Another barrel length question

iain.quayle

iain.quayle

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Question was why do the pro rimfire br rigs use such long barrels (~24"), these are scoped and have nothing to do with sight radius.

The best answer I found was that it minimized the ES of velocity between shots, and since they are using tuners and dampeners the length is not an issue with harmonics.

Was also wondering how much of a performance loss are you getting from the long barrels? and how much of a difference in ES is it (if that is correct)?


Any experience that could give a quick answer would be much appreciated.
 
I believe the extra length is the add weight and increase stability when shooting off hand Olympic style? If you want reduced velocity, might as well shoot subsonic ammo.
 
One factor certainly is weight as inertia is good for increased stability. Barrels with a very wide diameter are less responsive to tuners than those with lesser diameters, and longer barrels are more responsive to tuners than shorter ones of the same diameter. There may well be something to longer barrels helping to reduce the ES, but the evidence is not clear. Of course it could vary from one rifle to the next, since different rifles often produce different MV's with the same ammo. MV is influenced by not only barrel length. Among the other factors influencing MV are bore diameter (they're not necessarily exactly the same between all .22LR rifles), bore metallurgy, and bore condition, including rifling, smoothness and wear.

There is nothing to support the idea that maximum ammo velocity equates to better accuracy. Standard velocity ammo produces better accuracy at the ranges for which the .22LR round is most suited. The only performance that matters is POI down range.
 
weight, yea forgot that would definitely be a useful item for the br shooters.

I understand that not hitting the max vel for 22lr is no issue to the accuracy, it is just that the rig I am building is for rimfire prs so losing 100fps off of an already subsonic round leaves it bouncing around in the wind a bit more.
 
iain.quayle said:
weight, yea forgot that would definitely be a useful item for the br shooters.

I understand that not hitting the max vel for 22lr is no issue to the accuracy, it is just that the rig I am building is for rimfire prs so losing 100fps off of an already subsonic round leaves it bouncing around in the wind a bit more.
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Why would a slower round react more to the wind than a faster one? High velocity ammo is more susceptible to wind drift than standard velocity ammo.
 
You will be fine for prs type shooting with sv ammo. Better short range accuracy and the long range is still more consistent. Best thing you can do is pick a barrel weight you are comfortable with and find its favourite ammo. If your numbers are right the velocity does not matter.
 
The velocity thing with 22 is related to the speed of sound which is just over 1200 FPS but the exact speed of sound changes with temperature, altitude and humidity, so it depends where you are.

So here's the rub... if you fire a 22 bullet faster than the speed of sound, it become unstable as it slows down and gets close to the speed of sound... transonic velocity.

So accuracy with supersonic 22 is repeatable only until the bullet slows to roughly 1250 FPS but accuracy becomes unpredictable farther out than that.

Target ammo deliberately stays under the speed of sound so the "transonic barrier" does not become a factor to degrade accuracy.

So a longer barrel to get more speed with a 22 is not really your objective.
 
Actually works backwards, barrels over I think the number is between 14 and 16 is friction loss as the powder is gone, so the bullet is slowing for the last 4 inches
 
There is no evidence to suggest that the "trans sonic barrier" has any noticeable effect on rimfire accuracy at long range. Any effect it might have is eclipsed by cartridge defects, mv variation, and wind drift.
 
Ammo and barrel dependant fps starts to drop off any where from 14-18". General speed of sound is 1125fps.

While keeping the rounds subsonic, I just wanted my them to get to the target quicker to lessen the drop and drift. 40grns at 1050 vs 950

Anyways, my main question was about barrel length vs ES, and fps loss in those longer barrels.
I'm likely set on 20-22" ish barrel to get it closer to my current prs rig balance and weight


thanks for the replies
 
If the supersonic ran well in my gun I would, I personally don’t think the transonic barrier exists. As far as es I don’t think barrel length has anything to do with it, it is all ammo related. If the ammo has a bad spread with a short barrel there is a good chance it will in a long barrel
 
For what it's worth, the BBM HV ammo box says "1130+" fps.

