7mm at 300

[bsouthernau]

Thanks Richard. I half understand this gyroscopic stuff but solid body dynamics was never my forte and it's now 45 years since I studied it! My understanding was that it referred to the axis of the bullet relative to the trajectory of the centre of mass and that those corkscrew diagrams I've seen are the locus of the point as the bullet settles down to its angle of repose. If that was so the holes would be bigger as the bullet is going through partly side-on but still located in the same place.

Am I wrong in this and it's actually the centre of mass describing this convoluted helical path?

Barry

[RAVEN]

Barry what I also look for when load tuning is the carbon mark around the bullet hole through the paper (that why I use white or yellow) it need to be even for all shots.
There is a very interesting video on the web somewhere about it sorry I don’t have the link

If that was so the holes would be bigger as the bullet is going through partly side-on but still located in the same place

Exactly

[BATattack]

I think short range accuracy and long range accuracy are two different things and I'll try to explain my reasoning.

You can tune an extremely accurate load at short range without much regard to ES. This load is BARREL tuned. Ie the bullet leaves the barrel at the top or bottom of the barrels cycle (so the barrel is pointing in the exact same direction every time) lessening the effect of speed variations on the bullets impact.

This can also be done as Alan suggested for longer ranges but may require a BARREL tuned load for every distance.

The second method is to tune the LOAD to make a bullet leave the barrel at nearly the exact same speed ever time. Low ES. By doing this you may not be on a barrel vibration node and this will cause your short range accuracy to suffer slightly but because all bullets are leaving the barrel at a very similar speed they have they travel the same arc to the target and impact at the same elevation.

This is my theory on it. It might be bullshit and I have no way of proving it other than my own results.

[DaveMc]

By the way Richard - did you read Bryans response further down the page???

[AlanF]

I think short range accuracy and long range accuracy are two different things and I'll try to explain my reasoning.

You can tune an extremely accurate load at short range without much regard to ES. This load is BARREL tuned. Ie the bullet leaves the barrel at the top or bottom of the barrels cycle (so the barrel is pointing in the exact same direction every time) lessening the effect of speed variations on the bullets impact.

This can also be done as Alan suggested for longer ranges but may require a BARREL tuned load for every distance.

The second method is to tune the LOAD to make a bullet leave the barrel at nearly the exact same speed ever time. Low ES. By doing this you may not be on a barrel vibration node and this will cause your short range accuracy to suffer slightly but because all bullets are leaving the barrel at a very similar speed they have they travel the same arc to the target and impact at the same elevation.

This is my theory on it. It might be bullshit and I have no way of proving it other than my own results.

No its not bullshit Adam. At long range in particular, velocity variation is the main enemy. And its very rare to find a barrel/bullet tune that will compensate fully at 1000 yards.

[DaveMc]

We did a lot of work on this and you need compensation of 1 minute drop for every 40 fps increase. Short barrel block barrels can probably move this fast but generally with small amplitude (<1 minute total variation) so getting outside this zone means then negative compensation and velocity spread adding to the issue not helping.

To see this work at 1000 a ladder at 100 would really have to be dropping by 2 minutes over 80 fps (or in a short range 1 minute over 40 fps but with extreme care in loading and change of weather etc). If anyone has seen this or can demonstrate it I would love to see the results and the rifle design.

[RAVEN]

By the way Richard - did you read Bryans response further down the page???

Just did


Dave have you ever noticed that a tuned load will print the carbon evenly and a load that isn't will be somewhat lopsided

[AlanF]

Dave,

Did you do any testing with match rifle type barrels i.e. 34" thin profile? I know these have other drawbacks e.g. heating effects, but would have thought they'd have more amplitude in the vibrations?

Alan

[DaveMc]

Alan, not enough data (and only 32 inch palma)

So far I have seen very little evidence of 1000 yard compensation but I have heard of plenty of anecdotal stories - Would love to see it actually happening in the flesh.

