fitment question

[Tom]

I have a 788 in 308 that shoots great with Speer 165 spbt, but I have never tried cast in it.
I did a pound cast and it measures .3146 just ahead of the chamber. 1/4" up, it measures .3105.
I'm thinking I need to go with the .3105 number,and size to .31. Does that sound right?
The noe 315 saeco clone only measures. .307 at that point, cast from 50 50 ww/pb. I haven't tried straight ww with tin yet, maybe that would get me a little closer. I don't have lino, and don't really want to go that hard. Maybe just jamming into the lands would give good results?
The groove diameter at the chamber end is .3082"

 

[Ian]

Sounds like a lot of throat wear. Accurate has a 315 design already worked out, you could use that as is or alter it to fit your rifle.

What diameter is the chamber neck?

 

[Tom]

.3443 at the mouth of the brass.

 

[Tom]

My lc brass measures .014 to .015 at the neck.

 

[Tom]

I wanted to load some and see what happens, but the range has matches tomorrow, and I have to get back in the road Monday.

 

[Ian]

Might go for broke and try a .314" bullet that's sort of shaped on the nose like your throat is. Any chance you could post a picture of your pound cast?

 

[fiver]

I'd try to ignore that 314 area if you have a normal shaped throat in front of that.
and use a bit harder alloy and run on up into the throat like I do with the AR rifles.
lino-type is far too hard.
cut it in half with some soft lead or 3 parts ww's to 1 part lino-type.
a little more tin won't hurt either. [1.5%]
the 315 with a gas check would handle 2100 or so pretty easily.
it's a bit too square cut for my tastes something with a little more funk like a woman's hips or the fender area by the rear window of a 68 camaro is more my style in a boolit design.

 

[Tom]

Here it is, best I can do with my phone camera.

 

[Ian]

Fiver and I agree on bullet shape for sure.

Since you have the mould already, try expanding the case necks enough to give about .002" or a little less interference fit with the bullet AS CAST, and seat them as far out as you can. The more of the chamber neck you fill up, and less room you leave for the back end of the bullet to rivet or squish sideways, the better.

 

[James W. Miner]

Pound cast only is for the chamber and I see no benefit. Use a boolit just over groove or at groove and be done with it.
I did a pound fit to my 45-70 and found a .464" would fit so I made a mold and a .460" still is best. The premise is a straighter start but you make the barrel a size die.
Run out counts more. My 30-30 was showing .20" to .24" run out so I found necks were thicker on one side so I turned necks to even them out. I got to .00" to .002' run out and accuracy jumped way up even though I had more room in the chamber. Yeah, yeah but if the boolit does not stick straight out of brass you pound salt.

 

[fiver]

the pound is for the throat.
I agree on the straight part.
you need the boolit in the centerline of the barrel and you need it there straight.
to get the best results on target for sure.
but this ain't always possible, or the round becomes finicky so you have to leave some room to work with.
sneak up on everything and take what you can get where you can get it.
but always keep that centerline to centerline goal in mind.

 

[Ian]

If a bullet is throat size, it doesn't have a chance to get off center. I rarely slug a rifle bore, and if I do, it's only to diagnose tight spots or study the taper. If a throat is .314 tapering to .300 land and .308 groove, and you size .309, just how straight can that bullet possibly start?

 

[James W. Miner]

Been in the camp to neck size my .44's but soon I cant chamber because of expansion at the base so i need to FL now and then. I see no difference at all. It has been proven neck sizing rifle brass is no better the FL. It is more case to case evenness.

 

[JWFilips]

the pound is for the throat.

Yes The pound is for the throat!

 

[James W. Miner]

Yes, throat but still part of the chamber. Most guns have slop but run out reduction still works best. I pulled teeth with a Weatherby until I found I was sizing too much and the expander was pulling the round shoulders crooked. I sent the dies back with fired brass to get lapped to minimal sizing and the rifle shot 1/2" at 100 with any load. I held 1/2 minute to over 500 yards. I head shot a chuck at 550 yards once. Sitting position.
Cast is more touchy because the boolit will not pull straight.

 

[Ian]

Cast is more touchy because the boolit will not pull straight.

That's a good way to describe it. I've been asked about my assumption that a cast bullet will always try to turn sideways when coming out of the case neck if you give it any room, and I think virtually all bullets do. Even if everything is perfectly aligned at the start, the powder turbulence isn't going to act in a perfectly square or uniform manner every time on the bullet base, and there's gravity and extractor or ejector pressure, very minute misalignments, etc. all working to keep the bullet from being perfectly in line with the bore. The powder doesn't know which direction the muzzle is, anyway, so it just shoves all directions at once and follows the path of least resistance when the brass gives up its grip on the lead plug and lets it start moving out of the way. Really nothing but the case neck guides the bullet at first, then when the bullet finds some part of the cylinder or throat to start bumping/rubbing against it can follow that.

 

[fiver]

if you think about it everything is always at the bottom.
the base would get pushed up because there is more room there.
at least it's a consistent direction.