Gunsmithing Bolt vs. reciever tolerance

[jacq220]

I am looking at having chad build a rifle for me. In my search for a receiver a friend has offered me a Remington action that has already been blueprinted with PTG tooling. However the raceway was reamed to .705 and the bolt that comes with it is a standard bolt. What would the drawbacks be to this if any? I don't have a price on the receiver yet, but I believe I could get a one piece ptg fluted and ready to go for around 300 with a small wait. the receiver is of a 69 or so vintage.

 

[stenger]

Well Ptg bolts come .699-.700. That leaves you .0025 per side and that's about perfect for a tac rifle. If you are shooting benchrest you may want to tighten that up a little.

 

[jacq220]

Well Ptg bolts come .699-.700. That leaves you .0025 per side and that's about perfect for a tac rifle. If you are shooting benchrest you may want to tighten that up a little.

I am trying to avoid PTG if I can to save some dough hence the question. the raceway is .705 and it would be a factory bolt. I guess I am just assuming a factory bolt is .700 but it could be under that.

 

[jonaddis84]

That's gonna be like throwing a hot dog down a hallway haha. All kidding aside the stock bolt is likely around 694-696. If you want an accurate rifle get a ptg made in 702 for it.

Galaxy S3 on tapatalk

 

[jacq220]

that's what I needed to know, thanks.

 

[stenger]

Yes he is dead on. That bolt will be sloppy and accuracy will suffer.

 

[glbreil]

You could just bush the bolt you have and serve the same purpose for less money. The PTG bolts are very nice especially if you like the flutes and all but a bushed bolt will be just as accurate.

Thanks Gary

 

[STR]

In case you're wondering, the factory bolt is .696 inch. Replace the bolt is the correct thing to do. Bushing it will work, but if you're paying for it, then it defeats the purpose of saving money. I'm Chad would have told you this if ask him.

 

[turbo54]

I'd let your buddy keep his action and buy one that hasn't been dicked with. Let Chad start with a fresh virgin action to tune up.

Reminds me of a sign posted in my local hydraulic hose/hose-end shop:

LABOR RATES:

Standard - $50/hour
If you watch - $60/hour
If you help - $90/hour
If you've already worked on it - $150/hour

 

[300sniper]

...and accuracy will suffer.

Proof of this?

 

[LRI]

Sorry, but I have to disagree (Agree w/Robert aka 300S who's a smert feller and an all around bad azz mo fo)

Sure, if I bore a hole .75 and shove a .7 diameter bolt down the hole then there's all sorts of room for wierd stuff to happen.

But a diameter differential of .005-.01. I've yet to see it hurt a damn thing.

Not once!

Trig it out and see for yourself. If you have a .005" diameter difference between the bolt and the receiver it works out to a ridiculous angle of .0545" degrees. The OD of an M700 bolt lug sweeps a one inch arc. With .005" difference in diameter your tipped off the lug abutment by .0005". These numbers are for a long action where the nominal distance from the lug faces to the top of the primary extraction cam measures 5.25" in length. That is the maximum length that the bolt is supported when in battery and the cocking piece is loading against the trigger's transfer bar.

If it's a .480" Bolt face (say an L/A in a 280 or 06' for instance) the bolt face is out of square with the cartridge face (assuming it is truly parallel to the bore axis and that there's zero runout/out of squareness on a cartridge that's made by hammering the piss out of a brass slug a half dozen times) by a WHOPPING .0002" of an inch! If it's a .590" then its out by .0003". I chose these two very common applications because they offer the biggest possible deviation. A .390" head case is going to have less than .0002" because it's closer to center.

The Saturn V rocket didn't have a single tolerance on it this tight and we hit the moon with it. It couldn't with a 400+F temperature range difference. Look at the SR-71. It pisses fuel all over the tarmac as it sits on the ground because it had to get flying/hot in order to swell up and stop leaking. Yet it helped defeat a superpower. . .

Taking a big deep breath and an even bigger step back to look at this for what it is, I can't help but feel that those who'll go to their grave believing this stuff have all been duped by the BR crowd that insists that guns have to be built to the point that they won't function in order to shoot well. Your talking about tolerances smaller than what it takes to make an internal combustion engine run. -Yet manufacturer's are offering 100K+ mile warranties now on powertrains.

Two folks I deeply respect and admire for their shooting skills are Kent Reeves and Corbin Shell. Both have won sanctioned long range matches with a Mauser.

