I realise this is not what you're asking for but have you considered using a quick release clamp. Kirk do a 1inch one that fits perfectly on the end of a BR strap and slips straight onto your camera plate.
Hi Rob,
I use a BR FR-T1 fastener with a 3 Legged Thing Arca Swiss plate, it works well, no troubles fitting the plate to the head and it doesn't work loose.
I have only used the plate with a 3LT head, so I would give 3LT a call to check compatibility with your head.
Apparently they designed it to be compatible with the BR TR1.
http://www.3leggedthing.com/tripod-parts-accessories/ah1release.html
Chris
I use a Kirk 1 inch clamp on my black rapids, nice and secure as they screw tight onto Arca plates and L brackets.
markmullen said:Yes, standard connector onto the clamp, which then clamps up on the Arca plate, or in my case L Brackets.
It works really well. I religiously check everything is tight before use and have never had to tighten it up. If you were concerned you could Loctite the screw fastener.
its not the br connector im worried about coming loose, more the kirk clamp knob loosing and the swiss arca plate parting from the clamp. does this pose you a problem?
It hasn't yet, and I use a DR1 with a heavy body / lens / flash combo on each side.
Last week I was in Croatia and Bosnia and used the setup all week without issue.
The Kirk clamps are really good quality and not loose enough to undo themselves.
That's type of thing I'm looking for. I'm think (if possible) something like 100mm to be long enough to balance my 300 f4 and tc better and also be future-proof if I decide to move onto a 300mm f2.8.
its not the br connector im worried about coming loose, more the kirk clamp knob loosing and the swiss arca plate parting from the clamp. does this pose you a problem?
Most Arca Swiss plates have lock-stops at each end, so they can't slide out even if the clamp is loosened. It looks like yours doesn't, but see the underside of this plate as an example. The little studs slide into the recess of the clamp you have.
You're not the first person to have come across this issue with BR straps. If you google around, in addition to the good suggestions here (and on the BR site) you'll find loads of other solutions, both DIY and custom made.
FWIW, my own DIY method is similar to the Luma Membrane, here http://www.luma-labs.com/cinch
I wouldn't want a 300 2.8 on a black rapid. I just wouldn't trust it. I have a Kirk replacement foot on mine, £80 but much better than the stock foot.
For the 300 f4 I'd be fine with the setup suggested below using a good 1" clamp.