Physics of shooting a rifle

[davidsog]

If a 10mph wind can cause a bullet to go off trajectory,

Frame of reference issue that is leading a fundamental misunderstanding of what is happening. You are a very intelligent guy, John. I sense your frustration with this too.

You have a good grasp of this but the separating your frame of reference and being able to think from one frame to the other causes the wheels to fall off the bus on occasion.

[tangolima]

Originally Posted by stagpanther

Damaged crowns are easy to spot because (at least in my experience) they accumulate copper being torn from the bullet. I can see that the gas pressure behind the bullet probably aggravates that action.

Ummmm, no.

If the damage is smoothly fairing away from the bore, instead of encroaching into the bore like a burr, it may not tear on the bullet.

My SKS shot pretty lousy after exhausting all the tricks in the bag. I examined the crown with magnifier and couldn't catch anything wrong. It was the rounded military profile. As a last resort before giving up, I recrowned it with 11 degree profile. It made day and night difference. Perhaps the original crown was cut uneven smoothly, so visual inspection turned up no clue.

-TL

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[stagpanther]

My SKS shot pretty lousy after exhausting all the tricks in the bag. I examined the crown with magnifier and couldn't catch anything wrong. It was the rounded military profile. As a last resort before giving up, I recrowned it with 11 degree profile. It made day and night difference.

You mean it shot 5" groups at 100 yds instead of 6"?

[tangolima]

Originally Posted by stagpanther

You mean it shot 5" groups at 100 yds instead of 6"?

More like 6"-8" before and better than 2" after. Believe me, I went out of my way to make it shoot, including glass bedding the action, a trigger job, and carefully handloading the rounds.

-TL

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[JohnKSa]

Good. I think we can agree then that rule is muzzle gases have no real influence on the flight of a bullet in a properly set up rifle.

Correct. That's why I said this: "This is, in fact, why the muzzle crown is so important. If the force of the gases on the bullet as they escape is not reasonably symmetrical, the result can be that the bullet is displaced/reoriented after the initial small, transient, cyclical motion dies out."

Frame of reference issue that is leading a fundamental misunderstanding of what is happening.

I'm not exactly sure what you're trying to say, but if it's that a 10mph wind or the gases that escape from the muzzle can't affect a bullet's point of impact (indicating that the trajectory changed from what was desired), that's obviously incorrect. If you're trying to imply that I stated they change the POI via exactly the same "method", I didn't say that.

My SKS shot pretty lousy after exhausting all the tricks in the bag. I examined the crown with magnifier and couldn't catch anything wrong. It was the rounded military profile. As a last resort before giving up, I recrowned it with 11 degree profile. It made day and night difference. Perhaps the original crown was cut uneven smoothly, so visual inspection turned up no clue.

Yup. It doesn't have to damage the bullet to have an effect. It just has to result in a significantly asymmetric release of the gases behind the bullet as it exits.

[tangolima]

The muzzle gas does affect the first inch or two of the bullet's flight, which is critical. Beyond that it has no effect.

There was another thread here on poi shift of the 1st and last round in the mag where a member maintained that the shooter could steer the bullet with muzzle gas. I don't believe it.

-TL



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[stagpanther]

More like 6"-8" before and better than 2" after. Believe me, I went out of my way to make it shoot, including glass bedding the action, a trigger job, and carefully handloading the rounds.

I have a soft spot for SKS's since I had a nice Norinco that I paid I think $75 for--came with bayonet and bayonet mount even. On a GREAT day I could get it to group 4" to 5" at 100 yds. I've known of guys who have done ultra-custom trick-outs with their SKS; met one at a range once and he let me shoot his, except for the basic action it was impossible to tell it was an SKS when I first saw it. It was a very, very cool rig though. It managed 1.5 to 2 MOA @ 100 yds which is truly exceptional for an SKS, this guy's was the only one I've ever encountered that could do that. You could probably go into business selling them if you can do that!

