Why the precision versions have shorter barrel

[legi0n]

I don't have anything on 17hmr but here's data on 22LR up to 18"
you can compare to real-life up to 23" barrels in the following table
http://www.ballisticsbytheinch.com/22.html

 

[_Shorty]

With .22LR faster doesn't mean less sensitive to wind. It's the opposite. The faster a .22LR round is the more it drifts in wind. For minimizing wind drift, slower is better.

Well, I guess you can say that, given the typical speeds you can get 22 LR in. But it is basically just a constraint of the case size, and the velocities we can get because of it. Wind drift is related to velocity, but it isn't that straight forward. Here's what it would look like if you could slow down and speed up Eley Tenex to unrealistic levels, with wind drift in MOA with a 10 mph crosswind:

As you can see, way down low at 500 fps it is bad, but it quickly gets better as you go up in velocity. As you increase MV, for 50-yard targets it reaches the best point at 827.5 fps, and for 100-yard targets the best MV is slightly faster at 843 fps. So, up to those points, faster is better. They're unrealistically slow, though. Then, for a little while, faster is worse. For 50 yards it is worst at a MV of 1339 fps, and for 100 yards it is worst at a MV of 1413 fps. Obviously we're not able to reach velocities much past that with 22 LR, but if you could continue past that point it would continually improve as MV continually grows, and faster is better again. Unfortunately, you've got to get past about 2100 fps before it starts showing an improvement over what you can get with typical match ammo speeds in the 1000-1100 range, and that's obviously not happening. Kind of makes me wonder if they could still load Eley Tenex consistently at 200 fps less than they load it for now, actually. Hehe.

High velocity .22LR bullets don't experience the transonic turbulence that affects some projectiles. Transonic turbulence occurs when some bullets slow down into the transonic zone velocities, which are from about 1340 fps to about 890 fps. Most HV .22LR ammo spends the first 175 yards or so of it's flight entirely within the transonic zone speeds. So, too, does standard velocity .22LR match ammo. High velocity .22LR ammo is usually accuracy impaired for reasons of quality not velocity.

I'll have to disagree with you there. The transonic effects are called that because you're talking about crossing the sound barrier. The bullet's speed relative to the speed the shock wave can itself travel through the air is what's being talked about. If a bullet starts off supersonic then it will cross the sound barrier at some point as it slows down, and will have to deal with the effects of that shock wave. Typical 1280 fps HV rounds cross the sound barrier around the 55-yard mark. It's why match ammo is loaded subsonic, to avoid crossing the sound barrier altogether.

 

[_Shorty]

I don't have anything on 17hmr but here's data on 22LR up to 18"
you can compare to real-life up to 23" barrels in the following table
http://www.ballisticsbytheinch.com/22.html

I found this test:

https://www.bullberrylegacy.com/17-hmr-velocity-data#:~:text=Summary,average of the 19" length.

They only did 5 shots per length, though, which makes their answer murkier than they portray. There's enough overlap between the different lengths with so few shots per length to make the answer unclear. It hints at 18" probably being ok, but maybe not optimal, as far as velocity is concerned. Barrel length isn't something that tells you how accurate a gun might be, though.

If 18 inches are enough to reach max velocity with a 17 HMR, then why make a 22 inches barrel ?

Barrel length isn't just about what you need to get maximum velocity, and that will change depending on the load anyway. Within reason, you can make any length of barrel accurate. You just need to find a good contour for that barrel length with regard to typical loads and target distances you'll be shooting with it. Like most everything, it is a compromise.

 

[grauhanen]

I don't have anything on 17hmr but here's data on 22LR up to 18"
you can compare to real-life up to 23" barrels in the following table
http://www.ballisticsbytheinch.com/22.html

Unfortunately, this shouldn't be relied on as a definitive source for .22LR. It uses a small number of rounds in its testing. Casual rimfire shooters often mistake BBTI as reliable proof that shorter barrels are always faster. This idea gets repeated on internet forums and it gains wide but misplaced currency. There's too much data that contradicts the basic idea that there's a consistent relationship between barrel length and muzzle velocity.

