Case O.A.L. trim question...

[nikonNUT]

Morning all! So the time to start the reloading process draws near and I have a really dumb question. I understand how (and have the tools) to check for case O.A.L. but how much shorter to I trim the case than that measurement? .000"? .002? etc, etc. Not a lot of good information out there other that trim it .005" shorter than SAMMI spec. This seems like an incorrect assumption for ELR stuff and, if that were the case (HA!) why would we bother getting that data point in the first place? Anyways, thank you for the information and I'll try and do ya'll proud/not blow my face off!

-Chris

 

[spife7980]

Doesnt matter as long as its not too long, when its too long it jams into the ramped transition and pinches the bullet.

General saami specs say there is a .020 range that is in spec, I generally shoot for the middle of it, .010 short of max spec. That way Im not removing more than I need to but it also wont kill me if one gets through untrimmed.

To know for sure you can stick an empty case of fired and sized into the chamber and feed a bore scope down the barrel and actually look at it. Other than that just follow the printed spec, its there for a reason and you wont get any benefit out of deviating.

Edit: If you have the tols to measure that I assume its the sinclair? Some rilfes have that length extended a bit longer so in reality you could go father but without tools to measure you dont know which is why the printed spec exists. If you measure it and know then you can go however much shorter you are comfortable with.

 

[nikonNUT]

Doesnt matter as long as its not too long, when its too long it jams into the ramped transition and pinches the bullet.

General saami specs say there is a .020 range that is in spec, I generally shoot for the middle of it, .010 short of max spec. That way Im not removing more than I need to but it also wont kill me if one gets through untrimmed.

To know for sure you can stick an empty case of fired and sized into the chamber and feed a bore scope down the barrel and actually look at it. Other than that just follow the printed spec, its there for a reason and you wont get any benefit out of deviating.

@spife7980 Thank you for the info! I do have the Sinclar dohickey and that was why I asked. I've been a machinist for 25 years and I get to over thinking these things so I wanted to ask the professionals. BTW, this is a .338LM and I'll be running the 300gr SMKs to start if that matters.

 

[Doom]

Bullet doesn’t matter. One benefit of knowing your actual length and trimming just short of it is minimizing the buildup of a carbon ring. If you trim to the normal trim length all the time a carbon ring can form in the chamber. If a longer cartridge is then inserted it pinches the case mouth and binds the bullet causing chamber pressure to increase.

 

[Snuby642]

Pretty much all reloading manuals give you a trim length.
That is normally half way between minimum and maximum per saami spec.
It allows for some error and safety.
The trim is after resizing.

Since you know how to use measurement tools you could do the custom lenght to cut down carbon ring.

I am lazy and just trim to spec and clean my gun knowing it will take a few shots to run well.

In case you have to lend some ammo to another shooter that is one less thing to worry about.

 

[Redfoot Ranch]

Bullet doesn’t matter. One benefit of knowing your actual length and trimming just short of it is minimizing the buildup of a carbon ring. If you trim to the normal trim length all the time a carbon ring can form in the chamber. If a longer cartridge is then inserted it pinches the case mouth and binds the bullet causing chamber pressure to increase.

I recently purchased the Sinclair chamber length gauges but have not yet used. Based on your personal experience, how much longer are you finding chamber lengths to be compared to SAAMI specs? Are you still trimming your brass 10-thou short from the known actual length to help in mitigating carbon ring buildup, or using a lesser number now that you have more specifics?

 

[nikonNUT]

So a triple check shows that my chamber is .027" longer than SAMMI max per trimming a re-sized case way short, inserting the Sinclair chamber length gage, and closing the bolt on the assembly ( checked this 3 times) and coming up with 2.751". Aside from keeping the brass shoulder squared (I assume it doesn't grow squarely but would look more like material you see after deep drawing aka kind of ragged uneven edge) there's nothing to do but be mindful of the carbon ring that can form in the gap between where the neck stops and the leade starts correct?

 

[spife7980]

Yep. I trim every time but that’s because my trimmer also chamfer and deburrs too. The chamfer and deburr just keeps it nice and clean for every loading.

 

[Just Chuck]

I just received some new Lapua 223 brass and measured it before and after F-L sizing and am using that dimension as my standard. BTW - no difference in the case OAL between before -after. FWIW - SAAMI spec is 1.760" - Lapua was 1.750"

 

[Snuby642]

1.76 is max, 1.75 is the standard trim lenght.

Some brands (cheaper) don't trim much and are way long after resizing.