Range Report Harmonic Resonance test.

[jason bourne]

On 12-31-11, I was testing the effects on group size and POA/POI while changing a barrels harmonics by testing my rifle with the barrel threads exposed (developed load in this state) , adding the thread protector , then using the muzzle brake. I saw some interesting things and hope you guys enjoy.

44.3gr RL 15 - 175smk - Win Brass - WLR Primers - 2.310 ogive
700 SPS TACT AAC-SD - 20"

barrel was DIRTY through out testing, rifle had 120 shots total without cleaning when starting this test.

Velocities:

Threads exposed: LOAD DEVELOPED IN THIS STATE.

<span style="text-decoration: underline">group 1</span> <span style="text-decoration: underline">group 5</span>
1. 2525 1. 2460
2. 2478 2. 2455
3. 2473 3. 2455
4. 2450 4. 2473
5. error 5. 2469
Avg: 2481 Avg: 2462
SD: 31.45 SD: 8.23
ES: 75 ES: 18

Thread Protector on: POA/POI had minimal change, group size got much bigger.

<span style="text-decoration: underline">group 2</span> <span style="text-decoration: underline">group 4</span>
1. 2487 1. 2482
2. 2450 2. 2473
3. 2473 3. 2469
4. 2460 4. 2569
5. 2455 5. 2450
Avg: 2465 Avg: 2468
SD: 14.98 SD: 11.67
ES: 37 ES: 32


Muzzle Brake on: POA was on diamond two (top right), POI was a 3 MOA DROP (POI above diamond 3, bottom right)

<span style="text-decoration: underline">group 3</span>

1. 2487
2. 2482
3. 2492
4. 2506
5. 2492
Avg: 2491
SD: 8.95
ES: 24

In group 5 if i would not have pulled that one shot, the 4 shot group size is 0.111 MAX SPREAD CTC, 0.036 ATC


As always, use caution when working up a load and NEVER base your load off data designed for a particular rifle.
Each and every rifle is different, regardless of model.

 

[Graham]

Re: Harmonic Resonance test.

I take it that the rifle was not in a machine rest.
What were your conclusions (what did you find interesting)?
Are the accuracy variations statistically significant?

 

[rideHPD]

Re: Harmonic Resonance test.

You sure on the data for group 1? If I tried to pass that SD off in the lab I work at next to that for group 5 I'd get smacked. Given I work for a graduate student that would be understandable if I wanted to stay. Groups definitely look a lot healthier without the protector.

 

[jason bourne]

Re: Harmonic Resonance test.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">I take it that the rifle was not in a machine rest.
What were your conclusions (what did you find interesting)?
Are the accuracy variations statistically significant? </div></div>

It was not shot off a machine rest, my rifle has never been on a machine rest so for standard accuracy sake I completed the test in its normal shooting position.

The two main things I found interesting was that by simply adding a threaded cap to the end of threaded barrel, it changes the vibration enough to effect the group size. Secondly, I was amazed that a muzzle brake added to the rifle would be enough to lower the POI by 3 moa at 100. When talking to a few other shooters who use different brakes, a 2-3 moa drop seemed to be the norm.

 

[jason bourne]

Re: Harmonic Resonance test.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rideHPD</div><div class="ubbcode-body">You sure on the data for group 1? If I tried to pass that SD off in the lab I work at next to that for group 5 I'd get smacked. Given I work for a graduate student that would be understandable if I wanted to stay. Groups definitely look a lot healthier without the protector. </div></div>

Im not a scientist, and I dont play one on tv. lol. With that said, those are the numbers my chronograph gave me.

the first group was cold bore and it is possible there was some lube left in the barrel which would contribute to the deviation of velocity.

 

[MALLARD]

Re: Harmonic Resonance test.

I like your test. I did some testing with my tuner, adjusting it and shooting groups, some of my groups had allot of vertical to them like your group 4 , and some of the settings produced allot of horizontal spread , like your group 3. Can't post any pics, i shot up the target.

Adding or removing mass to the muzzle is going to change the harmonics of a barrel. Not the OBT part of it, but the varmintal beam bending theory.

 

[jason bourne]

Re: Harmonic Resonance test.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MALLARD</div><div class="ubbcode-body">I like your test. I did some testing with my tuner, adjusting it and shooting groups, some of my groups had allot of vertical to them like your group 4 , and some of the settings produced allot of horizontal spread , like your group 3. Can't post any pics, i shot up the target.

Adding or removing mass to the muzzle is going to change the harmonics of a barrel. Not the OBT part of it, but the varmintal beam bending theory. </div></div>

Mallard, thanks for your info. It's good to know my test results have been consistent with testing others have done.

 

[Grand]

Re: Harmonic Resonance test.

Jason: What the thread protector machined to fit or an over-the-counter model?

 

[jason bourne]

Re: Harmonic Resonance test.

Grand, the thread protector is the factory one that comes with the AAC-SD.

 

[bgweed]

Re: Harmonic Resonance test.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jason bourne</div><div class="ubbcode-body">Grand, the thread protector is the factory one that comes with the AAC-SD. </div></div>

What about the brake?

 

[jason bourne]

Re: Harmonic Resonance test.

Brake is a custom made by my local smith to match my barrel.

 

[sandwarrior]

Re: Harmonic Resonance test.

Jason Bourne,

I applaud the test you've done for your rifle. If you feel it is valid, then so it is. That is so long as you are sure of your shooting.

What I'm not understanding is a range of velocities that each in their own way affect harmonics, yet you seem to want to show here that those velocities translate into how the barrel is affected by having/not having a muzzle brake, or thread cap.

