“Blueprinting” an action... what and why
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  1. #1
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    Default “Blueprinting” an action... what and why

    I’m having a tough time understanding why this is a thing. Please correct me if I’m wrong because I’m not sure I get it, but it sounds like blueprinting an action is bringing it to as nominal to a print dimension as possible. To do it, you need a $300 kit with two bushings and some tooling. You trim the minor diameter to be “true” to the action, then chase the threads to match. Then there’s something about checking the lugs for even purchase.

    Is the idea that you keep the cartridge from being twisted inside the chamber? I did the Google, and there’s lots of people who perform this blue printing thing and there’s lots of people who say it’s a good thing but there’s nobody with actual data to back it up with. And I spent a whole 10 minutes on the Google so I’m an expert now. (Calm down, I’m just kidding. I know very little about it, which is why I ask)

    I’ve voiced my hesitation, but I’m genuinely curious. Is it just another buzz word or is there an actual benefit to making your firearm actions perfectly concentric to the barrel? For the price of the toolkit I could buy the same tools to make the same action that I’m supposedly blueprinting. If I had a blueprint I just make it at nominal the first time.

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    Accuracy in rifles is to some degree about vibrations and distortions - waves traveling back and forth. Thus, having a "floated" barrel that isn't restrained by anything makes some sense. I have read that in the black-powder to smokeless conversion era moving the bolt lugs from the back of the bolt to the front improved accuracy. Why? Presumably because the front of the bolt is helt more securely long enough for the bullet to the leave the barrel.

    Does this kind of work on a bolt matter? I don't have any idea. (Trigger jobs are usually about making the trigger easier to pull very precisely and smoothly....)

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    Blue Printing, is not a very good term, but it is useful just the same.

    The idea, as illuminated by b_m above is to make the parts solid and secure so they do the same thing with every round fired.

    It's really no different than hand scraping a machine tool. The idea being if everything is straight and true with maximum bearing surfaced consistent with the intended motion, the accuracy will be improved (repeatability really) and in the case of a fire arm, the projectile will land in the same place every time.

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    Its a well known fact that rifle actions with independant or floating boltheads ,are more easily manufactured to be accurate.Even more so ,if the bolthead locks up into the barrel..........This is the theory behind the Sportco 44,a relatively cheap rifle renowned for accuracy......the bolt head floated freely in the bolt ,retained by a loose fitting pin.The downside is replacement barrels must have locking lugs machined into them.

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    Quote Originally Posted by thunderskunk View Post

    Is the idea that you keep the cartridge from being twisted inside the chamber?
    The idea is if everything is concentric and square to the bore of the receiver and tighter tolerances there will be less flexing of the action than from eccentric axial loads caused by misalignment of components and unequal bearing during firing.

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    This question really applies more to someone who has been exposed to tool and die work. You single point the barrel threads and you face the collar (if present) and the face of the receiver ring dead nuts to the bore. You face the locking lug seats dead nuts true to the bore. It's like a bearing in a machine tool, if you want repeatability (read accuracy) it all must be very well aligned. We accomplish this by cutting as many surfaces within the same set up as possible. If we must change the set up we indicate everything back in as close as possible before we continue. That being said, a barrel is "live" like any other tube. We get as close as we can by holding a dozen variables to the smallest possible variation. Think about this a moment and all should come clear.

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    One must ask, "How does one "blueprint" an AR-10?

    The bolt locks on the barrel extension. But everything after that just flops in the wind.

    I have known of efforts to "loc tite fit" the barrel into the upper.

    But consider the torque tolerance for the barrel nut, or the "fit" of the lower to the upper.

    It's all a joke, and still, great scores at long ranges.... go figure...

    What is that .22 rifle in a Rem 700 chassis. ??? amazing long distance accuracy

    I;m still moving 50 grams up and down the barrel looking for that "perfect" spot.

    Watch a super slow motion of any barrel whip video for what is really being talked about. Amazing animation!

