Rifle Action Truing

[historicalarms]

Darn good point!

I'd only add that full length concentricity and clearance also affects accuracy. Even though the brake doesn't touch the bullet, pressure differences affect the projectile and many claim it can introduce wobble and deteriorating accuracy.

I have never fired a gun with a "can" on it but see them used all the time now for even long range shots & every time i watch one I cant help but think as you do...that must effect accuracy big time.

 

[thestelster]

Darn good point!

I'd only add that full length concentricity and clearance also affects accuracy. Even though the brake doesn't touch the bullet, pressure differences affect the projectile and many claim it can introduce wobble and deteriorating accuracy.

I honestly don't know about pressure differences. If we talk about a muzzle brake with equally spaced holes positioned 360° around the brake, would the gases not follow the path of least resistance and therefore impart minimal influence on the bullet?

 

[historicalarms]

Chicken, I concur with both Susk & Theselster on lath cut accuracy for the treads & bore concentricity of the muzzle brake.

Years ago when muzzle brakes were just an item on heave artillery and in their infancy for hand held sporting rifles, I and a buddy did an extensive testing regime on a home built muzzle brake for one of his custom rifles ( 32-378 Wby, a kicking, recoiling mule to say the least). This rifle was a two-shots-a-day proposition for me without a brake.
We had access to his dad's lathe so many different designs were tried at very little cost other than our time...and purple-black armpit bruising on the failures.
We tried 2-4-6 rows of holes, holes of different dia and holes of different angles to the bore direction...it was decided that 6 holes of a smaller dia at a very pronounced angle to the bore resulted in the most felt recoil reduction. We sprinkled fine dry sand on the shooting table and watched how the muzzle blast effected the dust...we could clean the table at the point of our shooting elbow with the design we thought worked the best...but man-o -man rearward directed the blast sure required excellent ear & eye protection.
After the design was finalized we started fine tuning the reduction felt by changing bore dia. As Theselster states a tight bore to bullet dia is needed. We settled on .0025" clearance was when we felt the least recoil....that rifle, un checked probably produces 90-95 ft lb felt recoil with the load he uses but after all our testing that thing is as tame as a .243.
Muzzle brakes can be a colossal waist of money & effort if not done properly.

 

[Susquatch]

I honestly don't know about pressure differences. If we talk about a muzzle brake with equally spaced holes positioned 360° around the brake, would the gases not follow the path of least resistance and therefore impart minimal influence on the bullet?

Since I have never actually used one myself (and never will) I can only relate the expertise of others whose shadows I am not worthy to walk in.

The way I've heard it is that the pressure disappation itself isn't as important as the vibrations (pressure waves) that the ports introduce and that those waves are imbalanced by extremely small variations in clearance.

I kinda look at it this way. Lots of shooters claim that the Crown doesn't matter. I'm here to say BS. Yet if we look at the Crown as a way to vent gases evenly and perfectly so as to avoid kicking the base of the projectile, it's a no brainer to me that something that reflects gas pressure waves back at the projectile has to be important too.

 

[Susquatch]

This rifle was a two-shots-a-day proposition for me without a brake.
We had access to his dad's lathe so many different designs were tried at very little cost other than our time...and purple-black armpit

And this is why I do not own anything that big and don't need brakes.

 

[historicalarms]

I honestly don't know about pressure differences. If we talk about a muzzle brake with equally spaced holes positioned 360° around the brake, would the gases not follow the path of least resistance and therefore impart minimal influence on the bullet?

Our testing soon showed you dont want holes full 360....the bottom holes will "jump" the bore before the slug has cleared the muzzle brake. It might sound very relevant to have an equal blast force for full circumference but the fact is that upwards movement of the rifle is the only direction it can move with no friction impediment when the shot is broke sideways & downward movement are all "friction slowed" by hand or bench contact.
We notice more "target fliers" with holes under the bore than without so surmised (without any mechanical effort or devise to prove) that the muzzle could jump quick enough to sometimes affect the slug travel

 

[Susquatch]

We notice more "target fliers" with holes under the bore than without so surmised (without any mechanical effort or devise to prove) that the muzzle could jump quick enough to sometimes affect the slug travel

I surmise that it isn't so much the muzzle jump itself as much as the resulting pressure variations that caused this result.

But we could debate all that till @6.5 Fan s cows come home.

I think the bottom line here is that close attention to the detail that only a good lathe in good hands can provide is required to have any reasonable hope of success.

 

[historicalarms]

Your right but i just looked outside & no cows yet...so..

Not convinced pressure variance is at play here as equal distance hole spacing for 360 deg should have essentially an equal pressure at the exact same time for wherever the slug is in its travel through the brake. The bore was out beyond the table edge so back pressure between table & bore is non existent ( along with the surmising that the slug would have long excited the bore before the blast force returned from the table to bounce the barrel) .
With no sophisticated testing equipment to be had we had to more or less theoretically remove each possible scenario until we were left with the one remaining possibility that we could not overrule, that being that the bore could not be directed downwards at all by the upwards direction of muzzle blast out of the top holes & sideways movement was slowed by front stock friction between it and the bench rest long enough for the slug to exit the bore. These and one other realization that happened convinced us...When we only had holes through the top and sides of the brake we had no more fliers.

