS principles apply.

This had me thinking as my 7/08 is chopped to 18" and wears a Dan can, I load 130 speers and the ADI book reckons 3000 fps for the load out of a 24" barrel. At the range I had it zeroed at 3" high at 100 yds, at 300 holding on the top edge of the Gong it impacted 3" low, good enough for me.