So, What is Blueprinting?

[Clemson]

I am a working gunsmith. I see suggestions fairly often that owners of inaccurate rifles have the "actions blueprinted." I'm not sure we are all on the same sheet of music in understanding what blueprinting is and how it affects accuracy. First off, let's pick a rifle action type. Blueprinting is different for different actions. A Remington 700 is a good place to start. To blueprint a Remington 700, the barrel must be removed, and all parts that attach to the receiver are likewise removed. Machining of the action then takes place to insure that the action threads are exactly parallel to the bolt raceway. That can be done by single point machining of the threads with the receiver dialed into a lathe fixture that holds it in alignment with the axis of the lathe. Alternately, it can be done with bushings that fit the bore of the receiver precisely and which align a tap that then recuts the threads. The end result is exactly the same. The receiver face is cut to be perpendicular to the bore and dead flat.

Now we have a receiver with the threads parallel to the bolt raceway. For a hunting rifle, I then lap the bolt lugs into even fit on both sides of the bolt. There are additional steps to insure a tight fitting bolt that can be taken with a benchrest gun, but, honestly, if you are building a benchrest gun, you are miles ahead to start with a custom "clone" action (Panda, Sturgeon, etc.).

The receiver threads are now oversized by about 0.010 inches. The old barrel will be a sloppy fit, so we need a new barrel with newly cut threads that are oversized to fit the receiver. Also, our recoil lug won't fit the new barrel tenon, so we need a new one. That gives us the opportunity to surface grind both sides to insure a great fit up to the receiver and the barrel shoulder. Thus ends our blueprinting.

Obviously, this is not a trivial undertaking. You are not only recutting the receiver, you are replacing the entire barrel. You can't "blueprint" the receiver to the existing barrel. Rant over -- Shoot straight!

Bill Jacobs

 

[DAVE]

Thanks, never knew what "blue printing" really meant.

 

[ryanh487]

On the thread I suggested it, the op wanted to put on a new match barrel.

 

[nmurph]

Blueprinting means machining to the spec on the design drawing (blue print) within the tolerances allowed.

 

[Dr. Strangelove]

Same with engines, for any day-to-day use it is a superfluous expense. If you want to race it, or get into serious benchrest with rifles, have at it, otherwise spend your money elsewhere.

 

[Jester896]

PT&G makes a standard tap as well as the oversized. If it is centered just bump the lugs and surface the face. Sometimes Remington gets it right . I have seen one so bad I'm not sure the oversized one would have straighten it out.

 

[Clemson]

The biggest factor in "hunting" accuracy is the nut holding the trigger. That said, the barrel plays a significant role in shooting small groups. Factory barrels are a crap shoot. Some are hummers, some are miserable, and lots fall in between. Aftermarket barrels from reputable manufacturers are much more likely to be straight shooters. With some exceptions, you get what you pay for.

Generalizations are dangerous, but to spur conversation, with all other things equal:
1. Heavier barrels group better than skinny barrels.
2. Short barrels group better than long barrels.
3. Aftermarket barrels group better than factory barrels.

Bill Jacobs
Bolt&Barrel Gunsmithing, LLC

 

[Jester896]

Generalizations are dangerous, but to spur conversation, with all other things equal:
1. Heavier barrels group better than skinny barrels.
2. Short barrels group better than long barrels.
3. Aftermarket barrels group better than factory barrels.

Bill Jacobs
Bolt&Barrel Gunsmithing, LLC

1. they are less susceptible from harmonics changes due to heat or other factors and far less whip (harmonics again)...IMO

2. OK...go into that more if you would...I have seen 20" shoot as well as 24". Is that from the rigidity of the shorter barrel? Again harmonics

3. After about 1500 rounds a good many factory barrels will shoot better. You could always try lapping the barrel and possible take out some of the chatter marks to see if the accuracy will improve sooner...IMO

 

[Clemson]

Yep. Generally, shorter equates to stiffer. That is a good thing from an accuracy perspective. If you were shooting open sights, however, the longer barrel would give you a longer sight radius and better precision. Also, if you pay for a magnum sized cartridge, you want a barrel long enough to take advantage of all that powder. Velocity will suffer from a barrel that is too short for the round used.

