Help!! Large Drop in FPS Using Same Load

[lgwatson]

Savage Model 12 FCV w/ factory barrel. !796 rounds thru the barrel. March 2014 developed load with 24.8 gr H4895, boron nitride coated 55 gr Sierra Blitzking, .005 jump, and have since had to chase lands a small amount. Have not fired max loads in this barrel.

12-3-18, loaded 100 rounds of this load and on 3-15-19 at 55 degrees it averaged 3231 FPS with an ES of 28. On 9-23-19, 7 rounds from the same batch averaged 2571 FPS with an ES of 66. I fired 26 rounds prior to the chrono test.

The components and ammo were stored in a climate controlled shop, The powder was purchased in January 2018. I have used Winchester primers since I developed this load.

I am baffled, and would appreciate any input regarding this

 

[sawcarver]

What cartridge? .223? Maybe chrono is not consistant? Is it the same chrono? Did you see the velocity drop on paper? 700fps drop I would think you would see a pretty masive zero change

 

[lgwatson]

What cartridge? .223? Maybe chrono is not consistant? Is it the same chrono? Did you see the velocity drop on paper? 700fps drop I would think you would see a pretty masive zero change

.223 Remington. They were 1 inch low at 100 from the last sight in. Same magnetospeed chrono. The chrono seems consistent. Have not noticed chrono problems with other rifles.

Savage Model 12 FCV w/ factory barrel. !796 rounds thru the barrel. March 2014 developed load with 24.8 gr H4895, boron nitride coated 55 gr Sierra Blitzking, .005 jump, and have since had to chase lands a small amount. Have not fired max loads in this barrel.

12-3-18, loaded 100 rounds of this load and on 3-15-19 at 55 degrees it averaged 3231 FPS with an ES of 28. On 9-23-19, 7 rounds from the same batch averaged 2571 FPS with an ES of 66. I fired 26 rounds prior to the chrono test.

The components and ammo were stored in a climate controlled shop, The powder was purchased in January 2018. I have used Winchester primers since I developed this load.

I am baffled, and would appreciate any input regarding this

Forgot to mention: .223 Remington.

 

[Shinbone]

With a 660fps change in velocity, it is not the components aging or a change in air temperature.

My first guess is that something is wrong with your chrono.

 

[natdscott]

What's the accuracy doing?

Barrels do die. When they die, it can be catastrophic, and drops in speed of hundreds of fps at a time can occur in as little as 20 rounds.

1,800 rounds is not a HUGE amount to be killing a .223 barrel, but the semi-premium buttoned tubes (eg: Wilson, Green Mountain, etc.) DO die in the 2-2,500 round range often enough to cause worry for a factory tube at 1,800.

 

[Uncle Ed]

I have a magnetospeed so I'm going to ask you is there any chance you used the wrong rubber spacer for a different barrel diameter.

This would change the air gap, the velocity reading and POI. Don't ask me how I know this, but if you wear bifocals you can blame your glasses.

 

[lgwatson]

I have a magnetospeed so I'm going to ask you is there any chance you used the wrong rubber spacer for a different barrel diameter.

This would change the air gap, the velocity reading and POI. Don't ask me how I know this, but if you wear bifocals you can blame your glasses.

No changes to the chrono set up, although in my case operator error is always a possibility.

 

[lgwatson]

What's the accuracy doing?

Barrels do die. When they die, it can be catastrophic, and drops in speed of hundreds of fps at a time can occur in as little as 20 rounds.

1,800 rounds is not a HUGE amount to be killing a .223 barrel, but the semi-premium buttoned tubes (eg: Wilson, Green Mountain, etc.) DO die in the 2-2,500 round range often enough to cause worry for a factory tube at 1,800.

This seems plausible. I will scope the barrel.

 

[BartsBullets]

Pull one of your bullets and check and make sure powder is the correct weight.

Bart

 

[memilanuk]

Try fresh batteries in the chrono

 

[lgwatson]

Pull one of your bullets and check and make sure powder is the correct weight.

Bart

Powder was weighed on my beam scale. Before seating bullets, I visually inspect each charged case to make sure the powder levels are the same. In March of this year I chronoed 10 rounds from this same batch of 100 at 3231 FPS.

