Best BHN for 6.5x55 Swede CG 63

[GregLaROCHE]

I am trying to subdue this monster of a cast boolit round, 6.5x55se 140gr from a RCBS mould. I have tried PC with and without gas checks and with normal lube with and without gas checks. I am now working on gas checked with Alox. I am sure my alloy is too soft, 10-12 BHN.

I now have some linotype to harden it up and I am wondering what BHN I should be trying to get to when mixing it with my range scrap. Not to hard. Not too soft. From what I have found, this round is a tough nut to crack.

I am looking for those who have experience with this round and the Swedish rifles. Not just a general BHN for cast boolits.

I am shooting a CG 63 with a lower twist rate than the original military versions.

How many of you have tamed this beast?

Thanks for all advice, even load development if you want.

[bruce drake]

What twist rate are you using as that will make a difference in accuracy compared to a standard mil-spec barrelled rifle.

[RPRNY]

The basic rules apply and should guide your effort: size to slightly over groove, and match BHN to MV and intended use with the goal of as soft as possible - as hard as necessary. 12 BHN dropped and air cooled is absolutely fine in this capacity, all the more so with the slower twist rate of almost 9:1. If you want BHN 14, that'll be fine too. There are only three reasons for needing lead harder than that: 1) you are a commercial caster and want boolits to look pretty when they arrive at the customer, 2) you know for a fact that you are getting nose slump on ignition that is negatively impact accuracy, and 3) you are pushing cast at 2000 + fps in a somewhat tight twist barrel.

More important than alloy hardness will be velocity and powder choice. I'm normally an advocate for IMR4227 with cast military loads, but the smaller caliber here suggests a faster powder might be a better choice and 2400, targeting the 1600 - 1700 fps staring range would be a good place to start. If you can get that working well, ratchet up to around 1800 fps and Hakuna Matata.

[waksupi]

My best results were with air cooled wheel weights, and bumping up the nose to better fill the throat.

[RPRNY]

and bumping up the nose to better fill the throat.

This is a good point for standard Swedish Mauser barrels with a throat designed for the original 160 grs RN loading, but I believe the CG 63 was designed for the 140 grs loading, thus the slower twist rate. In which case, it should have a less generous throat. Nevertheless, worth a chamber cast to determine whether it is the big long 160 grs throat or not. If so, filling out that throat will certainly aid in accuracy.

[GregLaROCHE]

What twist rate are you using as that will make a difference in accuracy compared to a standard mil-spec barrelled rifle.

My twist rate should be around 8.5 to one. I was always thinking my alloy was to soft, but I just got a Lee tester and my range scrap ingots are at 9.8 BHN, however, my cast water quenched boolits from five months ago are at 18.6 BHN. That should be pretty hard. No?