FWIW and I'm sure this'll raise eyebrows but I really don't care as we've done too many this way now for it to be intelligently argued. We KNOCK the bolt OD down to achieve a .007" differential between bolt/receiver. If Ceracoat is a .001" thick film then were reducing the receiver bore ID by a value of .002" The bolt increases in size by .002". That leaves .003" .0015/side isn't a whole lot but it is the difference between a bolt that runs like poop through a milk fed goose and one that requires an orange deadblow hammer as part of your field TO. It's the difference between coating a gun and having it last and having one rub off in 20 rounds. There's zero reason to scotch brite a bolt after coating if its prepped properly. This is if a bolt shows up super tight. Ones that are loose just get spun/blasted/coated and we let it lie where it does. They still shoot just fine and they feel like they are on little ball bearings when shot in Graphite Black C coat.

-And there is part of the clincher. Flat colors require flattening agents in the paint/coating recipe. These agents are often chalky and slightly gritty. They reduce the surface hardness of the product slightly because it can't glaze over the way a glossier finish will. It's porous in nature. Ever wonder why your new FDE ceracoat job is all boogered up with dirt 5 minutes after you own it? It's cause of the color choice/finish character. Your chosen shop who sprayed it didn't screw you, it's just how it is due to the material. It's not C coats fault either. It is what it is. . .

There's no reason IMO to use a stupid bushing. Yes, I said stupid because they are. Bushings are great for solvents to penetrate and loosen up the epoxy so that they fall off right in the middle of a shot string. Great for ruining the cosmetic elegance of a bolt, and great for making a rifle cycle like crap.

Great at gutting your wallet too.

If your bolt is truly that wore out then it should be tossed and a replacement should be used instead. Wore out means that the thing slam fires due to the cocking piece running over the transfer bar of the trigger when cycled hard/fast. That's wore out!

I've called this ultra tight bolt crap BS since day one. The math just does not add up. It stems from BR where guns are shot in a vacuum. They go from a case to a bench and get 5 rounds shot through them at a time before they are cleaned and shot again for 5 more rounds. Field duty guns are used in the real world where men crawl around and get dirty. Guns that go bang win gunfights and matches. Guns that don't result in funerals and DNF's.

It's about like trying to drive an NHRA TOP FUEL car at a tractor pull.

My two bits. It's a bit opinionated, but it's backed up with nothing more elaborate than high school math. Take it for what its worth. Check my numbers for yourself and see if I'm wrong on something. I've checked them at least three times and they repeat so I feel pretty good about it.

C.

 

[stenger]

I respect your knowledge and experience chad

These are my obsevstions in the rifles I have built. I have seen a rem 700 bolt out by .018. Now this rifle was all custom and the guy brought it to me cause it would not shoot. I sleeved the bolt and the gun went from a .60-.75 gun to a .25 gun. That's it I only sleeved the bolt. Another rifle I fixed was a custom 338 lapua that was a half moa gun. I sleeved the bolt and bingo the first group out of the gun shot in the .1's. the bolt was out around .010 on this rifle. I agree with chad that sleeving a bolt is not the best anymore. I would just spec a new bolt to match your shooting style if necessary . I also agree with chad that a bolt out. .005 is not going to hurt anything. My personal 338 lap ack has a bolt that is .005 out and I want it this way so it cycles. This gun shoots .25--.35 every time. So my point is that from my experience measure your bolt and see where you are at if you are only out .005 then I would not worry about it for a tac rifle. If shooting for world record groups I would want it snug. There is a theory out there that a loose bolt can put unnecessary vibrations into a rifle during the shot process so I think it goes a little further than a lug not touching or a bolt face that's not square. I am obsessive compulsive about accuracy so I try to eliminate every possible variable that may or may not effect accuracy. I don't think we will ever know everything about rifle accuracy

Just my opinion and observations
This is a good discussion a lot to be learned.

 

[jonaddis84]

I dont think the issue is so much the trigonometry of how much angle deviation there can be with a small bolt in a big hole. This is not proven by myself, but I think it makes sense along with all the other stuff thats been pretty much proven throughout the years that vibrations make up a big part of accuracy. Id like to see a high speed video of a small bolt in a big raceway during the shot. I have to imagine that sucker is rattling like crazy in there.

