Freebore is 100,000ths instead of intended 40,000th. Reamer screw-up, or the smith?

V

VaniB

New member
This is my first custom rifle, and I'm pretty annoyed to find that my 20Tac barrel has 2.5x more freebore in it (100,000) instead of the 40,0000 that the reamer was supposed to produce. :(

That is; when I use a 39 grain Sierra bullet, the minimal amount of case neck I need to hold the bullet firmly in place produces about 100,000 th's of freebore. On my ruler, that equals a little over 3/32" or slightly under 1/8" . (I'll sure not use any 32 grain bullets!)

Who messed up? Is the reamer cut wrong with too much freebore? Or did my smith cause the screw up? I can't understand how he could produce an overly long chamber without causing excess space and case bulging or head seperation??? (I fired one case which looked Ok)

I haven't fired this rifle at the range yet, and am not sure how this excess freebore will effect the groups. :confused:

Any input to educate me on what went wrong, and how accuracy might be effected, will be appreciated.


EDIT: 2/18/08 Neither the gunsmith or Dave at Pacific screwed up. I had mistakenly been pushing the bullet too far into the barrel when looking for the bore land marks. I have since learned how to identify where the lands actually make contact on the bullet.....and found that I have plenty of bullet grip still left in the case neck.
 
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Freebore

VaniB,

Since I have a copy of your reamer print, I gave it a quick perusal. Per the print, and depending on where one measure's freebore from, it is either .053 or .040. If you load a round that is 1.808 over all length to ogive, you should just be kissing the lands.

How much of the bullet do you have in the case?

Justin
 
My first thought would be someone forgot all the things that make up what I call freebore. You have the safety factor from the end of the case to the end of the neck area in the chamber.[ at least 0.010 maybe twice that] 0.015 for the 45 degree transition to the leade. If the leade was ordered at 0.040 and maybe 0.010 loss going into the throat you can get to 0.100 from the end of the case pretty easy. My 20 calibers have 0.065 total intentionaly and they handle the 39BK and the 32 Sierra and Hornady fine. Maybe a little more in the case wouldn't hurt. But I think you will be OK. Kenny
 
The reamer

Can't cut anything, but the size of the reamer. If one reamer was used to cut the whole chamber/throat, that whole chamber/throat is, what the reamer is. If a throat reamer was used to cut the throat as a separate operation, than go and kick the smith into his ass.

Shoot well
Peter
 
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Ok....to clarify; I have a gap that measures almost exactly 100 thousands. ( I believe that's equivlent to .1" ?) The various zero decimals on the dial caliper confuse me, but placing the caliper against my ruler it is certainly just right under 1/8" gap. (yes....my stainless ruler I certainly know how to read :D )

What I mean is; I can not get my Sierra 39 grain bullet any closer to the rifling without running out of good neck grip. That is the measurement of the gap for the Sierra to have to jump accross.....and what I call "free bore."

Just how bad is that gap? Tell me that it's not as bad what you guys always complain about with the factory Ruger 204
chambers? Tell me it can still deliver 1/2" groups.









Zebra....how are you! Now you see what I was saying about how sloooow I move on my projects? Just finally bought my Elite scope last month, and put it on my rifle last week.:rolleyes: What's it been.... exactly a year since I told you I was getting ready to have the rifle smithed?
 
To answer your question first: What you have lost is the *opportunity* to determine whether or not your rifle will shoot best with "jammed" bullets -- bullets into the lands. Not all rifles shoot best with jammed bullets. I have several that shoot best with a .020jump, a couple of 1,000 yard competition rifles, and a factory .223.

But more important, because it will affect the rest of your life, is that you come to an understanding of the terms involved. "Freebore" has a specific meaning, and does not directly translate into "OAL." It all works best with a picture, but freebore length is the straight-line distance before the forcing cone begins. This point was made in an earlier post -- how far out you seat a bullet to contact the lands is determined by (1) the step-down from neck diameter to freebore -- usually 45 degrees, but not always, (2) the freebore proper, and (3) the taper of the forcing cone -- usually 1.5 degrees half-cone angle (3 degrees included). Note that with this latter specification, bullets having a different ogive will need a bit more or less distance (seating depth) to contact the lands.

