Need help with a custom throat

[dtknowles]

I am thinking about setting back my barrel on my 30 BR and would like a custom throat for cast bullets. Any suggestions on the throat design.

Tim

[ulav8r]

Use a 3/8 inch masonry drill bit. It will accept any 30 caliber bullet you might want to use. :groner: If you want useful help, you need to determine what you want to do. Do you want to use one specific bullet or a range of bullets. Assuming you want to use .310 bullets, a .310 diameter throat is apt to be most useful. The length and profile of the reamer will vary depending on which bullets you want to use. Avoid sharp shoulders and steep angles. For better advice talk to someone who has much more experience with cast bullets than I do.

[B R Shooter]

I had a throat reamer made with a 1 degree taper and .3105" diameter. Works well.

[gnoahhh]

I use a 1½º included taper throating reamer in my dedicated cast bullet .30 rifles. I also used the same reamer to make a bump die to swage bullet noses for a perfect fit in said throats.

[Outpost75]

^^^^THIS^^^^ aka "Ardito" throat.

[DougGuy]

I had a throat reamer made with a 1 degree taper and .3105" diameter. Works well.


I use a 1½º included taper throating reamer in my dedicated cast bullet .30 rifles. I also used the same reamer to make a bump die to swage bullet noses for a perfect fit in said throats.

This right here is what you need to start with. You need half thou over boolit diameter, a smooth leade-in either one or one and one half degrees, and enough freebore to seat your boolits .025" or so back from engaging the leade ins.

BTW. Included angle means both sides from center, so 1½º included means 3/4 of one degree per side. It is more common to see angles described for a reamer as just one side so if I order a reamer with a one degree leade-in, it means 2 degrees included.

[dtknowles]

I could also use a recommendation for cast bullets for a 1 x 16 twist barrel. Can't really limit myself to one bullet as some experimentation might be needed. I expected that the chamber would not have any lead/freebore with the throat starting right at the case mouth and the bullets seated to jam. I was thinking to use bullets sized to .311" but I guess I could go to .310. So any recommendations on where to get this 3/4ths or 1 degree reamer? Also I would entertain more discussion about lead/freebore or seating to jam.

Tim

[DougGuy]

Manson Precision Reamers, JGS, Pacific Tool & Gauge, all make reamers as SAAMI stock items and all make reamers to custom specs.

Almost across the board, freebore (provided it's concentric and the right diameter) serves to hold the boolit in a whole lot better alignment to the bore than the boolit being pushed out of a case that has no physical part to hold it aligned. Freebore is like a sleeve that squares the boolit and starts it in the leade-ins perfectly aligned on center. Freebore is generally smaller in diameter than the inside of the expanded case so it serves a valuable purpose in the path of the boolit. The longer the freebore the better the alignment, the less resistance to movement compared to rifling, it's a better deal all around than the lack of freebore, a short freebore, or a freebore too small in diameter to be an aid but rather a detriment to accuracy.

[dtknowles]

My rifle is tight chambered and I use neck turned brass, the case holds the bullet in alignment with the bore and I was schooled to believe that the less jump from the case to the rifling the better and that long freebores are intended to allow for higher velocity with lower pressures at the expense of accuracy. With jacketed bullets in my 6mm PPC I have often had best accuracy with bullets seated to jam or 0.010 off the rifling. Nothing seems to work well with the 30 BR so I was thinking it needs a serious tune up. I know that cast is a different animal but I wonder if any lead is needed as the bullets are often seated with all the cylindrical part of the bullet in the case. I need to find my pound cast of the current throat.

Tim

[Outpost75]

Current issue of The Fouling Shot has some discussion and drawings of "Ardito" throat.

If you are not a CBA member, PM me and I can send a courtesy .pdf of the current issue.

When I shot IBS many years ago the conventional wisdom then espoused by P.J. Hart and Homer Culver was to have free bullet travel 1/10th of bullet diameter in the .22 and 6mm PPC as well as in the .30 BR and .308 Win.

I was never in the money, but never embarassed myself with the above advice.

John Ardito routinely cleaned my clock in CBA Unlimited matches and I think he had it right.

[dtknowles]

Current issue of The Fouling Shot has some discussion and drawings of "Ardito" throat.

If you are not a CBA member, PM me and I can send a courtesy .pdf of the current issue.

When I shot IBS many years ago the conventional wisdom then espoused by P.J. Hart and Homer Culver was to have free bullet travel 1/10th of bullet diameter in the .22 and 6mm PPC as well as in the .30 BR and .308 Win.

I was never in the money, but never embarassed myself with the above advice.

John Ardito routinely cleaned my clock in CBA Unlimited matches and I think he had it right.

Thanks for the heads up, I am or was a CBA member I have not gotten a copy of Fouling Shot for a couple months so either it is in my in box or I have lapsed. I expect they would send a notice of my membership had expired.

Tim