.223 FPS question...

[SMLEshooter]

Just loaded some 62 grain projectiles over 24 grains of Varget.

Fired out of a 16" barrel and found my FPS to be around 2,300 FPS.

Hodgdens reloading site indicates that I should be closer to 2,900 FPS with that load (out of a 24" barrel).

http://www.hodgdonreloading.com/

I double checked my C.O.L. and it's pretty much right on at 2.26"...

I didn't think a 16" vs 24" barrel difference would have that much of an impact on velocity.

Any ideas on what's going on?

 

[RamRoddoc]

About 20 FPS per inch give or take 2,460 FPS +/-

This is better info: http://rifleshooter.com/2014/04/223...gth-a-man-his-chop-box-and-his-friends-rifle/


Other information;

Stolen from bobhaverford the highroad.

http://www.chuckhawks.com/rifle_barrel.htm

The 2001 Edition of the Shooter's Bible states, in the introduction to the Centerfire Rifle Ballistics section, "Barrel length affects velocity, and at various rates depending on the load. As a rule, figure 50 fps per inch of barrel, plus or minus, if your barrel is longer or shorter than 22 inches." But they do not say what category of load to which this 50 fps average pertains.

Jack O'Connor wrote in The Rifle Book that, "The barrel shorter than standard has a velocity loss which averages about 25 foot-seconds for every inch cut off the barrel. Likewise, there is a velocity gain with a longer barrel." He went on to illustrate this using a .30-06 rifle shooting 180 grain bullets as an example, so his estimate was obviously for rifles in that general performance class.

Other authorities have tried to take into account the different velocity ranges within which modern cartridges operate. The Remington Catalog 2003 includes a "Centerfire Rifle Velocity Vs. Barrel Length" table that shows the following velocity changes for barrels shorter or longer than the test barrel length:

MV 2000-2500 fps, the approximate change in MV per 1" change in barrel length is 10 fps.
MV 2500-3000 fps, the approximate change in MV per 1" change in barrel length is 20 fps.
MV 3000-3500 fps, the approximate change in MV per 1" change in barrel length is 30 fps.
MV 3500-4000 fps, the approximate change in MV per 1" change in barrel length is 40 fps.

The 45th Edition of the Lyman Reloading Handbook also has a table showing Center Fire Rifle Velocity Vs. Barrel Length. Their figures apply to barrels between 20 and 26 inches in length and agree with the Remington figures. The Lyman table shows the following approximate velocity changes:

For rifles with muzzle velocities in the 1000-2000 fps range, the change in velocity for each 1" change in barrel length is 5 fps.
For rifles with muzzle velocities in the 2001-2500 fps range, the change in velocity for each 1" change in barrel length is 10 fps.
For rifles with muzzle velocities in the 2501-3000 fps range, the change in velocity for each 1" change in barrel length is 20 fps.
For rifles with muzzle velocities in the 3001-3500 fps range, the change in velocity for each 1" change in barrel length is 30 fps.
For rifles with muzzle velocities in the 3501-4000 fps range, the change in velocity for each 1" change in barrel length is 40 fps.

The 43rd edition of the Lyman reloading Handbook gave some concrete examples of velocity loss for specific calibers and loads. The Lyman technicians chronographed some high velocity cartridges in rifles with barrels ranging in length from 26" down to 22" with the following results:

The average loss for the .243 Win./100 grain bullet was 29 fps per inch.
The average loss for the .264 Win. Mag./140 grain bullet was 32 fps per inch.
The average loss for the .300 H&H Mag./220 grain bullet was 25 fps per inch.

For standard high intensity cartridges in the same test, the Lyman technicians chronographed the cartridges in barrel lengths ranging in length from 24" down to 20" with the following results:

The average loss for the .270 Win./130 grain bullet was 37 fps per inch.
The average loss for the .270 Win./150 grain bullet was 32 fps per inch.
The average loss for the .300 Sav./180 grain bullet was 17 fps per inch.
The average loss for the .30-06/180 grain bullet was 15 fps per inch.
The average loss for the .35 Rem./200 grain bullet was 11 fps per inch.

After a bunch of disclaimers, the Lyman people concluded, "The rule of thumb is that high speed, high pressure cartridges shed more speed in short barrels than do the low speed, large bore types." It's funny, but that is what I had suspected all along!

 

[1006]

check your chrony against another by setting one behind the other---

 

[SMLEshooter]

okay, I've verified the chronograph is accurately measuring the speed.

Looking through the links in Mr. Roddoc's posts, it does appear that my reloads are slower than they should be for a 16" barrel.


Has anybody experienced speeds slower than the books indicate certain powders and C.O.L.'s should produce?

 

[RamRoddoc]

Sure, lots of variables to deal with the true diameter of the bullet/rifle bore, the lot# of powder, the brass used, the air/ammo temperature, etc.

As mentioned your chronograph may be off too.

Try some other 16" rifles and see if any change is noted. If they are slower too, might try a different brand of bullet if that yields nothing consider that lot# of powder a little weaker than expected.

I'd feel ok increasing the charge a tad and check for excessive pressure to increase it if really an issue but I will use a slower charge if it seems to be more accurate. The reloading data is a guide and there will come a time that a rifle's maximum charge may be more or less than the amount listed.

 

[1006]

Your numbers do not sound that far off to me--I shoot a 55 grain bullet with 26.2 Varget out of a RRA 16 inche barrel. I have not chronoed it, but based on my experience with the gun and other chronoed loads used, I expect to get 2700FPS.

 

[1006]

I got this data using the pistol info From Hodgdon's web site the barrel is only an inch shorter.

BULLET WEIGHT 63 GR. SIE SP, 15 inch barrel, 1 in12 twist

VARGET

C.O.L.2.200"
Starting Load
Grains24.5
Velocity (ft/s)2,566
Pressure42,400 CUP

Maximum Load
Grains26.4
Velocity (ft/s)2,809
Pressure50,700 CUP

 

[kuduman]

You say you've ruled this out, but I've seen conditions where chronos read consistently low. Particular lighting and/or being too close to the muzzle. Had a situation the same as yours. Was clocking around 2400, but should have been more like 2900.

Went out another day, set the chrono up a few feet further from the muzzle-- 2900 fps. Good thing I didn't boost the charges up in the interim.

I can't wait for the Labradar unit to hit the market... That eliminates all this crap with lighting, muzzle blast, and so on.

 

[1006]

I would also check the scale.

 

[SMLEshooter]

During the same shooting session, the chronograph measured factory 62 grain ammo at 2,950.

Good idea checking the scale. An obvious thing that I hadn't even thought of that, though it seems to yield cartridges with expected FPS on others like .303, 300 blackout, etc...