Gunsmithing Bolt Lug Contact of High End Customs: Surprising Results

[Killswitch Engage]

edds like i said im not that familiar with the tikka and you may very well be right...it may be an action that simply has full contact. it may have less upward sear pressure then a rem or other two lugs. it may have tighter tolerances on the raceway/bolt fit. i dont know. i do know what ive seen on rems, surgeons, defiance two lugs and i am familar with those.

 

[my human host]

Fellas,

Pull the bolt out of your 700 or 700 style custom and take a look at the angles on the cocking piece of the bolt and where it engages the trigger. You'll find these parts are made in such a manner that when the bolt is closed and cocked, the trigger tries to push the bolt upwards until the bore of the action stops it. This has the effect of tilting the bolt slightly and pushing the upper lug of the bolt off the abutment inside the action ever so slightly.

When you fire the gun, the situation corrects itself. My 700's are all very accurate. If things slapping themselves into place has a negative effect on accuracy, I sure as hell can't shoot well enough to prove it.

 

[Blanman]

So if I were to repeat this test with the trigger assembly removed, since I can see where you're coming from on that count, would it be a more valid test? Seeing as that I do not have access to any of these jigs or fixtures is there another way to simulate the effects? Cleaning rods etc? I still can't wrap my head around it being okay with the lugs not making contact with a cartridge chambered due to the ejector creating a gap. If there is space wouldn't that increase the chances for peening/galling?

Also, on another note, after putting some further thought in. Would the camming motion of the lugs first engaging possibly create a false result of the contact? I'm no gunsmith but this is something that I'm trying to understand better after seeing the initial results. Is there a different product you would use other than Sharpie?

 

[Mgordon]

The Tikka rifles we have in the shop have a 90 degree connection between the trigger connector/sear and the cocking piece. A Remington, Howa, Winchester, and custom action designs have an angled trigger connector/sear and an angled cocking piece which will always push the bolt upwards as it pulls rearwards. The Tikka seems to have a neutral influence on the up and down as the relationship between the connector/sear and cocking piece pull the bolt backwards into the lugs.

May or may not be a better design, but by having the trigger installed with the firing pin assembly and simply putting Dykem or marker on the lugs is not going to show you anything. Pull your firing pin assembly out, mark the lugs and put the bolt back in the action. Lock in into battery and have your friend push a cleaning rod in the barrel from the muzzle and push against the bolt face. Assuming he is putting equal pressure on the bolt face, you can swipe it up and down with out unlocking the bolt and that will give you a better indication of what kind of contact you have.

We were offering the "Enhanced truing package" where you would have full lug contact, a square bolt face while the bolt was locked into battery (bolt tilted) but we could not see a difference in accuracy from conventional action truing. I'm always looking for the best techniques and methods, but I feel like your method of checking lug contact if flawed.

Mark

 

[sharac]

So if i understand things correctly only way to properly evaluate lug/action contact would be to put equal tension on the bolt face (as in various lug lapping contraptions which crew in the action threads)?

I really don't understand this as if you close the bolt (on a round or gauge) it should be fixed the whole point of accuracy being repetitiveness and more or less true and rigid system i find it very curios that any movement of bolt after the pressure rises wouldn't be a contributing factor to accuracy (or lack of it) i always assumed (could be totally wrong) that after one closes the bolt things are more or less unmovable and fixed.

 

[Killswitch Engage]

I think you could probably get a decent idea of contact with a stripped bolt with no ejector and a fired piece of brass from the gun. Much of this I think will depend on how perfectly concentric the chamber is at the back and how true your bolt face is. I would also prefer to have the fired brass oriented exactly as it was in the chamber when fired.

 

[Geno C.]

I'm not a gunsmith but I am pretty proficient with geometry and forces. I'll try to explain this.... OP I agree with your initial thought that he customs should make equal contact, however I can see the reason why given the explanation given by a few others.

The lugs are protruding at a 90 degree angle from the bolt body in the vertical direction both above and below the bolt. The forces that push up in the bolt will push it up till it touches the top of the bolt bore. This distance will vary based on the clearances the action has between the bolt and the bore. Let's, just for the sake of argument, say that it tilts enough to tilt the top lug far enought away that he sharpie ink would not be rubbed away when the bolt is cycled.

