Fire-forming 243 Win -> 260 Rem ?'s

[louielouie]

Hi - newbie question since I've never done this before:
New barrel with 'match' 260 Rem chamber & can't find 260 Rem brass so I buy a 49-piece (shoulda been 50) bag of 243 Win. Winchester brass to fire-form using 140gr Nosler HPBT's, 41.5 gr AA-3100 & WLR primer. All brass was FL-sized & trimmed to minimum length (actually less-than since the brass didn't grow when necked up).
The questions are:
1. How much spring-back is to be expected at the neck? On some brass I cannot push a bullet back into the fired case and others definitely have some drag but there were no pressure signs from the primer (still rounded at the edge of the pocket).

2. Is that starting load adequate for forming the brass?

I have asked the 'smith for a print of the reamer dimensions (he said it should be a no-turn neck) but haven't received it yet. I have the Forster inside neck reamer & the outside neck-turning tool but I've only fire-formed 18 rounds so far (cleaning in between each round is time-consuming).

3. Neck ream the fired brass and turn the FL-sized brass? This would basically be experimentation while waiting for 260 Rem brass to be available.

4. Opinions?

This is my first 'custom' gun - Shilen #3 with a 1:8 4-groove 'rachet' rifling on a accurized Rem 600 action so I've got a whole new bunch of things to learn. FWIW, even cleaning after every round, 5 shots would go in an inch with 3 in a cloverleaf. 'tanx in advance.

 

[Ol` Joe]

Measure the OD of a fired case neck and compare the measurement to a loaded rd. You should have a couple thousanths difference (0.002"-0.003") if so there is enough clearance. You can also compare a loaded cartridge neck diameter to the books max neck diameter in the cartridge drawing in your manual. The 260 should have a neck of 0.2970" max. I doubt the brass is too thick in the neck. Brass that has been sized up stretches and thins. That is why it seems to "shrink" from its original lenght too.

The brass is new and will have some "spring back". The fact it started as a smaller caliber cartridge may have something to do with the appearent extra tight tension. After a couple fireings the necks may seem to loosen up some, Just a thought...

 

[louielouie]

My dummy round measures about .292 near the mouth & .293 near the shoulder. The fired brass are typically .295 max so I guess there's enough tolerance at this point. Even with full-length sizing and about .010 bullet jump it was not easy camming the action closed. Maybe that's just the action & all tolerances being 'tight'.

Thank you!

 

[YoteSmoker]

Going up from 243 to 260 will make your brass slightly thinner vs going from 7mm08 down making it a littel thicker. I think you're on the right road. I would try IMR 4350, RL 19 and H414 to wotk up a load.

 

[todbartell]

I neck up 243 brass to 260 in my 700 Titanium, and it works well. Until Nosler builds me some 260 brass I will continue to use the F-C 243 stuff

 

[JD338]

louielouie

Welcome to the forum, glad you are here.
I agree with the others that necking up 243 Win brass is the correct way to go. Keep in mind that your accuracy will get better once you have 100-200 bullets down the bore.

Do a search on Powerstroke, he has posted some fantastic accuracy with his 260 Rem.

JD338

 

[louielouie]

Thank you, all. I'm gonna double (triple) check all my settings, refine my technique and see if I can at least repeat what I've already done before changing any parameters.