Actual VELOCITY FPS (guesstimation) w/out chrono

[Will]

Most loading manuals I have read or checked out on line list a velocity using a 24" (INCH) barrel. WHAT if you have a 30" barrel ? is there any definitive research done on how much 6 inches helps ? I'm particular interested in 170 - 185 gr projectiles. This is something that has been bugging me for sometime. I know, use a chrono but ... mine is dead / refuses to work so I need to SWAG it !!
Thanks

 

[MrMajestic]

Your barrel length is an input to Quick Load and it's known for its ability to closely estimate velocity.

 

[Catfish]

The burn rate and volume of powder will make a big difference in the optimum barrel length. With small volumes of fast burning powders you will get more velocity from short barrels.

 

[SS427]

Zero at 100 yards, then shoot at 200 and/or 300 and measure the drop. Using the drop calculators at the end of many reloading manuals you can get an idea of what the velocity would be. If I recall you only need bullet weight and ballistic coefficient.

 

[spclark]

Assuming you're asking about 308 (from the statement in your siggy about Lapua bullets) the 6+" extra barrel could be worth ~ 100 - 150 fps.

I've seen posts stating ~ 20 fps per inch in 308 but as yet never had an opportunity to gain info first-hand so take the above with a grain of, well, powder I suppose ;-/

 

[jbpmidas]

Hard to say. I shoot .308 through a 10 twist Brux and get 2665 with 185 Hybrids from my chosen load. A friend of mine has the same barrel chambered and installed by the same smith. His shoots about 65fps slower with the same loads. The difference? His barrel is 30" and mine is 28"! We don't understand his being slower, but according to the chrono, they are.

 

[danang]

Catfish..well sometimes. Chet Brown, of Brown Precision, years ago did some testing with the .270 Winchester to determine the optimum powder for his short barreled (18-20") Mountain Rifles. He found that traditional powders for that cartridge, i.e., the 4350 and 4831 at the time, proved to give the best velocity even when the barrels were shortened. Get down to pistol length, and lead bullets, with fast powders, that is quite true. Years ago, I had a .300 Weatherby that was 26 inches and way too long for my hunting area. Cut it to 22 inches. Lost 300 + fps. Had a hot .308 Win. With lots of muzzle blast. I guess each barrel is a piece to itself. I have seen quotes of from 20 fps to 50 fps lost per inch. All backed up with experiments. I think you have to try it yourself and cut till you feel good. JMHO

 

[K22]

If your goal is long range shooting at small targets then I wouldn't be too concerned with trying to determine precise velocity and drop from tables. True it will give you some idea and may even be very close but its no substitute for testing the performance of the load over the range you expect to shoot.

I've learn this lesson the hard way from personal experience - missing groundhogs by dialing in elevation data from drop tables. After testing at the actual ranges I was very surprised to see that I was off from the drop table data anywhere from an inch to several inches depending on the range. Also, changes in temperature which affect air density which will affect drop values.

 

[Nomad47]

I think velocity gain/loss is very dependent on powder burn rate.

 

[spclark]

Palma shooters know every inch counts, as much for velocity as for sight radius (being a discipline using iron sights only). With the prescribed (in international rules; here the NRA rules allow any weight bullet) <156 grain bullet, 30" is the "standard" barrel length, some use even longer to ensure velocities at minimum 2,950 fps.

I had a new Palma rifle built this past year. Selected barrel blank realized 29" finished barrel. Ammo giving 3,100 fps in my first rifle (different everything but cartridge!) gives but 2,925 in the new. Obviously I have some work to do once the weather warms up around where I shoot... and I don't at all believe the missing inch is entirely the problem, or that I can't get velocity needed with a tweak to my load.