Gunsmithing Bolt Lug Contact of High End Customs: Surprising Results

[BlackWhiskey]

A good friend of mine recently tested the bolt lug contact of his stock Tikka T3 action and compared it to the bolt lugs on his custom Remington 700. The gunsmith that did the work on his 700 was a very reputable gunsmith. The lugs on the Tikka had well over 80% contact on both lugs evenly, meanwhile the custom 700 only had a single lug making contacting, and the other one indicating no contact. We were both quite surprised.

This made me curious and we decided to test the two bolt guns that I own. Both are Surgeon actions, with one having been built by another extremely well-regarded gunsmith and costing over 4k. The other was built by a lesser know smith costing +/- 3k. The action built by the lesser known smith indicated near complete bolt lug contact, while the more reputable smith's action indicated only a single lug making contact, similar to my friends Rem. 700.

Method of testing: We used a sharpie marker to cover the back of the lugs in ink, then inserting an inert cartridge in the chamber, we cycled each bolt 25 times. We then examined the amount of ink removed from the lugs to determine amount of contact. A simple but effective test.

I am anticipating the response of "If the guns shoot well, who cares?" to which I will answer "What I paid for from these gunsmiths is the craftsmanship and attention to detail that they are known for, which it appears they have failed to deliver. Not to mention the massive amount of pressure being absorbed by a single bolt lug, and not the intended design of the action."

My reason for posting this is to help me answer a few questions:

1. Is this as common an issue in high end custom rifles as it appears?

2. Why is such a simple and easily remedied problem an issue with rifles that cost in excess of 3k-4k with wait times of 2+ years?

3. Why is a $550 gun making more contact than 2 very high end custom builds?

4. What is the best way to remedy these issues? (one of the gunsmiths is damn near impossible to contact)

I request that we keep this discussion on topic and keep the flaming to a minimum.

Custom Remington 700




Surgeon built by highly reputable and sought after gunsmith




Surgeon by lesser known smith




$550 bone stock Tikka T3

 

[300sniper]

All your test shows is how much contact is being made by the inert cartridge. It does not show how much contact there is when a real rearward force is placed on the bolt face. I would not rule out anyone's work based on your results.

 

[BlackWhiskey]

Thanks for the reply 300sniper. I would be interested to hear how a lug can make contact during firing and not during locking/unlocking.

It also doesn't address the issue of clearly unequal contact.

 

[ugsly]

I am with 300sniper on this, I dont believe putting a cartidge in and cycling it will tell you the whole story. When lapping the lugs with a jig I made I have a piece of brass with a spring behind it to keep a constant pressure on the bolt rearward. A dummy cartidage I dont believe could keep rearward pressure like a lapping jig can. If your rounds are that hard/tight to cam over you can gall you lugs.

Kc

 

[BlackWhiskey]

Allow me to rephrase: though this method may not simulate the back pressure of a fired cartridge, it clearly shows uneven lug contact. It would therfore be logical to assume that though it may be possible for both lugs to make contact during firing, they would still be making unequal contact during that process.

 

[Temp9]

I am with 300sniper on this, I dont believe putting a cartidge in and cycling it will tell you the whole story. When lapping the lugs with a jig I made I have a piece of brass with a spring behind it to keep a constant pressure on the bolt rearward. A dummy cartidage I dont believe could keep rearward pressure like a lapping jig can. If your rounds are that hard/tight to cam over you can gall you lugs.

Kc

I believe this is correct. A dummy cartridge in the chamber will allow the bolt to be forced rearward via the ejector. Being off centered, the ejector will naturally force the bolt back with an uneven force, possible enough to reduce or eliminate contact on one lug. When the round is fired, the bolt will be forced back evenly, and that contact is what matters for accuracy. I believe (hope) the test with a lapping jig putting pressure in the center of the bolt face would yield better results.

That said, I love Tikka's.

