HMR, legal barrel length

johngalway

Hi folks,

What's the legal length for a rifle barrel, in this case HMR?

I am going to change my Sako .22lr barrel for a HMR barrel later this year. I want to get it shortened to something like 14" - 16" for handiness sake. Just wondering what's legal.

Regards,

John

Kramer

50cm minimum rifle barrel length in CJA '06 but this refers to "shortening" a barrel.

Something already under 50cm from the factory like a CZ should be OK.

65:- The following section is inserted after section 12 of the Firearms
and Offensive Weapons Act 1990:
“Shortening
barrel of shotgun
or rifle.
12A.—(1) Subject to subsection (2), a person
who shortens the barrel of—
(a) a shot-gun to a length of less than 61
centimetres, or
(b) a rifle to a length of less than 50
centimetres,
is guilty of an offence.
(2) It is not an offence under subsection (1) for
a registered firearms dealer to shorten the barrel
of a shot-gun or rifle to a length of less than 61 or
50 centimetres respectively if the sole purpose of
doing so is to replace a defective part of the barrel
with a barrel of not less than 61 or 50 centimetres,
as the case may be.

Rovi

In the CRIMINAL JUSTICE BILL 2004 there is mention of "It is an offence for a person (except a registered firearms dealer) to possess without lawful authority or reasonable excuse—" "(b) a rifle the barrel of which is less than 50 centimetres in length", while leads me to surmise that it IS legal to have a shorter barrel provided you have "lawful authority or reasonable excuse", whatever they may be.
I suppose "lawful authority" would be some sort of licence/cert for the short barrel, but the word "or" before "reasonable excuse" seems to state that you don't need the " lawful authority" once you have a plausible "reasonable excuse" for possession of said short barrel. I doubt that 'because I want one' qualifies.

There's talk of a maximum legal length (of the whole firearm) of some sort in the fabled 'Restricted List', which might or might not have a bearing on this too.

It would appear, on face value, that you can have a rifle barrel shorter than 50cm (19.7ins) provided you get "lawful authority" from whoever, the Gardaí/DOJ presumably; I'd check it out and get the okay in writing before going ahead with the project, though.


edited to add-
Of course, I should have referenced the CRIMINAL JUSTICE ACT 2006 for the above, but it all appears to have gone in as described [Section 65-(6)(b)].

johngalway

:eek:

50cm = 19.68 inches...

Thanks for the info lads.

Bloody rubbish law :mad:

dimebag249

So, for the sake of arguement, should one purchase a shotgun with a ten inch barrel, wouldn't the firearms certificate issued for the gun be "lawful authority"? No guard has ever asked me for the barrel length of any gun I've applied for. To me the situation here appears much like it is in Canada, it is illegal to shorten a barrel below a specified length, but perfectly legal to buy a new gun with a short barrel.

Edit: Needless to say I'm not going to be the one to argue this in front of a judge, but the law is sufficiently vague that you might get away with it. (?)

rrpc

johngalway wrote:

Hi folks,

What's the legal length for a rifle barrel, in this case HMR?

I am going to change my Sako .22lr barrel for a HMR barrel later this year. I want to get it shortened to something like 14" - 16" for handiness sake. Just wondering what's legal.

Regards,

John

You're going to lose a good deal of accuracy by doing this. The round will leave the barrel in a very unstable manner causing it to be heavily influence by wind and the likelihood of considerably widened groups.

20" has been found (in the case of .22") to be the shortest you can go without affecting accuracy.

freddieot

I've just checked the 2006 Act and it looks to me like less than 50cm for a rifle is not allowed. ( See Sec 65, 6, b).

Maybe I've picked it up wrong. However, I would say that just because the local cops are unaware that someone has a shorter barrel does not mean that they have authorised it in some way. I suspect it would be a hard job to convince a judge of that but it would depend on the judge and the general circumstances. The cops would argue that you should have asked for special permission and that you deliberately tried to decieve the State and all that s*i**.

since when has ignorance of the law really been a best defence.

If you really want a shorter barrel then explain why to your local sargeant.

freddie

thelurcher

rrpc wrote:

You're going to lose a good deal of accuracy by doing this. The round will leave the barrel in a very unstable manner causing it to be heavily influence by wind and the likelihood of considerably widened groups.