    THE MOST ACCURATE 22LR BOLT ACTION I HAVE EVER SHOT - VUDOO RAVAGE - YouTube

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    Only part of the subject has been hit upon, the receiver. If the bolt is not machined and its OD is not a very close fit to the reamed receiver, you still have a problem. A loose factory bolt will raise in the rear and unload the top bolt lug. I've personally followed a couple rifles that were purposely modified in steps and shot between steps. The only notable steps that helped were a good trigger, great bedding, and a custom barrel. The so called "blueprinting" is just a waste of time and money.
    To properly straighten a receiver and replace the bolt or modify the bolt will cost about the same as a custom receiver with very little extra resale value.

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    Quote Originally Posted by CalG View Post
    One must ask, "How does one "blueprint" an AR-10?

    The bolt locks on the barrel extension. But everything after that just flops in the wind.

    I have known of efforts to "loc tite fit" the barrel into the upper.

    But consider the torque tolerance for the barrel nut, or the "fit" of the lower to the upper.

    It's all a joke, and still, great scores at long ranges.... go figure...

    What is that .22 rifle in a Rem 700 chassis. ??? amazing long distance accuracy

    I;m still moving 50 grams up and down the barrel looking for that "perfect" spot.

    Watch a super slow motion of any barrel whip video for what is really being talked about. Amazing animation!

    THE MOST ACCURATE 22LR BOLT ACTION I HAVE EVER SHOT - VUDOO RAVAGE - YouTube
    I' glad he qualified it by saying "that he has shot".

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    As Butch stated...this is a waste of money and time for the most part, considering the affordable cost of a properly machined action these days. Back when the Remington 700 was the only real choice available, it might have made sense to go all out and try to get everything to line up as it should and fit as it should. Whether you actually realized any benefit from it was more a function of the other components added (barrel, trigger etc.)and piece of mind knowing that it was as close to design as could be done with the original factory action.

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    On actions made from bar stock doing as many operations as you can in a single chucking would make everything machined in that chucking perfectly concentric and square. I have always thought that blue printing would make things worse.

    Old military actions where they were machined on many different fixtures are a different story. i machined the face of my Krag while it was chucked on a mock threaded barrel and that face was way off. In an original Krag it did not matter since nothing touched that surface.

    I have a commercial part that we make and every external surface and two of the internal dimensions are done in one chucking. Cost efficient and accurate to boot. We machinists have our ways!

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    Quote Originally Posted by FredC View Post
    On actions made from bar stock doing as many operations as you can in a single chucking would make everything machined in that chucking perfectly concentric and square.
    And then you cut a loading/ejection port in it, with some risk of warping. And a repeater is even worse.

    Barnard, at least, grinds the bolt bores on their's after heat treat. But that's maybe easier with a full body bolt.

    I think trueing an action makes barrel fitting easier. With everything square you can take measurements and cut the barrel to fit. The only thing needed 'fitting' being the thread diameter, and if you measure and record that you can make a replacement without needing the action.

    Crooked actions, especially those with the face out of square to the thread, can torque up and not be where you thought they would be on headspace.

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    I've always wondered how much "goodness" in a barrel comes from having a straight bore. Not an easy assignment, with most bores describing an arc from breech to muzzle. Small perhaps, and the smaller the better when it comes to generation of barrel distorting forces.

    It would seems like a specification that could be quantified with a laser interferometer.

    Are gunsmiths still clocking custom barrel installations to keep the plane of the barrel arc in the plane of the receiver? Straight line forces as much as practicable.

