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outdoorfan
03-25-2009, 10:50 PM
Here's the deal. I have a Savage bolt action with a McGowen 1-10 twist barrel that I want to start shooting cast in. In preparation to having a mold made, I slugged my barrel and made a casting of the throat. Turns out that McGowen does not chamber these with any reasonable amount of throat. There is virtually almost no freebore. The rifling starts pretty much right where the case mouth ends within .020 or so.

The rifling is tapered from where the case mouth ends, where it is about .310-.311, to no more than about .110 further down where I'm measuring a full .308 (groove diameter).

I want to shoot a 180 grain (or so) spitzer, and from what I've been learning it's good to have at least two caliber's width in bearing surface. Seeing that the bottom of the bullet should not be extending much below the bottom of the neck, that leaves me with less than .5 inch of bearing surface without having the bullet jammed into the lands.

So, it seems to me that in order to get .6-.7 bearing surface I'll need to create an actual throat and some freebore.

Does this make sense, or am I missing something? I could use some confirmation that I'm on the right track (or not).

felix
03-25-2009, 11:42 PM
Yes, you are on the right track, but only for an average shooting gun, assuming your gun is just average to start with. So, let's assume you have a gold mine there, and that everything is quite concentric. My approach would be to SHOOT the throat into a configuration you want. To save time, and have fun, use a hot burning powder for about 300-500 rounds of condoms at full throttle. The throat will wear in just the way the bolt and chamber together would like for it to be done. For this technique to work as expected, the cartridges must be sized only enough to hold the bullets straight into the lands. You can measure progress as the bullets have to be seated further and further out to accomplish contact. ... felix

runfiverun
03-26-2009, 01:28 AM
the regular savages are throated bout like that.
the wifes will accept the rcbs 165 silh boolit,near perfect, and you would think it would be the best boolit for it.
not so, it likes the rcbs 150 fn for the 30-30.
about the only difference is that the 150 has a shorter nose and more bearing surface.

outdoorfan
03-26-2009, 02:33 AM
I've got a Stevens .223, and just be looking down the chamber I can clearly see that it has some freebore to it.

As to shooting it into the configuration I want, I'm not up to that. However, will firelapping do the same thing?

Wayne S
03-26-2009, 09:21 AM
I've got a Stevens .223, and just be looking down the chamber I can clearly see that it has some freebore to it.

As to shooting it into the configuration I want, I'm not up to that. However, will fire lapping do the same thing?Fire lapping is more for the bore than the throat, but it also depends on how you go about fire lapping. I have in the past used a loverin style boolit, un sized and hand lubed with valve polishing compound to smooth out bores, I'm sure it worked the throat a little, but you'll are talking a long distance, with your "06", and it's longer neck, you should have no problem finding a bullet with enough bearing surface