OAL: 10 FCP, 175gr Sierras

Hi gang,

I'm somewhat new to reloading, and am in quite the quandary with overall lengths as I attempt to measure my new loads for my 10 FCP in 308. I'm loading 175 Sierras into Lapua brass to break her in, and am attempting to get the correct overall length before seating the Sierras - figure I'll seat to the lands, -.010, to start knowing the 175s like a little jump.

I paid for a rather dubious device from Hornady to check the length against the lands, unwrapped it today and it gave me 6 different readings with the same bullet, ranging from 2.120" to 2.621". Reading other posts, this length didn't surprise me as many other folks seem to go over the recc'd 2.800" max.

Then I switched up to a loose-necked fire-formed FC case, and the measurements after inserting it gently into the breech and closing the bolt read a little more consistently over six attempts, from 2.784" to 2.794".

It's important to mention here that the case I used in the latter test was fire-formed in a different rifle - would this impact the measurement? I have new Lapua and Hornady cases, but their necks are very tight - not sure I want to use the bolt to fit a bullet into that. Thoughts?

Thanks!

Chris

you mean use a new case to check CBTO as opposed to the fire-formed one? Maybe try opening the neck a bit with some kind of rod/punch etc enough to grip the bullet so that it can slide back as it engages the lands (a la sharpie score method).

With the variation you mentioned, it doesn't sound like your using you Hornady device properly? I use a case fired in my chamber, and run it into a full length die, just enough to size the neck where there is enough tension to slide the bullet into the neck and hold adequately, without sticking to the lands when the case is removed. I insert the bullet "long" into the case and insert the case into the chamber with my finger, then slowly close the bolt. Then slowly open the bolt and remove the case slowly, catching the case with your finger, not allowing the extractor to throw the case out. This is the best "poor mans method" I have found for finding the lands. And it is more accurate than the .010" variation that your method produced. It just takes some practice ;-)) !!

Hope you find this helpful......Jim

It's very helpful, thanks! I read up on the Hornady thing. Seems you gotta be sure the threads are tight, you might want to use a dowel "stop" down the barrel, and more... would have been nice for Hornady to include those tidbits in the instructions. I too loose-necked a casing and tried your method. Better results, but I am still coming up with COALs that are below the 2.80" minimum length for the 175gr Sierras... I'm pretty new to reloading, and below min length makes me nervous. So, back to the drawing board. I'll buy a comparator and try measuring to the ogives with that, then work out a COAL, after my OCW tests are done and I whip up a batch of varied lengths to see if groups are tighter with that variable. Meanwhile, I'll load 'em to 2.80", like the GMMs...

OK, so I have more to add, here. A thorough search of the Interwebs reveals that particularly with the 10FCP, the throats on the barrel can be a bit short... and even the manual cites that the rifle is optimized for the 168gr (not the 175 gr) - as an FCP (P-for police), this makes sense, as the 175gr. is a more long-range bullet. With that said, finding that the lands touch the bullet at 2.794-2.784" with the 175gr Sierra 178gr Matchking means that I have to seat the bullets deeper - a few threads specify 2.780" as a common denominator to keep it off the lands for a slight jump. More than a few guys tried to un-chamber an out-of-box Federal 175gr and pulled the bullet out of the cartridge in the process, it'd jammed in there so well. I worry a bit about the pressures by shooting a shorter than recc'd cartridge, but figure I should be ok (I'm using IMR 4064, which is a case-filler) if I watch for pressure signs. My next step is to get a hold of some 168grainers and see what the COAL is there on the test. My guess is that it'll be right at 2.830 or a little less at the lands.