Setting the power on a new PCP

[Trajectory]

Hi all. I am picking up a new non-FAC PCP in the next few weeks. I don't have a chrono of my own so the power will be set by the dealer. I understand that the power can change slightly as the parts 'bed in' over the first few thousand shots. So my question is this: what is the maximum power you would have it set at to be safe in the knowledge that it won't go above 12 ft/Ibs before you next have a chance to use a chrono a few thousand pellets later? Needless to say, I want the pellets to fly as flat as possible but I don't want to visit one of Her Majesty's prisons, either! Thanks all

 

[Guest]

I didnt think it was legal to make any changes to the regulator unless you are a certified gunsmith.

[Trajectory]

Hi DC177 - the distributor is a certified gunsmith. I wouldn't want to touch the regulator settings myself

[manthing]

Last time I bought an air weapon the dealer fired a few shots threw it, then chrono'd it and that reading went onto the sales ticket.

I would think around 11ftlbs to start with, but that all depends on the pellets of course.

[Guest]

11.5 ftlbs is normal.

[washerboy]

10.5 -11, wouldn't need any more

[bruno22rf]

The dealer does not set the power level, that's down to the manufacturer, however, the dealer would be wise to check the power level before handing you your new gun. Long term you can pick up a chrono for about £40.

[Ultrastu]

Really .really depemds on the pellet you want to set it with .

Of its a .22 pcp .then id set it with jsb jumbo at 16 grns or the heavies at 18 grn

For .177 id set it with bismags 10.4 grn or jsb heavies 10.3

And id set the energy at 11.4 fpe with these pellets at the guns peak energy in the shot string and no more .

[Mice!]

Just don't forget different weights give different energy. I know most already know this but if you set the power at say 11.8 with your pellet at say 14grn but then go to a lighter weight pellet it could easily push past the 12 limit.

 

A chrono is well worth the money.

 

Edit, hope that's the right way round and I don't mean a heavier pellet?

Edited June 7, 2017 by Mice!

[Guest]

Just don't forget different weights give different energy. I know most already know this but if you set the power at say 11.8 with your pellet at say 14grn but then go to a lighter weight pellet it could easily push past the 12 limit.

 

A chrono is well worth the money.

 

Edit, hope that's the right way round and I don't mean a heavier pellet?

We have discussed already! The energy remains fixed, the muzzle velocity changes. The power rating does not alter....

[Newbie to this]

We have discussed already! The energy remains fixed, the muzzle velocity changes. The power rating does not alter....

That's not right, the power rating would change

http://www.geoffwilsons.co.uk/ft-lb-calculator/4589590652

http://www.pyramydair.com/article/What_is_Muzzle_Energy_August_2003/5

Edited June 7, 2017 by Newbie to this

[Trajectory]

Thank you all for your comments. OK - the safest bet would be to ensure it's set a few notches above 11 ft/Ibs until I can recover from the rifle/scope cost and buy a chrono! Better to lose a few fractions of a ft/Ib than repent at leisure

[Ultrastu]

Is it worth running a pellet very close to the 12 fpe limit ?,

Lets looks at why its not .

Take a gun set at 11 fpe and one at 12 fpe exactly a 1 fpe difference at the muzzle

Now let presume your gun has lost about 50 % of its energy by about 50 yds (thats about right depending on on bc ) so 50 % of 12 fpe is 6 fpe and 50 % of 11 fpe is 5.5 fpe .so now at range you only have a 0.5 fpe advantage

But actually the faster you drive a pellet the more energy it loses ober a slower one so really the 12 fpe pellet will be more likely to loose 55 % of its energy over the same range so at 50 yds insted of holdingv6 fpe it could be lower around 5.85 fpe so now you only have a 0.35 fpe advantage at 50 yds .worth it ? .

How about starting with a 11 fpe verses a 11.5 fpe setting

The difference at 50 yds could be as low as 0.19 of fpe .

