LVLAaron
Gold $$ Contributor
I have a reamer cut for oil groove pilots. This reamer has chambered many 4 groove match winning barrels.
I introduce the reamer to a 5R barrel.. Seating depth of a known bullet is 30-40 thou short of where it should be.
I generally prebore and cut away as much of the chamber as I dare, especially on this type of barrel. Never had the freebore come up short. I typically avoid the pilot because I'm confident in my setup and chambers come out with maybe 1.5 tenths of runout, if that.
Got more 5R barrels to do.
Same problem.
I sat at my bench and stared at this reamer for two days and scratched my chin.
I assumed the problem with the first barrel was reamer flex or some other 5R gremlin. On the subsequent barrels I used the pilot to avoid it but same problem... so I looked at the pilot a little closer and a lightbulb appeared above my head.
"Those oil grooves are so big they're worthless in a fight against the lands"
And I came to the conclusion that the lands (or land) were getting centered in one of those giant grooves allowing the reamer to flex/move.
I got on McMaster and ordered a .219+ reamer and got busy making my own solid pilot. OD is a snug fit in the bore. (.3081) - I didn't want any play in the pilot.
I have a dummy round that should just drop into the chamber. Before the new pilot, I pushed the round in to a soft touch and measured it. Hand reamed with the new pilot, cleaned, and remeasured. The dummy round moved all the way forward to the shoulder without problem (30 thou difference)
Hope this helps someone.
PS- Making small super precision parts like this really makes me happy. I hope at some point I can find a small swiss lathe.
PS2 - Before someone mentions it, reamers made for oil groove pilots are not compatible with typical pilots, so a standard one could not be used.
I introduce the reamer to a 5R barrel.. Seating depth of a known bullet is 30-40 thou short of where it should be.
I generally prebore and cut away as much of the chamber as I dare, especially on this type of barrel. Never had the freebore come up short. I typically avoid the pilot because I'm confident in my setup and chambers come out with maybe 1.5 tenths of runout, if that.
Got more 5R barrels to do.
Same problem.
I sat at my bench and stared at this reamer for two days and scratched my chin.
I assumed the problem with the first barrel was reamer flex or some other 5R gremlin. On the subsequent barrels I used the pilot to avoid it but same problem... so I looked at the pilot a little closer and a lightbulb appeared above my head.
"Those oil grooves are so big they're worthless in a fight against the lands"
And I came to the conclusion that the lands (or land) were getting centered in one of those giant grooves allowing the reamer to flex/move.
I got on McMaster and ordered a .219+ reamer and got busy making my own solid pilot. OD is a snug fit in the bore. (.3081) - I didn't want any play in the pilot.
I have a dummy round that should just drop into the chamber. Before the new pilot, I pushed the round in to a soft touch and measured it. Hand reamed with the new pilot, cleaned, and remeasured. The dummy round moved all the way forward to the shoulder without problem (30 thou difference)
Hope this helps someone.
PS- Making small super precision parts like this really makes me happy. I hope at some point I can find a small swiss lathe.
PS2 - Before someone mentions it, reamers made for oil groove pilots are not compatible with typical pilots, so a standard one could not be used.
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