Hey guys I'm wondering what is an acceptable length for an indicator tip for dialing in my barrels before chambering etc? I've been using range rods to good affect but want to decrease my variables. I currently cannot afford an interapid long reach and was wondering if a 1.6" ish tip for my mit .0001 indicator would be sufficient. If you've got another idea please let me know. Thanks
Gunsmithing Length of indicator tip for chambering
- Thread starter hunter223
- Start date
I'm no pro, but I use a tip on mine that is about 1.4 (2x normal length) and I know more than one pro smith that does as well. Just remember your graduations will be .0002 with that long of a tip. I like it because I pre drill the chamber and can fit the indicator body into the chamber so the tip reaches about 2.75" into the barrel.
It's a pretty common practice to pre-drill, dial in the throat then do the rest of the tenon work and single point pre-bore the chamber.
Yup. And after you drill it, you can sometimes reach a bit farther in to triple check yourself before you single point cut it.
Thats the issue. Mine is a 2.75"/.0005" intrepid. Bought it used on ebay for $160. Works great, but at a certain cartridge length, that wont be long enough either.
IMO if you are bang on @ 2.74" and 1.0" the odds of the barrel hooking a left at 2.76" are miiiiiighty slim. Once you are bored for the reamer, you'll be able to reach in another. 250" or better.....and even if you could not, it goes back to the barrel not likely to take a major turn.
If you are going to zero the bore by indicating off of 2 points down the bore, the distance between those 2 points will be directly slaved to your accuracy of index. For example, if you have a curved bore (almost all are just the extent is variable) and you indicated 1 inch into the bore and then travel down only 0.250" further to check alignment again, you will have very little run-out to detect even if the bore is in fact off axis to the spindle. Accordingly, the further apart you can stretch your 2 check points, the more easily and accurate you can detect any existing curve and dial it out. ....... so the longer your indicator can reach, the longer you can stretch those 2 points.
If you subscribe to that theory, trying to detect and dial out any curvature with a short stem indicator is almost as bad as indicating off of only one point in the bore and assuming that the bore immediately downstream from that point is running with no axial run-out the spindle.
Truth is, that most better barrels have small enough curvature that you could likely get away with the lesser of the above and still never see any accuracy issues in the real world considering all of the other variables.
That being said, we should all try to execute our work with best practice and best technical theory we can to insure concentricity on the finished product.
This is just my own personal opinion on the way I should setup and cut. I have definitely found that a lot of this is like religion.. . . . . we can all have variations of how we believe things are and still live our lives happily with the results we see.
Terry, I'd think that a 2.75" indicator would be sufficient for most all cases wouldn't it?
As Hero's mentioned, whats happeneing in front of the test indicator would be a bit of a guess if you were chambering for something longer, but likely the bore isnt going sideways forward of that, if everything behind it(the part you can measure) is running true.
Terry, what would be your recommendation for guys like me using a long test indicator, when chambering for longer cartridges like .338 Lm etc? If i was doing a lapua, the pilot would be running about an inch in front of the deepest portion that i can measure with a 2.75" indicator, when the reamer reaches full depth. I usually dial in two points. One where the pilot will ride, and an inch back (towards breech)from there. i vary it slightly with cartridge size. Very easy to look further back at any other point as well. The longest ive done so far is a 338-06. My indicator was riding where the freebore ended up. Never touched where the pilot rode. Through the borescope, everything looked uniform, and there was no eccentricity in the chamber, so guess the bore forward of where I measured wasn't carrying the pilot off anywhere.
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Don't worry so much about it. Buy a good barrel and do as good a setup as you know how with proper dimensions and minimal headspacing and it'll likely shoot well.
Here's why. Why indicate grooves when your reamer follows the lands? You would have to have a super rigid setup aligned absolutely dead nuts perfect, no cant, no droop, no flex. You'd also run an undersized bushing to keep the lands from deflecting the reamer. Do you have that? I don't. Even then, if your chamber is perfectly parallel and concentric to the grooves, what happens if the two circles ascribed by the lands and grooves are not perfectly coaxial where you have indicated? Take a long stem interapid and you will find that groove depth is not always exactly uniform.
