My friend" who has no computer" has a log gun that he can't get to group.This is number onehundred rifle that he has built .he makes everything except the wood,lock and barrel. The barrel is made by a well known maker it is 1 1/4 x48 1-48 twist .40 cal. rifling looks .008 - .010 deep it is breached right and a lead lap shows that it is the same I.D. full length. He has tried balls from .390 to .403 with different lube and patch thichness different size powder and amount with no luck. He is a very good shot and the sights are still lined up with his spotter after the rifle is fired.Does anyone have any suggestions that he might try ? He is about ready to see the spiderman and get it bored and rerifled .Thanks for your help.
Likely some or all this has been done but....
Its likely mechanical. Has he tried resting at different points on the barrel/forearm?
If its flint the vent MUST be under 1/16".
If percussion change the nipple to a new stainless or steel version NO VENTED NIPPLES. Check that the hammer strikes the nipple perfectly square and flat.
Does he wipe every shot? *Exactly* the same every shot.
Is it a drum and nipple gun?. The flash channel might need cleaning every shot.
Has he tried both hot and standard caps?
Has he tried very dry patches.
Teflon patches shoot well I am told.
Friends have had very good luck with water soluble oil wet patches that are set aside to evaporate all the water.
But they wipe every shot. A friend just shot a 3.9" 10 shot string last month with a 1"x 42 45 caliber GM barrel with 1.5 f swiss, the WS oil on a .010 patch and a .451 ball. The rifle has a "Hawken style" patent breech.
Or oil such as neatfoot soak the patches then press till hardly any oil is left.
Try some FFG and 1.5F Swiss powder if this has not been done
The longer barrel might work better with slower powder.
Has he tried cutting the patches with the ball flush with the muzzle?
Is the crown perfect? How do the fired patches look?
Dan