[tangolima]

Originally Posted by stagpanther

I have a soft spot for SKS's since I had a nice Norinco that I paid I think $75 for--came with bayonet and bayonet mount even. On a GREAT day I could get it to group 4" to 5" at 100 yds. I've known of guys who have done ultra-custom trick-outs with their SKS; met one at a range once and he let me shoot his, except for the basic action it was impossible to tell it was an SKS when I first saw it. It was a very, very cool rig though. It managed 1.5 to 2 MOA @ 100 yds which is truly exceptional for an SKS, this guy's was the only one I've ever encountered that could do that. You could probably go into business selling them if you can do that!

Mine is a yugo. Not the newer type with grenade launcher, but the original type. Got it from classic arms for $200 or so.

I truely did it. I spent months to tinker it. Getting rid of the grease from everywhere, especially the wood, alone was already quite a task. Modified a lot of things, but didn't change its original military configuration. The trigger had dangerous negative sear engagement, and it was the first thing to be corrected.

If I ever do this to make a living, I will end up being homeless. Nobody is going spent the money to pay for it. I was once a paid part-time gunsmith. The work was fun, but hard to make a living, at least so the way I like to do it. You will ruin a hobby as soon as you turn it into business.

I collect and shoot milsurp rifles. Improving it till it shoots better than 2moa (100yr R50 10-shot) is the goal. The original military configuration must not be affected. Glass bedding is acceptable as long as it is hidden. There have been a few rifles that I have to throw in a towel, mostly because the barrel is far gone and replacement is nowhere to be found.

I like the SKS, but never the AK.

-TL

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[stagpanther]

I like the SKS, but never the AK.

Sorta a Pepsi vs Coke argument in my book, though I far prefer a good AK over any SKS.

[JohnKSa]

Me too. But I think we would both have a different opinion if our primary reason for owning one was to get it to shoot under 2MOA for 10 shot groups without substantially altering the original configuration.

[tangolima]

Originally Posted by stagpanther

Sorta a Pepsi vs Coke argument in my book, though I far prefer a good AK over any SKS.

It is far more than that for me. I'm a first generation immigrant from a communist country. I saw both there. SKS has redemption value as it fought the Nazis, however briefly.

-TL

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[czgunner]

Originally Posted by stagpanther

Sorta a Pepsi vs Coke argument in my book, though I far prefer a good AK over any SKS.

VZ-58 for me.

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[tangolima]

Velmet from Finland is ok. Don't have that sort of money though. I do have a VZ-52. Different kind of sks.

Come on guys. Stop rubbing it in. I can't have any of those without installing the dorky fin on the pistol grip. I live behind enemy line in CA, and I refuse to look stupid.

My life is cursed. I have to keep running.

-TL

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[JohnKSa]

Can you own one of the Hungarian AKs (SA85M) that came in with thumbhole stocks? Other than the large-cap magazine, they don't have any of the "evil" features.

I was going to change out my stock, but it was nice wood (as far as wood on that kind of rifle goes) and very comfortable so I left it in place. That gun points really well for me. It comes up to my shoulder and the sights are pointing where I'm looking without me putting any effort in.

This is not mine, but it looks very much like mine.

[tangolima]

The tyrants have deemed thumbhole evil.

-TL

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[stagpanther]

The tyrants have deemed thumbhole evil.

Move to another state.

[tangolima]

Originally Posted by stagpanther

Move to another state.

I'm thinking about it for my retirement, if the good Lord allows me to see that day. We are still here for reasons that are beyond my control.

That's why I said my life is cursed. Always have to run from same sort of tyranny. Sadly I am running out of destinations and strength. Even more sadly, a lot of people, Americans included, don't understand why I have to keep running.

-TL

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[stagpanther]

Always have to run from same sort of tyranny.

I have bad news for you--it never ends. We are free-range animals that live on tax farms.

[tangolima]

Originally Posted by stagpanther

I have bad news for you--it never ends. We are free-range animals that live on tax farms.

I'll keep going, till I can't go anymore.

