COL to engagement of rifling

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All handloading data posted on Full-Bore UK from 23/2/2021 must reference the published pressure tested data it was sourced from, posts without such verification will be removed.
Any existing data without such a reference should be treated as suspect and not used.

Use reloading information posted here at your own risk. This forum (http://www.full-bore.co.uk) is not responsible for any property damage or personal injury as a consequence of using reloading data posted here, the information is individual members findings and observations only. Always verify the load data and be absolutely sure your firearm can handle the load, especially older ones. If in doubt start low and work your way up.
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Gundog
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COL to engagement of rifling

#1 Post by Gundog »

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” ?
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Re: COL to engagement of rifling

#2 Post by snayperskaya »

Varying degrees of throat erosion perhaps?.The more throat erosion the greater the distance before the bullet engages the rifling.
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Re: COL to engagement of rifling

#3 Post by dromia »

Moved to correct forum, OP be aware mis-posts will be removed in future. Take some time to familiarise your self with the forums so that you do not mis-post in future.
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Gundog
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Re: COL to engagement of rifling

#4 Post by Gundog »

Firstly, my apologies for posting in the incorrect section of the forum!

In all the rifles tested in my quest to find COL to engagement of rifling, each and everyone has a bright clean and extremely well defined throat, no erosion visible whatsoever, but thank you for taking the time to mention it, I did of course check this before the test began, I beg your pardon for not mentioning this fact in the original post, this is what happens without providing all information no excuses my fault for omitting this aspect of the test.
Headspace in all correct, no visible wear at crown, rifling sharp and well defined, all barrels very good to excellent.
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