 

[lgwatson]

Savage Model 12 FCV w/ factory barrel. !796 rounds thru the barrel. March 2014 developed load with 24.8 gr H4895, boron nitride coated 55 gr Sierra Blitzking, .005 jump, and have since had to chase lands a small amount. Have not fired max loads in this barrel.

12-3-18, loaded 100 rounds of this load and on 3-15-19 at 55 degrees it averaged 3231 FPS with an ES of 28. On 9-23-19, 7 rounds from the same batch averaged 2571 FPS with an ES of 66. I fired 26 rounds prior to the chrono test.

The components and ammo were stored in a climate controlled shop, The powder was purchased in January 2018. I have used Winchester primers since I developed this load.

I am baffled, and would appreciate any input regarding this

1796 rounds fired thru barrel.

 

[Ned Ludd]

In my hands, .223 Rem loads with 80.5s or 90 VLDs over H4895 maintain expected velocity for *at least* 3-4 months after loading. After 6 months to 1 year, some velocity decrease is not uncommon, but we're only talking about a small decrease from ~2850 fps to perhaps 2815-2820 fps. The ES/SD values also seem to get a bit worse after 6+ months.

The simplest answer might be to load up a few founds of the *exact same load* fresh, and measure velocity of the old and new side-by-side. If your problem is due to something like powder degradation over time, bullets cold welding to the necks, or anything other time-dependent variable you might be able to imagine, the freshly loaded rounds will give the expected velocity, the old ones will not. In that event, I'd probably just pull any of the remaining "old" rounds and start over.

 

[rwj]

It’s been a while since I’ve used a MagnetoSpeed, but I recall there being a sensitivity parameter for bullet detection in setup mode...

 

[lgwatson]

Savage Model 12 FCV w/ factory barrel. !796 rounds thru the barrel. March 2014 developed load with 24.8 gr H4895, boron nitride coated 55 gr Sierra Blitzking, .005 jump, and have since had to chase lands a small amount. Have not fired max loads in this barrel.

12-3-18, loaded 100 rounds of this load and on 3-15-19 at 55 degrees it averaged 3231 FPS with an ES of 28. On 9-23-19, 7 rounds from the same batch averaged 2571 FPS with an ES of 66. I fired 26 rounds prior to the chrono test.

The components and ammo were stored in a climate controlled shop, The powder was purchased in January 2018. I have used Winchester primers since I developed this load.

I am baffled, and would appreciate any input regarding this

Thanks to everyone for your input! Problem solved. I thoroughly cleaned the barrel and used Boretech copper remover. Didn't notice a large amount of copper. Scoped the bore and didn't observe abnormal wear. Loaded 6 rounds of the same load. Installed new batteries in Magnetospeed chrono.

Today, I fired 5 rounds of the original batch of ammo and the new identical load. Avg. FPS was 3230. Verified my chono with a friend's Labradar (3222 FPS). Bottom line, I'm not sure if I forgot to clean barrel before or the Chrono's batteries were low. Also groups were tight after about ten rounds.

 

[Big_Daddy]

Something definitely wrong. I would suspect the chrono.
I prairie dog hunt during the first week of June every year.
When I get home, I process and do all of my reloading for the next year plus some.
I shoot a few rounds throughout the year and notice zero difference in FPS over the 10 to 11 month time span.

 

[Big_Daddy]

Glad to hear you got it solved...
Took me too long to type my first response....LOL

 

[lgwatson]

Glad to hear you got it solved...
Took me too long to type my first response....LOL

It was fun solving the problem. Got to shoot some.

 

[Steve Ladino]

It was fun solving the problem. Got to shoot some.

I see that you have had this gun since 2014 and have a fair number of rounds thru it. To prevent future dilemmas I would disassemble the bolt, clean and relube it lightly if you haven't done so in a while.

 

[lgwatson]

I see that you have had this gun since 2014 and have a fair number of rounds thru it. To prevent future dilemmas I would disassemble the bolt, clean and relube it lightly if you haven't done so in a while.

I clean the bolt assembly every 400 or so rounds.