 

[bjay]

It never bother me seeing my defiance surgeon phoenix or my trued tem700 with one lug is more shiny than other they shoot straight thats all i care..

 

[reximus]

I am no expert here, but I am with BlackWhiskey on this. I'm sure that his customs shoot straight - that's not what we're questioning here. For the money paid, I would also expect that my bolt would lock up evenly.

I think I recall reading about Mike's (from Tac Ops) process for building off of Remington actions and about all the detailed care and attention he puts into each build. I believe that one of his processes included doing exactly what you did - sharpie the bolt lug faces, cycle the bolt (no cartridge) one time, and check contact. From what I remember reading, Mike isn't satisfied until a single bolt cycle will indicate complete contact from both lugs. He will work it until there is even and complete contact.

I think one of the issues, here, is that many smiths (even some of the great ones) may take a Surgeon (or other custom) action with the assumption that it is 100% G2G from the 'factory'. While a Surgeon action is great and is 100% G2G, its not going to be absolutely perfect out of the box. Without some hand-fit love and some crazy attention to detail, you're just not going to get that "Tac Ops" 100% engagement from any 'factory' part.

No manufacturer is able to produce perfect parts - that is a fact. All manufactures have tolerances that they use to achieve some nominal spec. While I do know that Surgeon (and others) uses some of the best CNC technology available and some of the most advanced manufacturing processes known to man, I don't know how much 'custom' hand-fit work actually goes into their actions' manufacture. I don't care how great someone's manufacturing technology or process is is, you just aren't (yet) going to get custom/hand-fit parts off of a machine - period.

While a custom action is (or should be) going to be MUCH better out of the box when compared to a factory Remington/Savage/Tikka action, it still may not have the custom fit needed to achieve perfection. CNC technology has absolutely lessened the gap between high-end semi-custom factory parts/pistols/rifles. But that same technology hasn't yet been able to replicate the fit and finishes that can be achieved by hand.

...

Wow, that was a lot of rambling. I am by no means intending to take a shot at any of the custom action manufacturers, nor to take a stab at any of the high-end smiths here or elsewhere. I am just stating some of my observations - highly subjective, based on lots of research but also based on lots of opinions, and including much conjecture.

 

[Grump]

sure, bolts can flex and appear to give full engagement under thrust, but at what level of tilt? little effect with perfect ammo, but reloads with heads out of square by .003 or more are proven (by C Audette IIRC) to go out of the group at certain alignments with two-lug boltguns.

test it!

 

[jonaddis84]

This is no excuse for not lapping lugs, as I believe no matter how expensive the action is the lugs should get lapped before chambering, if nothing else to check lug contact. Shit can happen during machining that could cause zero lug contact, ie not enough chamfer on the action lug face for the radius of the cutter that turned the face of the bolt lugs.

Anyway, that being said, you need to use another method to test this. As 300 said, you need a even force acting directly rearward on the bolt to test this. Someone hit the nail when they pointed out the ejector spring pressure is exerted on one side of the case which could show uneven lug contact with your test. When lapping bolts I remove the ejector, and have a spring loaded mechanism that threads into the action pushing directly on the bolt face. I also like to put a trigger in to simulate the upward force the sear imparts on the bolt while in use.

Take one of those fired cases, cut it in half and put a pretty heavy duty spring in there. Remove the ejector. Remove the firing pin assembly. Try that and see if you get the same results. Its possible that you will, but Im thinking you will see slightly different results.

This is what the lapping tool looks like

 

[Blanman]

I am with 300sniper on this, I dont believe putting a cartidge in and cycling it will tell you the whole story. When lapping the lugs with a jig I made I have a piece of brass with a spring behind it to keep a constant pressure on the bolt rearward. A dummy cartidage I dont believe could keep rearward pressure like a lapping jig can. If your rounds are that hard/tight to cam over you can gall you lugs.

Kc

But you do in fact lap the lugs? It would be interesting to see what results you would get using the same test on any of the rifles whose lugs you've lapped, just for curiosity's sake.