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    Quote Originally Posted by Butch Lambert View Post
    Only part of the subject has been hit upon, the receiver. If the bolt is not machined and its OD is not a very close fit to the reamed receiver, you still have a problem. A loose factory bolt will raise in the rear and unload the top bolt lug. I've personally followed a couple rifles that were purposely modified in steps and shot between steps. The only notable steps that helped were a good trigger, great bedding, and a custom barrel. The so called "blueprinting" is just a waste of time and money.
    To properly straighten a receiver and replace the bolt or modify the bolt will cost about the same as a custom receiver with very little extra resale value.
    Yep. I am not a salesman. When people want my opinion on it, I say it’s not worth it. Sure, if they still insist, and want to pay for it, I’ll do it, but it’s not because I up sold them on it.

    If it was my own, and what recommend for customers, is to run a 1.062-16 2B tap in the receiver by hand to get rid of any burs, rust, and other crap that shouldn’t be there. Then thread a bar to closely fit this thread, with a smaller diameter up front that will bottom out on the lug abutments. While that bar is still chucked up, screw the receiver on and make a light facing cut on the front of the receiver just until fully square. Remove it all and lap the lugs.

    If you want to go beyond that, sell your action and get an aftermarket action with all the bells and whistles you want.
    Last edited by 300sniper; 09-25-2020 at 03:07 PM.

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    Default Back in the Day

    When I used to shoot a lot of high power I built my own across the course gun. I was always on a blue collar budget and never could afford top of the line equipment. I bought a Czech M98 military mauser and installed Brownell's Shilen .308 heavy chrome moly blank. I set it up for irons and scope. I blueprinted the old action, and lapped the bolt lugs in before I head spaced it. All of the work I did at my machinist job after hours. I made one mistake-- when I reamed the short chamber i had a bit of run out in my set up. I had no easy means to correct the problem, so I assumed the reamer would follow the bore alright. Not. As long as I shot that gun, every time I moved from the 200yd to the 300yd to the 600yd I had to put some left wind on ,and remember to take it back off for 200 again. Lesson learned. She shot like a house afire if I do say so myself, but the mistake was always there.

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    Quote Originally Posted by 300sniper View Post
    If it was my own, and what recommend for customers, is to run a 1.062-16 2B tap in the receiver by hand to get rid of any burs, rust, and other crap that shouldn’t be there.
    And taper. Last one I did was ... wow. Never seen that before.

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    Quote Originally Posted by wesg View Post
    And taper. Last one I did was ... wow. Never seen that before.
    I thought all Remingtons were threaded NTPF to make them more familiar to "gun plumbers". ;-)

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    Quote Originally Posted by CalG View Post
    I've always wondered how much "goodness" in a barrel comes from having a straight bore. Not an easy assignment, with most bores describing an arc from breech to muzzle. Small perhaps, and the smaller the better when it comes to generation of barrel distorting forces.

    It would seems like a specification that could be quantified with a laser interferometer.

    Are gunsmiths still clocking custom barrel installations to keep the plane of the barrel arc in the plane of the receiver? Straight line forces as much as practicable.

    Barrel bore in an ARC? How can you drill an arc with a deep hole drill? How about a spiral.

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    The vast majority of shooters- save for those in the BR game that need to shoot in the zeros- would not benefit from "trueing" the receiver threads. I've always felt it- along with reaming the raceway- is not a good return on investment for most that are not capable of shooting the difference. Unless you've got a really effed up action, facing the receiver, checking the lugs for even and adequate contact and lapping in if close (if not, the lug abutments and back of the lugs get faced) together with a top-tier barrel and chambering job will shoot better than most are capable of seeing at the target when placed stress-free in a stock/chassis.

    Besides, unless you already own the receiver- you're better off just buying one of the many precision clones now available. Cost will be comparable- but the resale value will be much higher with a precision action.

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    I think the inherent accuracy of the AR family of guns is due in a large part to the barrel extension, lug setup. Everything is aligned by the way they must be assembled. When the lugs are contained in the receiver, like an M14 or Garand the principle is the same, but perfect alignment not so easily achieved. Add a bolt misaligned enough to bind on a rail instead of backing the lugs evenly--it all makes for minute accuracy losses.


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