Chamber throat clearence?

[Marvin S]

What would be the ideal or minimum clearance you would want between the O.D of the case neck and the chamber throat on a single shot rifle. Let's say the O.D of my loaded round is .464. This is a Remington RB in 43 Spanish. Thanks.

[largom]

Tight neck chambers usually allow for a MINIMUM of .001 per side clearance. Therefore your neck would be a MINIMUM of .466 A word of caution is due. Unless you are skilled at case neck turning I would avoid minimum chamber necks. For these chambers a uniform neck dia. is a must to avoid dangerous pressures.
Larry

[felix]

In addition to Largom's statement, pay attention to the obturation capabilities of the boolit, brass, and barrel at the neck. For example, shooting soft lead will expand fast and would require a slower powder, or a thinner case neck. I would start with a total neck clearance of 0.001" using water dropped WW with gas check using typical 35-40K cup loads. ... felix

[BPCR Bill]

Marvin, I'm assumeing that this Roller is an original. Have you done a chamber cast? Dimensional drawings for the cartridge are one thing, but on the old rifles, chamber dimensions as well as groove / land diameters can be widely different from one rifle to the next. I've seen lots of vintage rifles that can have oversize chambers and barrels. Lots of 40 caliber barrels (like 40-65) can have barrels that slug out at as big as .412. I'd get a chamber cast and compare that to the dies you have. Wnen you do the casting, make sure you do the throat area as well, a couple inches ahead of where the rifling starts.

Regards,
Bill

[Marvin S]

Yes it is an original. I done a chamber cast also and it is .464 same as a loaded round with a .442 dia slug. I came up with the case neck measurement by taking 405gr hard cast 45-70 slugs and turning them in a lathe @ .439 .440 .441 and .442 .My bore slugs .442 I just wanted to see how close I could get to a proper size slug that would still chamber. I have on order the Lyman mold for the 43 Spanish and it will most likely make a boolit smaller than ideal size. Im going to the garage tonight to bore a set of mold blocks I have been working on. I have been considering buying a chucking reamer in say a .466 and then making a chamber guide and opening the neck area a few thou. Maybe 43 Spanish improved.

[Marvin S]

Please go to the special projects forum to see my mold blocks.