Pre-Drilling and Chambering Questions

M

mpatti

Guest
I am just getting into making my first barrel. I bought a Grizzly 4003G, tooled up, and have been practicing on alot of scrap. I think I am just about ready to go for my first barrel but still have some questions:

I only have a finish reamer and do not have a fancy flush system so I am going to pre-drill, then use a boring bar, then use the reamer. I was wondering how short to drill in and how far under the diameter at the shoulder I should stay with the drill, then bar, before reaming?

I was also wondering what a good way to polish the chamber is. Is there any burrs at the front of the chamber (end of neck) to worry about??

What cutting fluids are recommended for chambering. I have a cousin who is a machinist and I have been using some stuff he gave me that is sulfur baised.
Thanks to any input or advice you have.
 
mpatti said:
I am just getting into making my first barrel. I bought a Grizzly 4003G, tooled up, and have been practicing on alot of scrap. I think I am just about ready to go for my first barrel but still have some questions:

I only have a finish reamer and do not have a fancy flush system so I am going to pre-drill, then use a boring bar, then use the reamer. I was wondering how short to drill in and how far under the diameter at the shoulder I should stay with the drill, then bar, before reaming?

Look at the drawing for your chamber and stay about 1/32" under the shoulder/body intersection diameter. For depth, stay about 1/8" short of the shoulder

I was also wondering what a good way to polish the chamber is. Is there any burrs at the front of the chamber (end of neck) to worry about??

Polishing the chamber is not really necessary in most cases. If you wish to polish some, take a wooden dowel rod of about 1/4" diameter and saw-split one end for about 1/2". Then take a piece of 280 grit or finer and wrap a piece of it around the dowel. Polish at about 200-500 rpm. You may wish to slightly radius the chamber entrance with the 280 grit also,

What cutting fluids are recommended for chambering. I have a cousin who is a machinist and I have been using some stuff he gave me that is sulfur based.

Any good high sulfur cutting oil works best. Hog lard works surprising well too.

Thanks to any input or advice you have.
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I do a variety of different size cases here. From a 17 Ack Hornet to 50 cal. Over the years I have been lead by problems along the way to the procedure I'll lay out here.

Unless forced to I always chamber through the headstock
after the barrel is indicated in I turn the tenon and thread and put the counterbore in.
I then measure from the front of the bushing to the junction of the neck and shoulder. I subtract about .150 from that and drill the barrel at, or just below the neck diameter to that depth. This saves wear and tear on the the throat section. Which is the most important part of the reamer.
Next I go in with the reamer to a point that I have about .100" of the body in the barrel. As I said I learn from having problems and with the body of the reamer not being supported in the barrel I was having a chatter issues from time to time.
Next drill out the body of the chamber to within about .100" of the shoulder. Then bore the first section of the drilled hole out to very close to shoulder diameter.
Then head in with your reamer. I know, I know the first hole I cut with the reamer maybe off a little but with the bored hole and the bushing in the barrel it will straighten itself out in short order, all the while being supported. This pretty much put an end to any chatter problems.
I made a polishing stick out of alumimun with a smooth handle and with a split end. Use wornout 240 and finer.

Dave
 
Dave, when you go in with the boring bar do you set your compound to approximate the angle of the body of the case (for example 1/3 degree for a 243) or do you just drill and bore straight and let the reamer do the rest?
 
mpattii

no I don't. I can't say I bore all chambers. I've found that until a barrel has a certain amount of runout between the throat area and the end of the barrel that is doesn't make any difference. I'm talking about a few thousandths TIR.

Dave
 
mpatti said:
Dave, when you go in with the boring bar do you set your compound to approximate the angle of the body of the case (for example 1/3 degree for a 243) or do you just drill and bore straight and let the reamer do the rest?
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Where do you find the case dimesions that give you the taper, in this case 1/3 of a degree for a .243? Are you just doing the math, or is there someplace that has prints to get that information? I've looked through all my reloading manuals, and searched the web and found nothing.

Thanks In Advance, JKM
 
For taper boring

chuck the reamer up with the pilot in the chuck and a dead center (in the tail stock) in the rear of the reamer. Turn your compound to about 1/3 of a degree and put a test indicator on top of the compound with a magnetic base. Then, run the indicator along one of the reamer flutes (using the compound wheel) and change the compound angle till you eliminate the runout. If it's a cartridge that you'll chamber frequently, I'd scratch a witness mark on the degree scale of the compound.

Shelley
 
Thanks Butch,

I was just curious, I know that a lot of you guys pre-bore, but never new where you found specs.

Thanks to you too Shelley,

I had actually thought about that as well, but being a newbie and all, I wasn't sure if that was the right way to go about it. (But then again, what is right in this business?)

Thanks Again to both,

JKM.
 
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To arrive at the angle for the body I was just using numbers on the chamber print and doing a little math. I actually like the method described above better. Thanks for the idea.
 
Mpatti

On my Benchrest Chambers, I pre-drill, indicate the throat area, single point bore on the same taper as the reamer body, and then use the reamer ONLY as the instrument to establish the final dimensions and finish of the chamber. I bore the chamber to where the reamer sticks in about 40-50 percent of the way, with the live pilot making full contact with the throat area that was indicated dead true. You can ONLY do this if you bore with the compound set at the correct taper. It is on your reamer print.
As for polishing, I have found that for Benchrest Chambers, I do nothing to the finish that the reamer leaves. I have found that it is the correct finish for all around ease of extraction when shooting elevated pressure loads........jackie
 
jackie,
How do you indicate the throat area? I'm envisioning an indicator with a long probe that is riding on top of the rifling. Or is there another tool?

Eric
 
I will answer for Jackie. He uses a 513-504 Mitutoyo indicator. It has a small body and a short probe. After he drills, he can run the whole indicator into the hole to indicate the throat area. The short probe doesn't jump as bad as the long probe indicators.
Butch
 
and if you do a search...you will find that jackie has posted several times his process(THANK YOU JACKIE!)...just go look.

mike
 
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