Muzzle velocity loss after installing a barrel tuner

[fgregorio]

Hi all,
With no change to conditions, gear or location, I noticed that I lost a full 40 fps on my MV.
This is what I did:
2 ladder tests.
Caliber .308
True flite barrel 12T 4L 30 inch with a very long throat (100 thou extra) with 9800 rds
HBC palma projectiles 155.5 gr coated with hbn
Var get powder
15 thou jump
Both ladder tests going from 46.1 gr to 48 gr at 0.1 gr increments
Batched cases inside 0.1 gr.
5 ounce barrel tuner, weight forward of muzzle. Screwed out to put the primary barrel node at the muzzle.

1st test - no tuner- accuracy node 0.6 grain long at 2982 fps span 47.1gr to 47.7 gr
Es 90 fps . Ladder test elev spread at 300 metres 1.8 moa

2nd test - tuner installed - accuracy node 0.5 grain long at 2943 fps span 47.3 gr to 47.8 gr
Es 60 fps . Ladder test elev spread at 300 metres 1.2 moa.
Observations - tuner installed
Noticeable less recoil (?!)
Less extreme spread and overall elevation spread observed during the ladder test.

Any thoughts on why the accuracy node requires more powder and has less muzzle velocity?

Is it mass related?

FYI, although the barrel has 9800 RDS through it, it still shoots sub 0.3 moa on its own from a bipod/ sand bag. In my humble opinion, I put it down to hbn and honing the first 8 inches of the barrel from the chamber with valve grinding paste. ( that's why the long throat).

 

[JohnKielly]

Chronograph error?

 

[Erik Cortina]

Hi all,
With no change to conditions, gear or location, I noticed that I lost a full 40 fps on my MV.
This is what I did:
2 ladder tests.
Caliber .308
True flite barrel 12T 4L 30 inch with a very long throat (100 thou extra) with 9800 rds
HBC palma projectiles 155.5 gr coated with hbn
Var get powder
15 thou jump
Both ladder tests going from 46.1 gr to 48 gr at 0.1 gr increments
Batched cases inside 0.1 gr.
5 ounce barrel tuner, weight forward of muzzle. Screwed out to put the primary barrel node at the muzzle.

1st test - no tuner- accuracy node 0.6 grain long at 2982 fps span 47.1gr to 47.7 gr
Es 90 fps . Ladder test elev spread at 300 metres 1.8 moa

2nd test - tuner installed - accuracy node 0.5 grain long at 2943 fps span 47.3 gr to 47.8 gr
Es 60 fps . Ladder test elev spread at 300 metres 1.2 moa.
Observations - tuner installed
Noticeable less recoil (?!)
Less extreme spread and overall elevation spread observed during the ladder test.

Any thoughts on why the accuracy node requires more powder and has less muzzle velocity?

Is it mass related?

FYI, although the barrel has 9800 RDS through it, it still shoots sub 0.3 moa on its own from a bipod/ sand bag. In my humble opinion, I put it down to hbn and honing the first 8 inches of the barrel from the chamber with valve grinding paste. ( that's why the long throat).

I want to hear about the barrel honing with valve past. Reason behind it and who recommended it? Any data to support that it's a good idea?

 

[fgregorio]

Hi Erik,
This is what you are looking for:
http://forum.accurateshooter.com/index.php?topic=3859845.0
And
http://forum.accurateshooter.com/index.php?topic=3859845.msg36491504#msg36491504
Reply nr 36 and following.
It was recommended by a prone issf 300 metre shooter. Former world bronze medal. David Hollister.
You might find that in the first 8 inches or so, the surface of the metal heat corrodes and resembles crocodile skin. At that point the barrel constricts more than further down the bore, towards the muzzle. Once the projectile leaves the rough surface area, it is constricted to less diameter than the width of the bore. Thus gas overtakes the projectile in the last 20 inches of the barrel, sending the accuracy into the pit hole
That honing procedure removes that early constriction and makes the barrel progressively tighter towards the muzzle.
Definitely not a substitute for the accuracy of a new barrel.
But if you want a screamer to keep on screaming, that is how I would maintain it with a tamed version of that honing. 30 passes instead of a 100 passes after 3000 RDS.
I have electronic target records and chronograph readings + ladder tests.

 

[JRS]

Honing with valve grinding paste (removing steel) makes the bore progressively tighter towards the muzzle You can't be serious about that ???

Maybe Frank Green (Bartelin Barrels) will intervene here.

 

[Erik Cortina]

 

[fgregorio]

John, I used the same chronograph, 15 minutes apart.
In saying that, I guess that any chronograph would have at least a 0.5% error implied.
Mostly I use a chronograph as a qualitative tool and not a quantitative tool.
I find it hard to believe that it could read accurately a speed of 3000 fps down to 1 fps, but if it measures one shot at 2950 fps and another at 3000 fps, to me it means that the second shot is faster by a rate of approximately 50fps. May not be 50fps, could be 20 or 70fps. But still the first shot is slower than the second shot.

 

[fgregorio]

Honing with valve grinding paste (removing steel) makes the bore progressively tighter towards the muzzle You can't be serious about that ???

Maybe Frank Green (Bartelin Barrels) will intervene here.

Actually I am serious The fouling pattern changes on the muzzle doesn't lie Regardless of opinion, those are the facts.
I suggest that if you have an old barrel that you don't use anymore, try it.
Measure a ladder test, max oal and crown fouling pattern before the honing and after the honing procedure and please post the results on the appropriate thread:
http://forum.accurateshooter.com/index.php?topic=3859845.msg36491504#msg36491504
Still, this is no substitute to the accuracy of a new barrel. Akin to the Tubb bore maintenance system. Same principle.

