Barrel indexing; is it worth it?

G

Gene Beggs

Active member
Judging by the views and responses, there are a great number of shooters who are keenly interested in barrel indexing.

Is it worth the hassle? Yes, definitely.

Is it for everyone? NO! Barrel indexing should be left to the gunsmiths and shooters who do their own machine work.

Hopefully, we will soon discover a way to identify the best position in which to install the barrel before it is fitted to the receiver. That is the ultimate goal.

Later,

Gene Beggs
 
B.Johnson

When you cut the barrel tenon to .900, how much uncut wall thickness do you have left on the bushing? I'm just not sure my figures are right.
 
B.Johnson said:
When you cut the barrel tenon to .900, how much uncut wall thickness do you have left on the bushing? I'm just not sure my figures are right.
Click to expand...


Bob, I don't know; all I know for sure is it's enough. It would take someone smarter than me to figure it out exactly. I often use the TLAR method of measurement. Are you familiar with the term TLAR?

It stands for, "That looks about right." :D

Later,

Gene Beggs
 
B.Johnson

I was wondering about the best method to make the bushing, what material did you use?
 
B.Johnson said:
I was wondering about the best method to make the bushing, what material did you use?
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Bob, the three prototypes were made from tenons cut from old barrels. A half inch hole was drilled and the remainder bored out with a carbide boring bar. Threads were single pointed and the slots for the indexing tool was milled with a 5/32 keyway cutter. They're easy to make.

Later,

Gene Beggs
 
Gene

This is splitting hairs but wouldn't it be better to take a scrap piece of barrel and turn the OD and ID then thread both all in one setup?

Dave
 
B.Johnson

My question is, when you thread the bushing ID, and OD down to root dia. how much uncut bushing wall are you going to have left?.Assuming a .900 barrel tenon, using an action threaded 1.062. How is this bushing held for the threading operation turned that thin? I keep coming up with a .040 wall thickness using a 26tpi inside, 18tpi outside, are these figures correct?
 
B.Johnson said:
My question is, when you thread the bushing ID, and OD down to root dia. how much uncut bushing wall are you going to have left?.Assuming a .900 barrel tenon, using an action threaded 1.062. How is this bushing held for the threading operation turned that thin? I keep coming up with a .040 wall thickness using a 26tpi inside, 18tpi outside, are these figures correct?
Click to expand...

You're about right. If you are wondering about safety, and why the action makers have settled on the current diameters for assemblies without a bushing, consider also that the root of each thread is a continuous stress riser spiraling from one end to the other...both inside and out...and that they intersect repeatedly because of the difference in lead between the internal and external threads.

-Dave-:)
 
Dave Tooley said:
Gene

This is splitting hairs but wouldn't it be better to take a scrap piece of barrel and turn the OD and ID then thread both all in one setup?

Dave
Click to expand...

Yes, because it would ensure cylindricity between the inside and outside threads.

-Dave-:)
 
Dave Tooley said:
Gene

This is splitting hairs but wouldn't it be better to take a scrap piece of barrel and turn the OD and ID then thread both all in one setup?

Dave
Click to expand...


You're right Dave, that would be better and you would stand a better chance of maintaining concentricity that way.

Thanks,

Gene Beggs
 
B.Johnson

Dave Short: When you say stress riser, do you mean fracture point?
 
Dave Short said:
Yes, because it would ensure cylindricity between the inside and outside threads.

-Dave-:)
Click to expand...

I should have stated this as concentricity.......I was considering that we're dealing with 2 cylindrical features. Cylindricity actually is used to refer to a single cylindrical feature.

-Dave-:)
 
Stronger Alloys

The answer to doubts about the bushing would be to go to a stronger alloy. There are quite a few specialty steels that offer properties that are superior to that which most barrels are made. In all honesty, 416 would be my last choice in such a thin cross sction.

Gene, your initial post is the one I have been waiting for. I can amagine that Gunsmiths everywhere are cringing at the thought of bushings in actions, turning down tenons, and the such. You know how set in their ways many are, and they probably looking at a lot of work for little gain.

It is sort of like my idea of setting back my barrels on a regular basis to keep the throats fresh. I believe it works, and is worth the effort.

But then, I own a Machine Shop. I can do pretty well what I please. For the shooter who has to depend on a outside source, (ie, a Gunsmith), to do his barrels, the concept probably becomes impracticle when you consider shipping charges, set up time, and the like.

