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case trim length
 Moderated by: Slingshot, Rockydog, klallen, DesertMarine, -6
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 Posted: Fri Apr 2nd, 2010 01:57 AM
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pills
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Hey guys, I'm new here and just started loading over the winter.  I have been using the search button for the last 2 hours but havent really found what I'm looking for yet.  I am familiar with getting a OAL measurement by loading a fired case and letting the lands push the bullet into the case and subtracting .010.  I have been trying this with different bullets with good results so far.  However on my .222 the listed OAL is about .080 shorter than what the actual chamber is. So my question is if Im extending the OAL by .080 for better acuracy do I still trim to the listed "trim to length?" or would a longer case be more accurate also?  How whould I get the longer case measurement?



 Posted: Fri Apr 2nd, 2010 02:14 AM
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Dragon88
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Howdy and welcome to the forum! :thumbs:

If your cases are long right now and you have some room to play, you can definitely trim them a bit long. The "trim-to" length in the books is merely a guideline. Up to max SAAMI spec is no problem, and if your chamber will support it you can go longer. An extra .010 of neck or whatever will help you squeeze in a little more case neck tension when you are loading long. I have to do this for my Rem 700 which has a loooong throat and it helps a bit. That's the great thing about handloading, you make the round to fit your gun, not everyone else's guns.

As for finding a measurement, find your shortest case (after sizing) and see how that compares to SAAMI specs. Might help you find a safe place to start. If you don't know what your chamber will support don't go over SAAMI max length.

Last edited on Fri Apr 2nd, 2010 02:18 AM by Dragon88



 Posted: Fri Apr 2nd, 2010 02:15 AM
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Rockydog



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Without a chamber cast you probably can't tell. I would trim to rec. length. If cases are too long the neck can end up in the chamber throat where the taper begins. If the taper is, in fact, a step as it is in some guns or tapers rather abruptly there may not be enough room for the case neck to expand and release the bullet upon firing raising pressures dangerously. Best to trim to recommended length and not worry about it. RD



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 Posted: Fri Apr 2nd, 2010 11:18 AM
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Paul Tummers



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I normally trim 0.5 mm shorter than SAAMI specs;I never load very long and the bullets I load are long enough to make sure that at least 1 times the bullet diameter is gripped by the neck.

I do not like surprizes in pressure levels, so better a little bit on the safe side with my case length.

If too close to maximum a case from wich the inside of the neck has not been lubricated already can bring the by me unwanted pressure surprise- not immediately with danger for gun or health, but by a miss what should have been a clean hit by different POI caused by pressure variation. 



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 Posted: Fri Apr 2nd, 2010 12:43 PM
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pills
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thanks for the replies. Paul are you talking about trimming 5mm or .005 below max case length? I know the books recomend trimming to .010 below SAMMI max. Some guys I know trim every reloading and others dont trim until the cases exceed the SAMMI max so if that takes 3 shootings for example: 1st time shot at .010 below second at .006 below and third at say .002 below and all are SAMMI safe will they get the same accuracy with all 3 lots of brass?

I was just curious as to why it was safe to extend the OAL past SAMMI max to .005 or .010 off the lands but not safe to let brass grow over the SAMMI max as long as the neck doesn't touch. Maybe because there is no easy way to measure when the neck touches? or maybe there will be little to no accuracy gain?



 Posted: Fri Apr 2nd, 2010 01:58 PM
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Dragon88
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Yeah it's mostly because you don't have an easy way to measure how far forward the neck can go in your chamber safely. There are some ways, chamber cast as RD said. I doubt a couple thousands is going to affect your accuracy much, but trimming is just one more thing you can do to get the rounds as consistent as possible.



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