20" has been found (in the case of .22") to be the shortest you can go without affecting accuracy.

Do you have more info on this? I always hear different opinions on it 12" 16" etc.
For your last statement to be true it would mean that anything over 20" would NOT improve accuracy.

I'd like to see a study where they take say a 24" barrel and correctly shorten it 1" at a time firing groups at each increment.

Rovi

freddieot wrote:

I've just checked the 2006 Act and it looks to me like less than 50cm for a rifle is not allowed. ( See Sec 65, 6, b).

Maybe I've picked it up wrong.

Check my post #3 above.

CRIMINAL JUSTICE ACT 2006
Section 65-(6)(b)
"It is an offence for a person (except a registered firearms dealer) to possess without lawful authority or reasonable excuse—" "(b) a rifle the barrel of which is less than 50 centimetres in length"

I read that to mean that you can possess such a thing, provided you have "lawful authority or reasonable excuse".
What constitute "lawful authority or reasonable excuse" is another matter entirely.

Clare gunner

Which you do with your firearms cert. How many Rugers out there with 16.5 in barrels?It is up to the lawmakers to be clear on the law they propose to impliment.
The ten in shotgun barrel is a conomdrum here.It is illegal as a smoothbore,but if you were to get just a pistol grip on the gun with a rifled slug barrel,you could possibly register it as a large calibre pistol.Albeit a very inaccurate one.Dolphin arms did this awhile in the UK to sanction bust the big cal semi rifle ban.Before the pistol ban came in that is.

FLAG

Lads to put you all of your misery.

In the original form that the proposed legislation took we would have had a prohibition on barrel lengths shorter than 16.5" this was unintended.

We noted this during discussions and the very points made in the posts were brought to the attention of the legislators and the wording added to ensure that lawful possession of rifles with barrels shorter than 16.5" would not be an issue.

The original intent of the legislative change was to outlaw the unlawful shortening of rifle and shotgun barrels save by a RFD, posession of a factory or RFD modified rifle with a barrel lenght less than 16.5 inches as long as one has a firearms certificate or appropriate authorisation is within the law.

Vegeta

rrpc wrote:

You're going to lose a good deal of accuracy by doing this. The round will leave the barrel in a very unstable manner causing it to be heavily influence by wind and the likelihood of considerably widened groups.

20" has been found (in the case of .22") to be the shortest you can go without affecting accuracy.

Why does it become unstable??

Jonty

It goes unstable, because it is not in contact with rifling for long with a short barrel. The bullet needs to spin to be accurate. Its the rifling that causes the spinning.

Vegeta

Jonty wrote:

It goes unstable, because it is not in contact with rifling for long with a short barrel. The bullet needs to spin to be accurate. Its the rifling that causes the spinning.

Ok for a .22lr with a 1 in 16 twist and a 20 inch barrel the bullet gets rotated 450 degrees. Does that extra 90 degrees of rotation when compared to a 1 in 16, 16 inch barrel really make such a huge difference?

rrpc

Vegeta wrote:

Ok for a .22lr with a 1 in 16 twist and a 20 inch barrel the bullet gets rotated 450 degrees. Does that extra 90 degrees of rotation when compared to a 1 in 16, 16 inch barrel really make such a huge difference?

Yes it does. The bullet when it leaves the gun is not actually spinning in a straight line, the nose is rotating slightly around an axis from the centrepoint of the tail. This can vary from bullet to bullet and manufacturer to manufacturer. I have seen bullets strike a target at 25 yards sideways, i.e there is a long cut in the paper as opposed to a small hole.

It takes some time for the bullet to 'settle down' in flight. The longer it stays in the barrel the quicker it settles into stable flight on exit. While it is unstable it is much more affected by the wind and hence the overall accuracy is affected.

With the .22lr round the optimum performance is achieved within a 20" barrel. Some disagree and maintain that although this may be true for 50 metre shooting, a longer barrel is required for greater distances. This is a different argument however and other variables such as barrel 'flip' come into the equation.

Vegeta

rrpc wrote:

Yes it does. The bullet when it leaves the gun is not actually spinning in a straight line, the nose is rotating slightly around an axis from the centrepoint of the tail. This can vary from bullet to bullet and manufacturer to manufacturer. I have seen bullets strike a target at 25 yards sideways, i.e there is a long cut in the paper as opposed to a small hole.

