Shooting through a chronograph

klh8 · September 11, 2002, 06:42 AM

Was at the range yesterday and my buddy took his chronograph.My load with the 125gr sierra out of the .308 is 3000fps according to the reloading manual.
The chronograph was clocking the load from 2860 to 2904 fps.
Is this difference typical according to shooting and weather conditions?Chronogarph was set up around 3.5 to4 feet from muzzle of my rifle.
Thinking,maybe his chrono was not accurate.
Just curious.
Thanks fellas
Paul

NG Bruce · September 11, 2002, 06:58 AM

That is absolutely normal. I just chronographed some 45 Colt loads that the manual listed as 1398 fps avg - I got 1276 fps avg. The temperature, distance from the muzzle (I use 8' for revolvers and 10' for rifles), barrel length of your gun; all of these make a big difference. Some reloading manuals use a pressure barrel and 26" barrels - they measure different than barrels on field guns. Powder lots, primer lots and bullet lots can make a significant difference. Check out an old Hercules data manual (I have one from 1984 and one from 1990) they list the exact same data in several of my cartridges in the 2002 manual - obviously the data has not been re-shot to take into account the changes in the powder. I use the Hornady 165 grain BTSP in .308 in my .300 Win Mag. One lot of the bullets gave me 100 fps more velocity than the ones used before or after - seems the ogive was different and was touching the leads - spiking the pressure. The chronograph helped me pick up on the change. You have to work with a chronograph a while to learn to use the data, but I wouldn't dream of load development anymore without one. NG Bruce

Clint Tickler · September 11, 2002, 09:36 AM

I second Bruce's comments. I have a .308 in a Rem VLS and a 788-.308. Shooting a 125 gr Ballistic Tip with 48.5 grains of RL-15 out of the 26" VLS gives me an average of 2980 fps where the same load out of the 22" 788 clocks at 2812. I'm 10' from the chrony.

braindead0 · September 11, 2002, 10:24 AM

Luckily, so far I haven't shot through my Chrony...always above..

Poodleshooter · September 11, 2002, 10:27 AM

Velocities printed in manuals often have very little to do with actual results in your rifle. Ignore them, other than for reference, and keep using the chronograph.

**Mal H** · September 11, 2002, 02:50 PM

As they said above, your measured velocities sound normal. Don't take the figures from a manual as anything but a guideline. The manufacturers often use universal receivers and longer than normal barrels hence they will get higher velocities. But even with the same length barrels or even the exact same test gun as you are using, a fairly large difference in vel is not at all uncommon.

However, the main thing I wanted to point out is what the others have implied, you are shooting too close to the chrono. Four feet is way too close because you can get an occasional false reading from the gases starting and/or stopping the clock too soon. Ten to 15 feet is a good minimum distance for rifles. Depending on the caliber, 10 feet is also a good compromise for handguns.

klh8 · September 11, 2002, 09:05 PM

Thanks for the replies.

To what Mal H said,the muzzle blast on occasion would disconnect the rods from the front plastic hood(?)Do not know much about the chronograghs.Need to get one.
Regards
Paul

September 11, 2002, 06:42 AM	#1
klh8 Senior Member Join Date: January 24, 2002 Location: WV Posts: 120	Shooting through a chronograph Was at the range yesterday and my buddy took his chronograph.My load with the 125gr sierra out of the .308 is 3000fps according to the reloading manual. The chronograph was clocking the load from 2860 to 2904 fps. Is this difference typical according to shooting and weather conditions?Chronogarph was set up around 3.5 to4 feet from muzzle of my rifle. Thinking,maybe his chrono was not accurate. Just curious. Thanks fellas Paul

September 11, 2002, 10:24 AM	#4
braindead0 Senior Member Join Date: February 28, 2002 Location: Canton, Oh Posts: 896	Luckily, so far I haven't shot through my Chrony...always above.. __________________ DoD# 2223 Meum scapha volitare plenum anguillae

September 11, 2002, 06:58 AM	#2
NG Bruce Member Join Date: February 2, 2001 Location: Beaufort County NC Posts: 51	That is absolutely normal. I just chronographed some 45 Colt loads that the manual listed as 1398 fps avg - I got 1276 fps avg. The temperature, distance from the muzzle (I use 8' for revolvers and 10' for rifles), barrel length of your gun; all of these make a big difference. Some reloading manuals use a pressure barrel and 26" barrels - they measure different than barrels on field guns. Powder lots, primer lots and bullet lots can make a significant difference. Check out an old Hercules data manual (I have one from 1984 and one from 1990) they list the exact same data in several of my cartridges in the 2002 manual - obviously the data has not been re-shot to take into account the changes in the powder. I use the Hornady 165 grain BTSP in .308 in my .300 Win Mag. One lot of the bullets gave me 100 fps more velocity than the ones used before or after - seems the ogive was different and was touching the leads - spiking the pressure. The chronograph helped me pick up on the change. You have to work with a chronograph a while to learn to use the data, but I wouldn't dream of load development anymore without one. NG Bruce

September 11, 2002, 09:36 AM	#3
Clint Tickler Senior Member Join Date: August 12, 1999 Location: Seattle Area Posts: 184	I second Bruce's comments. I have a .308 in a Rem VLS and a 788-.308. Shooting a 125 gr Ballistic Tip with 48.5 grains of RL-15 out of the 26" VLS gives me an average of 2980 fps where the same load out of the 22" 788 clocks at 2812. I'm 10' from the chrony.

September 11, 2002, 10:27 AM	#5
Poodleshooter Senior Member Join Date: August 7, 2000 Location: Floating down the James River in VA Posts: 2,599	Velocities printed in manuals often have very little to do with actual results in your rifle. Ignore them, other than for reference, and keep using the chronograph.

September 11, 2002, 02:50 PM	#6
Mal H Staff Join Date: March 20, 1999 Location: Somewhere in the woods of Northern Virginia Posts: 16,950	As they said above, your measured velocities sound normal. Don't take the figures from a manual as anything but a guideline. The manufacturers often use universal receivers and longer than normal barrels hence they will get higher velocities. But even with the same length barrels or even the exact same test gun as you are using, a fairly large difference in vel is not at all uncommon. However, the main thing I wanted to point out is what the others have implied, you are shooting too close to the chrono. Four feet is way too close because you can get an occasional false reading from the gases starting and/or stopping the clock too soon. Ten to 15 feet is a good minimum distance for rifles. Depending on the caliber, 10 feet is also a good compromise for handguns.

September 11, 2002, 09:05 PM	#7
klh8 Senior Member Join Date: January 24, 2002 Location: WV Posts: 120	Thanks for the replies. To what Mal H said,the muzzle blast on occasion would disconnect the rods from the front plastic hood(?)Do not know much about the chronograghs.Need to get one. Regards Paul