scuba52 said:
If the supersonic ran well in my gun I would, I personally don’t think the transonic barrier exists. As far as es I don’t think barrel length has anything to do with it, it is all ammo related. If the ammo has a bad spread with a short barrel there is a good chance it will in a long barrel
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As far as the "transonic barrier" thing goes, it's not a matter of opinion whether it exists. The question is how much it affects accuracy. Once the HV bullet approaches the transonic zone, does it diminish HV accuracy appreciably? I don't know. It's worth bearing in mind, however, that SV match ammo is more accurate than HV ammo. It has much lower extreme spreads in MV, which is all important when ranges with relatively slow ammo increase beyond their designed range, and it experiences somewhat less wind drift.

If SV ammo is more accurate than HV at 50 yards and 100 yards, it has a very good chance of being more accurate at 200 yards. While it's never so simple as to double the size of a group when the distance doubles, and some ammo may not maintain its relative accuracy as distance increases as well as others, there is no reason to assume that HV ammo, which is less accurate than SV at 50 and 100, will overtake SV ammo in accuracy as distance increases. It was not as accurate to begin with.

The OP has asked about barrel length and MV in connection with PRS shooting. The most important thing for whatever rifle he is considering is that it balances well in his hands.

As an aside, it's good to note that some of the short barrel rifles, such as the Tikka T1X with the 16 inch barrel or the Anschutz 1416 with the 14 inch barrel, are made primarily for use with moderators. (I don't recall if all the CZ 457's with 16" barrels have threaded muzzles, but at least some of them do.) Here shorter barreled rifles don't become too long and unwieldy with a sound reducer -- an especially important factor in jurisdictions where hunting from a vehicle (even at night) is allowed. These rifles were not designed with PRS shooting in mind -- although the short barrel itself doesn't preclude that use. It all depends on what rifle provides a good balance when shooting.
 
iain.quayle said:
Ammo and barrel dependant fps starts to drop off any where from 14-18". General speed of sound is 1125fps.

While keeping the rounds subsonic, I just wanted my them to get to the target quicker to lessen the drop and drift. 40grns at 1050 vs 950

Anyways, my main question was about barrel length vs ES, and fps loss in those longer barrels.
I'm likely set on 20-22" ish barrel to get it closer to my current prs rig balance and weight


thanks for the replies
Click to expand...

What are you building up? Action? Barrel? Etc?
I just put an order in with Jerry for an 18” IBI barrel.
We’ll see how it works out. ��
 
We can all choose to believe what we want about the transonic thing but you can see it for yourself with a 22 easy enough if you have enough magnification on your scope to watch your bullets fly.

I spent a fair amount of time this spring comparing various 22 LR ammo and the Browning BPRs at about 1400 FPS were one of my high velocity favorites. For me they shot well at close range and I could see they flew straight to about 75ish yards, then started darting about and groups opened up at 100 yards a lot more than twice the 50 yard groups.

Comparing that to ammo under 1200 FPS, group sizes were far more linear between distances in calm conditions, and I have since removed BPRs from the competition grade roster. Probably great for semi auto plinking though.

I've also struggled with this transonic stuff in F-Class with a 308, where I could hold the 5 ring easy at 900 yards but at 1000 yards I had a hard time holding the 4 ring, and conditions became all but unreadable. In steady conditions I could not predict where on the target rounds would hit.

Once I changed to bullets with a higher BC, suddenly I was throwing bricks and things became repeatable.

I'm not going to tell you to believe in the transonic thing or not, but there are plenty of guys out there with the creds to validate that it exists. I do think it has an effect but that effect might depend on specific bullet designs which may or may not be more or less affected during the transition.
 
Some of the BR guys in the US are even starting to look at 26 and 28" barrels again. The old 40x and 52's use to run the long barrels.
 
TrxR said:
Another thing with br guns is that they have to watch their weight , so that can be a decision maker on barrel length.
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Indeed. There are various sanctioned matches and they have categories for sporter and several weight classes, which include the scope and mounts. There is also an unlimited category where weight is not a factor.
 
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