And I think this is mostly moot because why do we build custom rifles to begin with? So they shoot and FEEL custom, nobody likes how sloppy a factory remington is with a MAX 696 (youre lucky if you get 696) bolt inside a normally 702-703 raceway, so why would one want a custom rifle with that same bolt in a 705 raceway?

FWIW Ive put a 702 bolt in a 705 raceway and cerakoted both, with some good oil it feels quite nice. Sure its not as slippery as a nice chromed bolt would be, but that isnt tactical. Id say .004" clearance is the magic number for both surfaces being cerakoted.

My .01 cent, I havent been doing this long enough to give .02

 

[jacq220]

I don't think I am a good enough shooter to tell the difference between a .25 rifle and a .5 rifle, or a .5 and a .75 rifle. I would be able to tell if it were picky w/ ammo though as most of us would.

I had not taken into account the thickness of cerekote which would be .004 value. if the bolt was a full size .696, then I would only have .0025 per side of slop. that doesn't seem like throwing a hotdog through a hallway by any stretch of the imagination.

 

[300sniper]

My personal most accurate tac rifle has 7-8 thousandths of clearance between to receiver bore and bolt body. So obviously 7-8 thousandths is the correct clearance....

....Then again, I'm also using an un-bedded chassis that fails the "stress test" and a button rifled barrel, but I'm not scared to think for myself and ignore things I feel are no more than Internet "must have's" and "must do's".

 

[E. Bryant]

Id like to see a high speed video of a small bolt in a big raceway during the shot. I have to imagine that sucker is rattling like crazy in there.

I doubt very much that the bolt does any "rattling", since it has a few thousand to several thousand pounds of thrust acting on it as the bullet leaves the cartridge and begins its trip down the bore. As soon as the cartridge lights off, that bolt is going to be smashed up against the lug abutments. By the time this pressure drops to the point where the bolt would have a chance to move, the path of the bullet is likely unaffected.

Just so long as everything is reasonably square, good results should be produced (and the tighter the chamber, the less-affected the bullet would tend to be by an out-of-square condition at the bolt face).

I've messed around on a couple of my own builds with tightening the bolt clearance to around 0.002". The conclusion that I reached is that this is a great way to consume a lot of time and lapping compound getting things to run somewhat correctly, and little else was achieved.

 

[338RUM runner]

Has anyone ever Hard Chromed a bolt to increase the body size, just asking if it would work. Where I worked we Hard Chromed parts to make them wear better and we would put .004 of Chrome on them. You can mask of the places you don't need Chrome.

 

[monteboy84]

These are my obsevstions in the rifles I have built. I have seen a rem 700 bolt out by .018. Now this rifle was all custom and the guy brought it to me cause it would not shoot. I sleeved the bolt and the gun went from a .60-.75 gun to a .25 gun. That's it I only sleeved the bolt. Another rifle I fixed was a custom 338 lapua that was a half moa gun. I sleeved the bolt and bingo the first group out of the gun shot in the .1's. the bolt was out around .010 on this rifle. I agree with chad that sleeving a bolt is not the best anymore. I would just spec a new bolt to match your shooting style if necessary . I also agree with chad that a bolt out. .005 is not going to hurt anything. My personal 338 lap ack has a bolt that is .005 out and I want it this way so it cycles. This gun shoots .25--.35 every time. So my point is that from my experience measure your bolt and see where you are at if you are only out .005 then I would not worry about it for a tac rifle. If shooting for world record groups I would want it snug. There is a theory out there that a loose bolt can put unnecessary vibrations into a rifle during the shot process so I think it goes a little further than a lug not touching or a bolt face that's not square. I am obsessive compulsive about accuracy so I try to eliminate every possible variable that may or may not effect accuracy. I don't think we will ever know everything about rifle accuracy

These are valid, but they don't necessarily prove anything. When bushing a bolt improves the accuracy of a certain rifle, it does not automatically mean that a loose bolt will result in inaccuracy, it merely means that a tight bolt improved those rifles. The same outcome could have been achieved with other methods, but since the bushing job worked, that's where the story ended. The barrel could have been set-back with a new chamber, tighter headspace, etc. When you rely on the bolt raceway to center the bolt face in the barrel, you're introducing a number of tolerances into the equation that don't have to be present. On a Remington 700, I'd venture to say that you could run .020" clearance on the bolt body, and so long as the bolt nose is a close clearance fit to the mating cut in the barrel, with headspace set to a minimum, it will shoot lights out. Not every rifle has a bolt nose that you could use to center the bolt face, but you can do other things with the chamber and barrel machining in order to achieve your end goal of directing the bullet into the barrel as centered and consistently as possible from one shot to the next.