Richard, To be quite honest I haven't looked that closely but think I would have noticed if it was severe enough. Even in the 25m testing it is not overly obvious. One thing I do use is thermal printer paper for my load testing so this might leave a black (heat) ring in any direction. I find this paper easier to spot the shots at 3 and 500 yards.

[bsouthernau]

I've come to the conclusion that this is all too hard for this style of communication - requires face to face communication with a pencil and paper and a supply of strong drink. However a couple more questions before I go and pack for a holiday in SA.

If that was so the holes would be bigger as the bullet is going through partly side-on but still located in the same place

Exactly

From that reply I'm thinking that perhaps I DO understand the physics after all but don't know how to measure groups! I'm not equating the size of the hole with the size of the group. I know this started off as a 7mm thread but if we imagine a long succession of my beloved 210 SMKs going through exactly the same spot (obviously it's not me shooting) then if they're going through end on the hole is .308" across and if they're going through sideways it's 1.4" across. In both cases I'm thinking the group size is the same - zero. Am I barking up the wrong tree?

[quote=BATattack]The second method is to tune the LOAD to make a bullet leave the barrel at nearly the exact same speed ever time. Low ES. By doing this you may not be on a barrel vibration node and this will cause your short range accuracy to suffer slightly but because all bullets are leaving the barrel at a very similar speed they have they travel the same arc to the target and impact at the same elevation.[/quote]

Wouldn't you then go on and twiddle the knob on the end - if fitted of course - so you had both?

Barry

[RAVEN]

Dave I have only experienced it once with my old Rem Sendaro 7mm Rem Mag.
There is a video on the net somewhere on a renowned SR Benchrester give a talk on SR load tuning At the time I thought it was very relevant on what we try to achieve
If I find it I will sent it to you

BTW I didn’t read the comments on the visual I showed Barry because the right side of my brain is way stronger than my left

[bruce moulds]

getting back to chopper's question re results.
one result is that the only gun I have ever seen hit 10/10 eggs at 300m was a 6.5, shot off a bench with a bipod.
7mm and 6br/6x47l were not far behind.
6ppc benchguns shot by guys who knew the range were not in the race.
that 6.5 took home a lot of money from eggshoots for some years in a row.
the 6.5 splattered eggs with far greater emphasis than the 7mm, but a 6mm Ackley rem with a 30" barrel and 75 gn bullets just made them disappear.
that was a 6.5/284, and the super lr seems to be more accurate so far.
interestingly the br guys who ran the egg shoots stopped doing them after the fclass guys kept taking their money, even with our long bullets and fast twists causing excessive precessation and nutation.
keep safe,
bruce.

[BATattack]

I've come to the conclusion that this is all too hard for this style of communication - requires face to face communication with a pencil and paper and a supply of strong drink. However a couple more questions before I go and pack for a holiday in SA.

If that was so the holes would be bigger as the bullet is going through partly side-on but still located in the same place

Exactly

From that reply I'm thinking that perhaps I DO understand the physics after all but don't know how to measure groups! I'm not equating the size of the hole with the size of the group. I know this started off as a 7mm thread but if we imagine a long succession of my beloved 210 SMKs going through exactly the same spot (obviously it's not me shooting) then if they're going through end on the hole is .308" across and if they're going through sideways it's 1.4" across. In both cases I'm thinking the group size is the same - zero. Am I barking up the wrong tree?

[quote=BATattack]The second method is to tune the LOAD to make a bullet leave the barrel at nearly the exact same speed ever time. Low ES. By doing this you may not be on a barrel vibration node and this will cause your short range accuracy to suffer slightly but because all bullets are leaving the barrel at a very similar speed they have they travel the same arc to the target and impact at the same elevation.

Wouldn't you then go on and twiddle the knob on the end - if fitted of course - so you had both?

Barry[/quote]

Exactly mate! Either try and find a load that allows the barrel and load tuning to overlap or tune the load and then the barrel tuner.

[bsouthernau]

Exactly mate! Either try and find a load that allows the barrel and load tuning to overlap or tune the load and then the barrel tuner.

Hooray! I've got something right today.

[Chopper]

UM ,any one shot a screamer score with the seven at 300 Chop