Also, how's your headspacing? If your round sits three thousandths off the shoulder of the chamber it slides back and DOWN. The bullet will start below the centerline of the bore. How does the pressure of the ejector cant the round? What does the upward pressure of the trigger sear do to the bolt head and lug engagement? There may be answers to these questions out there but I've looked far and wide and nobody is sharing if they know. It'd take a lot of money and time to definitively say how to effectively mitigate all these factors. Like I'm saying here, agonize less, shoot more.
Get you a range rod and go to town. I had the good fortune this past weekend to talk about chambering with a very very well known smith. If it's good enough for him, it's good enough for me.
Here's why. Why indicate grooves when your reamer follows the lands? You would have to have a super rigid setup aligned absolutely dead nuts perfect, no cant, no droop, no flex. You'd also run an undersized bushing to keep the lands from deflecting the reamer. Do you have that? I don't. Even then, if your chamber is perfectly parallel and concentric to the grooves, what happens if the two circles ascribed by the lands and grooves are not perfectly coaxial where you have indicated? Take a long stem interapid and you will find that groove depth is not always exactly uniform.
Also, how's your headspacing? If your round sits three thousandths off the shoulder of the chamber it slides back and DOWN. The bullet will start below the centerline of the bore. How does the pressure of the ejector cant the round? What does the upward pressure of the trigger sear do to the bolt head and lug engagement? There may be answers to these questions out there but I've looked far and wide and nobody is sharing if they know. It'd take a lot of money and time to definitively say how to effectively mitigate all these factors. Like I'm saying here, agonize less, shoot more.
Get you a range rod and go to town. I had the good fortune this past weekend to talk about chambering with a very very well known smith. If it's good enough for him, it's good enough for me.
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Have you ever calculated how much that fictional situation would allow the bullet to fall down below the true centerline of the bore?
Look at the leade diameter on most chambers that are dimensionally cleaned up to get the SAAMI slop out. Look at that same dimension on some of the newer SAAMI standardized rounds. Almost every reamer I use has a leade diameter between 0.0008 and 0.0010" over nominal bullet diameter. That would leave 0.0004 to 0.0005" clearance all the way around the bullet. Theoretically, you could purposefully create a crooked round of ammunition and the bullet would still be brought into alignment (very, very close anyway) to the bore once it is chambered and ready to fire.
Most shops that chamber barrels do not have lathe bearings or instruments capable of dialing in and then keeping linear and axial alignments that STAY within that range anyway.
I that condition is true, then the choice is yours as whether to start the bullet toward a straight path into the curved bore (assuming that all bores have at least a little curvature) or start the same bullet headed into the ditch early into the same curve.
Again, we are just debating perfect theory and setup conditions and I do agree with you that you can do an awful lot of things crooked and still get very good results.
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I'm with you though Terry, I'd rather start straighter and have the piece of mind and know I chambered it as perfectly as I could.
Respectfully Terry yes I have. On a 6.5 Creedmoor, rise over run on the case body: half of the difference in diameter of case body from head to shoulder is .021/1.450"x.004" headspace=a little over half a tenth drop. This is about the order of magnitude we are trying to dial to.
Also, I failed to even address ammo concentricity and bullet cant in the round. What happens to the bullet in whatever jump to the lands when it travels in free air? It is not on a string. The bullet is pushed from the rear and not dragged from the front and will gimbal around its center of gravity when not constrained by the rifling. How does it go in? No way to know for sure with those variables present. The only way to control those variables is to eliminate them, i.e. zero headspacing and a jammed bullet. Even that requires theoretically perfectly concentric and straight ammo. Most of this is from Vaughn's book.
How do guys like Dave Tooley and Butch Lambert turn out such accurate rifles when they indicate at the throat and the crown in these curved tubes? Why can Ozzie Suarez build a rifle on video that is 1/4 MOA out of a steady rest?
https://youtu.be/epiGY0qFT3Q
One of the guys at Stiller made a good analogy to me. The benchrest game is formula one. Out game is Baja. Even all of these variables properly executed likely won't show up on a Harris bipod and rear bag. How many guys are capable of executing in the neighborhood of the .001's or even teens? Not many.
There is more than one way to skin a cat and we spend too much time fussing over who's crow is blackest. The guy is getting sub 1/4 MOA groups out of his builds and I'm just telling him to shoot more and worry less. I'm not trying to offend anybody and I'd love to sweep chips in your shop for a month. I'd learn volumes.
