Bore Diameter affect Seat Depth

[gsg5pk]

Hi,



I just received 2 rifles from local gunsmith. Both were build on Stiller Tac 30.

• Bartlein Barrel 5R HV 1:10 tw (.300/.308 Bore)

• Bartlein Barrel 5R M24 1:11.25 tw (.299/.308 Bore)


Both barrel were chamber with the same reamer PTG F-TR .342"nk , .168 fb with 1-30

The suffer problem that I got from different in bore diameter was their Seat Depth to touch the land.


(.300/.308 Bore)
168 SMK
COAL = 2.900" , CBTO = 2.325"
175 SMK
COAL = 2.910" , CBTO = 2.325"
175 LRBT
COAL = 2.990" , CBTO = 2.329"


(.299/.308 Bore)
168 SMK
COAL = 2.770" , CBTO = 2.200"
175 SMK
COAL = 2.780" , CBTO = 2.210"
175 LRBT
COAL = 2.890" , CBTO = 2.226


Do any members have an experienced of different in bore diameter?

The smaller of .001" bore will affect these huge number of Seat Depth around .100"?



Best Regards,
GSG

 

[Dave L Kiff]

The maximum difference in length I have seen between two bore diameters that have .001 differential is about .045 in free bore length . People purchase reamers and think every barrel will have the same throat length and diameter but different bore diameters can yield different free bore lengths . There is a compound problem I'm afraid here since you are not talking about .045 in length difference but .130 difference . I wonder if by chance the two barrels were chambered with the same .2989 bushing that would have been used on the .299 bore . Please fire a round in each rifle and measure the cases , if one is larger than the other it would explain the radical difference in free bore length. Thanks Dave .

 

[gsg5pk]

The maximum difference in length I have seen between two bore diameters that have .001 differential is about .045 in free bore length . People purchase reamers and think every barrel will have the same throat length and diameter but different bore diameters can yield different free bore lengths . There is a compound problem I'm afraid here since you are not talking about .045 in length difference but .130 difference . I wonder if by chance the two barrels were chambered with the same .2989 bushing that would have been used on the .299 bore . Please fire a round in each rifle and measure the cases , if one is larger than the other it would explain the radical difference in free bore length. Thanks Dave .

Dave,


Based on your experienced with .168 fb, what the seat depth should be for normal .300/.308 Bore?