It takes some time for the bullet to 'settle down' in flight. The longer it stays in the barrel the quicker it settles into stable flight on exit. While it is unstable it is much more affected by the wind and hence the overall accuracy is affected.

With the .22lr round the optimum performance is achieved within a 20" barrel. Some disagree and maintain that although this may be true for 50 metre shooting, a longer barrel is required for greater distances. This is a different argument however and other variables such as barrel 'flip' come into the equation.

so what are you saying effects yaw damping, barrel length or rate of twist?

rrpc

Vegeta wrote:

so what are you saying effects yaw damping, barrel length or rate of twist?

Barrel length.

Vegeta

rrpc wrote:

Barrel length.

hmmmm I must ponder on this as that is news to me.

Thanks for clearing that up, I was of the opinion that Yaw was caused by muzzle blast and barrel vibrations etc and the gyroscopic spin of the bullet (along with other things) damped out the yaw. Therefore I couldn't understand where the barrel length arguement was coming in. I am obviously mistaken and need to do more research

rrpc

While you are pondering, think about what is happening to the bullet when you fire it. The bullet is accelerating in the barrel while at the same time the rifling is appplying a spin to it. When the bullet leaves the barrel, it is still accelerating and is no longer confined to the restrictions to it's movement imposed by the barrel. The amount of twist will have different effects, but there is a limit to what can be achieved within a certain barrel length.

Somewhere in my archives I have a full article describing the various tests and effects on the flight of the bullet.

Vegeta

rrpc wrote:

While you are pondering, think about what is happening to the bullet when you fire it. The bullet is accelerating in the barrel while at the same time the rifling is appplying a spin to it. When the bullet leaves the barrel, it is still accelerating and is no longer confined to the restrictions to it's movement imposed by the barrel. The amount of twist will have different effects, but there is a limit to what can be achieved within a certain barrel length.

Somewhere in my archives I have a full article describing the various tests and effects on the flight of the bullet.

yes but an overly long barrel and the gas from the powder will have been expended and the bullet will be slowing in the barrel (due to friction of metal on metal) so I wonder for a .22lr at what length barrel does the bullet begin to slow.

Also I don't want to be pedantic but incase a someone else reads this, how can the bullet be accelerating after it has left the barrell. There is no longer any force driving it forward. Sure maybe for the first foot while still under the influence of gas at the muzzle but after that there is no force driving it forward. Surely 2 chronograhs would highlight this, one at the muzzle and one 20 feet away. Anyway that's a side topic.

Jonty

Vegeta wrote:

Ok for a .22lr with a 1 in 16 twist and a 20 inch barrel the bullet gets rotated 450 degrees. Does that extra 90 degrees of rotation when compared to a 1 in 16, 16 inch barrel really make such a huge difference?

Aren't we talking about a 17HMR with a 1 in 9 twist?

Vegeta

Jonty wrote:

Aren't we talking about a 17HMR with a 1 in 9 twist?

ok then a sako quad with a 22 inch barrel has a twist rate as you say of 1 in 9. That's 2.4444 revolutions.

Cut down to 16 inches it still has 1.777 revolutions

Jonty

Vegeta wrote:

ok then a sako quad with a 22 inch barrel has a twist rate as you say of 1 in 9. That's 2.4444 revolutions.

Cut down to 16 inches it still has 1.777 revolutions

which is a reduction of 27%.

.243

the .22 lr can be no less than 12.5 ins,this it the minimum length needed for the powder to burn,im not sure about the .17hmr but if you look at any of the recent shooting mags cz do a .17 hmr in a 16ins barrel, my last .17 was down to 16ins with no problems,

rrpc

I know Anschütz experimented with barrel length for their smallbore target rifles when they were developing the 2013 model (a marked departure from the previous models). They started with a 400mm barrel, but found that the best accuracy was achieved with a 500mm length. I was on a visit to their factory not long after this and I know they gave me a very detailed run through on the various tests and results they had got, but it being over ten years now I can only remember snippets.