I believe this is correct. A dummy cartridge in the chamber will allow the bolt to be forced rearward via the ejector. Being off centered, the ejector will naturally force the bolt back with an uneven force, possible enough to reduce or eliminate contact on one lug. When the round is fired, the bolt will be forced back evenly, and that contact is what matters for accuracy. I believe (hope) the test with a lapping jig putting pressure in the center of the bolt face would yield better results.

That said, I love Tikka's.

What if all the tests were repeated with no cartridge in the chamber for the ejector to push on and came up with the same results?

 

[cal50]

I would expect lesser contact from a production rifle but for a custom that was lapped the contact should be uniform and closer to full.

Lapping for contact should be pretty straight forward and if lapped and inspected it should be repeatable when checked as in the original post.
It looks as if someone lapped for "fit" but stopped short of going enough to get more contact.

Lapping a 1911 slide you go for fit and the contact area is of a lesser concern. Lapping bolt lugs you are going for consistent contact and some of the pictures show varying degrees of it.
Using Prussian Blue or die spotting ink is similar to the Sharpie in it shows the high spot/s clearly.

 

[dinc]

I assume you had the firing pin in the bolt when you cycled it and it was cocked when closed. Repeat the test with the firing pin removed. I'm interested to see the results.

Also you could cut the case in half and put a spring in it (making it longer) to provide some "bolt thrust."

 

[PRDRIVER]

I don't have a custom rifle to compare it to. But every tikka that I have used shot very well. Maybe this is one of the components on whey they shoot so great.

I would have expected better bolt contact on a custom rifle. How well do the custom rifles shoot that have less bolt contact?

 

[sharac]

I have a well used Tikka and i can report the same "print" on its lugs (last mm or so not engaged) and it has been used exactly as the original test-> cartridge in, bolt close, bum, cartridge out and repeat ~5500 times...

As to the other rifles it appears not all that shines is gold... Perhaps some rifles shoot great in spite of and not because of...

 

[ZombieSlayer]

Allow me to rephrase: though this method may not simulate the back pressure of a fired cartridge, it clearly shows uneven lug contact. It would therfore be logical to assume that though it may be possible for both lugs to make contact during firing, they would still be making unequal contact during that process.

How did you hold the bolt perfectly centered in the action or at least perfectly axially inline for your testing? Your moving a bolt handle either pushing or pulling and twisting the bolt of axis.

I'm with 300sniper. The only thing your test really proves is that your testing method was inadequate to draw conclusive results.

 

[sharac]

Didn't know American bolts and actions are made of jello which can be twisted and pulled in various ways. To me its perfectly clear that during normal and expected use one sees results as shown. Perhaps a qualified gunsmith can answer here (if this is normal or not?) but i would say if there is enough bind and play in bolt/action to affect lugs in such a way that only one is in contact and/or poor general contact in this simple usability test than i'd say something is simply not as it should be.

 

[Blanman]

I really don't think bolt lug contact should, not saying that it doesn't, but shouldn't vary enough to raise an entire lug from it's contact surface from using the special tool and a fired piece of brass. The bolt closes on a piece of brass when you're about to fire does it not? So under realistic scenarios, it still doesn't explain why two highly customized actions are having an entire lug just free float when chambering a cartridge, while a factory rifle makes almost perfect contact

 

[Blanman]

I don't have a custom rifle to compare it to. But every tikka that I have used shot very well. Maybe this is one of the components on whey they shoot so great.

I would have expected better bolt contact on a custom rifle. How well do the custom rifles shoot that have less bolt contact?

As do I. They shoot just fine, but that's not really the issue at hand here.

 

[D Miller]

Wouldn't you want fairly even lug contact from just the ejector springs pressure on a loaded round? Sure the other lug might make contact when fired but unsupported metal and high pressures don't always do good things. A few thou "flex" might be well with in the normal range for materials used in actions but im under the impression even contact is better.

