6.5 CM FL sizing/headspace questions(rookie)

[JelliedEagle]

Hello, this is my first post on SH- I'm a pretty new reloader, I started with pistol cartridges and am getting ready to move on to 6.5CM and .223/.30-06 after that! Anyways, I bought a few hundred once-fired Hornady 6.5CM cases, and measuring with my forster datum dial they seem to be coming out at about 1.559"(base to datum).. since this was fire-formed to the last guys gun and not mine, idk how irrelevant or not this info is to me, except i guess regarding how far back to bump the shoulder, but thats why I'm here trying to gather some wisdom from you guys instead of learning the hard way, especially in CA where life is hard enough for folks like us.

I've been learning how to read sammi specs- I have a 6.5 AR10 and 6.5 bolt gun, but will be loading for the AR first, so not sure If I should bump the shoulder back to the sammi cartridge min or max or somewhere in the middle. The brass as it is now already fits very well into my L.E. wilson case gauge, which seems weird.. so not sure what to take from that. Also, I have about 80 rounds of Federal factory ammo that I could use to fire-form factory brass to my chamber to get better chamber data, but that isn't much and since I have the components I'd really like to bring some handloads to the range for the maiden voyage as well.

Also length-wise it measures to about 1.915"-1.920".. but since it hasn't been sized I guess this is irrelevant info. Just wondering if I should trim after sizing or if it'll pass until next time. guess I'll have to check length after sizing to see, just wondering what the reasonable margin is regarding "trim-to" length. I know it's probably relevant, again depending on chamber dimensions.

I'm loading on a dillon 550 with a redding 2 die set for this cartridge, but have a lee factory crimp die also. any info/tips/wisdom you all can contribute would be awesome. I know it would be better if i had fire-formed brass to my gun first, but this is what i have to work with for right now. I'm sure I'll have more questions/answers based on what you all have to say/ask. BTW I'll be loading with winchester 6.5 staball powder, and 123gr. FMJ bullets with cci#34 primers for whatever thats worth. also have accurate 4350 for my rifle cartridges.
Thanks everyone.

 

[nn8734]

Fire ~5 rounds in the AR and same for the bolt gun. Measure casehead to shoulder datum for each batch fired in your gas and bolt gun respectively.

Adjust your full length sizing die so it bumps your gas gun’s shoulder back .004 and bolt gun .002” relative to the fired case measurements. You can use indexing marks via sharpies on your lock ring snd die body using different colors to represent each setting once youve dialed it in for each rifle.

Make a dummy round or two for each rifle so that you can confirm it feeds reliably into those respective rifles before producing live hand loads.

Also, Hornady brass has much thinner walls and more case capacity realative to Federal brass for 6.5CM so if you decide to use Hornady then want to switch over to Federal in the future you will need to restart load development and work back up from a starting charge weight.

Finally, don’t expect the charge weight to be the same or even similar for your two rifles as the gas gun will likely be at overpressure long before the bolt gun on the chargeweight curve.

PS - id run Lapua brass if you can swing it, cost-wise.

 

[OREGUN]

First, I’d recommend loading for your bolt gun first. It’s easier and there’s less to screw up.

If you insist on going with the AR: Shoot the factory ammo first so you have something to compare to. You need to size that old brass to AT LEAST a few thou smaller than the brass that comes out of YOUR chamber. Another way to achieve this without shooting the factory stuff first is to strip the bolt and just bump back to a size that chambers with no resistance with your bolt…minus the ejector and extractor…you want to be able to feel just the lugs locking the bolt closed with no resistance. With the AR, you could run into needing to small base size the brass…so…

If it was me, I’d figure out what base to datum measure gave me completely effortless chambering (so I had a reference size) and then I’d set up the die per the instructions and crush that brass all the way back to the smallest size your die set will give you. With a gas fed gun, more sizing is usually better. You can worry about .002” shoulder bump when you are trying to load perfect ammo for the bolt gun.

As for trim, measure after sizing. Anything shorter than book “max” length should be okay. It should be between max and trim to lengths.

 

[KnowNothing256]

If it fits in the case gage, it's below SAAMI spec (you can confirm the measurements with LE Wilson to make sure). You're correct that measuring case length before sizing is irrelevant, don't bother trimming until you've sized. Also agreed with @nn8734 that if you switch brass, you have to start your whole load development over for that different brass (typically not worth the headache).

I'm not familiar with gas guns, so I can't give good advice on how to check rifle-specific headspacing. On the bolt gun, you can check whether or not you need to bump the shoulder this first time (with fired brass from a different chamber) by removing all the guts of the bolt (including the ejector if it's a spring-loaded plunger-style one on the bolt face) then seeing if the bolt handle will fall freely closed when you try to chamber a few fired cases. If if hangs up, even gently, then you should bump the shoulders a bit this first time.

@nn8734 gave you good advice on what to do after you have brass fired in your guns. Good luck!