There are different ways to achieve any desired outcome, the trick of engineering is to observe the problem in such a way that you take nothing for granted. Less than 10 years ago, 90% of the custom tactical rifles were Remington 700's with McMillan stocks and Leupold Mark 4 scopes, fast-forward to today and that's obviously no longer the case. Times change and conventional wisdom is temporary at best.

-matt

 

[jrm850]

Never Chrome but I have used electroless nickle to close up some teloerances. It worked pretty well as long as I didn't get too much buildup on sharp corners and made sure the etch was deep enough for good adhesion. I masked the locking surfaces and threads and if I didn't etch it long enough, the nickle would tend to start flaking at that junction eventually. At the time it seemed more cost effective than sleeving, but if I were in the business today, I think a new bolt would put more dollars in the pocket. It sure did make a slick bolt though.

 

[xs hedspace]

I feel that any bolt slop will let the override sear to cam the bolt up in the receiver when cocked, then the bolt flops down as the locking lugs have to move back into full engagement when the case thrusts back. This vibration can't be good for accuracy. I improved accuracy in my Rem 700, by putting a 1/2" wide pad of Brownells 44 solder on the bolt, where the top of the bridge is when the bolt is closed. This is in effect a Borden Bump, as this pad pressure is released when the bolt is opened. Lapped the lugs with some 320 grit after doing this bump. Took some filing to shave the solder down to let the bolt close, and since this solder is vary close to tin babbit bearing metal, it seems to be holding up pretty well--better than my 6mm barrel throat looks after a few thou rounds, thru my Hawkeye scope.

 

[x ring accuracy]

Not tossing a dog into this fight but I have seen PLENTY of loose bolt bodies in actions, I means LOOSE. But as stated, once the lugs engage square, the pressure from the ignition sets a trued / squared / blueprinted action square on its lugs. The benchrest guys know a tight bolt is good. Tactical, I want some play for fast cycling. I have an old Mauser in 6.5X284. You can damn near wobble the action past the bolt release. It is a shooter since it was trued. I think the jury is still out on tactical precision versus bolt body tightness. This has NOTHING to do with clearance from bolt face to tennon.

 

[LRI]

Vibration, Harmonics, amplitude, fequency, wiggles, buzz, and rattles.

The terms range from clinical higher education to trailer park vernacular.

Most (and by no means do I wish to insult anyone) don't even know what they mean. -Myself included in many instances as I am a lowly H/S graduate.

I think there's something to remember/consider here.

Find a gunsmith that started in this trade building rimfire guns for the BR/International 3P crowd and listen to his/her observations/experience. A lot can be learned. Rimfire 22's and modern high performance CF guns only have one thing in common; They both send bullets out the barrel.

Beyond that they differ in many ways.

A RF travels roughly 1/3rd the speed of anything "cool" in CF. That means the bullet is loitering around in the barrel 3X longer than if it were shot from a different cartridge case. That's 3X longer for dumb chit to start screwing with it. "Dumb chit" is defined in line one of this post.

This is why the sicko's that shoot RF buy ammunition by the pallet once they find a lot that works. It's a great deal of work/expense to get one hammering to exceptional levels. If your ever in COS take a swing by the OTC and ask to see the ammo room. Every lot of Eley Tennex in the world exists in that room. That's what it takes to produce a gold medal gun.

The point here is a guy at the reloading bench has the divine intervention to resolve most of these issue. Seating depth/powder charger/powder selection will by and large tune out the dreaded "engineering terms/trailer park vernacular" that so many fret over.

If your shooting a factory gun w/factory ammo, you'll likely have to buy a few different brands to find what the gun likes.
If your hand loading, whip up a buffet of loads and test.
If your shooting a full effort custom, your gun should be less sensitive to ammunition but it'll still respond favorably to load work.
SD's on a chrony become a valuable tool with this. So does watching your elevation at longer distances.

If vibration is truly the devil, take an old junk M700 and cut an O ring groove at the back end inside the rear bridge. Go buy a high durometer "peter ring" and slip it over the bolt head. Size it to a slip fit and go shoot the gun. Does it get better? Now remove it and shoot again. Does it get worse?

Now play with the load with the rubber and see if history repeats itself... (that really sounds horrible after reading it twice)

Woo Hoo! More stuff to try!

