Thread: Shorter barrel = less velocity?

Have a browning xbolt in .308 with 18" barrel amd have over barrel suppressor on. Wondering if anyone knows what the fps would be roughly? Shooting factory 150gr Fusion ammo

Less than it would be from a 22" barrel

Maybe 25 fps per inch less. And the velocity quoted on ammo boxes is often very optimistic.

Originally Posted by GWH

Less than it would be from a 22" barrel

Maybe 25 fps per inch less. And the velocity quoted on ammo boxes is often very optimistic.

Yeah i read something similar about x amount fps less per inch. Has anyone done a chronograph on a .308 w/ 18" barrel?

I'd say it'd be about 2750 at a guess, maybe closer to 2700.

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Sweet thanks, wanting to put some info into a ballistic calculator

Originally Posted by XBoltstalker

Sweet thanks, wanting to put some info into a ballistic calculator

your pushing shit up hill with a twig to be honest mate
factory ammo speeds on the box can be quite a way off even with the full lenth barrel yours is 18inches which will be less but by how much is a geuss same as the 1st geuss of that the ammo would do in your barrel
if you punch a random geuss which at the end of the day is what it is into a ballistic calculator it will almost certainly be wrong and you'll end up just confusing your self
the only way is to crony your rifle with that load... even if you foud someone with exactly the same set up as you the speeds would be different

if you have the room you could zero your rifle at desired distance
go back 50m fire a shot go back another 50 fire again go back 50 fire again all the way back to the longest you want to shoot and make a note how far low of the 1st shot each shot at each distance
its the only way of working out your ballistics without all the gear

you may say its only to give me an idea but its better to have no idea than the wrong idea

Originally Posted by rambo-6mmrem

your pushing shit up hill with a twig to be honest mate
factory ammo speeds on the box can be quite a way off even with the full lenth barrel yours is 18inches which will be less but by how much is a geuss same as the 1st geuss of that the ammo would do in your barrel
if you punch a random geuss which at the end of the day is what it is into a ballistic calculator it will almost certainly be wrong and you'll end up just confusing your self
the only way is to crony your rifle with that load... even if you foud someone with exactly the same set up as you the speeds would be different

if you have the room you could zero your rifle at desired distance
go back 50m fire a shot go back another 50 fire again go back 50 fire again all the way back to the longest you want to shoot and make a note how far low of the 1st shot each shot at each distance
its the only way of working out your ballistics without all the gear

you may say its only to give me an idea but its better to have no idea than the wrong idea

Yeah ive zeroed my rifle at 100m and have gone out in 50m steps to 500m. Would just like to get an idea of how much fps it was putting out

Originally Posted by XBoltstalker

Yeah ive zeroed my rifle at 100m and have gone out in 50m steps to 500m. Would just like to get an idea of how much fps it was putting out

If you have done that and hopefully recorded your drops it's pretty straight forward to calculate the muzzle velocity, all you need to know is the bc of the bullets, or a close approximate from a similar bullet (as you may not know what brand of bullet is in the factory ammo).

Originally Posted by rambo-6mmrem

your pushing shit up hill with a twig to be honest mate
factory ammo speeds on the box can be quite a way off even with the full lenth barrel yours is 18inches which will be less but by how much is a geuss same as the 1st geuss of that the ammo would do in your barrel
if you punch a random geuss which at the end of the day is what it is into a ballistic calculator it will almost certainly be wrong and you'll end up just confusing your self
the only way is to crony your rifle with that load... even if you foud someone with exactly the same set up as you the speeds would be different

if you have the room you could zero your rifle at desired distance
go back 50m fire a shot go back another 50 fire again go back 50 fire again all the way back to the longest you want to shoot and make a note how far low of the 1st shot each shot at each distance
its the only way of working out your ballistics without all the gear

you may say its only to give me an idea but its better to have no idea than the wrong idea

That's the absolute verification! All the other methods are merely confirmed by real world data. Especially if your hitting smack on at all ranges in zero wind.

This is like the proverbial "how many jellybeans in the Jar" thing.
<2751 haha

Nah man I was just checking the MV on a mates howa .308 (1:10 twist rate same as yours) and it had 2950ft/s on the packet of ammo (Winchester super-x) and low and behold that's what it chronied. He doesn't have a suppressor and you do.
I'd say you'll be running 2770ft/s if they were running a 22" barrel for testing. You'd then take off 100 penalty for chopping off perfectly good barrel but then put it back on due to your suppressor (which can add upto the same)

Mine's 18" and was losing 150-170fps from what it said on the back from factory loads, 150 winchesters were getting 2650. wouldn't expect more than 2700 from the fusions.

Originally Posted by kiwigreen

Mine's 18" and was losing 150-170fps from what it said on the back from factory loads, 150 winchesters were getting 2650. wouldn't expect more than 2700 from the fusions.

What he said, i be amazed if it was getting more than 2700fps. Expect it somewhere in the 2600-2700 range. Normally tested in 24 inch barrels, will struggle to be dead on what the box states minus 25-38fps per inch chopped depending on the rifle .(150-230fps lost)

Don't count on the figure on the back of the box.
These are shot from test barrels and normally longer then hunting rifles

The only one way to know is to chronograph your rifle with the load you plan on using, no 2 rifles will give the same result even if they came off the production line consecutively,
If not able chronograph shoot at know ranges out to as far as you can and plot the trajectory that will give you the velocity and known sight settings

Zero at 100? Shoot a group at say 200 and measure the drop and then work out a pretty close velocity