How critical is reamer bushing fit when chambering new barrel?

[Kyle Schultz]

In process of building a 6 Dasher. Plan to use Krieger .237"/.243" 4-groove barrel. Reamer coming from JGS.

JGS reamer print advises gunsmith to use 0.2366" pilot bushing which they are providing with the reamer. I'm pretty sure JGS uses a default 0.004" under bore value for the bushing as other drawings from them indicate a 0.2356" bushing for 0.236" bore barrels.

But I know more than one gunsmith on the board has reported using 0.2368" bushings in recent Krieger .237" bore barrels. MY gunsmith does not have any bushings on hand in this range.

Question: How critical is this fit when cutting the chamber. Obviously the pilot has to be small enough to fit in the barrel. But, if it turns out that a 0.2368" bushing would work but all we have immediately available is a 0.2366" bushing, are we foolish to proceed? If it's critical, I can either specify a 0.2368" bushing initially and then order the smaller bushing if need be or I can just go ahead and order both bushings up front. It's not a huge cost (about the cost of a box of bullets) but I hate spending money I don't really need to spend.

TIA!

 

[billlarson]

Well.......... the reamer bushings are made in .0002" increments.They are made in sets...... I made a hand tool to insert bushings to approximate the actual neck position in the chamber to check for fit.Usually each end of the barrel is abit bigger because of adding lapping compound to the lap plug.

 

[savagedasher]

In process of building a 6 Dasher. Plan to use Krieger .237"/.243" 4-groove barrel. Reamer coming from JGS.

JGS reamer print advises gunsmith to use 0.2366" pilot bushing which they are providing with the reamer. I'm pretty sure JGS uses a default 0.004" under bore value for the bushing as other drawings from them indicate a 0.2356" bushing for 0.236" bore barrels.

But I know more than one gunsmith on the board has reported using 0.2368" bushings in recent Krieger .237" bore barrels. MY gunsmith does not have any bushings on hand in this range.

Question: How critical is this fit when cutting the chamber. Obviously the pilot has to be small enough to fit in the barrel. But, if it turns out that a 0.2368" bushing would work but all we have immediately available is a 0.2366" bushing, are we foolish to proceed? If it's critical, I can either specify a 0.2368" bushing initially and then order the smaller bushing if need be or I can just go ahead and order both bushings up front. It's not a huge cost (about the cost of a box of bullets) but I hate spending money I don't really need to spend.

TIA!

Bushing size I would say is a must for a good chamber. Larry

 

[Dusty Stevens]

Reamer print doesnt specify what bushing to use they specify what it comes with. They have no idea what your individual barrel measures. Your gunsmith will have a set of reamer bushings for each caliber in .0002 increments and will select the correct one while chambering. If he doesnt know what youre talking about you need to find an experienced barrel fitter

 

[butchlambert]

I chamber different than most and use a loose bushings. As far as the .237 barrel. It probably isn't .237. They vary a few tenths. That is the mean dimension that they shoot for. I have sets of Deltronic pins for each bore of the barrels that I chamber. They come in sets of 25. Say your .237 barrel is the mean and my middle pin is .237. It has 12 pins in .0001 increments lower and .0001 increments higher. The pins range from .2358-.2382. Pin your barrel and it will tell you pin size. I think your pin or bushing will be about .0002 smaller than bore size. A .237 pin will not fit a .237 hole unless you use a hammer.

 

[DCRYDER]

No way would I chamber a rifle without having several bushings to get the correct fit. All machine work has tolerances (+.xxx,-.xxx) . A .237" bore could range from .2365" to .2375" and still be acceptable. May even be larger. Bushings are sold in sets of 9 that span .0018" . That's +/- .0009, so 6mm bushings could range from .2358" to .2374" (these numbers are off the top of my head, not in my shop to look and see).

If your not going to use a bushing set you may as well use a solid pilot reamer.

My .02

 

[Cold Bore]

MY gunsmith does not have any bushings on hand in this range.

.... or I can just go ahead and order both bushings up front. It's not a huge cost (about the cost of a box of bullets) but I hate spending money I don't really need to spend.

No way would I chamber a rifle without having several bushings to get the correct fit.

If your not going to use a bushing set you may as well use a solid pilot reamer

Your rifle, your money, and your satisfaction ultimately on the line, but if your chosen 'smith doesn't have everything he needs to properly do the job, I'd either find a different 'smith or provide everything needed to the one you are using. Maybe you can split the cost of a bushing set with your 'smith. You get to have your job done correctly, he gets to keep them for future work. You both come out ahead, at half the cost each of buying it all yourself.

What is the total cost involved for the whole project (parts and labor charges)?

What does a set of bushings cost (or at least a couple extras, right around the "suggested" size)?

What is the relationship between those two figures?

 

[Steelnecktie]

There is also .0002" slop between bushing to reamer. You have to have a bushing set, each barrel is different size. Even with the play between bushing and reamer, I still get no runout in chamber, I think the heavy cutting oil takes up some of that .0002" space.
The problem I would worry about is not chamber runout, but a chip getting caught between barrel and poor fitted bushing.

 

[DaveTooley]

Get your reamer with a .2370" bushing. It may fit. If it doesn't it's very easy to put it between centers and polish it down to the size you need.

 

[Northridge]

If it's a krieger .2368 is your bushing most liklely , all though I would not assume this and verify every bore I work with. Rarely will you find a krieger above or below .2368. .237 bushing if all is not perfect in getting set up you will blemish riflings. If indicated in well and reaming at a safe rate you can use a undersized bushing on a properly bored pre chamber & ream a quality chamber with out massive run out or chatter. Ream smartly and you will ok.

Shawn Williams