 

[rosewood]

A longer barrel is also easier to hold steady than a short one. The longer barrel has a greater moment of inertia and therefore wants to stay in place more than a short one. A person can just plain shoot a longer barrel better (see site radius above mentioned also), but the short barrel will most likely be more accurate. So there is a happy medium between the barrel length and shooters abilities.

Rosewood

 

[Jester896]

A longer barrel is also easier to hold steady than a short one.

Rosewood

How so?

 

[rosewood]

How so?

Moment of inertia.

Think about a tight rope walker using a long pole to balance.

 

[Ray357]

I am a working gunsmith. I see suggestions fairly often that owners of inaccurate rifles have the "actions blueprinted." I'm not sure we are all on the same sheet of music in understanding what blueprinting is and how it affects accuracy. First off, let's pick a rifle action type. Blueprinting is different for different actions. A Remington 700 is a good place to start. To blueprint a Remington 700, the barrel must be removed, and all parts that attach to the receiver are likewise removed. Machining of the action then takes place to insure that the action threads are exactly parallel to the bolt raceway. That can be done by single point machining of the threads with the receiver dialed into a lathe fixture that holds it in alignment with the axis of the lathe. Alternately, it can be done with bushings that fit the bore of the receiver precisely and which align a tap that then recuts the threads. The end result is exactly the same. The receiver face is cut to be perpendicular to the bore and dead flat.

Now we have a receiver with the threads parallel to the bolt raceway. For a hunting rifle, I then lap the bolt lugs into even fit on both sides of the bolt. There are additional steps to insure a tight fitting bolt that can be taken with a benchrest gun, but, honestly, if you are building a benchrest gun, you are miles ahead to start with a custom "clone" action (Panda, Sturgeon, etc.).

The receiver threads are now oversized by about 0.010 inches. The old barrel will be a sloppy fit, so we need a new barrel with newly cut threads that are oversized to fit the receiver. Also, our recoil lug won't fit the new barrel tenon, so we need a new one. That gives us the opportunity to surface grind both sides to insure a great fit up to the receiver and the barrel shoulder. Thus ends our blueprinting.

Obviously, this is not a trivial undertaking. You are not only recutting the receiver, you are replacing the entire barrel. You can't "blueprint" the receiver to the existing barrel. Rant over -- Shoot straight!

Bill Jacobs

Just like "blue printing" a cylinder head or engine block. It means matching something about it to some spec sheet. Could mean anything, but sure sounds good. Don't it?

 

[Ray357]

PT&G makes a standard tap as well as the oversized. If it is centered just bump the lugs and surface the face. Sometimes Remington gets it right . I have seen one so bad I'm not sure the oversized one would have straighten it out.

The worst I have ever seen were Winchester 70 actions. The crookedest ones sure shot lights out with their factory barrel.

 

[Jester896]

Moment of inertia.

Think about a tight rope walker using a long pole to balance.

I don't get the part about the tight rope walker...I don't hold my rifle in the middle and it isn't as balanced as the tight rope walkers pole.

I do understand the concept of the walker and pole though and what it does for the walker.

 

[rosewood]

try this then, take a long heavy limb and try to swing it, then take a short light limb and swing that. Which swings easier? The longer one resist the movement more.

The tight rope walker would have the same effect if he could hold 2 separate poles at arms length straight out opposing each other, but he couldn't hold it that way. Them being attached makes it easier to control. The long pole resists rotation and helps him to maintain his balance, by becoming part of his moment of inertia and the entire system resists rotation which would throw him off balance.

Rosewood

 

[Jester896]

ha...and this whole time I thought it was to lower his center of gravity so his rotation was smoother...his rotation being that of his legs

 

[rosewood]

ha...and this whole time I thought it was to lower his center of gravity so his rotation was smoother...his rotation being that of his legs

It does that also.

It dampens the rotation.

 

[Ray357]

A longer barrel is also easier to hold steady than a short one. The longer barrel has a greater moment of inertia and therefore wants to stay in place more than a short one. A person can just plain shoot a longer barrel better (see site radius above mentioned also), but the short barrel will most likely be more accurate. So there is a happy medium between the barrel length and shooters abilities.

Rosewood

Yep. There come a point where extra barrel length quickly becomes counter productive.