This is why for such very very very small advantage in energy or trajectory its not worth goingvto jail for .

Personally most my sub 12 guns run around 11 fpe .

Some are 10.7 others 11 .3 .i cant shoot the difference

[Trajectory]

Ultrastu - That is very informative and well reasoned - thank you. I'll check it's a few notches above 11 ft/Ibs and leave it at that I think! Quite right - for such a small power advantage it's not worth the risk.

[Ultrastu]

This is a graph of the same pellet at 10.5 ,11 ,11.5 , 12 fpe settings .and the retained energy

[Mice!]

DC sorry your wrong vel * weight gives power, so different weights at different speeds will give different power.

 

Stu very informative I might knock the power down a touch after reading that 👍

[Ultrastu]

As the graph shows the difference in trajectory at 50 yds with the same 35 yd zero between a 12 fpe gun and a 10.5 fpe gun is about 10 mm and the difference at the 25 yd apogee is only about 4 mm .so less than a pellet width .

Basically if your gun shoots sweeter or you get more shots at 10.5 fpe .instead of say 11.7 .

Then you practically give nothing away in terms of performance .

Even wind drift difference is miniscule

[Mice!]

Chances are I would twitch it 4mm anyway 😆

[Guest]

DC sorry your wrong vel * weight gives power, so different weights at different speeds will give different power.

 

No. I was not referring to power at impact down range. That will obviously reduce with distance. The original comment was around getting into trouble because by using a lighter pellet you could take the rifle over the legal limit. The power setting is what it is and using a lighter pellet wont make the gun illegal. If that could happen, they would have to put a legal warning on the tin.

[Newbie to this]

No. I was not referring to power at impact down range. That will obviously reduce with distance. The original comment was around getting into trouble because by using a lighter pellet you could take the rifle over the legal limit. The power setting is what it is and using a lighter pellet wont make the gun illegal. If that could happen, they would have to put a legal warning on the tin.

That's not right, the power rating would changehttp://www.geoffwilsons.co.uk/ft-lb-calculator/4589590652http://www.pyramydair.com/article/What_is_Muzzle_Energy_August_2003/5

You are wrong the equation for working out foot pound energy is

 

Pellet weight(in grains) × velocity(ft/sec) × velocity(in ft/sec) ÷ 450240 = Energy (in ft lb), so quite clealy pellet weight affects Energy. I would have your rifles checked if I was you.

Edited June 8, 2017 by Newbie to this

[Gonk]

Who would have to put a legal warning on the tin?

[Rewulf]

No. I was not referring to power at impact down range. That will obviously reduce with distance. The original comment was around getting into trouble because by using a lighter pellet you could take the rifle over the legal limit. The power setting is what it is and using a lighter pellet wont make the gun illegal. If that could happen, they would have to put a legal warning on the tin.

 

To clarify , a heavier pellet gives a higher MUZZLE energy (power)

If the rifle is tested by the police ,they will use a heavy pellet ,and chrono at the muzzle, downrange power or speed is irrelevant.

[Hendrix's rifle]

No. I was not referring to power at impact down range. That will obviously reduce with distance. The original comment was around getting into trouble because by using a lighter pellet you could take the rifle over the legal limit. The power setting is what it is and using a lighter pellet wont make the gun illegal. If that could happen, they would have to put a legal warning on the tin.

If I had 2 pellets, both set at say 550fps, 1 is a 12g and the other is an 18g for example the 18g pellet will have a have more foot pounds. To get them the same, I would have to drop the velocity of the 18g pellet so it delivers less energy and speed

[Mice!]

This was why I said that different pellets give different power.

 

I hope enough people have said this for you now DC, when I use my chrono it asks me to put in the pellet weight because it matters, so if the guy in the shop uses a cheap light pellet and says there you go its running at 11.9 then you go home and start using bisley Mags you could easily go over.

[Mice!]

Info sheet from my chrono