 

[jrm850]

Honing with valve grinding paste (removing steel) makes the bore progressively tighter towards the muzzle You can't be serious about that ???

Maybe Frank Green (Bartelin Barrels) will intervene here.

I'm not saying I agree or disagree with the practice, but why wouldn't it make a barrel progressively tighter towards the muzzle? Just curious about your incredulous sounding reply.

 

[JRS]

Honing with valve grinding paste (removing steel) makes the bore progressively tighter towards the muzzle You can't be serious about that ???

Maybe Frank Green (Bartelin Barrels) will intervene here.

Actually I am serious The fouling pattern changes on the muzzle doesn't lie Regardless of opinion, those are the facts.
I suggest that if you have an old barrel that you don't use anymore, try it.
Measure a ladder test, max oal and crown fouling pattern before the honing and after the honing procedure and please post the results on the appropriate thread:
http://forum.accurateshooter.com/index.php?topic=3859845.msg36491504#msg36491504
Still, this is no substitute to the accuracy of a new barrel. Akin to the Tubb bore maintenance system. Same principle.

I have a pretty good idea what valve lapping paste does. I've ported and polished quite a few heads, along with valve jobs. I also know that valve grinding paste is going to turn those nice crisp sharp lands into rounded off wasted barrel money. No offense! Have you considered that by honing your barrel, and removing those sharp lands, the bullet no longer engraves the same way, thereby reducing velocity???

 

[JRS]

Honing with valve grinding paste (removing steel) makes the bore progressively tighter towards the muzzle You can't be serious about that ???

Maybe Frank Green (Bartelin Barrels) will intervene here.

I'm not saying I agree or disagree with the practice, but why wouldn't it make a barrel progressively tighter towards the muzzle? Just curious about your incredulous sounding reply.

You can't make the bore tighter by removing material.

 

[fgregorio]

JRS, you only apply that procedure to the first few inches of the bore. The other 24 inches towards the muzzle remain untouched. Those lands in the latter part of the are still sharp..er.

 

[fgregorio]

JRS, same way, if you remove material from the chamber end, the muzzle end will be comparatively narrower than the chamber end. Remember that you only apply that procedure to the first few inches of the barrel. You don't touch the last 3/4 or so of the barrel.

 

[timeout]

Hi all,
With no change to conditions, gear or location, I noticed that I lost a full 40 fps on my MV.
Observations - tuner installed
Noticeable less recoil (?!)
Less extreme spread and overall elevation spread observed during the ladder test.

Any thoughts on why the accuracy node requires more powder and has less muzzle velocity?

Is it mass related?

FYI, although the barrel has 9800 RDS through it, it still shoots sub 0.3 moa on its own from a bipod/ sand bag. In my humble opinion, I put it down to hbn and honing the first 8 inches of the barrel from the chamber with valve grinding paste. ( that's why the long throat).

It seems like the thread has done little to address the question asked, beyond suggesting possible chronograph error. I would imagine there are several gents on here that have used chronos and tuners. Since I have never used a tuner, I can't add anything useful to the topic. Now a whole new topic on using valve lapping compound in a barrel could surely be informative. I would certainly concede that a 308 with 9800 rounds down the tube and still shooting .3 MOA is worth exploring.

 

[jrm850]

It seems like the thread has done little to address the question asked...

Good point.


For the sake of discussion:
If one subscribes to the shock wave theory then it is believed that dimensional changes takes place according to which pressure phase is where. Adding length to your barrel in the form of a tuner will alter the shift frequency and, according to the theory, will contract or expand the bore which should alter velocities somewhat. It's unclear to me whether the threaded coupling of the tuner is solid enough to change the terminus or not, but it is something to think about.

http://www.the-long-family.com/OBT_paper.htm

 

[fgregorio]

I agree with you timeout.
Maybe we can continue on the appropriate thread:
http://forum.accurateshooter.com/index.php?topic=3859845.msg36491504#msg36491504
Two weekends ago that barrel shot 100.8x and 100.7x in the span of 20 consecutive shots at Hornsby, Australia from a distance of 660yards. I shot simultaneously with another F CLASS rifle shooter and his score was 100.9x when I shot the 100.7x. I shot with a single point sling and iron sights.
Please check the target plot on: http://shooting.hexsystems.com.au/shooting/20608
The odd shot numbers belong to the scope shooter and the even shot numbers are mine.
Where you see a "5" ring , in Australia that is our "10" ring (maximum score). The 10 ring is 2 moa, the V ring is 1 moa and the X ring is 0.5 moa.

 

[fgregorio]

Very good point jrm 850.
The tuner attaches to the muzzle via an interference fit. I.e. you need to heat the tuner with boiling water and then hammer it onto the muzzle. When it cools down, it constricts the muzzle.
http://www.shootingindustriesaustralia.com/Products.php
I'm checking out the link you posted.

 

[fgregorio]

In addiction to the link to the target plot, this link is the plot for the 100.8x:
http://shooting.hexsystems.com.au/shooting/20558

 

[jonbearman]

The tuners over here are threaded to the muzzle. not creating constriction from the interference fit. Yours is an interesting concept by the maker of it. If the muzzle is constricted you would think slightly higher pressure hence faster speed. I will watch for other posters trying to explain this better than me.

 

[Joe Salt]

Try things in reverse see it you get same results!

Joe Salt