Seems plausible.

Now, given the afore mentioned 90 degree angle of the lugs to the bolt, when the round is fired and the case pushes back on the bolt it would push the lugs back making perfect contact with the action. This is assuming that everything is perpendicular where it should be and square with things that should be... Ie. action trueing job... When he lugs are pushed back the bolt body would actually float in the bore of the action when the round is putting reward pressure on the lugs. This is assuming that this force would overcome the the upward forces acting on the bolt body.

The important time for lug contact is when the round is going off and pushing on the bolt. The 2 lug design does not lend itself to have both unless there is VERY little clearance around the bolt or in between the front of the bolt and the barrel I guess.


Let's see how that sounds.

 

[Grump]

Fellas,

Pull the bolt out of your 700 or 700 style custom and take a look at the angles on the cocking piece of the bolt and where it engages the trigger. You'll find these parts are made in such a manner that when the bolt is closed and cocked, the trigger tries to push the bolt upwards until the bore of the action stops it. This has the effect of tilting the bolt slightly and pushing the upper lug of the bolt off the abutment inside the action ever so slightly.

When you fire the gun, the situation corrects itself. My 700's are all very accurate. If things slapping themselves into place has a negative effect on accuracy, I sure as hell can't shoot well enough to prove it.

I understand the theory here and the supreme importance of the actual on-target results.

But we don't have any sharpie-marker pics of whether YOUR bolt lugs are doing the same thing.

 

[Grump]

The Tikka rifles we have in the shop have a 90 degree connection between the trigger connector/sear and the cocking piece. A Remington, Howa, Winchester, and custom action designs have an angled trigger connector/sear and an angled cocking piece which will always push the bolt upwards as it pulls rearwards. The Tikka seems to have a neutral influence on the up and down as the relationship between the connector/sear and cocking piece pull the bolt backwards into the lugs.

May or may not be a better design, but by having the trigger installed with the firing pin assembly and simply putting Dykem or marker on the lugs is not going to show you anything. Pull your firing pin assembly out, mark the lugs and put the bolt back in the action. Lock in into battery and have your friend push a cleaning rod in the barrel from the muzzle and push against the bolt face. Assuming he is putting equal pressure on the bolt face, you can swipe it up and down with out unlocking the bolt and that will give you a better indication of what kind of contact you have.

We were offering the "Enhanced truing package" where you would have full lug contact, a square bolt face while the bolt was locked into battery (bolt tilted) but we could not see a difference in accuracy from conventional action truing. I'm always looking for the best techniques and methods, but I feel like your method of checking lug contact if flawed.

Mark

Understood and well-stated.

But what do you expect from the results of the pics: First two on the R-700 show nice contact on what is the bottom lug when locked, while the next two pics ("Surgeon built by highly reputable and sought after gunsmith") show nice contact on the TOP lug when locked.

Put that into the "sear tilts the rear of the bolt up" analysis and smoke it.

Of course, from the OP, I'm really interested in whether that particular rifle has shown any tendencies for even 1/2-MOA flyers out of the group using *reloads from that rifle*. Others' experiences in rather exhaustive testing suggests that there might be vertical dispersion possible where when all things are perfect there would be only a horizontal one. That is IF the dimensional problem is large enough to have an effect on target.

The lack of lower bolt engagement on the "Surgeon built by highly reputable and sought after gunsmith" action is going to get WORSE when the rear of the bolt is no longer tilted upward by the sear/striker contact.

 

[knockemdown]

Wouldn't sleeving the bolt body against a trued up bolt bore minimize/negate any issues with a bolt 'canting' due to forces from the sear and ejector springs? Greg Tannel is a very reputable 'smith and proponent of bolt sleeving to maintain a true center alignment of the bolt in the action raceway when closed into battery. Since all of the machining aspects of truing an action are indexed off that true center alignment, wouldn't sleeving the bolt body allow 'trued' recoil lugs to maintain full contact during bolt manipulation?

