Speargun shaft diameter selection

As a rule for south Florida spearfishing I use 7mm shafts. I find 6.5mm shafts to be faster but they also lose momentum quickly over a short distance, resulting in not enough penetration on bigger fish. Using 7.5mm and 8mm shafts the speargun feels a little heavy, and they're harder for me to straighten if bent. But there's a right time and place for all shaft diameters. I want to share some loosely relevant experiences that may educate and influence someone's choice of shaft diameter.

I was using a 7mm 170cm Rob Allen carbon steel shaft with a 120cm Speardiver Phantom carbon speargun last weekend diving out of Pompano beach. Diving in about 45ft, clear visibility and a stiff current. I couldn't equalize on this day resulting in poor performance on my part, I couldn't even reach bottom. Saw a nice jack on the bottom from the surface. Tried to push through the pain to get to him but ended up more than 10ft away above, still took the shot, missed, and the shaft was stuck in the reef. Returning to the surface I was instantly swept away by the current with little hope of getting back on top of the shaft, much less being able to breath up sufficiently to get to the bottom and extract it.

My only hope to not lose the speargun was attracting the attention of the boat driver which fortunately I was able to do. In the meanwhile hanging on to the float, which was connected to the gun with a float line, I put significant pressure on the shaft, current was approximately perpendicular to the line of the shot. Boat picked me up, I sat on the transom holding on to my float and directed the driver to move the boat in the direction of my best estimate to end up behind the line of the shot, hoping the shaft will pull out. This would be the best case scenario, next best would be to cut the shooting line and leave the shaft on the bottom, but I was doubtful I could reach it in my condition. Anyways the float line tightened and I was hoping my crimps will hold. After a tense moment there was a pop and a release. I quickly reeled in the float line. The first relief came when I saw the white handle of the gun coming into vie, next a happy moment when I saw the mono shooting line was weighed down. When the shaft came into view I did not see a flopper. When I got it in my hands I realized the point has broken off at the flopper pin hole. I was amazed the 300lb mono did not break or slip through the crimps, it ended up stretched and a little loose over the line release but was perfectly usable. I think this is a testament to the quality of Speardiver monofilament shooting line.

Dennis from Puerto Rico on 7.5mm Rob Allen shafts.

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These 7.5mm Rob Allen are the only shafts I've used that hold up on Cuberas when they head for holes after being shot. This one is an even 50 lbs at 73 ft. Came in fast on a deep chum drop. Only had one band drawn (Speardiver 14mm small hole) on a vertical shot about 10 ft. I re-grind the points to a very sharp 1.5 in pencil point and the weight of these shafts punch right through a big fish. Especially nice for Ocean triggerfish.

As you know stainless steel tends to be pretty soft for drilling whereas the spring steel AKA carbon steel Rob Allen shafts are made of is very hard. You can't drill it with a normal metal bit, or even with a cobalt bit which I use exclusively for drilling stainless steel shafts. The only drill bit I know that will work on spring steel is a Carbide bit in high speed. These carbide bits are relatively expensive at $10 - $15 for the 3/32" diameter, and brittle, if you drop it on a tile floor it will break. They also tend to break if your drilling angle is anything but perfectly straight.

I've had a few, drilled a few holes in RA shafts, and broke my last carbide bit about a year ago. I will not be buying it again. Consider that RA shafts are galvanized after the flopper pin hole is made. When you drill a new hole the galvanizing is removed and the metal will rust quickly. A rusty flopper pin hole equals a flopper that doesn't move freely making the shaft useless.

I don't think weakening the shaft with a recess for the flopper is worth any practical benefit towards streamlining the shaft. I'd just get a good quality 7.5mm flopper.