Implications of correct shoulder bump (headspace) but longer than required Neck Lenght

[harry_x1]

Hi,
I have a question, which some experienced handloaders potentialy can answer.

If I have a situation where the distance from the base of the catridge till the datum line exactly matches the headspace within chamber, however the length of the neck is longer than SAMI by a significant margin. What are the implications of such a situation? Will the neck stop the case shoulder from even reaching the datum within the chamber and create excessive functional headspace situation? or something else....hopefully my question makes sense.

 

[Slides]

It may not feed correctly/allow bolt close, the bigger problem is if you do chamber the round but the effective neck tension is significantly higher, which could cause overpressure on firing.

 

[Halfnutz]

Are you new at this?
If you are measuring the overall length of the cartridge, you need to trim it.

 

[Hondo64d]

Hi,
I have a question, which some experienced handloaders potentialy can answer.

If I have a situation where the distance from the base of the catridge till the datum line exactly matches the headspace within chamber, however the length of the neck is longer than SAMI by a significant margin. What are the implications of such a situation? Will the neck stop the case shoulder from even reaching the datum within the chamber and create excessive functional headspace situation? or something else....hopefully my question makes sense.

Typically the chamber length as measured from base of the cartridge to the case mouth, is a bit longer than the max SAAMI cartridge length. Sinclair makes a chamber length gage to allow you to find the true length of your chamber if you wish. Having case lengths significantly shorter than chamber length does allow a carbon buildup just beyond the case mouth but it is my impression that this is not the carbon ring folks talk about. If you allow your cases to become too long, you may experience hard bolt closure and high pressures because the case mouth is bumping the end of the chamber, giving the neck no room to expand and release the bullet as it is fired.

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John

 

[918v]

If the case mouth reaches the end of the chamber before the shoulder, then the caming action of the bolt rotating into battery will cause the case mouth to curl inward, crimping the bullet and increasing pressure significantly. You’ll probably blow primers.

It is a good idea to find what the chamber length is so you know how much clearance you need. Typically, factory chambers are .050” longer than book trim length. I have found my 6.5 CM chambers are a little shorter than typical (.025” longer than trim length). My current 6.5 chamber starts to pinch the case at 1.940”.

 

[supercorndogs]

I can't tell you how much time at the trimmer the above information has saved me over the last few years.