rifle bore laping for accuracy

grumpyvette

Administrator
Staff member
If you've got a rifle that just doesn,t seem to shoot cast bullets well its more than likely the bullet alloy ,your sizing the bullets wrong for the bore or not seating them close into the rifling lead,your using the wrong bullet lube or the loads velocity is to low or too high for the bullet alloy and or bullet design, or rifling twist rate. thats usually the cause but occasionally its the rifling and bore surface condition, especially if the guns been used mostly with jacketed bullets and your now swapping to hard cast bullets,
the results depend a great deal on what your starting with as far as barrel surface condition, if the bores fairly smooth and consistent in diam. its not likely to do a great deal, but if theres numerous tool marks in the rifling it helps noticeably.
what your effectively doing is sanding out the rough surfaces, thats usually more of a help with rifles your shooting cast bullets, more than with jacketed bullets from what ive seen and heard,and in my experience, and I found that it helped reduce group size about 1" , or from 2.2" average to about 1.2" average 3 shot off the bench groups at 100 yards in a Remington bolt action 458 win I had that I used almost exclusively for 500 grain cast bullets, it had zero effect on an old single shot H&R 44 mag rifle I had purchased used.
follow instructions but start with a CAREFULLY CLEANED BORE
http://www.midwayusa.com/viewproduct/?productnumber=646612

http://tmtpages.com/twistrate.htm

http://www.bergerbullets.com/twist-rate-calculator/

http://kwk.us/twist.html

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

https://thebarreloutlet.com/twist-calculator/
13cal.jpg
 
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