The 500mm barrel only really caught on on the continent, many German shooters and some Americans used it, but the Brits always maintained vociferously that the 20" barrel (500mm) was not as accurate at 100 yards as the 690mm one and they never really took to it. To such an extent that Anschütz had to continue manufacturing the 690mm and in fact at this stage they seem to have dropped the 500mm barrel altogether.

ArthurJ

Vegeta wrote:

Also I don't want to be pedantic but incase a someone else reads this, how can the bullet be accelerating after it has left the barrell. There is no longer any force driving it forward. Sure maybe for the first foot while still under the influence of gas at the muzzle but after that there is no force driving it forward. Surely 2 chronograhs would highlight this, one at the muzzle and one 20 feet away. Anyway that's a side topic.

It’s a good point you raise and far from being picky. My understanding has always been the same as yours, so now I’m curious.

rrpc will you clarify this matter for us.

rrpc

ArthurJ wrote:

It’s a good point you raise and far from being picky. My understanding has always been the same as yours, so now I’m curious.

rrpc will you clarify this matter for us.

It is still accelerating because the gases are still behind it and driving it forward. I think there are photos illustrating this on one of the sticky threads. It's not for long, but long enough to have an effect on the bullets flight.

What Veg said earlier in his post about the bullet slowing in the barrel is not true. The rate of acceleration is dropping, but it still has an expanding gas cloud behind it. Rifle ammunition is slower burning than pistol ammo in order that the bullet continues to accelerate down the length of the barrel.

I'm not really sure what you want clarified, hope that helps answer your question.

Vegeta

well from my understanding barrel length only effects potential bullet velocity and not accuracy.

I still cant see how a longer barrel is more accurate (despite having a nose around yesterday). Shorter barrels are perfectly capable of making the bullet as stable as longer ones. So if a short barrel and a long barrel can both stabalize the bullet then what is it exactly about the longer barrel which makes it more accurate?

of course velocity helps accuracy, the faster it travels from barrel to target the less time wind and gravity can effect it, but velocity does not equal accuracy.

So what exactly is it about a longer barrel which makes it more accurate? (because its not twist rate and gyroscopic stability)

rrpc

Vegeta wrote:

well from my understanding barrel length only effects potential bullet velocity and not accuracy.

I still cant see how a longer barrel is more accurate (despite having a nose around yesterday). Shorter barrels are perfectly capable of making the bullet as stable as longer ones. So if a short barrel and a long barrel can both stabalize the bullet then what is it exactly about the longer barrel which makes it more accurate?

It's a matter of degree, they both stabilise, the longer one does it better. At least that's what the tests in Anschütz proved. The subsonic .22lr round reaches maximum velocity in about 15", but they found that a 16" barrel wasn't as accurate for 50m shooting as a 20". There are so many variables here. For example, the distance you are shooting will make a difference as well. The Brits maintained at the longer distances (which Anschütz weren't testing for) that the longer (69cm) barrel was better.

of course velocity helps accuracy, the faster it travels from barrel to target the less time wind and gravity can effect it, but velocity does not equal accuracy.

Wind has more effect on a high velocity round, which is one of the reasons why target shooters only use subsonic rounds.

So what exactly is it about a longer barrel which makes it more accurate? (because its not twist rate and gyroscopic stability)

It's a combination of many factors, stability is one of them, the rate of burn of the powder, the relative humidity, air temperature etc. Rifle rounds are designed with a particular barrel length in mind, so that there is a continuous burn until just before the bullet leaves the barrel. Pistol rounds on the other hand are designed to burn quicker.

The original question was about shortening the barrel of a .17 HMR. The arguments against such a course of action insist that loss of accuracy will result.

Vegeta

rrpc wrote:

It's a matter of degree, they both stabilise, the longer one does it better. At least that's what the tests in Anschütz proved. The subsonic .22lr round reaches maximum velocity in about 15", but they found that a 16" barrel wasn't as accurate for 50m shooting as a 20". There are so many variables here. For example, the distance you are shooting will make a difference as well. The Brits maintained at the longer distances (which Anschütz weren't testing for) that the longer (69cm) barrel was better.

I'll take your word for it on this

Wind has more effect on a high velocity round, which is one of the reasons why target shooters only use subsonic rounds.

I don't mean to come across arguementative but this is just plain incorrect. Yes target shooters use sub sonic ammo but the faster a bullet travels from A to B the less time wind can effect it and therefore cannot throw it off course as much.

