OzFclass

I have a query that I'd like people's opinion on.
It comes from a discussion some of us were having recently.
All of us are using the "standard" Berger 155.5 gr projectile - some shooting TR and others F Standard

Question
What is the minimum speed at the start to ensure the 155.5 Berger projectile will reach 1000yds comfortably above the speed of sound?
By "comfortably" I mean at least 100 fps above the speed of sound.

Now I realize that some of you will say the its depends on the conditions. Barometric Pressure, temperature, altitude, wind direction, wind speed, etc., and all other sorts of mitigating factors and that every range around Australia will be different.

What I'm looking for is starting speed that will ensure comfortably exceeding the speed of sound under all of these conditions, so that one can travel around Australia competing at various meeting and not have to worry about the "1000 yard" factor.

One of the reasons the discussion arose is that I have a barrel that groups best at about 2950 fps. It won't group at all in the 2990-3010 fps range. The first comment a couple of others made was that it won't reach 1000yds when starting off at the 2950 speed.

Over to others who are more expert. I hope I get some comments and opinions.

Cheers
Bob Pedersen

The calculations below were made in StrelokPro, using Berger 155VLD at a muzzle velocity of 2950 fps. 11 twist, 30” barrel @ 15 deg C.
As for “under all conditions”, I don’t know.

EDIT: at sea level.

PeteFox wrote:The calculations below were made in StrelokPro, using Berger 155VLD at a muzzle velocity of 2950 fps. 11 twist, 30” barrel @ 15 deg C.
As for “under all conditions”, I don’t know.


FC049EDD-B7B9-4662-A602-50B9BDA9D151.jpeg

If this calculation is for sea level it would then be a "worst case scenario" and would suffice for all likely conditions in Australia.
Keith H.

bob,
ideally look for mach 1.1 min under all conditions.
below this things can start to happen unless the bullet is extremely stable from mach 1.1 down to mach 0.9 - the transonic zone.
some bullets are better this way than others.
bruce.

While this does not answer your question, it may be very pertinent.

'comfortably exceeding the speed of sound' is hard to pin down. Some bullets designs are less compromised than others and not always is the highest BC bullet necessarily the best choice. Of course you may have little choice.

As a basis for some simple criteria, I would suggest basing your figures on Sea Level performance and decide on a cool morning air temperature. For years I shot a 22 in TR but much of that was at higher altitude on the Atherton Tableland which is significant.

BUT is 100 f/s margin adequate ? An even bigger problem is now emerging. Open Frame e-targets give very suspect results with bullets down around the speed of sound. Some seem to think that this is a sudden change in target performance but our tests used enough different cartridges to indicate that this becomes a significant factor at well over the '100 f/s' margin suggested. If you want an even playing field, you need much more than the suggested 100 f/s margin if you are shooting on Open Frame eTargets.

Peter Smith.

I have put 40 and 45 cal bullets through hexta targets at 700 fps striking vel and got readings.
like 2ranges on club shoots and no failures.
not sure how 30 and 22 cal bullets at these speeds would read.
this is certainly a consideration for those considering purchase of e.t.
bruce.

Hi Bob , for what’s its worth . It’s been a long time since F Standard days . However I found 2950 very marginal at 1000 yds . Above 3000 FPS I would feel a lot more comfortable.

I know with one of my rifles I can only get 2930 FPS with 155.5 , 12 twist , and it’s shoots great up 800 yds then starts falling away . My other barrel gets another 60 FPS and the difference is night and day .
Regards Graham.