Those who wish more information can read further. The same shooter who produced the often-cited ".22LR Rimfire Ammo Comparison Test" ( h ttps://www.accurateshooter.com/guns-of-week/22lr-rimfire-ammo-comparison-test/ ) tested MV of various ammos with the same rifle with a progressively shorter barrel. Over a variety of different ammos, he found that barrel length didn't predict ammo velocity. His conclusion "Amazing is in it? With center fire each inch means something, here not so much." (See post on March 5, 2018 on p.2 of the thread linked previously).

There are other sources that confirm that the relationship between .22LR barrel length and ammo velocity is inconsistent. As a Gun Digest editor concludes about .22LR, "I’d somehow expected a convenient linear velocity progression in direct relation to barrel length and ammo classes that would allow quoting easy rules of thumb. That proved to be a naïve assumption." (See "How Does Barrel Length Affect Accuracy and Ballistics?" https://gundigest.com/article/how-does-barrel-length-affect-accuracy-and-ballistics)

 

[tiriaq]

Wouldn't a .17HMR with its bullet design and velocity have more in common with centerfire ballistics and performance than a .22 rimfire?

 

[grauhanen]

Well, I guess you can say that, given the typical speeds you can get 22 LR in. But it is basically just a constraint of the case size, and the velocities we can get because of it. Wind drift is related to velocity, but it isn't that straight forward.

Shorty, it is that straightforward. Faster .22LR bullets drift more in the wind than slower ones.

I'll have to disagree with you there. The transonic effects are called that because you're talking about crossing the sound barrier. The bullet's speed relative to the speed the shock wave can itself travel through the air is what's being talked about. If a bullet starts off supersonic then it will cross the sound barrier at some point as it slows down, and will have to deal with the effects of that shock wave. Typical 1280 fps HV rounds cross the sound barrier around the 55-yard mark. It's why match ammo is loaded subsonic, to avoid crossing the sound barrier altogether.

Shorty, you may disagree with me but it's important to get the facts correct. When it occurs, transonic turbulence happens when bullets slow down into the transonic zone of velocities, which are about 1340 fps to about 890 fps. It's not simply crossing the "sound barrier".



In any case, it was confirmed in 1990 by Robert McCoy that .22LR ammo with transonic zone velocities (from about 1340 fps to 890 fps) doesn't suffer from the increased pitching and yawing that causes the flight instability associated with bullets slowing down into the transonic zone from considerably greater velocities. See conclusion #5, p.11 in Robert McCoy "AERODYANMIC CHARACTERISTICS OF CALIBER .22 LONG RIFLE MATCH AMMUNITION" https://apps.dtic.mil/dtic/tr/fulltext/u2/a229713.pdf

 

[_Shorty]

Shorty, it is that straightforward. Faster .22LR bullets drift more in the wind than slower ones.

Feel free to explain the difference between 700 fps bullets and 800 fps bullets. The 800 fps one is faster than the 700 fps one, right? And feel free to explain the difference between 1500 fps bullets and 1600 fps bullets. The 1600 fps one is faster than the 1500 fps one, right?

Shorty, you may disagree with me but it's important to get the facts correct. When it occurs, transonic turbulence happens when bullets slow down into the transonic zone of velocities, which are about 1340 fps to about 890 fps. It's not simply crossing the "sound barrier".

