Gun smithing advice for precision reloading

green_MTman · March 8, 2015, 08:27 AM

as some of you may remember i have a custom 6.5-55 se that has a very very short free bore.

i am looking to lenthen the free bore soon but wouldnt mind some advice on dementions.

currantly a 140 grain swift A frame contacts the rifling at a COL of 2.937 but most loads for a 140 gr give a COL at 3.030.also the 160 gr RN or the 156 gr orynx bullet often has a COL of 3.300.

what would be a good COL for both 140 GR and 160/156 gr non btsp or with a bullet like a 140 gr A frame maybe just lenthen enough for the 140.

any ideas ?

Bart B. · March 8, 2015, 08:36 AM

I'd use whatever freebore length is needed to let round's OAL 1/16th inch less than magazine length that allows about .010" bullet jump to the rifling. That should allow easy feeding from the magazine as well as good accuracy for the life of the barrel as the origin of the rifling lengthens with wear.

green_MTman · March 8, 2015, 11:10 AM

im thinking of giving the gunsmith a dummy round of 3.065 which should give me .035 of the grooves at a COL of 3.030

the only problem is could this over deep seat the 160/156 gr bullet if i wanted to use that.or if i gave a dummy rounnd centered at the 160/156 bullet with a 3.300 COL this could leave a lot of powder space on the lighter grain weights

March 8, 2015, 08:27 AM	#1
green_MTman Senior Member Join Date: March 27, 2014 Location: southeastern Vermont,USA Posts: 325	Gun smithing advice for precision reloading as some of you may remember i have a custom 6.5-55 se that has a very very short free bore. i am looking to lenthen the free bore soon but wouldnt mind some advice on dementions. currantly a 140 grain swift A frame contacts the rifling at a COL of 2.937 but most loads for a 140 gr give a COL at 3.030.also the 160 gr RN or the 156 gr orynx bullet often has a COL of 3.300. what would be a good COL for both 140 GR and 160/156 gr non btsp or with a bullet like a 140 gr A frame maybe just lenthen enough for the 140. any ideas ?

March 8, 2015, 08:36 AM	#2
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	I'd use whatever freebore length is needed to let round's OAL 1/16th inch less than magazine length that allows about .010" bullet jump to the rifling. That should allow easy feeding from the magazine as well as good accuracy for the life of the barrel as the origin of the rifling lengthens with wear.

March 8, 2015, 11:10 AM	#3
green_MTman Senior Member Join Date: March 27, 2014 Location: southeastern Vermont,USA Posts: 325	im thinking of giving the gunsmith a dummy round of 3.065 which should give me .035 of the grooves at a COL of 3.030 the only problem is could this over deep seat the 160/156 gr bullet if i wanted to use that.or if i gave a dummy rounnd centered at the 160/156 bullet with a 3.300 COL this could leave a lot of powder space on the lighter grain weights