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Pilot bushings

Alex Wheeler

Alex Wheeler

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Lots of talk about this subject. I will give my thoughts. This is my opinion on the subject only.

A pilot bushing centers its od in the smallest id of the lands. If that section of bore is dialed in as well as the section the throat will be in, the bushing will have no effect. Assuming that $20 bushing is made with zero concentricity error. If you dial both ends it may not be and if theres runout in the section of bore the bushing is in it will walk the front of the reamer around and produce a throat thats not centered in its part of the bore. Thats one of the reasons some guys use undersized bushings or none at all. You can produce equal quality chambers with or without a bushing so long as you know how to use them. Some barrels have grooves that are not uniform to the lands. If you choose to dial off the grooves the pilot may fight you. Some reamers have very long freebores. That means they are flexible. The pilot does provide support and can help with push off. Theres no right or wrong. Theres a good time to use one and a time you dont have to. The point is to understand what they do and dont do so you know.
 
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A customer-dealer who i fit a few barrels for nearly always supply's the the barrel blank and reamer.most of his reamers have fixed pilots and usually they are like a dick in a shirt sleeve in the bore.i dial in,pre bore and ream just the same as a reamer with removable pilots and the interapid shows a couple of tenths worst case and the chambers are consistent.i think set up and attention to detail and doing things consistently correct for one's chosen method are crucially important..just my humble opinion.
 
@Alex Wheeler lays out a conceptual case where you may not use a bushing and @DaveTooley gives a practical example.

Understanding that there is no one right answer, --I am asking-- does how you hold the reamer influence your choice about pilot selection.

I would think if you have a super straight bore or you've predrilled, indicated to your satisfaction and bored that no pilot or small pilot is good and reamer holding method is less important.

It looks like there are two varieties of floating reamer holders. There is the Gre-Tan type that can minimize angular misalignment problems and there is the Manson floating reamer that can minimize lateral misalignment problems. I'm not sure where the Bald Eagle holder fits in. It is more like the Gre-Tan but can also address lateral issues.

Not necessarily looking for something to purchase but more a guideline of when to use which. It seems like if I've done a great job of dialing in and pre-boring that the only issue I have to worry about is my tail stock and if that's the case then the Gre-Tan type holder is probably the right general tool.

I know y'all are going to say---"it depends..."

Hank
 
Henryrifle said:
@Alex Wheeler lays out a conceptual case where you may not use a bushing and @DaveTooley gives a practical example.



I would think if you have a super straight bore or you've predrilled, indicated to your satisfaction and bored that no pilot or small pilot is good and reamer holding method is less important.


Hank
Click to expand...
That's it in a nut shell.
If you don't have a true, concentric bore/ roughed in chamber you are chasing ways to compensate for the misalignment. Chasing being the key word there. Tight bushing gets you close but close it's good enough here.
I do not use a floating reamer holder. I haven't for 30+ years. With a true hole all you need is a simple pusher. The reamer wants to go to the middle of the hole. Let it.
 
I was "forced" to skip using a pilot on a tight bore 308. Was pretty nervous that something would go terribly wrong. Ended up being a spectacular shooter. Once I thought about how it all works... I quit using them unless it's not a 4 groove... and then only use it towards the last half inch or so.
 
DaveTooley said:
I have a 257 Wby reamer that has the bushing way way out front. I couldn't get a throat I was happy with until I figured out the bushing was pushing the reamer off center. Undersize bushing = concentric throat.
Click to expand...
This i why i never have reamers re ground. It just puts the bushing farther out.
 
I chambered up a cheap fire forming barrel to fire form 300 Norma Imp. brass instead of doing that process in the actual barrel for the rifle.

The barrel was a button rifled blank and I thought this would be a good time to try and see how the outcome would be without using a bushing on the reamer.

My chambering meathod is to drill, and then set the compound to the taper of the reamer and bore the chamber close to diameter up to the body/shoulder junction. After that I just run the reamer in to cut the chamber which is basically just opening up the body diameter a little, and cutting everything from the body/shoulder junction forward.

After I finished the chamber I ran the bore scope in to take a peek at how things looked. When I spun the chuck the chamber looked great. No uneven cut lands or grooves tapering off into where the neck was cut and everything symmetrical.

So I guess from this experiment I can maybe give it another shot on an actual barrel I want to keep on the action for use other than fire forming brass. It looks just as good as one of the previous barrels I've chambered using a close fitting bushing on the reamer.
 
That little pilot isn't going to drive the reamer any better than the reamer body in the single pointed prebored hole. It might do nothing, it might make the throat grow....it might hang a chip.....but it's not going to change the reamer from heading home. Honestly, I don't think a heavy 10 sized machine tailstock poked out 4" can induce enough to make enough difference to sweat....assuming it was OC to begin with. A prebored hole IS the best pilot made.
 
Since I am a pilot and I use bushings, I think I am qualified to ask questions here.

The guy that first showed me how to chamber emphasized using a snug bushing to help avoid chatter. I know of at least one other master machinist that thinks the same way.

I think I have fixed uneven rifling once or twice by going to a tighter bushings. Based on what's posted here, that must have meant I was dialed in straight.

I recently had to cut an 11 degree crown with an 11 degree reamer that I have used many times. The reamer chattered. I fixed it with emory cloth and decided I wouldn't use a crown reamer again unless I had a snug bushing.

I get it that the crown reamer doesn't have any chamber or prebore to guide it, and maybe that's the reason why it chattered.

Anyway, all the above has made me leary of not using a bushing. I direct dial the throat area and the breech. Maybe I just need to try it on barrel scrap and see.

Concerning the end dialers, we know their throats are running out. Wouldn't a good floating reamer holder prevent a wallowed out throat, or is the tolerance between the bushing and reamer and between the bushing and bore allow it to wallow?
 
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