Hi.
In the past I have used a Miroku Trap fitted with Teague chokes at ½ and 5/8.
On the teague info I have it has.
½ = 0.020 constriction
5/8 = 0.025 constriction.
Sadly the gun is not available to me anymore so I am now using a Browning Pro trap. This gun had a huge range of invectors...