Thx
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Man I appreciate the kind words about my rifles. I agree with you about there's more than one way to skin a cat. I know that 99 percent of the people that will shoot a rifle I barrel won't be able to realize it's accuracy potential simply because they don't practice enough or have bad fundamentals.
honestly I'm trying to make these things even better for my piece of mind. I want to build the best rifle possible and if ever an issue comes up it will help me Trouble shoot quicker. Also my thought is, the closer the rifle is to shooting "0" groups then anything that shows up on the target that's bigger than that let's me and the shooter know where to look and how to improve.
Also my thought process is, the better the rifle shoots the better the shooter shoots. Simply because if I was to take a legitimate 1/4 moa gun and I shot a 1/4 moa group I know I'm doing my part. If John Doe shoots the same rifle and is only able to shoot a 1/2moa group he will likely be very happy. Now if the gun is a 1/2moa gun and he takes it and shoots it now maybe he is pissed becuse he thinks I built him a 1moa rifle. That's my main drive for trying to build a great rifle. I want the product to reflect my passion for the sport.
honestly I'm trying to make these things even better for my piece of mind. I want to build the best rifle possible and if ever an issue comes up it will help me Trouble shoot quicker. Also my thought is, the closer the rifle is to shooting "0" groups then anything that shows up on the target that's bigger than that let's me and the shooter know where to look and how to improve.
Also my thought process is, the better the rifle shoots the better the shooter shoots. Simply because if I was to take a legitimate 1/4 moa gun and I shot a 1/4 moa group I know I'm doing my part. If John Doe shoots the same rifle and is only able to shoot a 1/2moa group he will likely be very happy. Now if the gun is a 1/2moa gun and he takes it and shoots it now maybe he is pissed becuse he thinks I built him a 1moa rifle. That's my main drive for trying to build a great rifle. I want the product to reflect my passion for the sport.
This.
I try to indicate the bore 1/2" in and where the throat will end up. With my 2.75" tip Interapid I can reach in as far as the chamber throat for all the short action calibers I've done thus far. If I do a long action, I'll just reach as far in as the indicator will go.
Might as well make it as close to perfect as you can, that's what I do.
I think what terry was describing was the very small freebore clearance around the bullet. If you load close to the lands, thats an additional centering element. The The plunger ejector in most of our receivers would prevent the cartridge from backing out, as would the firing pin blow.
If that's the case, how come my mausingfield shoots as good better than any rifle I've done? There's no spring ejector there. I'm not saying this is wrong I'm just curious.
Ejector would also can't the round down and to the right in any free play on the chamber. The trigger sear pushes up on the rear of the bolt so typically bottom lug has greater engagement and the bolt face is not perpendicular when in battery. Mausingfield gets around this with the toroidal lug design (donut in a bowl).
The ejector is off axis, but with the shoulder of the casehead against the shoulder of the chamber( and prevously mentioned freebore), there's nowhere for the front end of the cartridge to go. The case head wouldnt be in contact with breech face in this scenario either. When it finally does, the whole front end of the case is pressing out against the chamber, and the bullet is moving down the bore. That brings me to a gripe I have with people who neck size. Their rounds are too fat and to long, and nowhere near as straight as the chambers we cut. The crooked breech face caused by the tipped up bolt creates axial runout in the case head of the previously fired brass, which would still be present in the reloaded cartridge. But when they cam closed on one of those rounds, by golly the forces must be high, and certainly that cartridge is bending and contorting. Still may be straight at the front end, but not without a significant amount of stress.
A box stock remington still manages to shoot a decent group with all of its misalignment, go figure...
A box stock remington still manages to shoot a decent group with all of its misalignment, go figure...
...if you have good and snug headspacing. I've read just about everything I can find on how to get the most out of a chambering job, and admittedly I am a novice. That's why I wouldn't dare argue with guys like Terry. I just think there are so many variables that come to bear on what you ultimately get out of a rifle that we worry too much about things that really don't matter sometimes.
Don't get me wrong, I'm as manic as anybody who doesn't do this for living about building very accurate rifles. Heck I built a guest house with an air conditioned shop in the basement just so I would have a place to put my South Bend I spent two years restoring. When I see somebody present data that convinces me what I'm doing isn't as good as I could be, I'll change my technique up in a heartbeat. In the meantime, my rifles shoot beyond my abilities with boxed ammo, and that's all I can ask for.