BTW: We're selling "Trojan bolt rings" installed for $99.95 (at the dirty book store next to the Chinese food buffet!)

C.

 

[damoncali]

If anyone is interested in this, Harold Vaughn did some work and experiments in this area that he details in his book, Rifle Accuracy Facts. Not exactly, and not exhaustively, but it is interesting nonetheless. There is a page or two specifically dealing with the effect of a canted bolt's impact on bolt lug engagement (or non-engagement) and the impact it has on driving barrel vibration. As you might expect, it's not as simple as tight fit vs loose fit. He makes a pretty good case that the fit doesn't matter as long as the lugs bear evenly when cocked. And close fitting bolts are no guarantee of proper lug engagement. He even went though the effort of cutting the lugs and bolt face at an angle to compensate for the tipping.

Unfortunately, this is more of an aside in the book and measurement of its impact on vibrations wasn't done. Simply cutting the lugs and bolt face at an angle did change the POI by two inches @ 100 yards, however, so you have to assume there is a significant change.

He also makes a pretty good case that the symmetry of the front receiver ring matters - the holes should be balanced by equal sized holes 180 degrees apart. I don't see anyone doing this, so perhaps nobody knows (which would be odd since he wrote it all in a book), or people tried it and doesn't matter after all.

In any case, great read on this and many other topics.

 

[mcfred]

I think it would be an interesting experiment to make a r700 bolt using one of those "floating head" front pieces and then try some back-to-back tests. I think the idea with the floating head is the front of the bolt can line up with the lug abutments no matter how sloppy or crooked the body is.

 

[RTK]

I need a little edumacation here. I was under the impression that when the firing pin hits the primer it pushes the cartridge forward off of the bolt face to the shoulder or rim and as the powder ignites the cartridge expands in the chamber momentarily being captured there. While this is taking place the bullet has already been released before the cartridge releases from chamber and moves backwards to the bolt face.
My question is then, how can it matter if the bolt is loose as a goose or even square????

 

[damoncali]

The case head pushes against the bolt face while the bullet is still in the barrel- a brass case cannot withstand ~10,000 pounds of force (chamber pressure times the case diameter) without stretching a little. When the bolt face bears on the receiver in an uneven (off-center) manner, it induces an off-center force, which is how the barrel gets to whipping up and down.

 

[300sniper]

The case head pushes against the bolt face while the bullet is still in the barrel- a brass case cannot withstand ~10,000 pounds of force (chamber pressure times the case diameter) without stretching a little. When the bolt face bears on the receiver in an uneven (off-center) manner, it induces an off-center force, which is how the barrel gets to whipping up and down.

now the question is...

if that barrel gets whipped up and down do to what you mentioned, does it whip up and down the same amount shot to shot only with a tight fitting bolt? or does an action with .005 clearance between the bolt body and receiver somehow repeat the whipping consistently whereas one with .008" doesn't?

 

[damoncali]

The theory is that the clearance doesn't matter - what matters is that both lugs engage evenly, and therefore push back on the receiver in a balanced manner. If there is no off-center bias to the recoil force (and this is only one of several sources of that bias), then there is no force driving a whipping motion - it's straight back like you want it.

Similarly, if one side of the action is stiffer than the other, or if there is a large mass hanging off to one side (like a stock or a scope) there will be a tendency to whip back and forth.

 

[AKA-Spook]

I never realized how little I knew ? I cant get a .0015 feeler beside the bolt of my Bat and it shoots into the ones pretty regularly?

 

[damoncali]

I've always wanted to try an experiment with a dual port, completely symmetrical action (all action screw holes, vents, cutouts etc repeated 180% apart - perhaps even with some sort of round recoil lug (recoil lugs are another culprit of vertical vibration) and see how far you can push the concept. The rifle would look more like a crutch than a rifle. The the trouble is that a properly built "normal" rifle will shoot very well, so it would be hard to tell if there were improvements without instrumenting the rifle, and that is a lot of work and money that I don't have for what might wind up being nothing more than some academic fiddling. It would also be really awkward and impractical. But I bet you could figure out a thing or two as to how best to make regular rifles from such an exercise.

 

[hero's machine]

I would sure be more worried about the last 10" of my bullets life in my rifle than the first 1/2".

 

[MarineMD]

This is an incisive and concise eidtorial. Thanks for taking the time. I will seek out your other posts and try to soak up some of the wisdom.