Velocity loss in short barrel 308

Hey guys
Have just purchased a shortened 308 (17inches).
I am keen to make up a rough drop chart for it (very rough indication) and I will try and validate it as and when I can.
I don't reload, and dont have access to a chrono, so take the manufacturers data on the factory ammo boxes. From what I understand, the displayed FPS for 308 is based off a 24 inch barrel, what kind of approximate loss should I expect per inch, to roughly estimate my velocity from a 17inch barrel? I thought the collective forum mind might have a more accurate suggestion then google, as seems quite a range out there. I also know quite a few people have cut down 308s so might have some real world data.
Cheers!

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Originally Posted by JoelA

Hey guys
Have just purchased a shortened 308 (17inches).
I am keen to make up a rough drop chart for it (very rough indication) and I will try and validate it as and when I can.
I don't reload, and don't have access to a chrono, so take the manufacturers data on the factory ammo boxes. From what I understand, the displayed FPS for 308 is based off a 24 inch barrel, what kind of approximate loss should I expect per inch, to roughly estimate my velocity from a 17inch barrel? I thought the collective forum mind might have a more accurate suggestion then google, as seems quite a range out there. I also know quite a few people have cut down 308s so might have some real world data.
Cheers!

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My best suggestion would be to borrow a chrono from somebody. Or somebody with a Garmin or Labradar et take you to a range. I am sure somebody around the Waikato would be able to help?

https://rifleshooter.com/2014/12/308...ty-28-to-16-5/

looks like about 250 fps which is a bit less than I was thinking.
will vary with ammo faster/lighter ammo may loose more velocity
Z

16inch 1-8 Tikka, 168gn eldm handloads @2450. Not fast but good enough for what I need it to do to 300m
I know I could get more speed if I brought different powder but that means additional cost.
Never used factory ammo in it

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Originally Posted by JoelA

I don't reload, and dont have access to a chrono, so take the manufacturers data on the factory ammo boxes. From what I understand, the displayed FPS for 308 is based off a 24 inch barrel, what kind of approximate loss should I expect per inch, to roughly estimate my velocity from a 17inch barrel?

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Tried doing exactly that once upon a time and it was so far off, it wasn't funny.

Bergara 16.5 spitting factory Sako gamehead 150gn => 2650fps.

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Originally Posted by MB

Tried doing exactly that once upon a time and it was so far off, it wasn't funny.

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Good to know - thanks MB

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Originally Posted by ZQLewis

https://rifleshooter.com/2014/12/308...ty-28-to-16-5/

looks like about 250 fps which is a bit less than I was thinking.
will vary with ammo faster/lighter ammo may loose more velocity
Z

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Thanks for that Z!

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Originally Posted by STC

My best suggestion would be to borrow a chrono from somebody. Or somebody with a Garmin or Labradar et take you to a range. I am sure somebody around the Waikato would be able to help?

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I may have to try that!

Tika 308 22in barrel,using shop hornady 165gr ssts chronied at 2760ft/sec.Loss of 40ft/s /inch off the factory velocity 2840ft/s using at 24in barrel.Down to a 17in barrel would mean more velocity loss per inch.

@7mmsaum is the North Island Chrony still alive?

@JoelA. I shoot a 16" with supressor but do reload et al. The max range shot I'll take is at 300 metres.

That said; I have used factory ammo in several different brands of shortened .308's. The most consistent in terms of velocity and accuracy was Sako Gamehead. In your shoes I would forget about velocity seeing as you don't have the means to measure it. Assuming you've got access to a range, Zero your rifle @ 100 metres. Then step it out to 200 metres. Group and measure drop, should be roughly 3". That being the case you can safely assume an 8" drop at 300 metres from 100 meter zero.

I figure if I'm taking shots at the two latter extended ranges I've got time to faff about. That has proven to be exactly the case. My scopes a dial up variety. I don't compete but do knock over animals.

Hope this assists. Cheers

Il send you my chrono guessing is just to hard mate

Pick which ammo you think is gonna work, sight it @100, then do a tall target test at 200 and 300. Put your drops in an app - Strelok or Applied Ballistic's etc, and go from there. Should be able to sight it in with 5 or 6 shots, another 3 or 5 to group it, and 3@200, and 3@300. Should still have a few rounds left in the box to go shoot an animal.

I have the SI chrono coming to me next and once I have finished with it can send it south to him @Gibo

Oops just realised he is up north. So ignore above

it SHOULD be pretty close to .303 brit in speed.... UNLESS your intending to rangefind and dial....I PERSONALLY BELIEVE you will be better of to sight it in say 2" high at hundy and just go use it....the old rule of three still works today,just as well as it always has...
the really interesting thing about that old chart is when you do a sort of average across whats nearest to what you have got...untill you start strecthing barrel it really wont matter..will try to repost it for you to ponder

Attachment 248120

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Originally Posted by RugerM77

@JoelA. I shoot a 16" with supressor but do reload et al. The max range shot I'll take is at 300 metres.

