Sloppy Carrier/Bolt fitment

[JohnEd]

My Carrier has a lot of play between the Carrier and the top of the receiver.  My curiosity is would it be better to close up the rail on the top or the bottom?  I could weld a bead along the top of the groove or along the bottom and then mill the groove to match the thickness of the Receiver.

My head space is spot on and better than it ever was from D Tech.  With their assembly I could easily close on the NO-GO gauge but it had run a thousand rounds fault free so I wonder.

I read once that the Locking Lugs  came in many sizes for the reason of fitting the bolt to the Carrier but I have no source for that info.  The underside of the C seems to have some promise for cutting the slack were I to thicken that but the C would then be slamming "up" at battery.

My D Tech has a carrier that has a lot of play.  Maybe 10-20 thou between the rails and the grooves in the side of the C and the top rail of the Receiver.  The bolt is under that and cannot but have even more play/separation.  Looking from the underside the locking lugs (locking piece..LP)do lock up the bolt into battery but I can move the bolt up and down.  Only gravity keeps the LP engaged and were I to turn the gun upside down the bolt would have a terrible amount of head space play.

My kit gun is just that much worse.

The C is supposed to press down on the LP and trap the B and press it into battery.  With the play I have the gun must have recoil from the heavy C slamming up and down as well as into battery.

How would you "fit" the carrier to the top rails on the R.  My C has channels/grooves in it that are .189 inches and the top rail of the R(top surface with the hole opened up) is .139.  That is the D Tech.

In my Ohio Rapid Fire R the top is .107 thick and the C has .188 grooves.  That is a big difference from the D Tech.  81 thou rattle room vice 50 thou.

I can only think that I will have to tig the C groove full of weld and re-cut the thing with a mill.

I attribute this condition to my accuracy problem.

Anyone ever address this clearance problem?

[RSR]

Not sure I entirely follow, but play between carrier and rails and bolt and rails is supposed to be there for reliability reasons when fouled.  It allows crap to work through. 

When in battery, your recoil spring should be holding the carrier fully forward.  The locking block does so at angle in which it grabs/hooks the receiver groove and is effectively pulling down and pushing forward.  It's not just straight up and down.  Your bolt will be/should be locking in tight when weapon fully assembled. 

I definitely get more carrier wobble when carrier is not locked forward w/ bolt in battery. 

Also worth noting, that any paint/finish/etc will result in a tighter fit, at least temporarily.  All century guns have teflon which is a relatively thick coating and makes all parts fit tighter than original paint over park...

[JohnEd]

Not sure I entirely follow, but play between carrier and rails and bolt and rails is supposed to be there for reliability reasons when fouled.  It allows crap to work through.

So very very true.  They build and clearance the guns to a tolerance that will ensure operation in the hands of and intended shooter that is trained to the expected level shooting the expected ammo in the environment possible.  Whew!  So that explains that the AK is so loose it will fire when full of mud or gravel being operated by a retarded chimp in blistering desert where the gun hits 212+ without shooting to Siberia and is shooting Egyptian made ammo marked "for export only".

And then there is that close tolerance stuff that is expected to be used by thoroughly trained and supervised Professional Grade solderers.  The Germ,an stuff and the AR for almost $4K.  H&K and Sig also leap to mind as closer tolerance AND accurate.   

When in battery, your recoil spring should be holding the carrier fully forward.

I agree.

 The locking block does so at angle in which it grabs/hooks the receiver groove and is effectively pulling down and pushing forward.

I don't fully agree.  The locking block actually "pushes" against the rail opening surface when the LB is pushed down by the carrier sliding into battery over the Bolt.  There is no "pulling" down but rather pushing of the LB by the C.  The forward PUSH is done by the LB legs being curved and being "wedged" to press the bolt into battery and hold it tightly and bear the force of the chamber pressure, 60,000 psi for a short period of time. 
 

 It's not just straight up and down.

While the Locking Piece is actually "rotating" it operates like it was moving up and down at the point where the C impacts the LP. 

 Your bolt will be/should be locking in tight when weapon fully assembled.

