Lost 100 fps after 550 rounds

[Mc Fraser]

Any temperature change between load testing and the most recent shooting session?

Yes. I live in Canada; the rifle was shot from -13 to 95F and anything in between. I keep the ammo in my chest pocket to avoid big temperature swings. I recorded the MV in different temperatures from -10 to about 90F; the MV variance was so small that I didn't include it in my ballistic calculator. Honestly, I cant remember what it was, but I remember I was pleasantly surprised by the temp stability.

Did you use an abrasive to clean your barrel?

Yes. ISSO bore paste. I only started using it last year, and so far, I have cleaned the barrel 3 times with it and used it sparingly with less than 10 strokes each clean.

I would say temp to start . The other thing is can you get the original chronograph. I would not be surprised if the is a difference between the two also

I won't be able to get the original chrono. I will test the temperature now that winter is coming in Canada.

Are you using powder from same lot?

I've seen lot to lot variations greater than that.

No. I will try another lot.

Your throat has eroded enough to drop velocity, it's normal.
To get the velocity back, you need to add powder, not chase the lands.
My barrels for F-class do this throughout a season about 3-4 times and at the 6 month mark may get a setback and re-chamber depending on the amount of haze cracking.

Cheers.

Interesting, I sure hope it is the throat and not the bore paste. I will do another ladder test.

You're using bore paste every time you clean the bore? JB bore paste or??
I'd suspect that may have helped accelerate the throat erosion.

Not every time, just at the end of the hunting season and if I shoot 50+ at the range. I use ISSO bore paste. I only started using it last year, and so far, I have cleaned the barrel 3 times with it and used it sparingly with less than 10 strokes each clean.
Sounds like the Smith should be able to determine if the throat is eroded.

 

[VinceMule]

Second thought…they do say n570 is a throat eater like no other. Perhaps you've created some "freebore" at this point that's dropping velocity with equal charge weights.

Magnum pointed this out also.

Adding a tad bit more powder to get the velocity you once had is normal as the throat wears in dia. and length. At some point, a seating depth change may be required when you start losing accuracy. I must say that I am shocked that your accuracy has not changed.

 

[Mc Fraser]

I'll get back with more details once I play with powder weight.

 

[L.Sherm]

Vincemule and Magnum are correct.
People seem to be shocked when 570, 26 and +P have there barrel throats ate out, speed and heat equal short barrel life its simple as that.

 

[Pudgy]

Hello,
I have a carbon barrel that lost about 100 fps after less than 600 rounds. I looked at my order history, I have 400 bullets ordered, 100 that a buddy bought for me and 80 factory loads. I would appreciate some thoughts on the matter.
I went to the gun range two weeks ago and noticed that I'm low at 550 yds. I went back over the weekend with my labradar, and MV went from 2975 to 2877 I shot 50 rounds after a good cleaning.

History:

• 300 PRC, 78.9gr N570 not even close to max pressure, Hammer Hunter, defiance action, premium carbon wrapped barrel.
• I got the rifle 2 years ago from the smith, didn't have time to do load development, bought 4 boxes of Hornady factory ammo, broke in the barrel, 15 shots cleaned after 3rd, and then cleaned after every 10th. I did that for 3 boxes, and kept one for hunting. I did not have a Chrono. Shot a cow elk at 800 yds and a deer at 400.
• After the hunting season ended, we started load development and did a ladder test with H1000, Retumbo, and N570 - 50 bullets were used to find a velocity node. Found 2975fps to be consistent with N570 and 214HH.
• Moved to depth seating with N570, and another 100 bullets went down the barrel.
• Everything up to 550 ish was used for practice.
• I should mention that my ES is 3 and SD 1.4 on a 5-shot average.
• Equipment used: Redding type S dies, Forester press, AutoTrickler with FX120, the list goes on, but I pretty much have premium tools.
• Cleaning: Carbon rod, bore paste, usual cleaning supplies like first choice (pretty much what competition shooters use). The cleaning performance is checked with a borescope. I never used brass brushes, only nylon.
• Observations:
  • My first thought was the FX120i. I have yet to verify the load against another scale, but I reload for 2 other rifles, and their velocity has not changed.
  • I have not changed my reloading process, but I have not excluded me factor.
  • The Labradar I used over the weekend that yielded 2877 fps, was different from the one I used for load development.
  • The rifle still shoots well, 1/4 MOA at 100 and consistent 2 inch groups at 550 yds. I have access to another range that goes 900 yds, last time when I was there I shot 3 in groups. I have access again next week.
  • I am planning to take the rifle to my Smith, I checked the barrel and it looks fine but he has decades of experience.

Thank you in advance for your thoughts.

I lost close to 200 FPS in a 6 creedmoor / proof carbon after cleaning. And about 10-15 strokes bore paste.
Nothing I tried brought velocity back. After 100 round's trying everything I could think of I sent barrel to proof.
They tested it and said nothing was wrong with it.
When I got it back from proof, my velocity was back.

 

[Allen Kitts]

I have definitely seen differences like that with different lots of powder. Every time i use up a lot its back to the range for another 200 yard sight in and load testing at different ranges with the chrono. Just part of the game.

I have heard lots of guys complaining lately about the hotter powders eating the barrels up quick, there is a price to be paid for speed.