I mean, the first thing I don't see is specs for how each implement is installed. That would make a difference would it not? What is the thread tolerance? Standard class 2?, 3? IF? Dry/wet torque? What is the barrel torque? Wet/dry? Stock torque? Weight of said implements? Type of barrel?

What I'm trying to say here is how do you account for the non-intangibles? Your test could be very telling if we knew those.

 

[jason bourne]

Re: Harmonic Resonance test.

Sand warrior, I appreciate you taking time and putting thought into my post.
The original spark of intrigue came from my first f-tr practice/match. I shot the 1st round with a brake and then second round I was asked to remove the brake. When I did, POI at 600yards raised up 2moa and left 1 moa. I originally did not understand why this was happening so I sought out to find out (to the best of my abilities).

As far as specs are concerned, I can tell you that the barrel is a factory Remington AAC SD, 1:10rot and it's a 20". With regard to thread, thread torque and the rest, I have to say I have no idea. I have only been in the precision rifle world for around a year so I've been learning as I go. I have ran the above test several times to the same end result. There are usually unkown variables in any experiment, with that said minimizing them yields better results. If you can tell me how to measure/gauge the thread tolerance , torque and etc. I would gladly get to the range and re test and post up the results.

Thanks again for your feedback!
JB.


Edit: I have done some research on your post, and I found a post on here were there was a lengthy discussion on the effects or in some cases lack there of that barrel torque has on accuracy.
From reading the entire post, I can see how having proper threading being an important factor. As my rifle's threading is standard from Remington. I would assume it to be a good base for testing .

I still would like to do further research and testing, so any guidance is appreciated.

 

[sandwarrior]

Re: Harmonic Resonance test.

J.B,

First, I'm assuming those are 100 yd. shots? Congratulations, as I think they are outstanding groups. BTW, I should have said that in my first post.

Second, I had to do a little looking into AAC and HOW they manufacture their barrels. I see now (with a clearer head this morning) that all accessories are AAC, so the threading matches. And it should all be to a given tolerance. Provided you torque on each item correctly.

The question then comes up as to why the thread protector loosens up groups. The next question after that is why does the Compensator throw groups up and right.

To the thread protector, I usually find two things opening up groups. Loose items on the barrel, and harmonic dampeners moved out of position. The thread protector, to me wouldn't seem to be a big harmonic thing. Unless of course it was just a smidge loose. Are you hand tightening it or do you have a strap-wrench? You might try wet torquing it. Wet torquing is nothing more than lubricating the threads. The first thing that went through my mind was that would also help make it slip loose easier. Yes, it can, if not torqued to full value. If this is not a high torque item then I would refrain from doing that. See what getting a strap wrench will do to help you torque it on better. Same with the brake.

Which brings me to the next thing about how the barrel is made. Remington (Win. and Ruger as well) hammer forge their barrels. Basically, the barrel is drilled oversized. They then put a mandrel in that and run it through a machine that beats the barrel down onto the mandrel. This creates a lot of stress in the barrel. And, makes them sensitive (accuracy-wise) to accessories and heat changes. Basically adding thread protectors and brakes or cans and shooting a lot. I don't know how the AAC barrels are made. But, there are three basic methods in use today here in the U.S. Hammer forged (fast to make, high stresses), Button (fast enough but much less stress) and Cut-rifled (Slow, but very low stress). If AAC is the former your harmonics are just going to have to be accounted for.

The thing to do now is shoot more good groups like you have and see if your results tend to go the same way or vary more overall. Don't forget to factor all tangibles into your research. It really helps when diagnosing issues. No one can correct a barrel for a bad shot caused by a puff of wind no one will ever see again

-hope that helps a little more

p.s. -my apologies if it seemed like I went on the attack with my first post. I'd really like to see if this is what I described or another phenomena not yet uncovered.

 

[bgweed]

Re: Harmonic Resonance test.

Hate to keep beating this question to death, but can you post a pic of the brake? Just wondering how gas port design might play into the POI shift... Maybe a couple more people (myself included) could do similar tests with different brake designs and see? I bet a Miculek style (http://media.midwayusa.com/productimages/large/910/910504.jpg) with only horizontal ports would be different than 'quiet brake', YHM, etc...

 

[jason bourne]

Re: Harmonic Resonance test.

Sand warrior, once again I want to thank Your feedback. Just so you know, I didn't think your post was attacking at all. Like I sad, I'm still learning (as we are) and want to be as informed as possible.

Bgweed, I have a buddy on another forum using a badger FTE and he reports a 2moa drop. Here's a pic. I'd be interested in seeing yor results also. Keep in mind, when I developed this load used, it was with the threads exposed.

 

[sandwarrior]

Re: Harmonic Resonance test.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jason bourne</div><div class="ubbcode-body">Sand warrior, once again I want to thank Your feedback. Just so you know, I didn't think your post was attacking at all. Like I sad, I'm still learning (as we are) and want to be as informed as possible.

Bgweed, I have a buddy on another forum using a badger FTE and he reports a 2moa drop. Here's a pic. I'd be interested in seeing yor results also. Keep in mind, when I developed this load used, it was with the threads exposed.

</div></div>

That looks like a Vais brake. Typically, one can see how a brake will change the harmonics of the barrel from it's original poi. It shouldn't spread the group though.

Is this the 7.62x51? or the .300 Blackout?

 

[jason bourne]

Re: Harmonic Resonance test.

Sand, it's a custom brake made by my smith for my rifle.