This is how a reamer maker will understand those terms, & if your understanding is different, you will not get what you expect. And has already been pointed out, if the smith cut the chamber using the reamer only he made no mistake; all those spacings are built into the reamer.
 
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sicero said:
My first thought would be someone forgot all the things that make up what I call freebore. You have the safety factor from the end of the case to the end of the neck area in the chamber.[ at least 0.010 maybe twice that] 0.015 for the 45 degree transition to the leade. If the leade was ordered at 0.040 and maybe 0.010 loss going into the throat you can get to 0.100 from the end of the case pretty easy. My 20 calibers have 0.065 total intentionaly and they handle the 39BK and the 32 Sierra and Hornady fine. Maybe a little more in the case wouldn't hurt. But I think you will be OK. Kenny
Click to expand...

VaniB,

I am good, sir! I just got my .20 cal barrel from Lilja, so I don't move too fast either!

Sicero does a fine job of explaining things above. On your print, if measuring the safety factor as detailed above, you get a total of .053. Without the safety factor, you get .040. Look at your reamer print, and look for those two measurements...a picture is worth a thousand words.

I am curious as to know how much of the bullet you have in the case to get what you call a good neck grip. I use to think one bullet diameter was a good rule of thumb, and was a little twitchy because on my first chambering job, in order to touch the lands, I only had about .100 of the bullet in the case. I posted here about this, and most told me not to worry about it. I also talked to a friend of mine...an ex-benchrester. He told me don't worry about it, and as he has lots of wood on his walls, I tend to believe him. I have the reamer print for his .20 Tac and it shows something like .080 freebore. He is very happy with the reamer and the performance of his rifles chambered with it. My gun in question, I shoot .020 off of the lands, and it shoots great.

So...you may be able to seat your bullets a little longer and touch your lands. If not, shoot it anyway. As your first custom gun, the groups you shoot with it will probably make you blink.

Justin
 
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Charles E,

To avoid semantics and confusion, in my last post I simply explained that the .1" (1/10 of an inch) that I'm referring to is the length of the gap that the 39 sierra must make before it touches the lands.

This is the length that a Stoney Point indicator would read. I don't have a Stoney Point tool, but I started with the bullet far out of the case to where it practically has no more neck to grip it. I then used the bolt to push the cartridge against the lands. Then I removed this cartridge from the rifle chamber. I compared it to the length of another cartridge that contains the 39 grain Sierra seated as far out of the case as I can go before the grip on the bullet is too weak to hold it. (I settled on a .15" long grip.)

Comparing the difference of the two COL measurements of the two has given me a .1" difference. In other words, the case I intend to reload and has the bullet out as far as I can go, would have to be seated out another .1" of length before it would touch the lands and be just as long as my test cartridge.



If I were to leave the bullet so it touched the lands, it would barely be holding on into the case neck by about a 1/16".

I don't believe the gunsmith even owns a "rough" reamer. He only had one tac20 reamer and knew nothing about its history having only used it twice in 3 years. So, I had Dave at Pacific make me a reamer.....so I could have it made to my preference, and we know what we are getting. (yea...right...:rolleyes: we see how that turned out) So I think the problem lies with DAVE at PACIFIC. I had stessed to Dave over and over on the phone that the barrel was a 1-1 twist, and I was planning on using a Sierra 39 grain bullet and Lapua case....and that I wanted the bullet to be up on the lands. I settled for a .04 on his recommendations, figuring I would have flexibility one way or the other. I DIDN'T EXPECT A MANDATORY .1 GAP!!

