COL to engagement of rifling
Posted: Fri Mar 22, 2019 8:36 pm
My question has been puzzling me for quite some time!
Whilst checking headspace on three different service rifles just as a matter of interest and peace of mind my thoughts changed to I wonder what is the distance from COL of .303 round to engagement of rifling?
Using a fired HXP brass case with a sliding wooden dowel bullet (dowel bullet shaped to simulate the original) I first measured COL of unfired round and marked the dowel accordingly, sliding the wooden bullet out from the case then carefully inserting simulated round into the breach of commercial 1920’s SMLE and closing the bolt found that when extracted the COL had been extended by 5mm, great that is the distance from seated bullet to engagement of rifling question resolved, ok let’s try another, next rifle a No4 Mk2, repeated test as above this time the COL had extended by another 5mm, question entering my head was why the difference? Can’t stop now let’s try next rifle a P14, again repeated the test this time COL had extended yet again by at least another 6mm, a difference from COL of 16mm to engagement of rifling, “Questions” now buzzing round ‘why the difference’, will this differing distance affect recoil, pressure, safety, for me it’s thrown a multitude of questions up in the air !!
Please don’t think that my measurements were perfect, my tests were of interest only.
Could someone with greater knowledge please if possible explain “Why the difference” ?
Whilst checking headspace on three different service rifles just as a matter of interest and peace of mind my thoughts changed to I wonder what is the distance from COL of .303 round to engagement of rifling?
Using a fired HXP brass case with a sliding wooden dowel bullet (dowel bullet shaped to simulate the original) I first measured COL of unfired round and marked the dowel accordingly, sliding the wooden bullet out from the case then carefully inserting simulated round into the breach of commercial 1920’s SMLE and closing the bolt found that when extracted the COL had been extended by 5mm, great that is the distance from seated bullet to engagement of rifling question resolved, ok let’s try another, next rifle a No4 Mk2, repeated test as above this time the COL had extended by another 5mm, question entering my head was why the difference? Can’t stop now let’s try next rifle a P14, again repeated the test this time COL had extended yet again by at least another 6mm, a difference from COL of 16mm to engagement of rifling, “Questions” now buzzing round ‘why the difference’, will this differing distance affect recoil, pressure, safety, for me it’s thrown a multitude of questions up in the air !!
Please don’t think that my measurements were perfect, my tests were of interest only.
Could someone with greater knowledge please if possible explain “Why the difference” ?