 

[mcfred]

Has anyone tried this experiment with one of the floating bolt head designs? That might be interesting to see.

 

[FCrifles]

If your bolt is trued up and a clean up cut has been taken on the front of the lugs when the rear was done (same set up) you can take a measurement with your properly trued receiver.

Place your stripped receiver (no trigger) vertically by the front ring in a vise with padded jaws. Insert your bolt minus the firing assembly in the closed battery position. Now take a good depth mike and measure from the receiver face to the front of each lug face. If they are within a couple tenths of each other, it's safe to say you are square and the receiver is fine.

Make sure all surfaces are clean and free of any debris so you can get a accurate reading.

By doing this vertically, there is no influence on the bolt body by anything. The rear of your trued lugs should be positioned squarely on the squared up internal lugs of the receiver. As long as the face of the receiver is square and the cut on the front of the lugs are to, your measurement will tell you what you need to know.

 

[Killswitch Engage]

Wouldn't sleeving the bolt body against a trued up bolt bore minimize/negate any issues with a bolt 'canting' due to forces from the sear and ejector springs? Greg Tannel is a very reputable 'smith and proponent of bolt sleeving to maintain a true center alignment of the bolt in the action raceway when closed into battery. Since all of the machining aspects of truing an action are indexed off that true center alignment, wouldn't sleeving the bolt body allow 'trued' recoil lugs to maintain full contact during bolt manipulation?

Sleeving the bolt would negate some of the effects but keep in mind when you start tightening tolerances like that on a tactical or field use rifle you are more then likely going to run into problems at some point from dirt, debris, ice etc. i think it has been tested and proven time and again that a trued up sloppy bolt rem with a great barrel will shoot just as well as a sleeved one or more then likely any custom actions. Most people spending big dollars on a custom action don't want to hear that and or believe it. Not taking anything from custom actions but That's my .02 worth.

 

[BlackWhiskey]

Hey Gents, thanks for all the replies; this has been a very interesting discussion.

I retested last night with a stripped bolt and applying back pressure had different results. I'll post them up this evening.

 

[sharac]

Is slick operation of Tikka then the reason for uniform lug contact as bolts play in action is minimal while some other actions do have more "wiggle" room when cycling action?

 

[RTK]

Maybe someone can answer me this, "if" only one lug is making contact when a round is chambered, after firing will the bolt drop (or move) to make both lugs contact before the case head contacts the bolt face?? If not I would think that might put some undue strain or throw a weird inconsistent harmonic through the gun???

 

[colchester]

Is slick operation of Tikka then the reason for uniform lug contact as bolts play in action is minimal while some other actions do have more "wiggle" room when cycling action?

Possible explanation on the Tikka results from Mark Gordons post above

Quote from MGordon
"The Tikka rifles we have in the shop have a 90 degree connection between the trigger connector/sear and the cocking piece. A Remington, Howa, Winchester, and custom action designs have an angled trigger connector/sear and an angled cocking piece which will always push the bolt upwards as it pulls rearwards. The Tikka seems to have a neutral influence on the up and down as the relationship between the connector/sear and cocking piece pull the bolt backwards into the lugs".

 

[my human host]

Excellent thread, BlackWhiskey.

 

[AKA-Spook]

Howa

 

[KevinU]

Has anyone tried this experiment with one of the floating bolt head designs? That might be interesting to see.

Using the same method as BlackWhiskey, evenly removed the ink on both lugs on my Bighorn action. No surprise there, the lugs are equally polished with 7000+ rds on the action.

 

[zx1963]

Classic case of good smith getting so busy he forgets why he got so busy in the first place, sometimes he starts taking short cuts....if you pay 4k for a rifle it should have well defined even bolt lug contact....no matter how it shoots, its part of the recipe for building a custom gun......

 

[300sniper]

Classic case of good smith getting so busy he forgets why he got so busy in the first place, sometimes he starts taking short cuts....if you pay 4k for a rifle it should have well defined even bolt lug contact....no matter how it shoots, its part of the recipe for building a custom gun......

You got that from the OP?