He can call it "freebore", "tight bore", "45 degree chamber" or whatever technical terms he and others here would like to use....
BUT WHEN I'M ON THE PHONE ORDERING IT, HOW HARD IS IT TO UNDERSTAND THAT I WANTED THE SIERRA BULLET TOUCHING THE LANDS OR NO MORE THEN .04" FROM IT? :mad:



ZEBRA,

I have the 39 grain Sierra bullet seated into the case and what I checked carefully and considered a bare minimum for decent grip and to retain good concentricity: it is being held by a depth of .15" (Using the "bullet diameter" as a rule of thumb, the .15" is not even the diameter of a 17 cal bullet in this case!)
 
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Now don't get too hot with me.

If you made up a dummy round & asked a reamer maker to make you a reamer so that the bullet, as seated in your dummy, would make contact with the lands, then yeah, there was a screw-up, and I think the reamer maker has the lion's share of the responsibility. Hard to know just how much without being there, but I'd say you have a legitimate gripe.

If, on the other hand, you gave him specifications -- so much for this, so much for that, then if he followed those specifications and things didn't work out, the responsibility is yours. I've done this, by the way.

Yes, there is no need to learn the terminology of specifying a chamber or reamer if it satisfies you make up a dummy & have the reamer maker do the work. But if, as so many of this forum, you want to specify exactly what you want, then you gotta learn the terminology. That was the point I was trying to make.

IF you can't bear it, get up with the reamer maker & see if he will re-work it. I'll bet that if he feels it was his fault, he'll do it for little or no cost. You can probably set the barrel back just one or two threads with a new reamer & have exactly what you want.

But finally, if you are single-loading, I wouldn't hesitate to try what you've got using only 1/16 (.0625) of the bullet in the neck. If it shoots better, load that way. If it shoots better jumping the bullet, & I suspect it might, you'll have more bullet in the neck.
 
VaniB said:
...

This is the length that a Stoney Point indicator would read. I don't have a Stoney Point tool, but simply fit a snug bullet sticking way far out of a case, took the cartridge COL measurement, and then drove the bullet home into the case with the rifle bolt until the bullet contacted the lands. I would then carefully take the cartridge out of the chamber and take another measurement. When doing the math and comparing the COL differences of before and after, 3 different times it indicated the same 1/10 of an inch, or slightly under 1/8". To be exact it measures .1002"
Click to expand...

Sounds like you drove the bullet DEEP INTO the lands not touching them.

Long seat a bullet into prepped brass with no primer or powder and use a black marker where the lands should contact.

Continue to adjust your seating depth until no land marks show up on the black. This is the spot where jump STARTS, measure how much bullet is in the case now and report back to us.

Put things in writing when ordering, then you know exactly where you stand.
 
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PEI Rob,

Ooops, I stated it wrong about how I measured it.

What I meant to say was that I started with the bullet far out of the case to where it practically has no more neck to grip it. I then used the bolt to push the cartridge against the lands. Then I removed this cartridge from the rifle chamber. I compared it to the length of another cartridge that contains the 39 grain Sierra seated as far out of the case as I can go before the grip on the bullet is too weak to hold it. (I settled on a .15" long grip.)

Comparing the difference of the two COL measurements of the two has given me a .1" difference. In other words, the case I intend to reload and has the bullet out as far as I can go, would have to be seated out another .1" of length before it would touch the lands and be just as long as my test cartridge.

I'll try the majic marker method you requested.

Al Nyhus,

The length from the ogive to the boat tail base is about .375" Of this, the base has a boat tail on it which looks about .04" long of non-bearing surface.

The length of my loaded round from case rim edge to ogive is 1.922" And from the green tip point to rim is 2.295" in COL.
 
Did you specify boattail bullet?

This could well be the problem.

But I dont really see a problem, I shoot a 66gn boattail in my 6PPC and it is only just held in the case, but it shoots. Just go shoot it.

