Velocity Loss with Round Count

[chkunz]

Has anyone measured the loss in velocity from a new barrel to a well-worn barrel?

 

[Dave M.]

From new barrel to broke in 60-80 rounds, you will see at least 50-80 fps increase. Then it’s a long time until your velocity drops off depending on the cartridge you are shooting. The drop off could be only 50fps or I’ve heard as high as 200fps. It should be fairly obvious your barrel is on the way down when you see your X count really drop off, scores drop and group sizes open up.

 

[alf]

I did a couple years ago.

I had a retired 28" Krieger Heavy Varmint 6 Dasher barrel off my Bat gun for the test.
This barrel was gradually losing accuracy to the point I felt wasn't competitive any more, so I pulled it after the last match. The barrel now had 2629 rounds down it. I read where guys will run a barrel till the velocity drops off before replacing, and since I had never chronoed a barrel in it's later life before, so now was the perfect opportunity, as I still had a few loaded rounds left over from the last match.

I setup the bench, the chronograph, and ran the target out to the 600 yard line. Conditions were light, a slight breeze, but I didn't bother with wind flags. I shot two, 5 shot groups, writing down the speeds after each shot. Loads were with Varget and moly plated 105 Bergers. I had run the same load, regardless of temps or conditions, it's whole life, at 3075 fps. I was surprised that the velocities today were exactly the same as when it was new. The two groups average a half MOA, nice, but not competitive.

I have shot nothing but moly plated bullets for years, and typically never see a velocity increase as it gets broke in, and at least in this case, had not lost any velocity at the end.

 

[chkunz]

alf, thanks, this is exactly the type of test data I am looking for. Your result is not what I was expecting but that is why we do testing. I wonder if the moly coating gives a different result. I would expect less velocity loss with moly but your result is amazing. Hopefully someone else will give us another data point with uncoated bullets.

 

[Dusty Stevens]

I have never seen one drop off when accuracy drops off. Admittedly i dont think ive ever ran a competition barrel to much more past half of what alf did above though

 

[284winner]

I have never had a barrel lose speed when it's accuracy drops off from round count. I've never chronoed one at that point but my drop numbers never changed in terms of turret adjustment before I replaced any of my barrels. Interesting that they would lose velocity to that extent.

 

[chkunz]

I have never seen one drop off when accuracy drops off. Admittedly i dont think ive ever ran a competition barrel to much more past half of what alf did above though

It is common for us XTC shooters to run over 3000 rounds thru a barrel and some even much more than that. We shoot at a much bigger target than F Class and some of the other disciplines so our "accuracy " requirements allow us to do that. I am wondering if there is an increase in wind drift and maybe shooters are not noticing it as long as the accuracy is holding up and they are still getting good scores in mild conditions.

 

[Tempest]

Shot an FTR barrel much longer than I should have (3,500 rounds).
Velocity and accuracy change was pretty noticeable after certain point.

Changed to new barrel in same specs and so far right back where it was before.

Your comment on wind conditions is interesting. 1st match this year with new barrel in some pretty negative wind conditions, it shot better than the previous barrel did the entire last year in good conditions.

 

[ebb]

Frank green mentions it when he talked about the new alloy they came up with for longer barrel life. He said that the test barrels they make for ammo companies are all scrapped when FPS falls off.

 

[chkunz]

Shot an FTR barrel much longer than I should have (3,500 rounds).
Velocity and accuracy change was pretty noticeable after certain point.

Changed to new barrel in same specs and so far right back where it was before.

Your comment on wind conditions is interesting. 1st match this year with new barrel in some pretty negative wind conditions, it shot better than the previous barrel did the entire last year in good conditions.

I think it may be something that shooters forget about, they work hard to get the best accuracy and favorable wind drift with a new barrel and then do not think about the increase in wind drift when velocity starts to decrease (if it does). That is why I am looking for some numbers on decrease in velocity vs round count. Do you have these numbers from your experience?

 

[chkunz]

Frank green mentions it when he talked about the new alloy they came up with for longer barrel life. He said that the test barrels they make for ammo companies are all scrapped when FPS falls off.

Did he provide any data on velocity loss vs round count?

