Bore Diameter / Bushing Question

P

pdhntr

Guest
I was looking at bushings on PTGs site and noticed something that is confusing me.

The .243 bushings run from .2378 - .2362 and the 6mm bushings run from .2368 - .2352.

I thought .243 and 6mm were virtually the same? Does this have something to do with the BR crowd and the barrels they are using?

Thanks.

Jim
 
Most 6mm BR barrels are either .237 or .236 in bore diameter, this is why the bushing are offered in the respective sizes............ Jan
 
Thanks Jan.

OK, so does anyone have any experience with Shilen barrels with respect to the bore diameter? I really can't afford to spend $160 + just for the bushing sets.

Thanks.

Jim
 
The bore size is .243, but the tops of the lands (where the bushing for the piloted reamer has to go is .236 or .237) Kiff has the pilots in every .0002.
 
pdhntr said:
Thanks Jan.

OK, so does anyone have any experience with Shilen barrels with respect to the bore diameter? I really can't afford to spend $160 + just for the bushing sets.

Thanks.

Jim
Click to expand...

You sort of have to. As was said, the bushings are in .0002 increments. Unless Shilen can tell you the exact land diameter, or you can meaure it accurately to that level, you need a set. I guess you could buy 2-3 bushings if you can get a close enough measurement, but as I remember, when you order them one at a time, it costs more. There will always be anoher barrel . . .

BTW, we select the bushing by feel. Put it one a range rod, and see how it feels. When it's too tight, back off one size. Maybe the pro's have a better technique?
 
Charles E said:
You sort of have to. As was said, the bushings are in .0002 increments. Unless Shilen can tell you the exact land diameter, or you can meaure it accurately to that level, you need a set. I guess you could buy 2-3 bushings if you can get a close enough measurement, but as I remember, when you order them one at a time, it costs more. There will always be anoher barrel . . .

BTW, we select the bushing by feel. Put it one a range rod, and see how it feels. When it's too tight, back off one size. Maybe the pro's have a better technique?
Click to expand...

Thanks Charles. That is the information I was looking for.

I will get the .243 set and hope it fits the Shilen. And you are correct also in that there will be other barrels. The investment is "feeling" better all the time.

Thanks again.

Jim
 
Selecting the right bushings.

Measure the bore with a pin gauge and determine what bushings you need and then buy what you need. You can order your reamer with the bushing size you desire.

Remember when measuring in .0001" that temperature will effect the bore diameter.

I alway double check the bore diameter and rarely find the manufactures measurements to be exactly the same as mine. Usually within +/- .0002

Most competent gunsmiths have a selection of bushing in .0001 increments for each caliber.

Most good barrels have approximately .0003 or less of taper from the breech end to the muzzle. When using bushings for indexing rods and crowning tools you may need different bushings for different ends of the barrel during setup.

Examples of bore variance in one caliber:

30 caliber shooters who shoot Palma tend to like "tight bore" barrels .297-.299 and shoot 155 grain bullets with a shorter bearing surface with a slower spin 12-14 tpi.

Benchrest and F-Class FTR shooters tend to shoot .3000-.30008 bores with heavier bullets with longer bearing surfaces. They tend to shoot 9-12 tpi barrels.

p.s. Hearing you whine about spending $160.00 for pilots tells me you should not be in the gunsmithing business. Tools are expensive and to do the job right you need the right tools.
Most of the gunsmiths I know have an extensive collection of bushings usually several thousand dollars worth. Just ask Dave Kiff at PT&G.
Nat Lambeth
 
Rustystud said:
p.s. Hearing you whine about spending $160.00 for pilots tells me you should not be in the gunsmithing business. Tools are expensive and to do the job right you need the right tools.
Most of the gunsmiths I know have an extensive collection of bushings usually several thousand dollars worth. Just ask Dave Kiff at PT&G.
Nat Lambeth
Click to expand...

I am not a gunsmith, or in the business of gunsmithing, and I am not a whiner.

I build a few stocks to make some extra money as my profession is not a high paying one. All of the money I spend on this hobby I have to make outside my regular income. That means working two jobs sometimes and working for the neighbor during the summer. (statement, not whining)

It took me 4 years to save up enough money to buy the lathe that I just got. I figure it will take me another year to outfit it. (statement, not whining)

There are two sets of bushings. One for the 6mm and one for the .243. If I can save $80 + shipping by getting the right set for the one barrel I am doing, then I have saved $80 and I can use it for something else.