I'm not going to through that routine of trying to explain something to you 73 times again. Suffice it to say you do not seem to understand what's going on as well as you think you do, and linking documents you apparently do not fully understand doesn't help your case. A 1085 fps bullet starts off subsonic and by definition never crosses the sound barrier and therefore never experiences any transonic effects, which is precisely why match ammo is loaded in this velocity neighbourhood. A 1280 fps bullet starts off supersonic and by definition will cross the sound barrier at around 55 yards out, and will then experience transonic effects because it is crossing that sound barrier. It doesn't matter that 1280 fps is below Mach 1.2, because there's nothing magical about starting above Mach 1.2. It has everything to do with how it is travelling relative to the shock wave and turbulence around it during that time that it goes from above the sound barrier and falls below the sound barrier. That's literally why it is called transonic. The fact that some effects can begin to rear their head around Mach 1.2 does not mean you have to be going above Mach 1.2 for it to happen. The worst stuff happens right around Mach 1.0 because the airflow and shockwave start going mental with things randomly going above and below the sound barrier around the bullet for a short period. That's what disturbs its flight. The further you are from Mach 1.0, above or below, the smaller the chance of those things happening, and the smaller the effects if it does happen. If you're never above Mach 1.0 to begin with you can't be affected by what happens when you're going from above Mach 1.0 to below Mach 1.0, so starting off below Mach 1.0 is relatively safe. It has everything to do with the sound barrier itself. That's what every study about this subject has to say. If you fail to understand that then you still need to study it some more.

 

[grauhanen]

Rimfire shooters who are reasonably familiar with .22LR will be aware that slower .22LR bullets drift less than faster ones. This has been known for a long time.

If any reader believes that faster .22LR ammo drifts less in the wind than slower .22LR ammo, please post any reliable sources that help support the contention.

Regarding transonic turbulence, the majority of .22LR bullets can't experience it because they never exceed transonic zone velocities. The majority of HV .22LR ammo isn't accurate because of quality not velocity. It is not match ammo and so doesn't shoot like it is.

On the other hand, there are good quality higher velocity match ammos such as RWS R100. The factory rates this particular variety of ammo at 345 m/s (about 1132 fps). That's near or above the speed of sound. As with all match ammo, RWS R100 lots that are appropriate for a rifle will give very good accuracy. This is because RWS R100 is match quality ammo, not because it's subsonic.

 

[Suther]

Rimfire shooters who are reasonably familiar with .22LR will be aware that slower .22LR bullets drift less than faster ones. This has been known for a long time.

If any reader believes that faster .22LR ammo drifts less in the wind than slower .22LR ammo, please post any reliable sources that help support the contention.

Regarding transonic turbulence, the majority of .22LR bullets can't experience it because they never exceed transonic zone velocities. The majority of HV .22LR ammo isn't accurate because of quality not velocity. It is not match ammo and so doesn't shoot like it is.

On the other hand, there are good quality higher velocity match ammos such as RWS R100. The factory rates this particular variety of ammo at 345 m/s (about 1132 fps). That's near or above the speed of sound. As with all match ammo, RWS R100 lots that are appropriate for a rifle will give very good accuracy. This is because RWS R100 is match quality ammo, not because it's subsonic.

So you're saying CCI quiets going 710fps will drift LESS than CCI SV going 1040fps?

 

[_Shorty]

Rimfire shooters who are reasonably familiar with .22LR will be aware that slower .22LR bullets drift less than faster ones. This has been known for a long time.

Evading the question because you don't agree with the reality of the situation. Thumbs up.

Regarding transonic turbulence, the majority of .22LR bullets can't experience it because they never exceed transonic zone velocities.

Again, you do not understand the concept. You just think you do. Watch the plane fly-bys in this video. Here are some timestamps of interest to this discussion.

0:32
0:50
4:22
4:32
4:52 probably the most obvious as it happens many times

At those timestamps you will see multiple supersonic cones forming and disappearing in rapid succession. I guarantee you the planes are not accelerating from below Mach 0.8 to above Mach 1.2 and decelerating from above Mach 1.2 to below Mach 0.8 as quickly as those supersonic cones are forming and disappearing. Your understanding of the concept is wrong, plain and simple. The reason the examples with multiple supersonic cones forming and disappearing are doing so is because the planes are very close to exactly Mach 1.0 and they are briefly breaching it slightly, falling back under it slightly, breaching it again, and falling back under it again. They are not going Mach 1.3, and then Mach 0.7, and then Mach 1.3, and then Mach 0.7 in the space of less than one second as those cones form and disappear rapidly. They are incapable of accelerating and decelerating that quickly. The supersonic cones appear when they breach Mach 1.0 and disappear when they fall back below Mach 1.0 again. There are also examples in the video of planes breaching Mach 1.0 and continuing to go faster than that, and that's when the supersonic cones appear and remain for quite a while. As soon as they fall below Mach 1.0 they disappear. There are reasons for considering the region of Mach 0.8 to Mach 1.2 as the transonic region, and it has to do with what can happen with the shockwaves all through that region, but it is not some safety zone where you're ok if you stay between those extremes. The most violent stuff happens right at Mach 1.0 as you cross from one side of it to the other. The fact that some stuff can still happen further away from it does not change the fact that the most disturbing things happen right at that point. The airflow is changing most dramatically right at that point, and that's why it disturbs the bullet the most at that point. And also why if you stay away from that point then you avoid the most drastic disturbances.