 

[L.Sherm]

I've shot alot of different powders and I've never seen a different lot have 100fps difference not even half that

 

[Barehandlineman11]

I just had h50bmg 75anniversary shoot 90fps same charge. I dropped it a 2 full grains and still shooting 15fps faster then other batch.
This was in two guns both nearly identical

 

[Jeff Heeg osoh]

Just a few

Throat erosion from rounds fired, add a little powder to match speed.

Chrono reads different then original.

Not a fan of bore paste, in time can change overall diameter of the complete bore but if using leadcore bullets versus solids the leadcore will still expand and seal any gasses from blowing by.

Your powder may be slower now if it has increased in humidity inside the jug causing the burn rate to drop some thus causing slower speeds as well.

Or a slight combination of all above

Try adding a few 10ths of a grain and get your speed back where it was to check accuracy and pressure.

Osoh
JH

 

[skipglo]

The shooter next to you "Stole" some of your ammo.

And replaced it with his slower ammo

 

[Dean2]

You have changed at least 4 variables, powder lot, Chronograph and Temp, as well as 600 rounds of use on a barrel that has an expected life around 1000. I would be surprised if there WASN'T a change in velocity.

 

[Country5175]

Hello,
I have a carbon barrel that lost about 100 fps after less than 600 rounds. I looked at my order history, I have 400 bullets ordered, 100 that a buddy bought for me and 80 factory loads. I would appreciate some thoughts on the matter.
I went to the gun range two weeks ago and noticed that I'm low at 550 yds. I went back over the weekend with my labradar, and MV went from 2975 to 2877 I shot 50 rounds after a good cleaning.

History:

• 300 PRC, 78.9gr N570 not even close to max pressure, Hammer Hunter, defiance action, premium carbon wrapped barrel.
• I got the rifle 2 years ago from the smith, didn't have time to do load development, bought 4 boxes of Hornady factory ammo, broke in the barrel, 15 shots cleaned after 3rd, and then cleaned after every 10th. I did that for 3 boxes, and kept one for hunting. I did not have a Chrono. Shot a cow elk at 800 yds and a deer at 400.
• After the hunting season ended, we started load development and did a ladder test with H1000, Retumbo, and N570 - 50 bullets were used to find a velocity node. Found 2975fps to be consistent with N570 and 214HH.
• Moved to depth seating with N570, and another 100 bullets went down the barrel.
• Everything up to 550 ish was used for practice.
• I should mention that my ES is 3 and SD 1.4 on a 5-shot average.
• Equipment used: Redding type S dies, Forester press, AutoTrickler with FX120, the list goes on, but I pretty much have premium tools.
• Cleaning: Carbon rod, bore paste, usual cleaning supplies like first choice (pretty much what competition shooters use). The cleaning performance is checked with a borescope. I never used brass brushes, only nylon.
• Observations:
  • My first thought was the FX120i. I have yet to verify the load against another scale, but I reload for 2 other rifles, and their velocity has not changed.
  • I have not changed my reloading process, but I have not excluded me factor.
  • The Labradar I used over the weekend that yielded 2877 fps, was different from the one I used for load development.
  • The rifle still shoots well, 1/4 MOA at 100 and consistent 2 inch groups at 550 yds. I have access to another range that goes 900 yds, last time when I was there I shot 3 in groups. I have access again next week.
  • I am planning to take the rifle to my Smith, I checked the barrel and it looks fine but he has decades of experience.

Thank you in advance for your thoughts.

Have you measured the distance to the lands of your rifling now with the same bullets you are using? As the rifling in the lands erodes, the bullet has more "jump" before it contacts the lands which decreases the pressure of your loads and therefore decreases the velocity of your load. If you measure the lands and seat the bullets further out where it's back to however far off the lands you were to begin with, it should bring your pressure and velocity back to where you were originally.

 

[esshup]

If I had to guess I'd say the difference in fps is due to the difference in powder lots. I always try to buy powder in the biggest quantity that I can of the same lot number. It seems every time I change lot numbers I need to re-visit the load to change something to get velocity or accuracy back to what it was with the first lot. I just bought H-4895, I couldn't find it in bigger than 1# containers, but all 4 containers that I got were the same lot number.

If throat erosion was the culprit, wouldn't the OP see a gradual change over time, not a huge difference from one shooting session to another? Throat erosion is also a function of how hot you get the barrel during your shooting sessions. Since I am not a target shooter where I have to get all my shots in during a certain time limit if the barrel is too hot to rest my hand on it as close to the chamber as possible, I stop shooting until the barrel cools back down.

When I bought the 7mm Allen Magnum, I bought enough powder and primers of the same lot number to last for at least 1,500 shots.

 

[VinceMule]

OP, 600 rounds of 570 and expect your bore to look like a sewer pipe, flyers are the first sign that the barrel is approaching the end. If you are running a hot rod and love running a hot rod, then just ante up the pot by having several barrels chambered at the same time.

I learned a hard lesson on 570, 560, and 550...$2000 later, I figured it out!

Having multiple barrels chambered with the same reamer, and same barrel maker, the first is a sacrificial lamb on load development, the second is for hunting and verifying zero from year to year with long barrel life.

I have never seen the downside in ordering 3 barrel blanks at a time in the caliber I like to shoot along with the reamer design I prefer.