 

[Grump]

I think there's a LOT of uninformed/NOT thought out thinking in this thread.

Run some trigonometry and tell us how many thousandths you can lift a bolt lug off of the locking lug at X distance off center, with a bolt body axis of Y to the rear-most point of receiver contact, and a radial "slop" of +/- whatever you can measure as common on rifles as delivered.

Betcha the math will show something amazingly small.

Then compare that with the thickness of a Sharpie ink deposit.

THEN let's get some Plastigage or something to quantify the clearance on these floating locking lugs.

Then compare that with the "no effects until above .002" standard (correcting the bolt lug figure inward to the casehead diameter) that Creighton Audette documented in these two articles (sorry, I couldn't find them on-line when first citing to them in a post here on the Hide exactly a year ago today): Cartridge Cases and Accuracy, Creighton Audette, American Rifleman, June 1981, p. 27 and January 1982, p. 30.

From that post last year, however, I did include this link and description thereof:
There's kind of a summary of all that here, halfway down the page: http://riflemansjournal.blogspot.com...1_archive.html
Look for "Reloading: Audette Case Checking Method"
What was important there was, IIRC, Mr. Audette's finding that case heads went out of square in the "up" or "long" dimension *usually* where the case wall was the thinnest.

Yes, "how does it SHOOT" is a valid question, but unequal locking lug engagement most likely will NOT show any inaccuracies/group size problems with nonce-fired factory loads, or with reloads from other rifles with bolts that don't flex out of square on firing. OTOH, cases with walls too thin on one side *can* stretch out of square in a perfect two-lug gun if that thin spot is aligned halfway between the two lugs, BUT that defect will not screw the group unless it is like .003" or more AND the resulting high spot is again aligned between the lugs on the next firing.

So, testing of the questions arising from these disappointing findings, to be truly valid, must include a lot of measurements, time and trouble. What I don't like about the findings is that the chances of a thin-wall case becoming out of square to an accuracy-compromising degree can be more than likely 50% greater in such defective "custom" rifles, and the chances of it showing up on the next firing is also probably 50% greater because of that same lug--most likely if the lug allows enough flex in the firing cycle for the high spot to do the same thing it does if lined up on the unsupported spots on either side between the lugs.

All this crap is why I keep toying with the idea of a 3-lug gun for my next rifle. Either that, or a big AR system in 6.5 Creedmoor...

 

[Pusher591]

Very surprised no site smiths or well known smiths have weighed in on this. I would like to hear their thoughts. Wondering if this is the kind of stuff Mike @ BlackOps Precision was talking about in that last big thread.

 

[my human host]

The Remingtons I've seen that truly had a floating lug shot like complete ass until the problem was corrected. Remington triggers have a tendency to put upward force on the ass end of the bolt until you hit the boom switch.

 

[RTK]

Any gun from a custom shop should have the lugs addressed, that's what you are paying your good money for. How big a difference it will make is debatable, but that is not the point here as I see it.

 

[300sniper]

do you want your bolt lugs perpendicular to the bolt body axis or not? do you want your bolt lug abutments perpendicular to the receiver bore or not? how much clearance is there between your bolt body and receiver bore? how much and what direction are you physically forcing the rear of your bolt when lifting the handle up and down? how much upward force is the sear putting on the rear of the bolt when cocked? how much pressure is the ejector placing on one side of the bolt face? is the head space exactly the same on each of these test rifles: is your inert case placing exactly the same rearward force on each?

if the bolt lugs and abutments are truly perpendicular to the bolt body/receiver bore and there is any clearance, without even rearward pressure on the bolt face (like when there is 55k psi acting on it), the other forces involved will most likely show what you have here.

 

[300sniper]

If there is enough clearance between the bolt body and the receiver bore for both lugs to make contact, they will when the chamber is pressurized. The question is, do you want full contact when the rifle is cocked sitting idle or do you want full contact when it's pressurized? I know which one I choose.