As for R50 vs R100, there's a reason RWS markets R50 and R100 the way they do. They go on and on about how great R50 is, holding records, used by Olympic shooters, etc. And basically "Oh yeah, R100 also exists if you want pretty good supersonic ammo." If they don't think R100 produces results as good as R50 does then I don't see why anyone should think so. Same for Eley and their Tenex and Tenex Biathlon rounds, which have speed differences similar to R50 and R100. Eley markets Tenex as having a 3.75 mm RSD with a velocity range of 1040-1085 fps. And they market Tenex Biathlon as having a 4.50 mm RSD with a velocity range of 1100-1160 fps. Given that Mach 1.0 is 1086.7 fps at freezing that makes the latter supersonic at intended use temperatures. And I would surmise that this is the main reason it has a 0.75 mm larger RSD, it being supersonic, since presumably they're attempting to make it just as accurately as they make Tenex. Something has to account for the slightly worse performance, and I'm fairly confident it is because it has to deal with crossing over Mach 1.0 while regular Tenex does not.

edit: Found it. In this video you can see one of the things that happens with the shockwaves when the bullet is subsonic. The whole thing's worth a watch, but around the 5-minute mark you can see one of the transonic region quirks, and then someone explaining why that's being seen in that case. But the important thing to know about this is that the turbulence that occurs with it is nothing like what happens when you're crossing that Mach 1.0 barrier. The smaller things going on at this speed may have some smaller detriment to accuracy, but the magnitude of everything going on there is much smaller than what's going on at that sound barrier. The stuff going on at the sound barrier is what can cause the most negative effects to accuracy. The longer the bullet, the more effect it will have, and so the effects on 22 LR bullets are going to be relatively small compared to a much longer 180-grain .284 bullet, for example. But the effect isn't zero. I'll again refer to the RSD difference that Eley advertises between Tenex and Tenex Biathlon. 0.75 mm difference in RSD isn't much. And probably more than small enough for the 1990 paper to consider insignificant. Benchrest shooters might not deem it an insignificant amount, though. Grouse hunters might.

 

[Hunter7]

Theoretically a shorter barrel should give you a faster lock time, from when the trigger is fired to bullet exiting the barrel, that was always my reasoning for the shorter barrel. Not sure how much difference it really makes in the big picture, but I thought that was the reasoning behind Anschutz using the shorter barrels on their newer match rifles but using the longer barrel shroud to still provide the long sighting plane.

 

[_Shorty]

Just to get some terms correct:

Lock time is the time between trigger pull and firing pin impact.

Ignition time is the time between the firing pin impact and the powder burning enough to start building pressure.

Time until max pressure is an obvious one, which is the time between the end of ignition time and when the maximum pressure point is reached.

Barrel time is the amount of time the bullet spends moving through the barrel until it exits.

I don't know if anybody would select a barrel length based on barrel time or not. Possibly. Whether anyone does, I do not know.

 

[grauhanen]

So you're saying CCI quiets going 710fps will drift LESS than CCI SV going 1040fps?

The fact that slower .22LR ammo drifts less than faster .22LR ammo is not a "theory" offered here to inconvenience anyone. It's a fact that's been known for a very long time. It may be counter-intuitive, but it applies to bullets like .22LR that have typical .22LR muzzle velocities. If anyone has doubts about this, go to a ballistics calculator. There are several free to use online. Compare HV to SV .22LR ammo and see for yourself.

