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What is the purpose of lapping bolt lugs? How do you know if they need to be lapped? What is the process? What is the desired result? | ||
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The purpose of lapping bolt lugs is to achieve full engagement of the lug with its recess, i.e. no high spots. The reason is that as the round fires the lugs are fully supported ensureing the maximun strength and more importantly the lack of give or flex in the action to achieve max. accuracy. Side benefit is the smootheness of the action is improved. This is a delicate operation to be done by a qualified gunsmith as you can affect headspace. I hope that helps. | |||
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quote:Kevin is most definately correct about the purpose of lapping your lugs, however, more times than not, your average gunsmith or hobbiest tends to want to begin fixing the problem by literally lapping the lugs. What needs to be accomplished to begin with, is to first remachine the locking lugs square with the boreline of the receiver, as well as remachining the bolt lugs in the same fashion. Most times if the machining is done correctly, it is unnecessary to lap the lugs by hand. In fact, by hand-lapping the lugs, you'll actually introduce error into the process that wouldn't normally be there after the machining process. If the machine work is done correctly, lapping the lugs should only take about 1-2 minutes, tops, if done at all. However, the rule of thumb should always be to have this area gone over by a qualified gunsmith unless you've purchased an action from a company that has indicated that this process has already occured. | |||
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triggerguard1 - quote:What error? I think I am one of the "average hobbiest"'s you mention, as I've been hand lapping my lugs, primarily Rem 700's, for years. I've never noticed any problems ![[Confused]](images/icons/confused.gif){kind=icon} KevinNY - Don't you think the headspace changes are relatively minor (0.001" +/-), and can be compensated for with your sizing die? R-WEST [ 07-17-2002, 00:47: Message edited by: R-WEST ] | |||
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The bolt locking lugs on most if not all commercial receivers are rarely square with the receiver centerline. This is because of the practice of heat treating the receivers once fully machined ( it's cheaper with respect to tooling,but they warp). The bolts may have the same problem. Lapping the two together helps to correct this problem and more importantly will provide full contact with even remachined receivers and bolts. Lapping is easily done by anyone with patience and dyechem. Be aware that this will increase headspace sometimes excessively. Remachining receivers and bolts needs to be done by a very experienced machinist who knows how to accurately allign a receiver which may itself be out of round. This is not trivial and the number of gunsmiths who really know how to do this rather than think they do is very limited.l! Re-cutting the bolt lug faces also needs to be done on the same lathe and on the same centerline as established for the receiver. Otherwise an out of square condition will have been created rather than rectified. Final lapping even after machining usually corrects this if the error is not too great. For what it's worth I've, made bolts and receivers myself and have a pretty good working knowledge of how this needs to be done.-Rob | |||
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quote:What error? I think I am one of the "average hobbiest"'s you mention, as I've been hand lapping my lugs, primarily Rem 700's, for years. I've never noticed any problems The error that I'm referring to is the human error and the fact that you are performing this action by hand rather than with precison machine tools. I'm not saying that you cannot achieve desired results with simply handlapping your reciever, but for the optimum in accuracy, you are much better to remove the majority, if not all of the material from the bolt and reciever by means of machining it. It only stands to reason that the precision of a quality lathe will outperform our own abilities in the world of precision. I've machined some pretty tight tolerance aeropsace parts in the past that needed to be lapped in order to aquire the finish and tolerance call out, but that was after the machining process had been taken to it's highest level. The amount of material removal was around .0001". Anymore material removal than that, we risked scrapping the parts. It's definately tricky business, and I would agree with Rodgunbuilder about the fact that "the number of gunsmiths who really know how to do this rather than think they do is very limited.l!" If you have a gunsmith that is encouraging you to have this operation performed, make sure that he goes into great detail as to how he plans to do it. After all, it's your receiver, and you don't want it messed up by someone who doesn't know what there doing. ![[Razz]](images/icons/tongue.gif){kind=icon} | |||
