chambering / throating for accuracy...with both jacketed & cast bullets

[Magnum Wheel Man]

...chambering / throating for accuracy...with both jacketed & cast bullets...

So... I'm building / restoring a Remington Rolling Block rifle this coming winter, that was customized in in the early 60's as a bench rest gun...

I'll be rebarreling the rifle with an uncontoured Shilen 1 in 10 twist 8mm match barrel, that we'll be chambering in 32-40 ( using .323 jacketed bullets, & .325 cast 8 mm bullets )... my goal is to build a rifle that shoots sub MOA out to 300 yards with both jacketed, & cast bullets... because the action is a #1 Black powder action, we are also concerned about chamber pressures ( the gun was converted to 225 Winchester in the 60's, & several of the action parts have likely been changed out with smokeless parts to help the old action deal with the higher pressures of the 225 Wincester ) we also built & refitted new pins, even though the action was still reasonably tight... so we are planning on starting with the jacketed cartridge, & chambering the gun, with maybe 1/8" - 1/4" freebore in the throat ( chambering for a 180 grain jacketed spire point flat base bullet seated out as far as practical at least to start with... then once chambered, either casting the chamber for a custom bullet mold, or finding an existing 200-220 grain 8 mm mold that should put the cast bullet engaging the rifling... just enough to get the breech to close... a 15 X Unertl scope will be added. & this is just a "fun" gun, not a specific competition gun... I also have my own rifle / pistol range, so tweaking of loads is as easy as walking out door, to the Mule ( Kawasaki, not the 4 legged kind ), & a quick 75 yards to the shooting bench... the Mule makes 300 yard target changes less tiring, & much quicker...

I'm more curious about the specifics of differences needed in throating between cast bullets & jacketed bullets, & I have no intention of breech seating bullets, only shooting fixed ammo... I also have started collecting bags of new Bulk Winchester 32-40 brass... the 8mm barrel is rough chambered now, & being contoured to fit the contour of the 225 Winchester barrel it'll be replacing, & will be final chambered & throated when the back ordered Nosler Partitions finally get here

BTW... the firing pin retractor was removed from my gun prior to my purchase... I don't know if it was robbed for another gun, prior to my purchase, or weather the owner / builder of the 225 Winchester removed it for some reason in building it into a bench gun??? both my builder & I feel it's unsafe without one, just curious if there was any functionality or accuracy reason to remove it ???


I'm not fully understanding freebore & accuracy... I assume guns chambered for Weatherby were freebored for lower chamber pressures, & at least some jacketed bullets are capable of good accuracy with a space between the bullets nose & the rifling, while from what I understand, cast bullets shoot better ( maybe less deformation ??? ) if they engage the rifling when the cartridge is inserted...

1st... is my logic flawed,

2nd... any suggestions for throating to accurately fire both jacketed & cast bullets ???
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[Jim Watson]

It is my unsubstantiated (because I don't know anybody trying to shoot bisexual ammunition) opinion that you should throat the chamber for the soft, delicate cast bullets and let the jacketed look after themselves. Freebore? Nyet.

[Bogie]

I'd do the leade so you can just barely jam the bullets at a "middle" seating depth. That way you can jam more, or jump more, at your discretion.

Also, start low, and work up... Accuracy is NOT nascar - there are folks out there shooting very light loads that shoot as well as the guys who are popping primers.

[stubbicatt]

If you have your cast bullets handy, seat them to where the first grease groove behind the first driving band (ring) is about halfway exposed. This should be your seating depth. Have the rifling *just* fully engrave the first driving band. Some guys crimp into that first grease groove. Some don't.

This might not be a good idea with your rifle as unless the cartridge is fully seated on the rim, the block won't close completely, and the rifle won't fire. The force of seating the cast bullet into the rifling would have to come from something other than closing the action. Unlike a falling block of whatever flavor, your rolling block has no "camming" action to help with this process.

Neat thing about a single shot is that you can now adjust seating depth on your jacketed bullet to where it rests just off the lands as well, as you are not constrained by any magazine dimensions in your cartridge.

Too, you could consider paper patching, where the engraving is on the patch, not the bullet.

[kraigwy]

Freebore and accuracy dont go together. Free bore allows bullets to get started before they reach the rifling, this allows higher presures. Target shooters try to get the bullet as close as possible to the rifling.

In my 30 plus years of target shooting I've found velosity and higher presures dont normaly coinside with accuracy.

So it depends one what you want to do with you're rifle, NORMALLY.

However, the type rifle you appear to be building is not a high pressure round so you dont have to worry about free bore.

Now as to the two differant type bullets, cast and jacketed. The only way I see that working is to have the same shape bullet in each. If the ojive is the same you can pull it off, If the ojive is differant you can't.

The ojive is basicly the shape of the nose of the bullet.