“Parallel, square, straight, concentric and true, extreme rifle accuracy lives and dies by you.”
Let’s be honest, all incantational chants, black magic and voodoo aside, if the basic components of any given rifle build are perfectly parallel, square, straight, concentric and true, then producing an exceptionally accurate rifle is an easy task for virtually any competent person. Unfortunately, they rarely are and it almost never is. Actually, in my experience they NEVER are and it NEVER is! This is why most gun-builders are contemptible old geezers with the bench side manner of a cross-eyed badger with bursitis. To build the extremely accurate guns people pay us to build, we need every component to be absolutely perfect! But, they never are! Consequently, we spend more time “fixing stuff” than actually building guns. Is it any wonder some of us become just a wee bit cranky?
Which brings us to basic receiver “blueprinting.”
Now, just what does this strange word “blueprinting” mean? Well, in the automotive world it means to “totally rebuild an engine to the most precise tolerances possible.” But, in the firearms world the definition is (perhaps intentionally) a bit more nebulous. You see, in reality “blueprinting” is a technically sounding but nonsensical word that a nefarious “Master Riflesmith” made up just so he could pay for his kids’ college education. After all, who wants to pay big money to have their “junk fixed;” even if that is the marrow of the matter.
So, on we go to actually “fixing” (blueprinting) a receiver. Any make or model of mass produced receiver will do because they all need fixing. Yes, it is true that some receivers are higher quality than others. Also, that some are easier to work on and more conducive to exceptional accuracy than others. But, in my experience there seems to be no rhyme or reason between getting a fairly good one and getting a really bad one. Even within the same make, model and serial number run, I have seen the good, the bad and the downright ugly. Consequently, if you desire topflight accuracy from any non-custom, mass produced receiver you should just assume that some machine work will be required.
For this particular article and project, we started with a brand new unfired Remington 700 SPS rifle. Although we are sometimes coerced into working with “used” receivers at our shop, we always prefer to begin with a virgin receiver whenever possible. When you consider that “blueprinting” is basically the act of removing metal, and that only a limited amount of metal can safely be removed, it is best to start with as much steel as you can get. Plus, starting with a new unfired receiver helps avoid any previous owner induced flaws of which there can be many; some non-repairable.
In picture #1 you see the new intact rifle. In picture #2 it has been disassembled into basic components. In photo # 3 you see the tools we typically use to separate the receiver from the barrel; I stress the word “typically” because we use completely different tools when we encounter a “really tight one.”
In photo # 4 both the receiver and barrel have been tightly clenched in our homemade aluminum bar clamps. You will note that sheet lead has been wrapped around the barrel in order to give the clamp more holding power on the steep, short factory contour. Once these bar clamps are in place, the smaller barrel clamp is placed in a large bench vice and tightened securely. Then the beating commences.
Exactly why they employ a highly motivated 700 pound gorilla at Remington is a mystery to me; but, I have found that you can usually overcome his legendary work by striking the receiver loosening clamp both very hard and very fast. That’s VERY HARD and VERY FAST. If you hit it hard and fast enough, “the easy ones” will often separate with just one mighty whack. However, if you are unfortunate enough to get “a really tight one,” well just remember, “what does not kill you makes you stronger.” Yea right!
In photo #5 our maniacal whacking has been successful and receiver and barrel have been separated. Hallelujah! But, wait, what is this; it appears that there is quite a bit of rust on both faces of the recoil lug? How could a perfectly mated, parallel lug that is sandwiched between two other perfectly parallel surfaces be rusted? How indeed?
Photos #6 and #7 should be self-explanatory to anyone but a blind simpleton. Just look closely at the photos and repeat the first sentence of this article: “Parallel, square, straight, concentric and true, extreme rifle accuracy lives and dies by you.”
Photos #8, #9 and #10 show our sixteen piece 0.0005" receiver raceway bushing set and GTR - PTG, 0.705" bolt raceway reamer/mandrel/indicator rod. Although this rod/reamer is designed to perform multiple functions, due to the inherent limitations of a magazine article, we will simply be using it as an indicator rod and not a reamer. Note that the tang end of our receiver raceway required a 0.702" bushing and the face end took a 0.703" bushing. This is only a 0.001" difference and it gives us the option of not reaming out both holes to 0.705" if we so choose. A discourse on bolt and raceway diameters/relationships would be appropriate here, (also trued factory bolts -vs- aftermarket custom) but we simply do not have the time or space. Just try and match the two as close as possible while still allowing them to function properly. Too tight is worse than too loose; believe me.
Photos #11 and #12 show our GTR receiver blueprinting jig. This is the workhorse of the entire operation that makes everything else possible. Because it is very difficult to see the entire receiver truing set-up in a photo, I will briefly explain how all these tools fit together: First, the correct size raceway bushings are inserted fore and aft into the receiver; the fit should be tight, but not so tight that they must be “driven” into place. Second, the small end of the reamer/mandrel is inserted into the center of the raceway bushings and the mandrel is pushed back toward the tang until the reamer flutes come up against the internal lug seats; a squirt of WD-40 goes a long way here. Third, the receiver and mandrel are placed into the blueprinting jig and everything is roughly centered by adjusting the eight bolts on the jig. Finally, the entire apparatus is placed in the independent four jaw chuck on the lathe. Then, the real fun begins.
Now, although it is not mandatory to “zero” the jig itself, I would strongly suggest doing so; simply because anything with “run-out” spinning 600 RPM right off the end of your cutting tool messes with your depth perception (at least it does for me) and there is no room for error here.
Photos #13 and #14 show the jig, receiver and mandrel in the lathe. You will note the large dial 0.0005" Mitutoyo indicator out on the extreme right-hand end of the mandrel. Although it is hard to visualize, in this right-hand position you are indicating the tang end of the receiver; and when you move the lathe carriage and indicator to the left (toward the receiver face) you are indicating the breach end of the receiver. Some guys use two dial indicators simultaneously for this operation, but because our lathe has an accurate DRO that allows us to return to the EXACT same indicating position, we only use one – sliding it back and forth the length of the rod.
Next, it is just a matter of indicating both ends of the rod to absolute zero/zero. Which is a lot easier said than done. The trick is just to have both patience and fortitude; whether it takes one hour or three, just keep adjusting the jig bolts until the needle on your 0.0005" indicator doesn’t even wiggle. Then, when you are satisfied that you have indicated both ends of the rod as close to perfection as humanly possible, stand back, turn on your lathe and let it run for five minutes. Now, go back and start all over! (And you wondered why some guy’s guns always seem to shoot better than others.)
So now that we have the receiver spinning on its true center axis, which is what this entire process has been about, we are finally ready to make the “face cut.”
Photos #15, #16 and #17 vividly show the progressive “clean-up” of the receiver face. Obviously, the cutting tool removes the blue Dykem from the “high spots” first, advances to the “low spots” and eventual overall clean-up. Total “run-out” on this receiver from first tool touch to complete clean-up was 0.008"; better than some, but not as bad as others.
Photos #18 and #19 depict the truing of the internal receiver lug abutments. Because this is a totally blind machining operation, and very difficult to execute and photograph, I failed to capture a picture of one “high” lug in a state of “total clean-up” and the opposing “low” lug in an “untouched” condition; which happens often, and if left unchecked, creates the common factory rifle condition of having one bolt lug bearing 100% and the other lug floating in space like a drunken cosmonaut. Which is one of the many reasons why ¼ MOA factory guns are few and far between.
Finally, we come to photo # 20 and the finished product. But wait, you exclaim, what about the internal threads!!! Aaahhh yes, the threads and other loose ends; well that my friend will just have to wait for another day.