 

[RTK]

I know I don't want one hitting before the other throwing some weird unpredictable harmonic through my gun. I want everything true, square, perpendicular, in-line and more for my money Again, it might be debatable or even insignificant, but that is not what I pay money for........... Every gun I have had built for me over the years has always had contact on both lugs, guess I just expect it to be that way.

 

[ZombieSlayer]

do you want your bolt lugs perpendicular to the bolt body axis or not? do you want your bolt lug abutments perpendicular to the receiver bore or not? how much clearance is there between your bolt body and receiver bore? how much and what direction are you physically forcing the rear of your bolt when lifting the handle up and down? how much upward force is the sear putting on the rear of the bolt when cocked? how much pressure is the ejector placing on one side of the bolt face? is the head space exactly the same on each of these test rifles: is your inert case placing exactly the same rearward force on each?

if the bolt lugs and abutments are truly perpendicular to the bolt body/receiver bore and there is any clearance, without even rearward pressure on the bolt face (like when there is 55k psi acting on it), the other forces involved will most likely show what you have here.

We have a winner.

 

[mavrickarcher]

Amazing how screwed up those Tikka T3 turned out to be!!!!!!! Hell you thier so messed up you don't have to true them!!!

The custom should have been as messed up, you did not get what you paid for.

 

[dmg308]

A little information is amazingly dangerous.

 

[671RTO9513]

Y'all could get a Savage and quit anguishing over this shit.

Just sayin'.........

 

[bjay]

Amazing how screwed up those Tikka T3 turned out to be!!!!!!! Hell you thier so messed up you don't have to true them!!!

The custom should have been as messed up, you did not get what you paid for.

Amen.
I love my 2 sako 85 3lugs

 

[300sniper]

I know I don't want one hitting before the other throwing so weird unpredictable harmonic through my gun. I want everything true, square, perpendicular, in-line and more for my money Again, it might be debatable or even insignificant, but that is not what I pay money for........... Every gun I have had built for me over the years has always had contact on both lugs, guess I just expect it to be that way.

So you want an action with zero clearance between the bolt body and receiver bore? A clearance that will make the action inoperable? That is what you are saying whether you realize it or not.

 

[gminor]

So you want an action with zero clearance between the bolt body and receiver bore? A clearance that will make the action inoperable? That is what you are saying whether you realize it or not.

I dont believe that is what he is saying brother..

He wants contact on both lugs (rear face of the bolt lugs) equally. That has nothing to do with the chamber. Typically, headspace is set AFTER the bolt lugs are trued and lapped..

 

[RTK]

So you want an action with zero clearance between the bolt body and receiver bore? A clearance that will make the action inoperable? That is what you are saying whether you realize it or not.

Nope, don't know how ya got that out of what I said.

I think gminor gets it

 

[300sniper]

I dont believe that is what he is saying brother..

He wants contact on both lugs (rear face of the bolt lugs) equally. That has nothing to do with the chamber. Typically, headspace is set AFTER the bolt lugs are trued and lapped..

True/lap your lugs square/perp to their axis. There's still clearance between the bolt body/receiver bore. Put any force other than inline with that axis, one of the lugs is gonna unseat. Small, maybe. How thick is the sharpie marking, like mentioned earlier.

 

[300sniper]

Nope, don't know how ya got that out of what I said.

I think gminor gets it

You either want a square/true bolt or you don't. Clearance and angles will make lugs unseat/show uneven contact without rearward pressure on the bolt face. Draw it out.

 

[okiefired]

Yet another reason I dont buy customs.

okie

 

[gminor]

Yet another reason I dont buy customs.

okie

Never handled a Bighorn then I guess...

 

[300sniper]

Y'all could get a Savage and quit anguishing over this shit.

Just sayin'.........

Never handled a Bighorn then I guess...