That said; I have used factory ammo in several different brands of shortened .308's. The most consistent in terms of velocity and accuracy was Sako Gamehead. In your shoes I would forget about velocity seeing as you don't have the means to measure it. Assuming you've got access to a range, Zero your rifle @ 100 metres. Then step it out to 200 metres. Group and measure drop, should be roughly 3". That being the case you can safely assume an 8" drop at 300 metres from 100 meter zero.

I figure if I'm taking shots at the two latter extended ranges I've got time to faff about. That has proven to be exactly the case. My scopes a dial up variety. I don't compete but do knock over animals.

Hope this assists. Cheers

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Good to know - haven't used much Sako GH ammo before, but will give it a try out! Yeah, I think a real world drop chart will be the way to go. I don't have a dial up scope, I will just be using a burris droptine with a ballistics drop reticle, so might try work something up off using that reticle.

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Originally Posted by Kelton

Il send you my chrono guessing is just to hard mate

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That's very generous mate - I can try developing an actual drop chart first as suggested by @RugerM77 above.

eg look at bottom 5
say zeroed for 190-245 will be hold dead on to(less than 4" low untill)230-285 and hold 12" over at300-370

so I would try the 303 figures and wiggle your height at 100 yards till it suits what you intend to do...
pointblank online on www.huntingnut will allow you to play with your numbers and via the bullet curve picture SEE what it should be doing....
yip you will have to validate by shooting a couple of groups out further but by using these two things as A STARTING POINT ,you should be on the money reasonably easily

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Originally Posted by Micky Duck

it SHOULD be pretty close to .303 brit in speed.... UNLESS your intending to rangefind and dial....I PERSONALLY BELIEVE you will be better of to sight it in say 2" high at hundy and just go use it....the old rule of three still works today,just as well as it always has...
the really interesting thing about that old chart is when you do a sort of average across whats nearest to what you have got...untill you start strecthing barrel it really wont matter..will try to repost it for you to ponder

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Wouldn't that still rely on a consistent velocity MD?

yes and no....... see chart.... if you used rough enough...she'll be right thinking (not ideal but reality for many) and just sighted in 3" high at hundy...
and were shooting at animal at 250 by holding right where you wanted to hit
using numbers off that chart(because its got fair old range of levels and its on hand)
30/06 dead on
heavy 30/06 4" low
308 tiny bit high
303 slightly too low???say 5"???
8x57 about 3" low

so using really rough idea..you can see by sighting in 3" high at hundy you CAN hit and cleanly kill out to 250 yards without over thinking it..yeah yeah the 303 will be say 5" low but because you have validated it by shooting out to 250yards previously you KNOW it will be so held a bit high on shoulder.

no they not the 308 you using but its all still relevant...some a bit faster,some a bit slower,some a bit blunter others are more aerodynamic....remember that chart was made before most of us were born...other than Rushy and Keith Richards or course!!!

if your using the same load....you will be as constant as that load is...factory loads = what it is,is what it is.

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Originally Posted by Gibo

@7mmsaum is the North Island Chrony still alive?

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Yes it’s at my place and working well

No chony,just zero at a hundy.Do 3 shots at 300yds n 400yds.Work yr speed with yr drop and bc.Will work very close for you

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Originally Posted by Trout

No chony,just zero at a hundy.Do 3 shots at 300yds n 400yds.Work yr speed with yr drop and bc.Will work very close for you

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That’s how I do it. Hadn’t validated the new 18” barrel on my Kimber .308, only sighted at 100yd last year. The other day I fired one shot at a hundy to confirm zero, then two shots at 300yd to measure actual drop. https://uploads.tapatalk-cdn.com/202...2b6f57ba31.jpg
https://uploads.tapatalk-cdn.com/202...766cbfdb36.jpg
Can see the two shots at 300, well below the paper, bottom of paper being the aiming point as I wasn’t concerned about windage here. Target was on a bit of a lean.


Sent from my iPhone using Tapatalk

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Originally Posted by Trout

No chony,just zero at a hundy.Do 3 shots at 300yds n 400yds.Work yr speed with yr drop and bc.Will work very close for you

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Thanks guys - I will do this. Have access to 100 & 200m distances, and will try work something off for a 300 distance. Cheers! Seems simplest!

Where are you based and what ammo are you using? I chronied remmy 150 corelokts from my 17 inch kimber 308
the other week just for the sake of it..

4 shots, 2609, 2651, 2606 and an outlier at 2751.

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Originally Posted by Nick.m

Where are you based and what ammo are you using? I chronied remmy 150 corelokts from my 17 inch kimber 308
the other week just for the sake of it..

4 shots, 2609, 2651, 2606 and an outlier at 2751.

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Based in Te Awamutu. Haven't even fired the rifle yet as I only purchased it secondhand recently, still as yet to grab some ammo. I've often used the Hornady whitetail with satisfactory results, but I'll probably grab a few boxes of different stuff to try out. That's faster then I would have thought from the 17inch barrel.