Brass Trim Length

J

JEC

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Thought this may be of interest ... and help with understanding trim length. The photo is a cut-a-way of a chamber with a loaded cartridge. Just below the blue arrow you can see a “gap” between the lead edge of the neck mouth and the chamber. This cartridge could grow considerably in length before it needs to be trimmed. If it gets too long, it is possible for the neck to get compressed/pinched as it would in a forcing cone, which could result in a nasty pressure spike.
If you zoom to the “trim gap”, you can see where it enters the bore (leade) it is “angled” to provide a ramp that guides the bullet as it enters the bore. If brass gets too long and is forced into this ramp, it can create a very non forgiving “crimp” which spikes pressure...which could be dangerous.
Hope this helps.

 
Last edited:
OP:
Thanks for putting this and the headspace pics up. Some people have a hard time visualizing things from a description, and this should clear things up for at least some of them.
Like the old saying goes, a picture is worth a thousand words.
 
I have the Sinclair chamber length gauges. On the dozen or so rifles I have measured my chamber is about .030" longer than SAAMI max length

thanks for posting pic, nice visual
 
Thanks for the picture, OP. This is good for novices to see.
I have understood this concept for a long time.

Many chambers are cut with ample room to exceed max
length a bit without getting into trouble. [.015" to .030"]

However, I have a Husqvarna 8x57 that has only about
.003" more than max case length, and you can tell by
the effort required to close the bolt if the case is too long.
Dave.
 
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