 

[E. Bryant]

Understood and well-stated.

But what do you expect from the results of the pics: First two on the R-700 show nice contact on what is the bottom lug when locked, while the next two pics ("Surgeon built by highly reputable and sought after gunsmith") show nice contact on the TOP lug when locked.

Put that into the "sear tilts the rear of the bolt up" analysis and smoke it.

Before getting too confident in your dismissal of 300sniper's comments, keep in mind that the ejector is located at the 12 o'clock position when the bolt is closed. This, combined with a cartridge in the chamber, will attempt to engage the top lug and press down on the rear of the bolt - countering the upward force being applied by the cocking piece to sear interface.

Which one wins? It probably depends upon a multitude of factors, including the spring force of that particular ejector assembly, and the exact nature of the trigger/bolt interface.

Yet another reason why this sort of test is interesting, but by no means conclusive.

 

[Layton]

So when I pull the trigger, the primer goes off(hopefully), ignites the powder, pressure builds expanding the case and the bolt face will tilt a few thousandths as the case puts pressure on it so both lugs make contact? And that's ok and normal on a high end custom? And I'm worried about a few thousandths when I reload?

L

 

[Gene Poole]

So when I pull the trigger, the primer goes off(hopefully), ignites the powder, pressure builds expanding the case and the bolt face will tilt a few thousandths as the case puts pressure on it so both lugs make contact? And that's ok and normal on a high end custom? And I'm worried about a few thousandths when I reload?

L

I would think that if there was any tilt in the bolt from being cocked, the lugs would square up at the instant the trigger releases the sear from the cocking piece. This would indeed be a necessary response in order for the trigger to release.

 

[Layton]

In order for the lugs to square up there would have to be some sort of movement at the case head/bolt face after you pull the trigger and before ignition I would think. Is that acceptable?

 

[300sniper]

So when I pull the trigger, the primer goes off(hopefully), ignites the powder, pressure builds expanding the case and the bolt face will tilt a few thousandths as the case puts pressure on it so both lugs make contact? And that's ok and normal on a high end custom? And I'm worried about a few thousandths when I reload?

L

Realistically, were only talking a few tenths of bolt lug differential at most. More than the thickness of sharpie ink? Sure. If you want less, you're going to need to tighten up the bolt body/receiver bore clearance. Are you going to gain any accuracy? If so, is it enough to justify the potential for a non-functioning rifle in the field? Decisions. Decisions.

 

[Killswitch Engage]

In order for the lugs to square up there would have to be some sort of movement at the case head/bolt face after you pull the trigger and before ignition I would think. Is that acceptable?

its necessary unless you want to have some roller bearings installed in there somewhere and never shoot in the dirt, mud, shit, rain, snow.

ive seen some nice low tolerance actions bind up tighter than a bulls ass in fly season at some tactical matches...funny how they didnt win especially since they couldnt even finish with it.

 

[Layton]

I understand the reasoning on both sides of this fence. I just don't understand that even at a few tenths, if both lugs are not making at least slight contact with the bolt closed on a loaded round how that could be just 'OK' with a high end custom. If both lugs are not making even contact with the bolt closed on a loaded round then it seems there will more uneven rearward movement than what's possible to eliminate and still have a reliable field rifle. And more movement than what people are paying for. Regardless of the net affect on accuracy.

 

[Killswitch Engage]

thats not neccesarily whats being said here. its very possible or probable a loaded round in the chamber, ejector pressure and sear pressure that both lugs are engaged at least minimally. whats being said is putting a sharpie on bolt lugs with an empty chamber and a trigger shoving on the bolt is probably yielding some unwanted results and that this test is not conducive to knowing if there is true contact.

 

[Layton]

thats not neccesarily whats being said here. its very possible or probable a loaded round in the chamber, ejector pressure and sear pressure that both lugs are engaged at least minimally. whats being said is putting a sharpie on bolt lugs with an empty chamber and a trigger shoving on the bolt is probably yielding some unwanted results and that this test is not conducive to knowing if there is true contact.