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For what it's worth I've seen two guns whose headspace had been increased by .003 by people who thought they could improve things by hand lapping their bolt lug engagement problems away. Heck some folks think that if they get >50% lug engagement as judged by Dyechem wear patterns that they have "blueprinted " their action despite these changes in headspace. Unfortunately, their are a few books out there written by the unknowing who have promugated this crap. There just isn't any substitute for precision machined surfaces. Thats what good Lathes are for. As was said above, final hand lapping after precise machining is one of those differences between guns that really shoot and those that don't. Hope this helps.-Rob | |||
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Gentlemen - I'm not trying to beat this horse completely to death, however, as I noted earlier, I've been hand lapping the lugs on my rifles for years, and, have noticed definite accuracy improvements in some, but not all, instances, with no signs of headspace problems. If the bolt will not close on a "no-go" gauge, there's not a headspace problem, correct? R-WEST | |||
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R-West- Just because your bolt won't close on a No-Go guage means very little other than it's safe to fire it. It does not mean that your receiver locking surface and bolt lugs are in complete contact or that even if they are, that these surfaces are square with the centerline of the bolt or receiver. This is why those custom actions like Stolle,Nesika etc. cost so much. They are machined absolutely true. or at least as true as those guys know how to get it and IMHO thats been pretty good. Now you can make a Rem 700 action for example, to the same standards, but it will involve bolt sleeving, boring a new bolt raceway and remachining the locking surfaces and the bolt lugs square with the receiver centerline. Only then is final lapping done to ensure near 100% surface contact. Lapping lugs on box stock receivers( with bolts with .0005-010 axial play or more) may help or hurt the situation depending on what you are starting out with. Heck even if you were lucky and got the lapping perfect what makes you think the threads in the receiver are really parallel and the barrel isn't cocked when it's screwed in? Lapping lugs is no substitute for real high quality machine work, if your after tiny little groups. If it's for a hunting rifle, why bother?-Rob | |||
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Rob - quote:Great!! Another accuracy secret I thought was really helping me. Maybe I just THINK it will shoot better, so it does? On the other hand, I can't imagine that a box-stock rifle that has only one lug bearing in its recess will not shoot better if lapped to the point that both lugs bear equally. I'm telling you, I keep meticulous records, and, post-lapping, at least two of my 700's (hunting rifles, one 7RMAG and one 30-06) definitely shoot the same loads better than they did before. None of them shoot any worse, and, I've not had any headspace problems. R-WEST | |||
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I'm glad your hand lapping helped you. Good luck! | |||
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quote:The purpose? Heck, so's we kin make money! How do we know if they need to be...? Shoot, Cheetum can smell 'em when someone brings one in! What is the process? Oh, that's a BIG secret only WE know about! It does involve a SECRET INGREDIENT we use in our lapping compound. What is the desired result? Heck, Dewey still wants a new 4x4 and I'm lookin' to pay off my mortgage this year! Thanks fer inquirin' Dewey ![[Roll Eyes]](images/icons/rolleyes.gif){kind=icon} , Cheetum ![[Eek!]](images/icons/shocked.gif){kind=icon} , and Howe Custom Gunsmiths Special this week: Recoil pad fitted to your .22, $199.95 parts AND labor! [ 07-18-2002, 00:42: Message edited by: sonofagun ] | |||
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I have lapped several actions then had the barrels screwed on to the correct head space. No trouble then. I would think that lapping with the barrel aready in place would cause you trouble. | |||
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quote:You're absolutely right. There are a lot of pieces to the puzzle that get overlooked if you're only lapping the lugs. The face of the receiver needs to be faced off square with the boreline. The threads need to be recut. The locking abutments need to be refaced. On Remingtons, the recoil lug needs to be either ran on a surface grinder or replaced by one that has been to ensure that it is precisely flat to within .0002". I also like to insert a dowel pin in the end of reciever to align the recoil lug so that it does not spin out of alignment when the barrel goes back on. Once this has all been done, the bolt lugs needs to be remachined square with the boreline. And last but not at all least, the barrel needs a tight concentric chamber with minimal throat and a almost a crush-fit on the headspace. Then you'll see what you're rifle after being properly crowned and bedded can do. ![[Wink]](images/icons/wink.gif){kind=icon} | |||
