.30 carbine case length.

Maxx424

Started to get a number of light strikes on my .30 carbine and finally woke up to the fact that some cases were too short. So the loading manual says max is 2.90". I checked some PMC cases that had been fired once and they were at 2.73". Military surplus I checked and they were at 2.85". I actually have some cases that are all the way down to 2.50". My question is if the max is 2.90" then what would be the minimum? I'm thinking that the PMC at 2.73" is probably as short as I should allow?

62fuelie

The .30 carbine headspaces on the case mouth so you don't want to go below the "trim-to" length - Sierra lists it as 1.280". If too short you will get light strikes as the case is pushed into the chamber by the movement of the bolt and the fall of the firing pin.

victorj19

Maxx,

Are you sure about it being a .30 carbine? There is no way a 2.5" case would fit in a carbine magazine or chamber. The case length is 1.280 per 62fuelie's book and an older Speer manual shows 1.290. Even a loaded cartridge wouldn't approach 2.5".

Jim

Maxx424

Thanks for the info. As to the 2.5" my error. In fact all the numbers are a brain fade. Should have been 1.290 for max. with the PMC at 1.273 and some down to 1.250. Can I blame this on early drinking? Sounds like 1.280 is the minimum which makes sense but interesting that the PMC is below that.

Tailgunner1954

I don't have the drawings in front of me (you might look on the SAAMI site), but the general rule of thumb is that Min is .020 shorter than Max, and that Trim-to is .010 shorter than Max.
There are a couple exceptions to the above, where the trim-to and Min are the same dimension (and in those cases they are both .020 shorter than Max).

Maxx424

Tailginer - checked out the site - did not have a minimum but did say max is 1.290 with a trim to of 1.80. Makes sense that .20 would be minimum especally since the PMC cases were 1.73.

Thanks all.