In the meantime, to illustrate the issue below is an example of two commonly used rounds, one a CCI SV at 1070 fps, the other a CCI Mini-Mag at 1234 fps. The wind is a 1 mph crosswind. For a 10 mph crosswind, for example, multiply the 1 mph drift by ten.





As for the comparison of CCI 40 grain rounds at 710 fps and 1040 fps, below is a chart generated minutes ago using GunData.org. It shows the wind drift each round experiences in a 1 mph crosswind.

It's worth noting that, unlike the previous example, in this case with an extremely slow round with a MV of only 710 fps, it drifts less than the faster round out to about 200 yards, which is likely well beyond the extent of its useful flight. Further out from 200 yards, it begins to drift more than the faster round.

 

[grauhanen]

Theoretically a shorter barrel should give you a faster lock time, from when the trigger is fired to bullet exiting the barrel, that was always my reasoning for the shorter barrel. Not sure how much difference it really makes in the big picture, but I thought that was the reasoning behind Anschutz using the shorter barrels on their newer match rifles but using the longer barrel shroud to still provide the long sighting plane.

Shorty offers a good explanation of the terms in his last post.

Anschutz continues to use the 69 cm and 66 cm barrels on the latest Match 54 single shot target rifles such as the 19xx and 20xx models. These are the lengths Anschutz has used for over half a century. In the early 1990s, when the 20xx model was first produced, one model had a shorter barrel at 50 cm. Contemporaneous Anschutz literature suggested the shorter barrel was linked to a "shorter lock time" but it is misleading as lock time is as Shorty explained. The 50 cm barrel hasn't been available in decades.

The newest Anschutz model, the 22 Max which has a unique bolt action, appears to have a 66 cm barrel and extension, as does the 54.30 model.

 

[Suther]

The fact that slower .22LR ammo drifts less than faster .22LR ammo is not a "theory" offered here to inconvenience anyone. It's a fact that's been known for a very long time. It may be counter-intuitive, but it applies to bullets like .22LR that have typical .22LR muzzle velocities. If anyone has doubts about this, go to a ballistics calculator. There are several free to use online. Compare HV to SV .22LR ammo and see for yourself.

In the meantime, to illustrate the issue below is an example of two commonly used rounds, one a CCI SV at 1070 fps, the other a CCI Mini-Mag at 1234 fps. The wind is a 1 mph crosswind. For a 10 mph crosswind, for example, multiply the 1 mph drift by ten.





As for the comparison of CCI 40 grain rounds at 710 fps and 1040 fps, below is a chart generated minutes ago using GunData.org. It shows the wind drift each round experiences in a 1 mph crosswind.

It's worth noting that, unlike the previous example, in this case with an extremely slow round with a MV of only 710 fps, it drifts less than the faster round out to about 200 yards, which is likely well beyond the extent of its useful flight. Further out from 200 yards, it begins to drift more than the faster round.

What is the reasoning behind this? Higher rotational velocity resulting in more spin drift?

 

[_Shorty]

What is the reasoning behind this? Higher rotational velocity resulting in more spin drift?

Not even talking about spin drift yet, hehe. The coefficient of drag for a given bullet changes with regard to speed, and not in a linear fashion. If you look at the G1 drag data that JBM uses you can see from 0 to somewhere between Mach 0.5 (562.5 fps) and 0.55 (618.75 fps) the CD drops up to that speed, and then begins to rise until somewhere between Mach 1.4 (1575 fps) and 1.45 (1631.25 fps), and then as speed increases beyond that the CD continues dropping from that point on.

https://jbmballistics.com/ballistics/downloads/text/mcg1.txt
Which is from: https://jbmballistics.com/ballistics/downloads/downloads.shtml

Wind drift is related to the bullet's drag. The amount of time it spends with a given CD will affect how much it drifts, and since the CD changes with speed, the amount it drifts will change as the speed changes.

 

[Suther]

Cool thanks for explaining it for me.