-TL

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[tangolima]

Alright. I tried starting discussion on spring, but there seemed no interest, or it was drowned out by some other bigger talks. Let me try again in some other way.

From time to time, we need to reduce a coil spring's strength, to lighten a trigger's weight for instance. We were taught at gunsmithing school never to cut coils off. Instead we should thin the wire's diameter. In practice we often end up cutting coils because it is easier. Certainly both methods work in reducing the spring's strength.

What's the difference? Why gunsmiths are so adamant about cutting coils, even though at least sometimes they still choose to do it? There are even talks saying that cutting coils makes a spring stronger, not weaker. How comes?

-TL

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[stagpanther]

There are even talks saying that cutting coils makes a spring stronger, not weaker. How comes?

I'll bite--why is that?

[tangolima]

Originally Posted by stagpanther

I'll bite--why is that?

It is a bit convoluted and counter intuitive. I'm holding off for a few days so that I can put together a better explanation. Hopefully someone will come along and do a better job than I could.

-TL

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[davidsog]

The muzzle gas does affect the first inch or two of the bullet's flight, which is critical. Beyond that it has no effect.

No, it is not correct nor is it critical in a properly designed weapon. You must understand that much of the minutia in this is not fully understood by those who have dedicated years of study in science/engineering disciplines. Maybe you have special insight others do not possess.

Transitional ballistics is a complex field that involves a number of variables that are not fully understood; therefore, it is not an exact science.

The general consensus, just like wikipedia article you posted....
Is that in a properly designed rifle it has little effect but that is only an educated guess by those with engineering and science education in the field.

Throughout the trajectory, including the initial transient period, the bullet has an “average” angular orientation which aligns the longitudinal axis almost exactly with Vbullet relative to the air.

That means muzzle exit gases have no effect on a properly designed weapon.

So no, the natural color of a Sperm Whale is not white.

[JohnKSa]

That means muzzle exit gases have no effect on a properly designed weapon.

This is almost exactly the same thing as saying that they CAN have an effect. I don't understand how you can't see that.

They CAN have an effect on firearms with crown problems. This can be demonstrated in the real world. Which means that they must be a consideration when there are accuracy issues. The muzzle gases are moving very fast and have a lot of momentum upon exit--more than enough to cause bullet displacement/misalignment if they don't exit symmetrically due to a problem with the crown.

Yes, if the gun is set up right, you don't need to worry about muzzle gases. Just like when the gun is set up right and aimed right you don't need to worry about a lot of things that can affect the ability to hit the target as desired. But for the purposes of a discussion about the physics of shooting a rifle, it's important to understand that they are one of the factors that CAN have an effect since that's one of the avenues that must be explored if there are problems with the accuracy.

What you're doing at this point is like someone saying that "Bedding does affect rifle accuracy." and then you respond. "You're wrong. Bedding has no effect on rifle accuracy if the rifle is set up properly." Which is both incorrect and correct. The person is NOT wrong because bedding is a factor that affects rifle accuracy. But it is correct because bedding only affects rifle accuracy if there's a problem with the rifle that can be corrected with bedding. But more to the point, it's totally unhelpful.

It doesn't provide any useful insight at all because, in the current case, no one is arguing that muzzle gases always deflect bullets, even when things are working properly. Everyone already understands that if the muzzle is set up properly the gases aren't a problem.

So, if your point is that muzzle gases do not ALWAYS cause accuracy problems, then your point is duly noted. It should also be noted that: 1. No one ever made that claim. and 2. If someone says that muzzle gases do affect the bullet, that does not contradict your point since they can and do have the potential to affect the bullet and it's important to keep that in mind. and 3. Your original claim was that there was no way that they could affect the bullet, a contention which is obviously and demonstrably false.

[davidsog]

This is almost exactly the same thing as saying that they CAN have an effect.

Almost exactly like saying when the wings fall off an airplane it does not fly as well.

But is still an airplane without the proper wings it was supposed to have when it was deemed airworthy?

It is nothing like your stock bedding example.

We are talking about something that is fundamental to actual working order and design of the system.