Jim
 
If you are going to get your bushings from PTG, I'd think they would be willing to help you get the smallest size "set" with the best chance of fitting. Can't hurt to give them a call.

Even with the right tooling, experience is needed to measure in the .0002 region (*measure*, not gauge *difference*). I'd still opt for the range rod and selecting a bushing by feel, if machine work is an occasional thing for you. And if you shade things, shade toward loose. The barrel is going to get hotter when you chamber.
 
Charles E said:
If you are going to get your bushings from PTG, I'd think they would be willing to help you get the smallest size "set" with the best chance of fitting. Can't hurt to give them a call.
Click to expand...

Yes, I was going to get the reamer, bushings and range rod from PTG. I don't know if the bushings fit just the range rod, or range rod and reamer. But that was one of the questions I was going to ask Dave.

Charles E said:
Even with the right tooling, experience is needed to measure in the .0002 region (*measure*, not gauge *difference*). I'd still opt for the range rod and selecting a bushing by feel, if machine work is an occasional thing for you. And if you shade things, shade toward loose. The barrel is going to get hotter when you chamber.
Click to expand...

I think you are telling me to go with feel, not measure to try to get the right bushing. That is what I want to do. And that if there is a choice in the "feel" of the bore, that I should opt for the smaller bushing, not the tighter one. Makes perfect sense to me.

I don't have a problem at all buying the complete .243 bushing set from PTG. I feel that is a good investment at this point. I just didn't want to have to order both sets for a Shilen barrel that is marked .243.

Thanks again Charles.

Jim
 
Do you already have the Shilen barrel? If so go to ebay and get a set of small hole gages, you can get a set for as low as $10 and the 4 gage set will measure bores from 1/8" to 1/2". Measure the bore then order the bushing accordingly. If you do not already have the barrel, have whoever you are getting it from to measure it for bushing fit. At Shilen, Bill or Wade Hull, the owners, will be glad to measure and sell you a particular barrel.

http://cgi.ebay.com/4-SMALL-HOLE-GA...931?pt=LH_DefaultDomain_0&hash=item45edaf4c3b
or
http://cgi.ebay.com/Small-Hole-Gage...817?pt=LH_DefaultDomain_0&hash=item53de61e3c1



As is stated above, eventually you will end up buying several diameters, but for now, and your beginning, 3 sizes will suffice.

Measuring the only Shilen blank I have right now. it would take a 0.2362 bushing for reaming.

The reason for all these diameter variations is that each barrel is hand lapped and one 6mm barrel will not finish exactly the same size as another. Barrel manufacturers will label them, for example, 0.243/0.236 or 0.243/0.237 but the exact diameter will vary.
 
Jerry -- correct me if I'm wrong, but once upon a time, I had to buy a single bushing in an oddball size -- I think it was for reaming a Wilson Seater blank. Was kind of stunned at the price -- far more than the equivalent per-each in a set. But that was long ago & probably far away . . .
 
when you buy a reamer, a pilot will be included. Specify what size you want. Purchase
additional bushings .0002 in increments from that. You can somewhat cover the range
of bore sizes by purchasing 4 bushings. Start with .236 and go up.
 
Shilen will tell you their mean dimension for 6mm is .237. I would want a .2368 on the reamer and get you a set with equal numbers of bushings on either side of that dimension.
Butch
 
If I remember correctly the rod you're probably referring to as a "range rod" will be called a "Grizzly Rod" at PPG. The terminology is imprecise but if you're using the Gritters method of chambering get the Grizzly rods, they're a foot or so long and parallel taper. Some of the originally termed "range rods" are tapered monstrosities that just flop around on the bushings and are designed to be used like deltronic pins, in other words you basically drive 'em in, let them hang out the end and indicate off them..... NOT at all like Gordy's method.

hth

al
 
so I went and looked

http://www.pacifictoolandgauge.com/products/gaugesnbushings/indicatorrods.htm#grizzly

I've been chastised quite severely of late for championing "range rods" when referring to the Gritters method of chambering. Once it was explained to my WHY, once I was told what the original "range rod" WAS I've felt it hoovis to correct my misuse of the term whenever possible.

In any of my previous posts where I've referred to a "range rod" I've meant a Grizzly rod. IMO a tapered range rod is good only for use as a bushing holder if one doesn't have Deltronic pins.

al
 
Charles, I have one of those odd-ball 6mm bushings too. It was for a Hart 3-groove. About 0.2386" as I remember. Got it from Hugh too!! I don't remember having to pay a premium for it though.
 
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