Hi everyone!
I thought I would pass along some recent testing information.
I have been experimenting this fall / winter trying to optimize the performance of the Lapua smallbore ammunition – specifically the chambering.
I have used several configurations since 2009, the most successful was (is) a 2 degree leade angle, set at a dimension of .600 from the contact face to the start of the leade. Of all the 2 degree leade chamber configurations I have tried, this was the optimum dimension for bullet engraving in all of the test barrels I have used. This dimension engraves just to the second band.
1.5 degree chambers have been the topic of conversation on several forums, so I purchased several 1.5 degree spiral reamers and began testing. The chamber I am using is the "Meyers" profile (with a very small amount of body taper, something I prefer). The “standard” setup dimension is .600”. The engraving is more pronounced due to the more shallow leade. I had always assumed more engraving was better (a carryover from developing HP loads with VLD bullets!), so I started testing at .580”. The results in all barrels were not promising – vertical dispersion even though the chronograph numbers looked reasonably good. I moved it out in .005” increments until I reached .620” and nothing looked exceptionally promising – so I stopped and pretty much gave up.
Last week I was revisiting a post from Dr. Kolbe (Border Barrels) regarding chambering, and he mentioned some success with less engraving. So………I started moving the leade out in my test barrels. When I reached .660”, results (in all barrels) improved dramatically. Engraving is just barely visible on the first band. The vertical disappeared, and groups became round (and small!).
I was always hesitant to move the leade out – I had always thought that the bullet deformation from the gas pressure should happen with as much of it (as possible)supported by the bore / rifling.
Food for thought (for those chambering with Lapua ammunition in mind).
PS - The testing is limited to (2) Hart barrels, a six groove and a two groove - hardly a large scientific sample, I know! I use a lot of Hart barrels mainly because of their consistent quality and internal dimension. Experimenting with them translates very well from barrel to barrel - so I am very hopeful of any positive results I see with them.
Just thought I would share,
Have a great Christmas all!
kev
I thought I would pass along some recent testing information.
I have been experimenting this fall / winter trying to optimize the performance of the Lapua smallbore ammunition – specifically the chambering.
I have used several configurations since 2009, the most successful was (is) a 2 degree leade angle, set at a dimension of .600 from the contact face to the start of the leade. Of all the 2 degree leade chamber configurations I have tried, this was the optimum dimension for bullet engraving in all of the test barrels I have used. This dimension engraves just to the second band.
1.5 degree chambers have been the topic of conversation on several forums, so I purchased several 1.5 degree spiral reamers and began testing. The chamber I am using is the "Meyers" profile (with a very small amount of body taper, something I prefer). The “standard” setup dimension is .600”. The engraving is more pronounced due to the more shallow leade. I had always assumed more engraving was better (a carryover from developing HP loads with VLD bullets!), so I started testing at .580”. The results in all barrels were not promising – vertical dispersion even though the chronograph numbers looked reasonably good. I moved it out in .005” increments until I reached .620” and nothing looked exceptionally promising – so I stopped and pretty much gave up.
Last week I was revisiting a post from Dr. Kolbe (Border Barrels) regarding chambering, and he mentioned some success with less engraving. So………I started moving the leade out in my test barrels. When I reached .660”, results (in all barrels) improved dramatically. Engraving is just barely visible on the first band. The vertical disappeared, and groups became round (and small!).
I was always hesitant to move the leade out – I had always thought that the bullet deformation from the gas pressure should happen with as much of it (as possible)supported by the bore / rifling.
Food for thought (for those chambering with Lapua ammunition in mind).
PS - The testing is limited to (2) Hart barrels, a six groove and a two groove - hardly a large scientific sample, I know! I use a lot of Hart barrels mainly because of their consistent quality and internal dimension. Experimenting with them translates very well from barrel to barrel - so I am very hopeful of any positive results I see with them.
Just thought I would share,
Have a great Christmas all!
kev