Setting headspace for heavy cast bullets?

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Setting headspace for heavy cast bullets?

Postby 07Kingpin » Sat Mar 21, 2020 5:31 pm

Putting together a 450BM on a Savage action, will be be setting headspace on a fast twist prefit barrel.

Plan to exclusively use heavy (350+) bullets with Keith style or wider meplats.

Understanding that the BM headspaces off the case mouth, what considerations might be worth keeping in mind when setting headspace?
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Re: Setting headspace for heavy cast bullets?

Postby Al in Mi » Sun Mar 22, 2020 4:58 am

No difference than a shouldered barrel, clean chamber, lube threads, forget the recommended torque for the nut, I've just gave the wrench a whack with a 3# deadblow hammer and been good.

The 450 has .200 of freebore so you can use that to gain some case capacity with those heavy lead slug.

Who's barrel and what twist did you go with?
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Re: Setting headspace for heavy cast bullets?

Postby Tbk » Sun Mar 22, 2020 9:41 am

Kingpin, will you be using gas checks on the base of those bullets? When you say fast twist rates, what rate of twist?

Your post really got my attention because I've been considering the same thing. I've got a vz24 action barreled to a Rhineland Arms 450 tube. It's got a 1:16 twist and uses a Savage type "nut" to lock it in place when headspaced. It's also got a fairly generous lead before the bullet contacts the lands, so theoretically anyway, a little more powder capacity.

So, I'm just wondering how you're approaching the project so I can learn a little bit more!

Regards.
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Re: Setting headspace for heavy cast bullets?

Postby 07Kingpin » Sun Mar 22, 2020 11:46 am

Thanks for the replies.

Setting headspace is a relatively routine procedure, the only reason I am thinking about any kind of adjustment is the fact that I plan to use such long bullets with effectively no, or very little taper.

The barrel I will be using is a Rhineland 18" with 1:16 twist.

As far as gas checks I eventually plan to have two loads, a super and subsonic. The super will have gas checks the sub may or may not.

As of today (3/22) the barrel is still out for deliver so have not had a chance to examine, check throat etc so this all may be moot anyway.

Will probably just set a saami headspace and accept seating limitations for simplicity sake.
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Re: Setting headspace for heavy cast bullets?

Postby Tbk » Sun Mar 22, 2020 12:43 pm

Ok, it looks like you're going down the same road as I did with Rhineland. I don't imagine you're going to give up any case capacity. I know my loads using Hornady 250 flex tips are seated out a good .10" beyond the factory stuff and still well off the lands.

What kind of ballistic performance are you anticipating with your "super" load?
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Re: Setting headspace for heavy cast bullets?

Postby 07Kingpin » Sun Mar 22, 2020 1:17 pm

I don't know really.

My first work will be on a sub load, accuracy being paramount.

At that point it will be an exercise in trading accuracy/report/recoil for energy delivered down range.

With the right sub combo may not even need a super.
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Re: Setting headspace for heavy cast bullets?

Postby Tbk » Sun Mar 22, 2020 5:12 pm

If you've got access to a chronograph, you might want to run some rounds across it. It was remarkable how much higher/faster my loads were running, compared to the published data, all components being equal except the short, fast twist barrel and bullets being seated out a bit farther.

All I can imagine is the fast twist might contribute to increased pressure and that translates to higher muzzle velocity? Anyway, it's not what I anticipated from a short barrel. On the positive side, I couldn't detect any obvious signs of excessive pressure in my fired cases.
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Re: Setting headspace for heavy cast bullets?

Postby 07Kingpin » Sun Mar 22, 2020 5:20 pm

OK.

Yes I run everything over a chronograph.

You understand the relationship between bullet length and weight in any given caliber (not cartridge) for stabilization, not speed- correct?
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Re: Setting headspace for heavy cast bullets?

Postby Tbk » Sun Mar 22, 2020 7:48 pm

Yes I do. I just don't know what else I can attribute the increase in velocity to. With a 16.5" barrel, you'd think velocity would be less than the test barrels in the load data would suggest. Little Gun is a relatively fast burning powder, so maybe in a short barrel you're not giving up any velocity?
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