It's a combination of many factors, stability is one of them, the rate of burn of the powder, the relative humidity, air temperature etc. Rifle rounds are designed with a particular barrel length in mind, so that there is a continuous burn until just before the bullet leaves the barrel. Pistol rounds on the other hand are designed to burn quicker.

Fair enough but barrel length doesn't have much to do with some of the above such as humidity, air temp etc.

The original question was about shortening the barrel of a .17 HMR. The arguments against such a course of action insist that loss of accuracy will result.

The only thing I can think of is that by chopping off a few inches from the barrel is that the expanding gas will be in greater volume at the muzzle increasing yaw angle and taking longer to damp out. Other than that none of the above explain it.

Vegeta

Jonty wrote:

which is a reduction of 27%.

yes in the number of revolutions, which has nothing to do with the rate of twist which governs static (gyroscopic) stability

rrpc

Vegeta wrote:

I don't mean to come across arguementative but this is just plain incorrect. Yes target shooters use sub sonic ammo but the faster a bullet travels from A to B the less time wind can effect it and therefore cannot throw it off course as much.

Not being argumentative either , but although it seems counter-intuitive the opposite is true. Wind doesn't actually 'blow' the round. What actually happens is that air pressure increases on the side of the round the wind is blowing from causing the bullet to veer towards the area of lower pressure on the opposite side. With a higher speed round, the veering effect is more pronounced due to lower pressure on the leeward side and the bullet is deflected more. This is more pronounced at the muzzle (where a small deviation has far greater effect on the point of impact than would be found were the deviation to occur closer to the target). The movement isn't left/right either, as the spin of the bullet changes the area of high pressure so that a wind from the right will cause the bullet to veer left and up and from the left, right and down.

The only thing I can think of is that by chopping off a few inches from the barrel is that the expanding gas will be in greater volume at the muzzle increasing yaw angle and taking longer to damp out. Other than that none of the above explain it.

That's what I said at the start. The longer barrel will help the bullet 'settle down' in flight quicker.

Vegeta

rrpc wrote:

Not being argumentative either , but although it seems counter-intuitive the opposite is true. Wind doesn't actually 'blow' the round. What actually happens is that air pressure increases on the side of the round the wind is blowing from causing the bullet to veer towards the area of lower pressure on the opposite side. With a higher speed round, the veering effect is more pronounced due to lower pressure on the leeward side and the bullet is deflected more. This is more pronounced at the muzzle (where a small deviation has far greater effect on the point of impact than would be found were the deviation to occur closer to the target). The movement isn't left/right either, as the spin of the bullet changes the area of high pressure so that a wind from the right will cause the bullet to veer left and up and from the left, right and down.

That's what I said at the start. The longer barrel will help the bullet 'settle down' in flight quicker.

The magnus force in't it

but in general for ammo above the speed of sound (the .17 HMR for example) what I have said is correct, the faster and heavier the bullet the better when it comes to wind.

but the .22lr sub sonic ammo is a special case because air turbulance and pressure changes occur above the speed of sound. 22lr match ammo is specifically designed not to go into the upper transition range of the speed of sound as drag increases disproportionately with velocity in this velocity range

So if I was John Galway I would have no problem cutting the barrel of the .17HMR when I had researched how efficiently standard ammo would burn powder in the new length and that the re-crown is a top notch job so it doesn't add to the initial yaw angle.

rrpc

Vegeta wrote:

The magnus force in't it

but in general for ammo above the speed of sound (the .17 HMR for example) what I have said is correct, the faster and heavier the bullet the better when it comes to wind.

There's one thing that I didn't make clear in my previous post. When wind exerts force on a bullet, it doesn't shift the bullet sideways but changes its direction. This is why the wind deviation at the muzzle is much more detrimental to the point of impact than a wind deviation closer to the target.

It's a bit like the change you make to your windage adjustment screw on your sights. If one click is 1/6 moa that's an angular change from muzzle to target hence the difference at the target will be much greater the farther the target is from the muzzle. One click on my sights is .5mm at 25 yards, 1mm at 50 metres and 2mm at 100 yards. The wind will have the same effect. If you are shooting at 100 yards and a 1/6 MOA gust of wind pushes the bullet at the muzzle the round will strike the target approx 6mm off. If it hits the bullet 25 yards from the target the impact will only be perhaps 1.5mm off.