 

[Susquatch]

Your right but i just looked outside & no cows yet...so..

Not convinced pressure variance is at play here as equal distance hole spacing for 360 deg should have essentially an equal pressure at the exact same time for wherever the slug is in its travel through the brake. The bore was out beyond the table edge so back pressure between table & bore is non existent ( along with the surmising that the slug would have long excited the bore before the blast force returned from the table to bounce the barrel) .
With no sophisticated testing equipment to be had we had to more or less theoretically remove each possible scenario until we were left with the one remaining possibility that we could not overrule, that being that the bore could not be directed downwards at all by the upwards direction of muzzle blast out of the top holes & sideways movement was slowed by front stock friction between it and the bench rest long enough for the slug to exit the bore. These and one other realization that happened convinced us...When we only had holes through the top and sides of the brake we had no more fliers.

Again, I'm just providing my thoughts on this for whatever they are worth to you. If that is zero, I take no offense. Sometimes we must accept the results we get whether or not we fully understand why.

In trying to visualize my thinking on this, try not to think about combustion gases venting out of selected holes or symmetric holes. In fact, try not to think about gases venting at all. Instead try to think about this gas as though it were standing still but vibrating with entrained sound pressure waves. More or less the same concept as an AM radio signal carried by a radio frequency signal. In reality, the gases are moving and venting, but they also carry pressure waves within the gas that bounce around in there much much faster than the gases themselves. And because the gas is so highly compressed and dense, these waves travel through the combustion gases much much faster than the speed of sound and much much much faster than the speed of the gas itself.

If you are familiar with the OBT (Optimum Barrel Time) theory of how accuracy nodes arise, you will understand that barrel vibrations caused by charge detonation travel up and down the barrel faster than the projectile does and that these vibrations (not the same as barrel whip) affect the projectile's internal ballistics. Mind you, despite its very widespread adoption, I don't buy the OBT theory in total. I think there is a lot more to it than that. But nonetheless, the principles are similar enough to be worthy of the comparison.

I am only "suggesting" that these density waves (not the gas movement itself) that are inside the gases themselves reflecting off of various surfaces could cause various things to happen and that they could be both bad and good depending on their precise timing, direction, and consistency.

All things being equal, I am a very firm believer in consistency - everything and anything that could have an effect should be controlled as consistently as possible for the best results. Hence my position that the axis of the brake ID should be concentric to the axis of the bore.

I totally understand and accept your findings about the brakes affect on the target results. This is quite similar to the difference between constrained and unconstrained recoil. The difference matters and your results show that.

Anyway, it's just my thinking on the matter. You didn't seem to understand what I meant about the difference between gas pressure and pressure waves within the gas so I thought it might be worth an explanation.

 

[Former Member]

I'm going to chime in here the OBT has some merit, but more so with the harmonics of the barrel and vibrations introduced by the bullets motion (ands its related mechanisms). If they are in phase they they amplify the problems of they are 180 degrees out of phase they cancel each other out.

These is some what controlled by length, shape diameter and so on.

Compensators on the other hand act in two fashions, the air passing through ahead of the bullet this starts recoil reduction and venting of gas behind the bullet. If you look at well designed ones they actual have a little large "land" as the bullet finally exits to create mitigate the potential of off set thrust vectors as @Susquatch suggests. Yes they do impart some potential variations but again as with well design barrels, well designed compensators do the same. However for the best performance they must be integrated in the barrel design system.

 

[Susquatch]

I'm going to chime in here the OBT has some merit, but more so with the harmonics of the barrel and vibrations introduced by the bullets motion (ands its related mechanisms). If they are in phase they they amplify the problems of they are 180 degrees out of phase they cancel each other out.

These is some what controlled by length, shape diameter and so on.

Compensators on the other hand act in two fashions, the air passing through ahead of the bullet this starts recoil reduction and venting of gas behind the bullet. If you look at well designed ones they actual have a little large "land" as the bullet finally exits to create mitigate the potential of off set thrust vectors as @Susquatch suggests. Yes they do impart some potential variations but again as with well design barrels, well designed compensators do the same. However for the best performance they must be integrated in the barrel design system.

I just used OBT as an analogy to introduce the concept of vibrating pressure waves within the expanding gases. I didn't mean to imply that's what is directly going on here.

In my mind it's too simplistic to think of the expanding gases as a single process with a relatively long time interval. I think it's important to remember that the gas column also contains very fast pressure waves that move much faster through the gases than the expanding gas column moves itself. I mentioned OBT only because these gas pressure waves are similar to the barrel ringing that travels back and forth the length of the barrel faster than the projectile does.

Whether that really matters or not? I don't know. But I'd bet that it does.

 

[Former Member]

@Susquatch we are on the same page.

It does matter, with or without compensator. These are call Standing Wave Ratios, the trick is to have them cancel each other out at the right time.

Think positive and negative nodes traveling in opposite directions, if the meet at the exit point when both are either same extreme, bad....when the meet when both at at the opposite side then excellent (with hands rubbing together ).

