Muzzle Velocity Loss Across Different Ammo

Hi guys

I might be barking up an unclimbable tree here but I've got a wee query that you guys might be able to help with.

Up until now I have been using Sako Gamehead Pro 165g with great results through my .308, unfortunately, these now appear to be discontinued and I'm all out! I've picked up a box of Hornady Precision Hunter 178g & Nosler 165g BT to see how they shoot and rezero with the best candidate .

My question is around drop charts, I chrony'd the Sako through my 18 inch barrel and had a drop chart that was working really well, I currently don't have a chrony and was wondering how to figure out a rough drop chart based on the specs on box (I know these aren't the most accurate but its all I have right now and I'm off for a roar hunt in a couple of days).

Does anyone have any idea if there is ANY consistency across different ammo when looking at velocity drop in a shorter barrel? Ie if the sako was 2600f/s out of a 24-inch barrel per the box and this dropped to 2500f/s out of an 18 inch could I expect:

a) a consistent reduction in fps? (ie 2800 fps becomes 2700fps)
b) a consistent % reduction in fps (ie 2600 to 2500fps = 4% velocity loss than 2800fps becomes 2688fps)
c) nothing consistent and I best just 200yard zero it and hope my hold overs are close
d) someone has some chrony data for the Precision Hunter or Nosler BT's out of an 18inch barrel that I can use
e) I'm an idiot and there's an easy answer Im not thinking of. (note I only have access to a 100 yard range so can't really walk out the drop myself)

Any help would be appreciated, I would hate to end up missing out, or worse wounding and losing, a good animal because I've got this wrong.

Cheers!

I wouldn't trust the box numbers even if you had the same length barrel. Chrono'd some Sako Blade stuff for a fella with a full length barrel. Box reckoned 3084fps. Chrono read 2885fps.

But... How much of a perfectionist do you need to be? Velocity loss won't ever be perfectly linear. But if all you need is rough enough for 300m, then I'd be surprised if the box number minus 25fps per inch didn't get you close enough. You can use a ballistic calculator and see for yourself how much a change in velocity actually effects drop at distance.

zero rifle 2" high at hundy,point n shoot out to 250,hold a bit higher out to 300.... anything past that you should be a bit more presise... 99% of shots I would take are well under that range.

You need either a chrony or a longer range, the box data is for a test barrel typically over 24 inches long and won't be relevant. How far do you intend shooting? 3 inches high at 100 would be a good average for most ammunition at a 200 yard zero and 3 low at around 250 and about 6 at 300. @Micky Duck often refers to the rule of 3 and it's been around for ages. Your target area is approx 8 inches in diameter on a mature red, so anywhere between point blank and 300 should land you on target.
Yes it's nice to know exactly where your rounds go to the half inch off a bench but huntings often different you rarely get time to take a perfect rest for a precision shot just aim for the big bit. Someone will correct me I'm sure but this worked before rangefinders, twiddly dials, strelok and mobile phones became necessary for shooting.

look at a combination of all the 308 30-06 and 303 figures and yo uwill see what is being said..... yip new stuff might be going a bit faster and projectile will be slipperier but its still in ball park your 30/06 150grn figure above is possibly closer to what you are using now.

Greetings,
In the .308 the velocity loss is around 25 fps for each inch of barrel lost below 24 inches down to about 18 inches. This won't help you much if you don't know the start velocity. Even if you know the actual velocity in another barrel this wont help either. There is not much point in doing a drop chart if you don't know the start velocity in your rifle. I am sure that there is someone in Taranaki who can help you with some chronographing.
Regards Grandpamac.

the above will get you near enough for a chest shot wit hvelocity of between 2600-3000 ish...its not rocket science...
look at a drop chart if you dont believe me....or look at 303 brit compared to 30/06 in above.... its not that huge of difference untill you start to stretch barrel

the 180grn figure will equate to a slower 150grn..near enough for a chest/shoulder shot...its not that complicated

The easiest way is to give me a yell after Easter and shoot them over my Chrono.
I'm just in Bell Block if you want to save a few rounds can sight it at 100 then check it at 300 or 400.

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Borrow the NI chrony on this forum. I have used the SI one before and most likely will again in the future.

Yep as above, start again. You'll need to chrony and verify or alternatively, estimate and verify at a couple of different ranges.

Cheers all, appreciate the feedback and the answer is about what I was expecting! Think i will go for the 2 inch high at 100 for this weekends hunt

Quote:

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Originally Posted by 25/08 IMP

The easiest way is to give me a yell after Easter and shoot them over my Chrono.
I'm just in Bell Block if you want to save a few rounds can sight it at 100 then check it at 300 or 400.

Sent from my CPH2145 using Tapatalk

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Thanks Mate I will take you up on that! I am also in Bell Block.

Quote:

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Originally Posted by NakiNewbie

Thanks Mate I will take you up on that! I am also in Bell Block.

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Just pm me after Easter

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Greetings,
As luck would have it I chronographed some Remington 150 grain Corelokt .308 ammo in a 24 inch m700 barrel yesterday. It gave 2,850 fps over my Oehler 35P chronograph with a 4 foot screen spacing. I was expecting something closer to 2,750 fps.
GPM.

If all else fails , download a ballistics app and use the velocity validation.

I shot a hole right through my chronograph a while ago whilst testing 22 subs over it so haven't had one for a bit. Have shot a few loads through my 243 since then and I just zeroed bang on at 100 then shot them at 350, measured the drop then adjusted the velocity in strelok until it matched up, changed to a 200yd zero and then used my new data to shoot out to 550yds and works perfect, I think it's actually easier than using a chrono and can do it with the same or less rounds

Quote:

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Originally Posted by Ryan_Songhurst

I shot a hole right through my chronograph a while ago whilst testing 22 subs over it so haven't had one for a bit. Have shot a few loads through my 243 since then and I just zeroed bang on at 100 then shot them at 350, measured the drop then adjusted the velocity in strelok until it matched up, changed to a 200yd zero and then used my new data to shoot out to 550yds and works perfect, I think it's actually easier than using a chrono and can do it with the same or less rounds

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100% I've never used a chrony.

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Quote:

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Originally Posted by Ryan_Songhurst

I shot a hole right through my chronograph a while ago whilst testing 22 subs over it so haven't had one for a bit. Have shot a few loads through my 243 since then and I just zeroed bang on at 100 then shot them at 350, measured the drop then adjusted the velocity in strelok until it matched up, changed to a 200yd zero and then used my new data to shoot out to 550yds and works perfect, I think it's actually easier than using a chrono and can do it with the same or less rounds

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Amature, I did it twice, again it was with .22 ammunition, on the bright side I was pretty much on the center line with both shots, some black lectricians tape and it will be fine👍