Sunday, 9 July 2017

Crossbow Sights

I've made some quick adustable sights for the crossbow and got it sighted in a 10 yards, made another couple of bolts too for some shooting this morning.
Very strange thing, the two new bolts kick high and left by about 20" at 20 yards whereas the two original ones go straight true and right next to each other. the odd two are made form the same batch of shafts, have the same points and fletchings from the same source although not from the same actual packet. My guess is that the fletchings are interfering with the bow mount, I might try an unfletched bolt.

So, I just used the 2 good bolts and managed to get some idea of trajectory out to 40 yards, and some long shots at 120yds.
My mate JT had a go with the crossbow too and he put 2 bolts withing about 1/4" of each other.
The trajectory was rather disappointing and I think the prod has lost weight. I've since re-weighed the prod on the tiller, it's down to 70# , I s'pose this isn't too surprising as it been exercised now and has had time to settle, the damage to one limb probably hasn't helped either.

I've got the bow mounted on the bench so I can try and work out what's happening with the rogue bolts. First step see if I can repeat the result...
Test 1:-  Shoot one good, one bad bolt. The "bad" bolt is 18" left and high compared with the good one!!!
Test 2:- Trim the fletchings of bad bolt to a low profile. It still flies high and left by about 18".
Test 3:- Remove fletchings of bad bolt. It flies true, striking the target just below the good bolt with a slight nose down attitude.
Conclusion:- it's the fletchings wot dun it guv' and no mistake.

I can't be certain exactly what is happening but my guess is the quill part of the fletching is catching on the 'shoot through' part of the bow mounting, which I shall adjust and then try the second bad bolt.
See results (left) the bad bolts had orange cock feathers, the good bolts had white.
I cleaned up the shoot through aperture, one trick being to reverse the front part and bolt the two together, that showed up any asymmetry and by filing the two together and reversing them back and forth I've enlarged and evened the aperture in the two plates The bow was them bolted back inbetween the plates and the wood rasped to match.

I've also got a few minor issues with the trigger mechanism, so I've ordered two 600 grit diamond needle files off the interweb. They do sets in Toolstation but I have it on good authority that they are 'crap' (prob too coarse for what I need).

No comments:

Post a Comment