Velocity vs Barrel length

[Dmitri Popov]

I have a Savage Axis, 22" barrel. It shoots the Hornady 80255 55gr. SP superbly (easily under 1moa when I do my part). I am trying to set up a Nikon Prostaff (came on a Savage Trophy Hunter XP package) and get some ranges set up on Spot-On.

Now this ammo is rated at 3240 fps out of a 24" barrel, but how much velocity loss am I looking at by being 2" short? My research indicates somewhere close to a 40 fps loss, but I'd like to hear some other opinions.

Thanks

 

[moxie]

The only way to know is to run it over the chrono. The original "rating" could be way off, in your gun, as well as any reduction due to shortened barrel.

 

[Dmitri Popov]

Unfortunately a chronie is not an option. Trust me if it were, I wouldn't be posting this here!

 

[MachIVshooter]

I'm assuming it's a .223 based on the numbers. If so, yeah-somewhere in the 35-50 FPS range would be my guess.

Most rifle cartridges will gain or lose about 20-30 FPS per inch within 4 or 5 inches of their ideal barrel length. For .223, that's 20" with most loads, and the rule of thumb tends to hold true between 16" and 24". Below 16", the loss becomes more pronounced, and longer than 24" you see increasingly smaller gains.

For future reference, a rough guide to optimal barrel lengths would be something like:

<50 gr. capacity: 22"-24"

50-70 gr. capacity: 24"-26"

70-100 gr. capacity: 26"-28"

>100 gr capacity: something longer

Of course, few rifles are equipped with >26" tubes because they simply become unwieldy, so we generally find the larger magnums in 24"-26" guns, while .30-06 class rounds are normally 22" or 24", and the short action rounds are found in 20" or 22" barrels much of the time.

 

[USSR]

Now this ammo is rated at 3240 fps out of a 24" barrel, but how much velocity loss am I looking at by being 2" short?

Simply no way of knowing without running it across a chronograph. I have 2 match rifles in .30-06, both with 26" barrels, and with the same load one gets 2950fps while the other only does 2875fps.

Don

 

[jmr40]

That 75 fps difference is not at all uncommon. I've seen guns with 20" barrels shoot the same ammo 20-30 fps faster than another gun with a 22" barrel.

It would be rare for a common production gun to actually match published ballistics even if it has the same length barrel. Most companies test in high quality barrels with chambers cut to minimum dimensions. They get the highest pressure and velocity this way. It is not meant do deceive buyers, but to ensure that if a load is not over pressure and safe in their barrels, it won't be over pressure and dangerous in a common factory barrel and chamber with far looser tolerances.

I'd use 3150 or so for my calculations and just see how things work when you shoot at the range. The difference of 50-100 fps is going to make less difference than you think until you start shooting at extreme ranges, well over 500 yards.

 

[Caseless]

The only way to know is to run it over the chrono. The original "rating" could be way off, in your gun, as well as any reduction due to shortened barrel.

+1.
Like the OP, I estimated my 18-in barrel rifle would shoot the ammo at 2670 fps, since factory pulished data for Hornady 75gr BTHP is 2790 fps. I sighted in the rifle at 100yds using a BDC scope. Then tried shooting 500 yd and 600 yd steel targets using the BDC lines, no hits.
Asked a buddy to chronograph this ammo...2550 fps.[emoji46]