In my opinion, the real solution to the tenon thickness problem is to take the threads of the action out another .062 to 1.125. That might be the most practicle solution in a senario where every little bit helps.......jackie.
 
barrel indexing

Gene is right on about barrel indexing. Do you ever wonder why some barrels are hummers and some not?
I've had both. Mostly not. The last new barrel I chambered shot with only anoccasional flier. After 400 rounds the groups started going diagonal.
I fought this barrel on tuning for the next 500 rounds. So, I decided to index the barrel 60 degrees by moving the shoulder back .006" and rechambering etc. With adjusting the powder charge .3 grs. and bullet seat by .003" the barrel will now agg. in high 1's.
Before all this time of indexing I never knew when shot 2 thru 5 would go out or maybe 2 shots out. Heck, maybe the first shot was the flier.
The 60 degrees was just a guess and maybe 90 degrees would be better. I will go 30 degrees more next.
The type of steel to use for the thread insert would best be served if it was of a different type or hardness than both the barrel and the receiver to avoid gaulding.
Joe
 
B.Johnson

Jackie: I also have my own machine tools, and can make the bushing.I have thought about different method's to do this, first no set screw. Second, I am leary of that ,040 wall thickness. I am not in the gunsmith business, and work only on the rifles for my sons', and I don't think I want to use them as a test bed. Gene feel's he has his theory nailed down, and it look's like it will fly. I just think there should be some pressure test's on the bushing idea. That means more than bolt lift, case appearence, and a couple of check's with a head space gage. I would be shy of putting those bushing's on the market, and saying "try this" at this point. There are some gunsmith's out there that are really a little more than the law should allow. I like the machine aspect of this forum, but let's keep it a little more understandable for those who need there work done elsewhere.
 
Dave Short said:
consider also that the root of each thread is a continuous stress riser spiraling from one end to the other...both inside and out...and that they intersect repeatedly because of the difference in lead between the internal and external threads.

-Dave-:)
Click to expand...


Not if a 3/4 profile thread cutter were to be used, which would also increase the solid material thickness between id and od thread cuts..............Don
 
jackie schmidt said:
In my opinion, the real solution to the tenon thickness problem is to take the threads of the action out another .062 to 1.125. That might be the most practicle solution in a senario where every little bit helps.......jackie.
Click to expand...


Good point Jackie. Jerry Stiller also said in one of his posts that taking the receiver threads out to 1.125 would probably be okay. That sounds like the best option to me and although it would involve a slight modification to the action, I think it would be better than reducing the tenon diameter. Making the bushing from stronger material is also a good idea.

Someone suggested today that another option would be to use a four-start thread on the barrel tenon. In this way, there would be no modifications to the receiver, the tenon could be left full 1.062 diameter and the shooter would then have four positions in which to install the barrel instead of one. No bushings, no concern for strength, simple, easy; what do you think?

Later,

Gene Beggs
 
Gene Beggs said:
Good point Jackie. Jerry Stiller also said in one of his posts that taking the receiver threads out to 1.125 would probably be okay. That sounds like the best option to me and although it would involve a slight modification to the action, I think it would be better than reducing the tenon diameter. Making the bushing from stronger material is also a good idea.

Someone suggested today that another option would be to use a four-start thread on the barrel tenon. In this way, there would be no modifications to the receiver, the tenon could be left full 1.062 diameter and the shooter would then have four positions in which to install the barrel instead of one. No bushings, no concern for strength, simple, easy; what do you think?

Later,

Gene Beggs
Click to expand...

No, a four-start thread barrel tennon would not work unless you were to also re-cut your action thread also as a four-start thread................Don
 
It seems too simple - - -

Gene Beggs said:
Good point Jackie. Jerry Stiller also said in one of his posts that taking the receiver threads out to 1.125 would probably be okay. That sounds like the best option to me and although it would involve a slight modification to the action, I think it would be better than reducing the tenon diameter. Making the bushing from stronger material is also a good idea.

Someone suggested today that another option would be to use a four-start thread on the barrel tenon. In this way, there would be no modifications to the receiver, the tenon could be left full 1.062 diameter and the shooter would then have four positions in which to install the barrel instead of one. No bushings, no concern for strength, simple, easy; what do you think?

Later,

Gene Beggs
Click to expand...

Just at first blush, what if none of the four pionts are the right points?

Cureently two or three of my rifles print a diagonal group. I think a correct index might make them into a verticle grouping and perhaps even take the verticle away. Whadda ya think?
 
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