These and the barrel (and compensator) harmonics (among other things) are what determine your ultimate performance.

Creating a load that performs best does exactly that by playing with those items (yes I know you are better than it than I)

 

[Chicken lights]

@thestelster was explaining some of the bullet dynamics and I think I just figured out a parallel, a football!! Think about it, how and where you grip it dictates the spiral, and depending on how long or short you’re throwing it, changes the angle of the throw. He was explaining the boolit spiral doesn’t slow down (much) yet the velocity does, and thats the same with a football, if you watch a long pass

 

[Susquatch]

@Susquatch we are on the same page.

It does matter, with or without compensator. These are call Standing Wave Ratios, the trick is to have them cancel each other out at the right time.

Think positive and negative nodes traveling in opposite directions, if the meet at the exit point when both are either same extreme, bad....when the meet when both at at the opposite side then excellent (with hands rubbing together ).

These and the barrel (and compensator) harmonics (among other things) are what determine your ultimate performance.

Creating a load that performs best does exactly that by playing with those items (yes I know you are better than it than I)

OK. I think so too.

I'm not so sure that a standing wave is an accurate description of what happens inside a brake with a plethora of excitation sources but that's a whole nuther conversation not worth having on the forum. Maybe beside a campfire someday. For the primary discussion I agree we are on the same page.

@thestelster was explaining some of the bullet dynamics and I think I just figured out a parallel, a football!! Think about it, how and where you grip it dictates the spiral, and depending on how long or short you’re throwing it, changes the angle of the throw. He was explaining the boolit spiral doesn’t slow down (much) yet the velocity does, and thats the same with a football, if you watch a long pass

Yes, its a very good parallel. And for many of the same reasons. It is a good place to start and I like it. You can build on that.

 

[Chicken lights]

OK. I think so too.

I'm not so sure that a standing wave is an accurate description of what happens inside a brake with a plethora of excitation sources but that's a whole nuther conversation not worth having on the forum. Maybe beside a campfire someday. For the primary discussion I agree we are on the same page.


Yes, its a very good parallel. And for many of the same reasons. It is a good place to start and I like it. You can build on that.

Boolit weight- it’s easier to keep a larger mass moving straight once you get it moving, but harder to get moving?

I realize that’s not a yes/no question

Easier to stabilize a heavier projectile? Heavier projectile harder to deflect?

I’m guessing it’s all a trade off on what you’re trying to achieve

 

[Susquatch]

Boolit weight- it’s easier to keep a larger mass moving straight once you get it moving, but harder to get moving?

yes, - and YES it is a yes no question LOL!

Easier to stabilize a heavier projectile?

Depends on what you mean by easier. In general weight is not as important as length weight ratio - what is generally called sectional density. But even that isn't the total answer. There are calculators out there that can be used to estimate stability and some manufacturers publish ratings and recommended twists.

Heavier projectile harder to deflect?

Generally Yes

I’m guessing it’s all a trade off on what you’re trying to achieve

Yes yes YES! There is no such thing as perfect in this game. Just better and worse for your goals.

 

[Former Member]

In term of these shock waves (vibrations), think of active noise cancellation used in some cars (or other applications), same base theory just method of application is different.

(Remember the tune wt started by Browning on the barrel end which lets you dial in your barrel to you load vs making the load fit your barrel).

Believe it or not in a barrel doing this is significantly easier than in other forms as you have a controlled space to start with.


As to stability, this gets into some weird stuff. It has to do with perceived rotational mass vs presented surface area vs drag vs a lot of other things. The math gets beyond my realm very quickly. The actual concepts are relatively simple however hit the right combination is the trick.

 

[Chicken lights]

yes, - and YES it is a yes no question LOL!



Depends on what you mean by easier. In general weight is not as important as length weight ratio - what is generally called sectional density. But even that isn't the total answer. There are calculators out there that can be used to estimate stability and some manufacturers publish ratings and recommended twists.



Generally Yes


Yes yes YES! There is no such thing as perfect in this game. Just better and worse for your goals.

I very briefly looked at Hornady’s boolit chart last night, holy crap there’s some math for you!

That’s too much for this driver right now, I’ll follow along and ask the odd question but I’ve other things needing attention before winter prep

 

[Former Member]

I very briefly looked at Hornady’s boolit chart last night, holy crap there’s some math for you!

That’s too much for this driver right now, I’ll follow along and ask the odd question but I’ve other things needing attention before winter prep

Yeap, so do what some of the old shooters do, change only one thing till you've exhausted the change for performance and forget the math.

 

[Susquatch]

I very briefly looked at Hornady’s boolit chart last night, holy crap there’s some math for you!

That’s too much for this driver right now, I’ll follow along and ask the odd question but I’ve other things needing attention before winter prep

As they say - different strokes for different folks. I love the math. But this is one sport with lots of room for every stroke there is. Just relax and enjoy the trip!

When you are ready, I know lots of ways to describe the complicated math in simpler terms that work for everyone!

Of course that will invite lots of the inevitable debate.... LOL!