That I can understand.
L

 

[RTK]

Some gunsmiths believe contact should be made equally on both lugs with bolt closure, especially with large caliber rifles.
Bad ju ju harmonics and what not

 

[Layton]

Reading the original post, didn't the OP test with a dummy and still didn't have contact on 1 lug? And that's ok?

L

 

[RTK]

Here is a copy and paste.....................From elsewhere


This next comment is not directed toward your rifle or tests in any way, just a general comment for other members. Sometimes, especially in factory rifles chambered in large magnums, if you seat the bullets to contact the lands, you will get some group stringing. In my testing, this has been a result of bolt preload.

Bolt preload, especially in an out of box factory rifle can cause noticeable and measureable stringing in groups. This is generally a result of inconsistent bolt lug contact to the receiver bolt lugs support or simply an unsquare situation as a result of machining in the total receiver. GENERALLY, uneven bolt lug contact will result in vertical stringing. Unsquare condition in the receiver can result instringing in pretty much any direction.

Anyway, back to what can cause bolt preload. There are three major things that cause this.

1. Bullet contacting the lands of the rifling which puts pressure against the bolt head when the bolt is closed causing bolt preload.

2. Cases that are tight in the chamber, when the bolt is closed on a case that contacts the should or the chamber solidly, again, there is pressure on the bolt head when the bolt is closed.

3. Foreign matter between the bolt nose and the barrel breach can also cause bolt preload and serious accuracy issues.

Again, these three issues are seen mostly with factory rifles. WITH custom receivers and rifles, generally things are much more finely machined so bolt load does not cause as much of an issue.

Now why does bolt preload cause stringing, well, simply put, it will create inconsistent vibration patterns in the bolt, receiver and often barrel, the larger the diameter of the case head, the more dramatic it can be as seen on target.

This is why I have always said to build a rifle in a 223 that shoots well under 1/2 moa is EASY, to do the same thing in a 338 Lapua is MUCH more challenging. Not hard, anyone can do it, just more attention to detail is needed whereas with the small diameter 223, you can get away with ALOT more because the bolt thrust generated by the very small case head is extremely small and often times, even a bolt with only one bolt lug supporting the case will still shoot very well because the 223 does not have enough bolt thrust to compress the bolt to the point where it flexes enough that the floating lug I forced to contact its support surface.

In a 300 RUM however, or example, again, not referring to your rifle, just in general, if there is a floating bolt lug, even moderate pressure loads will produce enough bolt thrust to flex the bolt head until it contacts the bolt lug supports. This will result in inconsistent vibration patterns in the rifle system and as a result, generally stringing on target.

 

[Stonewall2]

Just for interest search "Borden Bumps".

Glenn

 

[Layton]

That was interesting read. Thanks Stonewall.

L

 

[microsuck]

I would worry more about how it groups.

 

[Grump]

1. No one has directly addressed the issue of one high-end custom having more contact on the much-discussed bottom lug (effect of sear displacing bolt body upward), while the other one has more contact on the top lug. IF (yes, I understand the importance of that) these dimensions are enough to affect accuracy, seems to me that the top lug with more contact would be more of a problem.

2. Still no pics of the "different results" obtained from a follow-up test.

3. Still no report of the average thickness of Sharpie ink vs. Dykem in normal applications.

4. Only one real report of effects of uneven bolt lug engagement, valuable though not quantified with group sizes before and after the fix.

5. The report that all with badly unequal lug engagement shooting badly lacks measurements of what the gap was.

6. Do they still make Plastigage for checking clearance in crank bearings? I suspect that this could let us quantify the gaps in various "good" and "bad" shooting rifles.

7. Is anyone here even familiar with Audette's findings on out of square caseheads? This typically shows up on the RELOADS. It is associated with case walls thinner on one side than another, but I strongly suspect the accuracy-killing condition can also be induced through out of square bolt flex on firing. Audette did find to his satisfaction, IIRC, that the cases would stay more square if the thin spot were aligned with the bolt lugs, and would be worse if aligned halfway between them.

8. What sorts of groups do those three rifles pictured in the OP produce with *reloads* from their own chambers?

We could be looking at the difference between a half-minute rifle and one that prints groups in the .2s or less at least half the time.