If bolt lug contact percentage is a real life factor, certainly the benchrest guys that will go to the nth degree to get the best possible groups are all using floating bolt heads, right? Right?

guess what? unless your oem or smith has really shit the bed, our entire bolts are floating and both lugs can and will make contact when the insignificant forces of the sear, ejector and bolt handle manipulation are released and max chamber pressure is pushing against the bolt face.

 

[300sniper]

I dont believe that is what he is saying brother..

He wants contact on both lugs (rear face of the bolt lugs) equally. That has nothing to do with the chamber. Typically, headspace is set AFTER the bolt lugs are trued and lapped..

Equally when? When an inert case (fireformed to what?) is chambered? When you are manually cycling the bolt by the bolt handle? When the sear is pushing upward on the rear of the bolt? When the ejector is pushing on one side of the case head? When the chamber pressure is maxed out pushing equally on the bolt face?

Which of these are you paying for? If you specify in advance, I'm sure any builder can give you any of these but probably not all of these at once. Which one do you want? which one did the OP show? Sure about that?

 

[jonaddis84]

It's funny how some people only listen to certain big names on here isn't it 300?

Galaxy S3 on tapatalk

 

[Killswitch Engage]

300 is dead on with his posts. some of you guys apparently have no mechanical understanding of what you are talking about. who gives a rats ass what the lugs do on a fired case or empty chamber? that is not indicicative of much at all. with a bolt body having at least a few thousands clearance to the raceway and two spring forces along with your uncalibrated hand running the bolt handle up and down how can there possibly be full contact if the lugs are cut or trued to the bolt body axis? my bet would be your sharpie mark is wiped off the lower lug or the lug on the bolt handle side since that is the one receiving force from the sear.

 

[Edds]

300 is dead on with his posts. some of you guys apparently have no mechanical understanding of what you are talking about. who gives a rats ass what the lugs do on a fired case or empty chamber? that is not indicicative of much at all. with a bolt body having at least a few thousands clearance to the raceway and two spring forces along with your uncalibrated hand running the bolt handle up and down how can there possibly be full contact if the lugs are cut or trued to the bolt body axis? my bet would be your sharpie mark is wiped off the lower lug or the lug on the bolt handle side since that is the one receiving force from the sear.

Why did the Tikka make contact on both lugs?

 

[sharac]

We perhaps have no mechanical understanding but we're ready to be schooled. No one was born smart and all knowing so any information why that would happen or why it shouldn't matter is welcomed...

 

[Killswitch Engage]

Why did the Tikka make contact on both lugs?

how do you know the tikka makes contact under chamber pressure when fired? you might have the exact opposite happening with that action where it has full contact idle and does not with chamber pressure...

 

[Killswitch Engage]

next time i have a rem or other 2 lug down i will do a test for you guys. we can take a trued action that has not had the raceway reamed or the bolt sleeved but the lugs and abutments trued/lapped and put the trigger assembly in it. put a dti on the top lug off the action face and cock the bolt. we can then get an idea of exactly how much this shoves the lug off the abutment with sear pressure. one could also simply leave the trigger out and do the same test just picking the back of the bolt up. if any one else would like to do this first please do...

 

[Edds]

how do you know the tikka makes contact under chamber pressure when fired? you might have the exact opposite happening with that action where it has full contact idle and does not with chamber pressure...

You believe chamber pressure will cause a lug to move away from contact?

 

[Killswitch Engage]

You believe chamber pressure will cause a lug to move away from contact?

not necessarily but the force from chamber pressure would be far more excertive than the sear or ejector is providing. i am not that familiar with tikka actions so anything on those is purley speculative from me. i dont know what type of metals they use in their actions and bolts as far as wear resistance and or hardness etc. also what are the tolerances of the bolt to raceway fit? theres alot of posssibilities as to why it appears the tikka has full contact.

 

[Edds]

theres alot of posssibilities as to why it appears the tikka has full contact.

Why don't you list a few of them. The only reason I can think of is that they appear to have full contact because they have full contact.