fps to ft lb

[clarkey0423]

I have seen a rifle which states 600 to 650fps. Ive looked at calculators to convert into ft lb and it works out around 6ftlb. My question is does pellet weight/grain have an effect? I need a rifle which is not over 6ft lb. Any suggestions? Smk qb78 target looks ok and suitable. Anyone have this gun?

[KeithW]

In short, yes. Download the free Hawke Chairgun, and it will calculate what Ft/lbs for any given weight / calibre / fps. Also, there are other free apps you can download to your smartphone.

[clarkey0423]

I have used the apps and found conversions online but reading forums the ft lb varies from 6 to 8.5 or of the box. So I guess I need some one who had got a qb78 target. Also read cant fit front sight on this rifle to go with diopter...

[Turnup]

Yes - 'ish

Energy is proportional to mass (of the projectile) and the velocity squared. I'm sure you can google this and find the appropriate formula.

In airguns, the energy is broadly limited by the energy stored in the spring (for springers) or in the air or C02 reservoir (for PCPs or C02 guns).

For a given gun, a heavier pellet will go slower than a light one, so as the "M" part of the equation increases, but the (v squared) part decreases, more or less in exact proportion.

However the efficiency of energy transfer (from wherever it is stored) to the pellet will change with pellet weight.

Thus it is possible that an airgun producing 6 ft-lb with pellet x might produce more or less with a pellet of different weight.

Commercial air pistols are unlikely to exceed 6 ft-lb with any commercially available pellet (ditto for 12ft-lb air rifles), but meddling with them can take the power over the respective limit, so sensible persons who engage in airgun tuning take care to measure the resulting velocity, and by calculation the resulting energy, in order to keep on the right side of the law.

Does this help?

[clarkey0423]

Ive seen the formulas yes. Im nt looking to exceed legal limit. But for competition bell target I need 6ftlb no more. So 8ftlb out of box although uk legal is over power for bell target

[p.m.h]

Many manufacturers post fps readings on their boxes, but this is meaningless without the weight of the projectile.

If this rifle is available at your local shop, and he has chrono facilities, ask you can put a few shots over the chrono with your choice of pellet to see what results you get.

Kind regards,



Phil

[clarkey0423]

Good idea. Ill see if any local dealers have in stock

[thimblehouse]

Ive seen the formulas yes. Im nt looking to exceed legal limit. But for competition bell target I need 6ftlb no more. So 8ftlb out of box although uk legal is over power for bell target

Most club restrict the power for Bell Target for safety reasons due to bounce back. Most restrict to 7ftlb some less. There is one with more but they use a different plate.