And you're right about the weight of the bullet, A heavier bullet will defeat the wind far better than a faster bullet. That's a bit simplistic obviously as there's a weight/velocity balance. The shape of the bullet also makes a difference with the FMJ type being better in the wind than a soft point.

With .22lr, a 40gr target round with a muzzle velocity of 325m/s has 30% less wind drift than a 40gr 390m/s round at 100m. The only difference is the speed of the round.

It's harder to compare centrefire rounds because of the many different calibres and weights, but taking two 55gr rounds; a 222 Rem (880m/s) and a 6.5x55 (780m/s) the slower round shows 26% less wind drift at 300m than the faster one.

Vegeta

rrpc wrote:

With .22lr, a 40gr target round with a muzzle velocity of 325m/s has 30% less wind drift than a 40gr 390m/s round at 100m. The only difference is the speed of the round.

but under normal atmospheric conditions the speed of sound is 344m/s so that comparison is not valid

It's harder to compare centrefire rounds because of the many different calibres and weights, but taking two 55gr rounds; a 222 Rem (880m/s) and a 6.5x55 (780m/s) the slower round shows 26% less wind drift at 300m than the faster one.

Ok well there'd be the problem of the BC's not being equal. Do both rifles have the same twist rate? Wouldn't a 6.5x55 rifle usually have a slower twist rate than a .222

Its not that I don't believe you rrpc (and i am enjoying the education I am getting) but having re-read the chapter on wind deflection in my ballistics book it definitely says that everything else equal (a statement not to be taken lightly) that for ammo in the super sonic range a faster bullet is effected by wind less. It does mention the .22lr sub sonic ammo as a special case which I have tried to explain above.

bullets

Vegeta wrote:

Its not that I don't believe you rrpc (and i am enjoying the education I am getting) but having re-read the chapter on wind deflection in my ballistics book it definitely says that everything else equal (a statement not to be taken lightly)

Damn interesting thread. I really got to start reading that ballistics book
myself I only got to the first chapter in it and never got the time to
continue reading it.

My HMR has a 20.9 inch barrel. I have been using 17grains all along
but yesterday switched to 20grain after re-zeroing the difference was
noticeable. All day long was firing 5 Round groups that were about
10-13mm at 50m. Which was better than I was shooting before.
(If I could get that at 100m consistently I would be content)

CZ 452 American BBl has 16" barrel and the scout version is a
little over 16". Only appear to chamber it is .22LR though
have not seen a rimmy for a .17hmr with a very short barrel


~B

rrpc

Vegeta wrote:

but under normal atmospheric conditions the speed of sound is 344m/s so that comparison is not valid

Why is it not valid? The supersonic round is more susceptible to wind drift than the subsonic one, both the same weight. I'd accept there being a difference across the sound barrier, but 30% is a compelling figure.

there'd be the problem of the BC's not being equal. Do both rifles have the same twist rate? Wouldn't a 6.5x55 rifle usually have a slower twist rate than a .222

OK I've found some figures I had for the .308 Rem. Again it's very difficult because of different bullet weights and formats, but this is the closest I could find. 150gr, 150m/s Vs 165Gr, 165m/s The difference between the two is 15% less wind drift for the slower round, which can't be accounted for totally by weight as the weight difference is only 9%.

Its not that I don't believe you rrpc (and i am enjoying the education I am getting) but having re-read the chapter on wind deflection in my ballistics book it definitely says that everything else equal (a statement not to be taken lightly) that for ammo in the super sonic range a faster bullet is effected by wind less. It does mention the .22lr sub sonic ammo as a special case which I have tried to explain above.

And what i'm trying to say is it's not as simple as that. In fact, I can't find any ballistics figure that show a faster bulllet being less susceptible to wind than a slower one. I can find the opposite, but in most cases the rounds are different weights. I've even found that faster lighter rounds show more wind dirft than slower heavier ones, especially at longer distances.

Incidntally, the figures I gave in my previous post were from a 600mm barrel (.222) against a 740mm barrel (6.5x55). So the longer barrel with the heavier/slower round gave the best wind drift figures.