 

[SKWERLZ]

I only have kept good notes on two barrels throughout life.
A 7 saum (brux) went 1500 and speed started dropping but accuracy was still good, I adjusted the load twice to maintain speed and at about 1900 it nosedived on speed and I had vertical develop pretty rapidly.
A 260 (Shilen) went 2700 then started quickly losing speed, I adjusted once but it had Hornandy 147 start blowing up so I started another barrel.
147’a continuing to blow up on new barrel.

 

[chkunz]

I only have kept good notes on two barrels throughout life.
A 7 saum (brux) went 1500 and speed started dropping but accuracy was still good, I adjusted the load twice to maintain speed and at about 1900 it nosedived on speed and I had vertical develop pretty rapidly.
A 260 (Shilen) went 2700 then started quickly losing speed, I adjusted once but it had Hornandy 147 start blowing up so I started another barrel.
147’a continuing to blow up on new barrel.

Can you give an approximate loss of velocity in fps vs round count?

 

[ebb]

He discussed it in the recent thread about barrel steels.

 

[Tempest]

I think it may be something that shooters forget about, they work hard to get the best accuracy and favorable wind drift with a new barrel and then do not think about the increase in wind drift when velocity starts to decrease (if it does). That is why I am looking for some numbers on decrease in velocity vs round count. Do you have these numbers from your experience?

Can only give you info I noticed from a match. I had two rifles there, rifle #1 at the time had 3,000+ rounds and the other maybe 400-500. Both same barrel, same load, bullet etc. Everything the same. I know some say velocity at the target is not accurate but it's all I have for data. Point is, was same day, same conditions for both rifles.

At 1,000 yards on average over entire match rifle #1 was approx 50 FPS slower at the target. I plugged both of them into JBM and for that load it suggested around 65 FPS difference at the muzzle. Sorry I didn't chrono again. Wish I had as from what I recall rifle #1 needed more elevation in the scope than what JBM is saying.

Point being, difference was clear and I'll never run a barrel that long again. I bought the myth that .308's will last many thousands of rounds before they go south. Probably true for most but not a pretty hot FTR load.

 

[chkunz]

Can only give you info I noticed from a match. I had two rifles there, rifle #1 at the time had 3,000+ rounds and the other maybe 400-500. Both same barrel, same load, bullet etc. Everything the same. I know some say velocity at the target is not accurate but it's all I have for data. Point is, was same day, same conditions for both rifles.

At 1,000 yards on average over entire match rifle #1 was approx 50 FPS slower at the target. I plugged both of them into JBM and for that load it suggested around 65 FPS difference at the muzzle. Sorry I didn't chrono again. Wish I had as from what I recall rifle #1 needed more elevation in the scope than what JBM is saying.

Point being, difference was clear and I'll never run a barrel that long again. I bought the myth that .308's will last many thousands of rounds before they go south. Probably true for most but not a pretty hot FTR load.

This is good information, thanks for sharing. Based on your experience with the 308 I would conclude that one could expect approximately 100 fps velocity loss for 3000 rounds on the barrel. If it is still accurate at that point one could decide if the increase in wind drift was worth changing the barrel., probably not for me.

 

[chkunz]

I just measured the velocity of my 223 AR at 4600 rounds with two identical loads that I had measured at 2600 rounds in this same gun. There was no velocity loss between these two data points.

The barrel is from White Oak Armament and is 26 inches in length and 1:8 twist. I use this for XTC and the two loads that I measured the velocity for were my short range load for 200/300 yards with the 75 HDY BTHP bullet and my mid range load for 600 yards with the 80 SMK.

So now I have real data that says I do not have to worry about velocity loss over the life of a barrel for this application.

I am ready to replace the barrel and I am wondering what velocity difference I can expect from a similar make and model new barrel with the same load. Anyone want to guess?

 

[dannyjbiggs]

In 1990, I purchased a pair of Obermeyer SS, .308 barrels for XTR competition from the maker. Ironically each of them became instant one hoss shays on-the-target at the 5,000-round mark. Didn't have a chronograph then, just measured my velocity by the Sierra loading table.

 

[dannyjbiggs]

Anyone want to guess?

Huh-uh. I've never been able to get close on my new barrels, that's where load development comes in!

 

[PRECISIONWELDING01]

Danny I would bet you have worn out a pickup truck bed full of barrels. And still going