And thereby hangs the tale.  This is the rub.  My C rattles around like a toy on both my Kits and the D Tech.  The D is better.  If I reach under the bolt thru the empty mag hole I can push my Bolt up quite a ways.  The Bolt, LP and C have much to great tolerance.  It is receiver peculiar as switching my sets of pieces and interchange them helps very little, if at all.  My problems are the relative locations of the rails, primarily, and loose part tolerance, secondarily.  One problem is the machine work on the Rapid Fire Receiver  in that it is some 80 thousandths thinner than the D Tech(CSA) and that accounts for the additional C rattle and B not being captured.

I definitely get more carrier wobble when carrier is not locked forward w/ bolt in battery.

I assure you I am talking about the bolt being as far into battery as it will go and head space being spot on.

Also worth noting, that any paint/finish/etc will result in a tighter fit, at least temporarily.  All century guns have teflon which is a relatively thick coating and makes all parts fit tighter than original paint over park...

My kit Receivers from RFire were all phosphor coated.  I applied GunKote and that is spec'ed at a couple thou thick after baking.  But you are certainly correct and my D Tech is heavily coated with what seems to be Powedr Coat.  I intend to remove all those coatings in this process.

If I continue I expect I will have a set of parts that are "made" for each of my guns.  That isn't smart or needed for this guns application/intended use.  But, I took lapping compounds and lapped in all the moving parts of my D Tech, including the C Sear interface, and i was very pleased that the gun seemed to run silently and fired with apparent less vibration.  It is a labor of love.  In this case, however, I know the tolerances are affecting accuracy and will affect reliability and safty may be an issue now or down the road.

RSR,

Thank you for your comments.  hey are thought provoking.

John

[RSR]

I will have to examine play from under the magwell. 

I still think the locking piece is pulling down -- the predominant force might be forward, but it should pull the front of the bolt down while lifting the back up slightly cantilevering/wedging the bolt stationary up and down in addition to forward and back... 
Now it is on a pivot in the bolt sort of like a knee or elbow joint, but b/c of angles in pushing forward the locking piece is also pulling down.  So in pulling the bolt forward into battery, the locking block's angles also pull the front down tightly against receiver lower rail.

Further, it is the weapon design of bolt--locking piece--rails--bolt carrier--recoil spring that all work together to lock into battery.  It is not primarily a function of gravity.  Gravity may perhaps affect a small degree of change (especially if something is out of spec), but definitely a minimal one.  In fact, it is the locking piece bolt carrier interplay that forces the locking block down.  And the recoil spring holds the carrier in that forward position.  You can see this easily with the bcg out of the weapon -- and why tilting assembled bcg forward (same position as when bolt unlocks to eject spent case), moves bolt forward, and lifts the locking block so that it can be reinstalled....  With bolt back and locking block lugs down (in-battery position), you can't reassemble. 
Point being that firearms are a system that is greater than the sum of individual parts...

[JohnEd]

I will have to examine play from under the magwell. 

I will do that again as well.

I still think the locking piece is pulling down -- the predominant force might be forward, but it should pull the front of the bolt down while lifting the back up slightly cantilevering/wedging the bolt stationary up and down in addition to forward and back... 

I don't agree with the pulling part but that might not matter.  The top of the LP has a flat surface that interfaces with the underside flat spot in the C.  The C actually forces the LP down onto the bolt and locks the LP to the rails in a "wedge"

It is not primarily a function of gravity.  Gravity may perhaps affect a small degree of change (especially if something is out of spec), but definitely a minimal one.

OK, when my B/C are in battery, there is a space between the C and the LP.  I was being flip but what can be pushing the LP down?  Sure it is pushed down by the C initially but the C cannot follow through due to the gap....right?

  In fact, it is the locking piece bolt carrier interplay that forces the locking block down.

We agree.


And the recoil spring holds the carrier in that forward position.

I was deceived by this from the beginning.  The C and the recoil spring are really not involved with "in-battery" forces on the B/LP.  As the B slides forward, near battery, the carrier quits pushing the B.  From just off battery to battery it is the Striker Spring that is pushing on the bolt through the Striker.  With the bolt in battery the bolt tightens up quite a bit but I can still wiggle it with my index finger pressing down through the mag well on an inverted gun.  The C will rock back and forth and the B seems to not move till the movement gets large and hard so there must be a gap between the C and LP at battery.