Rob Carnell
Sydney, Australia
 
Van B:

Do you have any idea how far you can push the bullet into the lands with the bolt without actually feeling when it touches? With only one and a half degree per side on the taper of the leade it is almost impossible to feel it using your method. Even using a Stoney Point tool, one can push the bullet into the lands further than you want.
 
The magic marker method didn't work....at least not for me. The bolt extractor and chamber walls cause more marks along the sides of the black bullet, then any discernable micro marks being produced by the starting edges of lands.

Jkob,
I have been assuming that the bolt pushes the bullet ogive onto the start of the lands, and not into the lands/bore. You may correct me if I'm wrong, but I would assume it takes some good PSI combustion to get the bullet started into the lands....enough pressure that a brass case can be reshaped, and a bullet is left with grooves through it. Even if the bolt has the power to cam the bullet forward into the bore, the soft metal brass case neck is not capable of holding the bullet that firm. Especially not with the neck being sized only 1,000th or two tighter then the bullet diameter.

The Stoney point tool concept would not otherwise work. No ??


Well, I guess what's done is done, and I have no other choice but to head to the firing range in the next week or so and see what groups a .1" gap produces.

If the rifle barrel needs to be pulled off the action and resmithed, then there's no sense in me coming back to my smith, or Dave at Pacific a year later, and being accusatory and bitching them out . I'll just drop the stuff off to them, nicely explain the situation, and pay whatever bill they give me.

Thanks gentlemen for the input.
 
Yea Charles E,

I assumed when I told Dave that I was intending on using Lapua cases and Sierra 39's EXCLUSIVELY (and that I'd also try Hornady 40's).... he suggested that I go with .04 off the lands.....I figured he knew all the meaurements. I agreed with a .04 off the lands, because I figured I would still have enough bullet base and case neck to seat the bullet how I needed. Never did he suggest that I send him a dummy round. And never did I expect to get stuck with a .1" off the lands.

Like I said....you live and learn. Next time, I'll buy my reloading dies first, and send a dummy round.
 
VaniB:

Let's try a little something and see if we can get a better handle on what's happening. If you would...do this:
1. Remove the firing pin assy. from your bolt.
2. Make sure your chamber and throat are perfectly clean..no oils or solvent.
3. Neck size an unprimed case .004-.005 under what the loaded neck dia. is.
4. Seat one of your 39gr. Sierra's about .050 into the neck.
5. Polish the bullet with 0000 steel wool.
6. Insert the round and close the bolt.
7. Open the bolt and remove the round. The bullet should stay in the neck.
8. If it doesn't, take a wooden dowel and tap the bullet out from the muzzle.
9. Examine the marks the lands made on the bullet.
10. If the bullet came out of the neck, reseat it to the original depth.
11. Seat the bullet .010 deeper and repeat. Make sure and use the 0000 wool

As you continue to do this (seating .010 deeper each time) you'll notice the marks on the bullet beginning to change shape/width/length.
When the marks disappear, you've found where the lands just start.

Now, measure how much of the bullet shank is in the case neck.

Then let's go from there, okay? :) -Al
 
VaniB said:
PEI Rob,

Ooops, I stated it wrong about how I measured it.

What I meant to say was that I started with the bullet far out of the case to where it practically has no more neck to grip it. I then used the bolt to push the cartridge against the lands. Then I removed this cartridge from the rifle chamber. I compared it to the length of another cartridge that contains the 39 grain Sierra seated as far out of the case as I can go before the grip on the bullet is too weak to hold it. (I settled on a .15" long grip.)
Click to expand...

AGAIN I think your are deep into the lands. Not to be a smart ass but probably about .060" into the lands.

Don't use the bolt, put it aside.

Smoke the shoulder with long seated bullet with a match or lighter, much easier to see marks. Make sure there is no primer or powder in the case :D

Drop the dummy round into the chamber, gravity should bring it all the way to shoulder contact.

If you have any marks on the bullet from the lands your bullet is seated into the lands. The throat is the beginning of the lands and still counts as lands.

Cheers,
Rob
 
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