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quote:Sorry to come into this thread so late. Lapping lugs is just about the best low buck thing that one can do to a bolt action rifle. For those of you wanting to spook the serious amatuer I'm not suggesting that this is equivalent to blueprinting a receiver. Damn few factory rifles I've ever looked at over 30+ years had good contact between bolt lugs and receiver. Many show no, or very little, contact on one lug. This is not good for accuracy, brass, and certainly not what the engineers had in mind. For a few dollars invested in lapping compound full contact can easily be achieved. I prefer to remove the barrel, strip the bolt and lap using Brownells lapping kit and their 600 and 800 compound. This alows me to correct any change in head space and prevents getting lapping compound where I don't want it. Cycling the bolt 90 degrees (typical 2 lug receiver) 50 times with 600 grit and another 50 with 800 grit usually shows near 100% contact. More than 0.001 increase in headspace is rare. HOWEVER since manufacturers can't seem to get good contact on the lugs you must assume that their chambers are often marginal. Don't lap until you've borrowed, bought or rented guages. You just might need to correct the headspace. Please don't just make an adjustment to your dies. It only takes a thin coating of lapping compound on bolt lugs to lap. This is particularly important if you don't remove the barrel and strip the bolt. Once good contact is achieved meticulously clean receiver and strip the bolt to clean it. Now it is true that once you've lapped lugs they may be 89deg 56' 42" to the bore axis. So what? You have full contact and your bolt is not going to flex. Wally | |||
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I strongly agree with Wally's post. I think the process can do a lot to help factory rifles of hunting configuration. Also like Wally, I wouldn't try lapping lugs with the barrel in place. Brownell's sells a neat little gizmo that screws into the receiver in place of the barrel, and keeps spring pressure on the boltface while lapping. It pays to "work" the bolt up and down less times than you think necessary, then check with dychem (or black felt tip pin ink, or Rapine mould prep) to see how things are going. It's a lot like the old carpenter's rule, "measure twice, cut once", as steel is HARD to put back on, once cut off. One can "German Engineer" (overdo) any rifle almost to death. For the benchrest shooter it may be worth it (although I've won bench matches with rifles using very simple approaches to "accurizing"), but for the hunter it is usually not. You can get meaningful improvement in sporters with cheaper, easier techniques which don't require investing a fortune in compulsively perfect and very expensive machining. Good luck! AC | |||
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Boy, this one does go back a ways Wally. All this kinda boils down to one thing, are you the kind of person that does things the right way, or do you prefer to come up with easier, simpler methods of performing the task, that never measures up, but is justified becuase it really doesn't have to be done that well anyway? When you lap lugs, and you don't remachine the lug faces, your bolt and reciever will mate at the locking abutment area, but they are not square with the boreline. They never will be because you didn't qualify the threads, receiver face, and abutments in the same setup. This is the cold-hard facts. There are some out there that have obtained better groups after they lapped their bolts, but it would improve even more had they taken the time to remachine the receiver. How much more? Hard to say, but it will improve. You also eliminate the problems with excessive headspace that can occur as well. Lapping of any object is intended to accomplish one thing, and that's to even out the peeks and valleys that are associated with the tool marks that are left behind after finish machining has taken place. It is not for removing material from the start, and the difference in measurement before and after lapping should not be anymore than about .0002". If you lap anymore than this, you are ruining the precisionly machined surfaces. Blueprinting a Remington receiver for instance, is a simple process, and if a guy spends more than an hour on the project, he doesn't know what he's doing. This shouldn't cost you a lot either, although I see some that are pretty proud of their work recently. | |||
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quote:Matt, 1 hour huh? That would depend on what your definition of "blue printing" the Remington 700 action envolves. To me, blue printing the Remington 700 action entails dialing in the bolt tunnel, rethreading the receiver, recutting the receiver lugs, squaring the face of the receiver. Then, truing the bolt nose, squaring the bolt face and squaring the bolt lugs to the bolt's body, and then, squaring the receiver/barrel lug. What do you figure a fair cost would be for this work? Malm | ||
