Pressure sweet spot

[daylite]

I've got a 0.177 Theoben MFR, currently doing around 24ft/lbs for the purposes of legally practicing 'Practical Long Range Shooting' in my own back yard (18 acres). We don't need a license over here for air rifles below 0.25 no matter their energy rating.

I've recently been thinking of upgrading it to a .20 (flatter trajectory, less affected by wind, etc) and hoping to keep muzzle velocity to over 1000fps, but below the speed of sound so as not to affect pellet flight stability.

However the more I read, the more I'm not sure about really needing that high a velocity.

Objective: Hit 1" targets at 10m through to 3" targets at 100m+ . 1 round per target, and a hit is a point scored. (60 targets, highest score wins)

So the variables that I could play with are:
1. Pellet (weight and BC)
2. Barrel length & twist
3. Pressure (amount and consistency)

1. Pellets: (not a lot to choose from in .20)
Crosman Premier .20, 14.310 grain, 0.0260 BC
H&N Barracuda .20, 13,27 grain, 0,027 BC
...and they're fairly similar

2. The 19" barrel seems to be a good option, but I'm just not sure on twist for long range.

3. I would prefer to keep a regulated system in place for consistency between shots. However; In order for me to achieve a velocity of around 1050 fps, I would need around 37ft/lbs of pressure, which to me seems excessive, and secondly I'm not sure I'll get a regulator to handle that pressure (if so where?). I can also only think that the pellet skirt would get significantly deformed in the barrel at this pressure, and that would probably increase the chance of tumbling rounds which would in turn reduce the accuracy of the rifle, let alone adding reams of lead down the barrel after each shot, resulting in cleaning, priming, etc (round in circles)... and ultimately reducing barrel lifespan.

This got me to thinking... there must be a sweet spot balance between pressure, accuracy, barrel length and twist...

So based on the above objectives, any comments, solutions, etc ?

[air-tech]

If you can run the power, go .22.

You need to stay below 950fps for best accuracy, calibre irrelevant, otherwise you enter the transsonic range and you have problems.

So if you can get your gun to give you ~925 fps with a heavy .22 then there is no reason to go with .20 and plenty of reasons not to.

Your 3) - sorry, but little of that is correct, probably nothing at all...

[daylite]

Thanks AT

Point 3. That'll teach me reading dodgy airgun forums...

Ok the transonic advice makes sense.
So after doing a bit more reading, it seems the fuzzy transonic zone at around 20 degrees celcius at sea level is between 900 FPS and 1,470 FPS, with the speed of sound around 1,130 FPS.

So we cap the velocity factor at 920fps (just bleeding into the zone) and work backwards...

I emailed H&N a while ago about weights and BC values, and they very kindly sent me the information on their whole range. (really nice chaps)
The Baracuda is the only round produced in all 4 calibers, which seemed like a nice range for a comparison (probably misguided).

Pellet.......Cal...Wt....BC
H&N Baracuda 0.177 10,65 0,021
H&N Baracuda 0.200 13,27 0,027
H&N Baracuda 0.220 21,14 0,033
H&N Baracuda 0.250 31,02 0,045

With 920fps as constant across the range, and as each pellet has a set weight (or extremely close to) and BC value we can work out the rest.

Pellet.......Cal...Wt....BC....ft/lbs required
H&N Baracuda 0.177 10,65 0,021 20
H&N Baracuda 0.200 13,27 0,027 25
H&N Baracuda 0.220 21,14 0,033 40
H&N Baracuda 0.250 31,02 0,045 58

Obviously with the higher weight the bigger pellets have more energy and less drop, so logically create a flatter trajectory with the same muzzle velocity; so I should therefore choose the heaviest legal caliber possible.

Now 2 questions come to mind...
1. What's the highest rated regulator for a MFR ? (and where to get one)
2. If any thing over 925fps is effected by sonic turbulence, how come so many shooters are pushing their air rifles over 1000fps ?

[air-tech]

Now 2 questions come to mind...
1. What's the highest rated regulator for a MFR ? (and where to get one)
2. If any thing over 925fps is effected by sonic turbulence, how come so many shooters are pushing their air rifles over 1000fps ?

1) This gun already has a regulator? I'd be VERY surprised if it were not adjustable to whatever output you desire. BUT - I read that your gun is already a "full power" one, so that may not even be necessary? I suppose you know that a barrel change (an up-calibre) will increase the ft/lbs dramatically? It is likely that you will get to the standard figures for a full power .22 simply by changing the barrel, and possibly more considering that a .177 is less efficient (requires more pressure/air) so the gun may have been adjusted to beyond a standard adjustment for a full power .22. Latter hypothetical of course.

While you are at the barrel change, go for the longest possible, 23" generally. This will give you more fps.

2) You did not expect everyone to have the same priorities or sense did you