Gimme $10,000, loan of three rifles with trued actions, carte blanc to systematically remove metal from the lugs in carefully-measured increments, 40 fired cases from each rifle, and components for each one's best load, and I'll settle this argument in three months or less while still keeping my day job.

Really, I'm quite disappointed that no one has addressed the rifle that has more contact on its top lug. Sorta screws up a lot of theorizing in the thread.

 

[long range newbie]

wish I had money to throw at people to do this test. I don't even know what were trying to accomplish from this. If this makes my gun a guaranteed .25moa gun I'm in on trying this on my gun.

 

[Layton]

Grump, after reading this I started asking questions of folks who should know this answer. Although I agree that not having contact on both lugs may not be a deal breaker I was left with the impression that those stating it's ok to only have contact on one lug with a loaded round in the chamber after trueing are wrong. May not affect accuracy but that's not what was paid for. I would love to hear from someone else on a public forum that does this for a living and feels it's ok for single lug contact with a loaded round in the chamber on a trued receiver/bolt. Especially since the expectation has been set here that it will all true up after ignition so it's ok.

edt: I'm not questioning testing methods or how accurate the rifle will be with or without trueing. Nor am I questioning the work done on the OP's rifle. I'm just questioning the logic of a trued action only making contact on both lugs AFTER ignition.

 

[Greg Langelius *]

When I read through all of this, I get a headache. There's a ton of informative thought and opinion here, and I appreciate that.

But when my day comes to have custom work done, I keep coming back to the element of trust that brings me to the particular smith's doorstep in the first place. I tell my smith what I want the product to do, and I neither ask nor specify to the smith about how they make it happen. That's their business, and I wouldn't be there in the first place of I didn't trust their judgment in the matters of the 'how'. I judge their success on the degree of improvement I see in the rifle's performance.

Am I qualified to determine whether the full potential for improvement has been achieved? I am not.

Am I qualified to second guess the smith's judgment about what they will or will not allow to leave their shop? I am not.

If a disaster occurs and the outcome is not ideal, or, forbid, even worse than before, I have only one person to blame. That's me, because it was my choice to have the work done when and where it was done.

I don't see gunsmithing as an obligation to slavishly follow a prescribed path, but rather as a process where the path is dictated by observation and response, and where perfection is never a goal, since it is a human endeavor.

When things go badly, character is the deciding factor, and neither something that depends on a micrometer nor a layer of Prussian Blue.

When things go getter, I am grateful for the improvement, and try to refrain from looking the horse in the teeth overly much.

Greg

 

[300sniper]

those stating it's ok to only have contact on one lug with a loaded round in the chamber after trueing are wrong. May not affect accuracy but that's not what was paid for.

How far back do you bump your shoulders? how much clearance is between a factory loaded round's shoulder and the chamber shoulder? How much clearance is there between the bolt body and receiver bore? The answer to these better be zero, or less if you think there is going to be 100 percent contact on both lugs in that condition.

Can you please tell me what you paid for? Did you pay for bolt lugs being square to the bolt body? Did you pay for lug abutments being square to the receiver bore? Did you pay for something else?

 

[Layton]

Greg, thanks for your post and I agree on your points. I'm not questioning any smiths work. I'm just trying to understand the mechanics of this process as I don't agree with the logic of the bolt face having to cant after ignition to make contact on both lugs which is what was described. If my rifle shoots I could really care less and don't want to know if the lugs are making proper contact. And I don't want to look down the bore with a scope for the same reasons. One less thing to worry about

L

 

[Layton]

How far back do you bump your shoulders? how much clearance is between a factory loaded round's shoulder and the chamber shoulder? How much clearance is there between the bolt body and receiver bore? The answer to these better be zero, or less if you think there is going to be 100 percent contact on both lugs in that condition.

Can you please tell me what you paid for? Did you pay for bolt lugs being square to the bolt body? Did you pay for lug abutments being square to the receiver bore? Did you pay for something else?