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I have only lapped the lugs on one gun: a VZ24 action 257 RAI. I have never got this kind of accuracy before, but I did 50 new things with that rifle. I came up with my own way of lapping lugs, but I don't know how much it helped. I true the reciver face located to the bolt bore. I true the inner stop ring located to the reciver face. I true the bolt position located radially to the bolt bore. I lap the lugs located radially to the bolt postion. I lap the lugs longitudanally fixtured with a spring loaded cartridge. I make the threads on the barrel located to the grooves. I make the shoulders on the barrel located to the grooves radially. I make the distace between shoulders match the distance between reciver rings. I make the chamber located to the grooves radially. I make the chamber located longitudially to the bolt face. I have dozens of other bent VZ24 bolts, maybe I could swap bolts and shoot some groups and see if it makes a difference. | |||
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quote:Matt I qualified my post on lapping by pointing out that it is NOT blueprinting. In answer to your question yes I like to do thing right. Right for the customer commissioning a 6mmPPC for competition is not necessarily the same as right for the guy wanting to "accurize" his brand new Remington ADL in order to put Bambi in the freezer. quote: Please understand Matt that even though my statements seem blunt and dogmatic I am extemely interested in learning and improving. In a recent post I posited my concerns regarding blueprinting. Approaching 4 years now I have been following Greg Tannels method as it made the most sense to me. However I can't get past some doubts regarding using the bolt way as a reference. If I ream the action and sleeve the bolt to very tight tolerance it makes sense. However sleeves wear and tight bolt tolerances are no good for the High Power Shooter, hunter or even the benchrester that wants to run his string during a lull. Better to purchase a custom action with a conal bolt or borden bump for the bench competitor. As to machining the bolt and receiver lugs perfectly perpendicular to the bolt ways What is our goal? I maintain that it is simply to insure that the rearweard thrust of our cartridge will be exactly in line with the path of the bullet. However whether we machine the lugs or lap them all that is accomlished is to insure that lugs make good contact. This must be followed by machining lapping or otherwise truing the bolt face 90 degrees to the bore. I remain unconvinced that it matters if bolt lugs are a few minutes or even a degree or two out of square so long as they do not move and flex. quote: I agree with the above so far a barrel lapping is concerned. Lapping lugs is exactly the same as lapping automotive valves. Its the best way to achieve a perfect fit. If the machined surfaces were precise wouldn't we just leave them alone? quote:Agreed IF I've got a lathe dedicated to that single purpose. Also I'd add an hour for sleeving the bolt without which I'm not sure their is any gain to using the receiver threads as reference and squaring bolt face, chamber and bore to that. Matt, blueprinting the Remington Model 700 as it has evolved over the last decade or so is, at least, a confidence builder for the benchrest shooter. However nothing can be done to it that will make it equal to and have the resale value of the custom benchrest action IMHO. My brother armorers at Quantico are not building the M40A3 this way. Weld magazine box to receiver for a little stiffness, tack weld a good recoil lug to receiver, lap the lugs. Had Winchester been able/willing to supply Model 70s in 1967 the 700 would never have been used. Respectfully, Wally | |||
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quote:If a fella can do about 1 a week pretty steadily, so as to stay in the habit, the customer shouldn't be spending over $100.00 for the work. That's fair to the customer, and the smith makes good money too, so long as he doesn't waste too much time. My definition of blueprinting is the same as yours. You have the obvious surfaces that need to be requalified for both the bolt and reciever. There's no smoke and mirrors, and with the proper equipment it is a simple task. Without the proper equipment and knowhow, it will take longer, just as it takes longer to do any job without the right equipment and experience. I suppose if I told you I could polish the outside bow of a Model 70 triggerguard to a finish, free of any machining marks, ready for blueing, that was superior to the factory finish in 11 sec., you'd be skeptical? Well, we do it everyday, because we have the proper equipment and the experience in running production finishing. And, we get finished with the part, there are no washed out screw holes, ever. But, that's are little secret. I'm sure you have some of yours too that you don't let out the door. | |||
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quote:That's exactly why we rarely ever lap the lugs. You should get full contact on the bolt after it's machined. If you don't, you have machined the two surfaces incorrectly. As I mentioned earlier, lapping reduces the peeks and valleys in the surface of the parts, improving the surface finish, but the surface needs to be at least a 32 finish before you ever lap the surface. I have seen many Remingtons and Winchesters that were closer to a 125 finish, and none better than a 63. This higher surface finish will also reduce friction, but almost unnoticeble. More of that friction resides in the camming acton and the cocking piece-bolt shroud area. | |||
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