 You can see this easily with the bcg out of the weapon -- and why tilting assembled bcg forward (same position as when bolt unlocks to eject spent case), moves bolt forward, and lifts the locking block so that it can be reinstalled....  With bolt back and locking block lugs down (in-battery position), you can't reassemble.

That's true.  You have to tilt ther gun to the rear so that the B will stay out of batter or the BCG won't drop into the rails.


Point being that firearms are a system that is greater than the sum of individual parts...

And unsuspected subtlties keep creeping in.

At this point I can get my bolt to wobble and twist when in battery.  It IS NOT as loose as i thought it was by memory but I think it should be locked.  I'll try next with the Dust Cover installed and the springs in play.

It may be escaping you that my RF R is so very much looser.  Some of the parts are a little bit different but that doesn't account for all of it.

Thanks for all your thought provoking answers and statements.  I wish I had better questions.

[RSR]

I can feel and hear (clacking on rails when moving) a very slight wobble (I'd say less than 1/32") from side to side and even less from up to down w/ bolt in battery and recoil spring in.  I certainly can't see visual movement. 

[JohnEd]

Iwas confusing and missleading in my comments.  What's new, right?  After the trigger is pulled the S slams into the primer and continues on a couple thousandths to push on the B and press it into battery.  However, before the S is released, there is no direct pressure from anything to keep the B in battery and pressed against the barrel.  My LL drop/are pushed, down by the C underside hitting the LL but there is also a clearance between the C and LL at battery.  In my gn the LL actually wedge in a little but they can be loosened by almost any force acting on the B.  Chamber pressure should push the bolt back a few thousandths at least.  As well, the C is mearly pressing down of it's own weight on the LL(if it is in contact) but if the LL try to move up then the C will lift quite a bit and let the B disengage from battery many thousandths.

In the grand scheme, the inertia of the C and B and the LL just sitting in battery will keep everything in place....I imagine.  Otherwise there is a 20 thou head space.  Do you recall my mentioning that when I finally bought head space gauges to support my builds I tried my D Tech for the first time?  The B closed on the NO-GO gauge without flinching.  Head spacing is a "most critical" feature that can result in the destruction of the gun, maiming and death at least in bolt guns.  Really serious issue and the NO-GO gauge bothered me but I learned that after thousands of rounds down the barrel in a gun I was loving.  No sense till I read an article that said that the all mil rounds were undercharged by design.  Having replaced the barrel in that gun the gauges all read as they should and I am amazed at how far out of battery that NO-GO keeps the bolt.  In all the chatter i recall that there were many that said that the NO-GO kept the C back 3/16ths and a few said 5/16ths while mine was @1/4 inch.  Never got the feeling that the issue of just what was right was was resolved.

I bought plasti-gauge yesterday and I will get outg my dial indicator.  By this afternoon I will advise on all the clearances in firm numbers.  Then the real argument can begin on how to resolve any over clearances that may exist which was my point.

All in all this is headed towards accuracy as this gun shoots with no recoil and fires every time on sched and shows no sign of hurting itself.  I had poor accuracy with the OEM barrel and found that it had a 313.5 bore for 308 bullets and should not have had any accuracy though 4 MOA was claimed by Mfr. and many said they did much better than that.  I got maybe 12 MOA using every ammo in the book including spendy brass U ro pee'n stuff.  I installed a new longer barrel with a 308 bore and broke it in right and i got 6-8 inch groups and a migraine.   I actually duplicated a VZ 2008 like the kanucks but without the performance that is typical for them.  I have spent enough time lapping bolt lugs and etc. in my guns, over the years,  to know that minute clearances in bolts is critical and easily demonstrated in groups before-and-after.  OK, I eliminated bullets, powders, brass, barrels, crowns and head space and the quest continues for 4MOA.  I have verified ALL my performances with at least two other shooters at each step so my impressions are related to The Gun and not the shooter.  All my guns shoot way better than I can except for this one and it is my favorite....almost.  (Savage Striker in 6 mm BR is Top Dog)

Laterr

John