I never said 100% contact. I'm talking no contact on 1 lug and that 1 lug only making contact after ignition. If that's ok then so be it. A couple of gentlemen I spoke to seem to think different. I don't completely understand that logic with a trued action but I don't have to either. I can ask honest questions though which is what I'm doing in order to try to.

edt: And what you pay for is between you and your smith. The folks I've spoken to seem to think they are paying for that contact on both lugs. I guess that was just an industry myth.

Another ed: And I'm not trying to start crap. I just don't have to accept that logic just because you said it's ok.

 

[300sniper]

I never said 100% contact. I'm talking no contact on 1 lug and that 1 lug only making contact after ignition. If that's ok then so be it. A couple of gentlemen I spoke to seem to think different. I don't completely understand that logic with a trued action but I don't have to either. I can ask honest questions though which is what I'm doing in order to try to.

edt: And what you pay for is between you and your smith. The folks I've spoken to seem to think they are paying for that contact on both lugs. I guess that was just an industry myth.

I'll put it this way, if you have .003" clearance between your bolt body and receiver bore and an effective bolt body length of 4.25" (random numbers but probably pretty close) you have an allowable taper of .0007" per inch. Your bolt lugs are about an inch across. that means there is a potential for .0007" of clearance at the extreme end of one lug. How thick is Sharpie ink? What forces do you have in a cocked rifle to overcome this potential?

 

[Layton]

Thanks. And again if you read my previous post I'm not questioning the testing methods. And I'm talking about having a round in the chamber. At that point you are saying there will/could still be a gap with one lug so that it does not make any contact until after you pull the trigger?

edt: in the end it doesn't really make a bit of difference. Just trying to learn something or rather unlearn something in this case. What I thought I knew has been thrown out the window but I don't give it up without asking questions.

 

[300sniper]

Thanks. And again if you read my previous post I'm not questioning the testing methods. And I'm talking about having a round in the chamber. At that point you are saying there will/could still be a gap with one lug so that it does not make any contact until after you pull the trigger?

edt: in the end it doesn't really make a bit of difference. Just trying to learn something or rather unlearn something in this case. What I thought I knew has been thrown out the window but I don't give it up without asking questions.

Unless you are crushing that round when you close the bolt, yes, there still can be a gap. As far as the OP's pictures, we don't know if that "inert" round was even making contact with the bolt face or not. We don't know how much influence working the bolt handle had on the rear of the bolt. It only showed swipe marks in the ink from working the bolt, not necessarily the condition it is when in battery. There are quite a few variables. Most likely, all of the pictured actions would bench measure out very close to true.

 

[Layton]

Thanks. I do want slight resistance when I close the bolt but that's me. Just for grins I ran this test on one of my 3 lug Sako's with one of my dummies. I don't believe it would pass the OPs test as 1 lug of the 3 had no contact. But I'll be damned if anyones going to touch it. lol



L

 

[Greg Langelius *]

This topic is another reason why I like the Savage action with its floating/pivoting bolt head. Contact may not be perfectly flush/even with the cartridge base, but it is equal; providing a feature or two from a custom action without the custom action's price tag.

Greg

 

[E. Bryant]

1. No one has directly addressed the issue of one high-end custom having more contact on the much-discussed bottom lug (effect of sear displacing bolt body upward), while the other one has more contact on the top lug.

Really, I'm quite disappointed that no one has addressed the rifle that has more contact on its top lug. Sorta screws up a lot of theorizing in the thread.

Well, Grump, somebody did address that point. Like, 8 days ago:

http://www.snipershide.com/shooting...customs-surprising-results-2.html#post2734328

Before getting too confident in your dismissal of 300sniper's comments, keep in mind that the ejector is located at the 12 o'clock position when the bolt is closed. This, combined with a cartridge in the chamber, will attempt to engage the top lug and press down on the rear of the bolt - countering the upward force being applied by the cocking piece to sear interface.

Which one wins? It probably depends upon a multitude of factors, including the spring force of that particular ejector assembly, and the exact nature of the trigger/bolt interface.

Yet another reason why this sort of test is interesting, but by no means conclusive.

Hopefully your disappointment can be assuaged somewhat.