Perfect Union banner
1 - 20 of 82 Posts

·
Registered
Joined
·
80 Posts
Discussion Starter · #1 ·
My first post. I know its overly long, but I hope you don't think it sucks.. I bought my 195 series mini 14 ranch in 99. It has always been fun to plink with in the desert, but then I just had to go put a scope on it to see what it could really do. I put on a Vortex 3-9x40 bdc diamondback with ruger high rings, but otherwise the gun is bone stock. With Rem Umc 55 gr fmj my best 5round group over sandbags was 4.0" at 100 yards, most were 4 to 5. that may be fairly normal but its not ok!

I am a machinist and welder, and a generally fearless modifier, so this gun is going to get it. I started yesterday by machining two gas bushings from hardened 4130 rod, one with no hole and one with a .052 hole. Today I went to put it back together but I had to stop. The sloppy bolt caught my eye, then the crazy thoughts kicked in.. I am going to do a series of mods, shooting between each step, and documenting exactly what does what, starting with the bolt.

Obviously you need solid and consistant bolt lockup to have any hope of accuracy. Mine has more than .015" play from front to back, with also a ton of side to side and even angular play. No bolt gun shooter would tolerate that. I know its like that for complete reliability, but it still makes me ill.

When my go/no-go gauges get here, I will check headspace with the bolt forced forward. If its good, I am going to build up the bolt lugs with weld metal to reduce play. I plan to bead-blast the bolt to bare metal, then build up the back sides of the lugs with er-100s (100 kpsi yield as-welded) tig rod. Then grind and reshape the weld metal to get perfect lockup. Will it make an accuracy difference? Will zero play still be reliable? We will know within a week.

Of course mine is a pencil-barrel, measuring from .560 to .575 at the weird and irregular high spots in the middle. Really Ruger? Hellen Keller could run a lathe better than that. Anyway I will try adding a muzzle brake and maybe a sleeve after the bolt and gas bushing tricks. I am hoping for 2+" with cheap factory ammo and under 2 with reloads.

I will need to reblue the bolt. Has anyone tried any of the cool mil spec anti-friction platings or coatings on their moving parts? There is a bake-on teflon/graphite coating and a teflon impregnated nickel plating which is just awesome. Hmm this could get interesting!
 

Attachments

·
Registered
Joined
·
494 Posts
Hi Scott

I admire your go-get-em attitude. That said, I think you might find the lug play is much smaller than you think once you have a GO gauge in the chamber.

My 581 RR has a "loose bolt" until you close the action by hand on a unfired commercial round without the oprod and trigger group installed - then there is zero play. Now, it only has 500 rounds through it, but most of the play is "in front" of the lugs, not behind.

The bolt is probably harder than 40RC and that implies a yield strength closer to 200 KSI. If you soften the bolt or the wearing surfaces of the lugs, they may wear faster or peen - doubt they will bend or break off - but you may destroy your bolt.

Worst case: headspace opens rapidly after you "fixed" it, leading to cartridge case head separation with attendent hot gas and high speed particle liberation.

If you proceed with this, fire a few shots with the rifle strapped into a leadsled type rest; pulling the trigger with a string. Then immdeiately check headspace to see if it is opening up before shoulder firing. After not too many more shots check headspace again.

Hardness and stregth as a function of tempering temperature for 4140:
http://forums.1911forum.com/showpost.php?p=3662651&postcount=7

Looking forward to your report on headspace gauging.
 

·
Registered
Joined
·
1,117 Posts
have you thought about a barrel strut? The consensus around here is that's the first thing you do with a pencil barrel. Seems most cut their groups in half or more.

How do you like that vortex diamondback? im thinking about the 1.75 - 5x32 for my mini 30.
 

·
Registered
Joined
·
1,589 Posts
Slow down. The Ruger chamber is a 5.56mm chamber, not .223, and Ruger uses a proprietary headspace gauge. If you drop a field gauge in the chamber it will close and fire in every Mini I have checked except the Target model which has a real .223 chamber. The bolt is also a cast part, as is the receiver, extractor and op-rod. I'm sure you're very skilled but these parts are not available to you (or me) and will require a trip to the factory for replacement if you go too far.

I encourage experimentation and look forward to your tests but I wanted to make sure you knew the above issue before you get started. Just think hard about what you're going to do and how you'll do it.
 

·
Registered
Joined
·
80 Posts
Discussion Starter · #5 ·
Thanks for the input guys. Subscriber you were close, actual hardness is RHC 36. That implies a pretty high-carbon alloy like 4130 or 4140. Since there is at most .015" excess clearance, it will require only a small dot of weld. If anything there is a risk of excessive hardness due to rapid cooling of a small weld. The proper procedure is to pre-heat the part 100F for every .1 percent carbon, or 400F for 4140.

Thanks for the input gundoc, I appreaciate your expertise. If Ruger says 'we use a proprietary gauge', I hear "due to our sloppy tolerances and crude machining techniques, normal headspace gauges wont work half the time, so we invented our own". I wont do anything until the gauges get here. Is it safe to say that if the go gauge fits in with the bolt forced all the way forward, the slop clearance can be eliminated?
 

·
Registered
Joined
·
494 Posts
Subscriber you were close, actual hardness is RHC 36... Since there is at most .015" excess clearance, it will require only a small dot of weld.
Scott, at RC36, yield strength is 66% higher than the weld material you want to add. This is similar to the ratio between normal pressure to proof round pressure - not trivial.

The "dot" of weld would need to build up the entire lug contact area by a little more than 0.015" to dress it back down.

Shaping the bolt lug contact surfaces is also not trivial: The have a helix angle and to get that spot on, you will have to finish lap against the receiver lugs. Screw up the bolt too badly and the receiver is scrapped along with it.

What would it take to make a complete bolt from prehard 4140 at 36 to 40 RC?
 

·
Registered
Joined
·
494 Posts
Good to see you have the right equipment, Scott.

The bolt lugs are probably harder than the "shank"...
 

·
Registered
Joined
·
80 Posts
Discussion Starter · #9 ·
You are right, except the entire angled ramp doesnt need to be built up, just the flat spot on top. Also 100 ksi is the average as-welded condition, so a small weld on a relatively larger part will self-quench to a higher level. I can demonstrate on a grade 8 bolt or 4130 scrap if you want.

Here is the coating I was talking about, MP-3 teflon impregnated nickle. Robar is less than 1/2 mile from where I am now, so it's likely my bolt will get this coating, modified or not.

Robar's NP3 Finish
 

·
Registered
Joined
·
80 Posts
Discussion Starter · #10 ·
Here is an example of hardening from rapid cooling. This pic shows a 3/8" bead-blasted grade 8 bolt I 'modified' in the last few minutes. The bare bolt measured hrc 24. The first weld from the head was a 2 second tig arc, just enough to melt the surface. It measures hrc 36. The second weld from the head was a 3 second arc with er80s2 filler added. It measures hrc 44. I didnt belive it myself, so I tested it three times! If the bolt had been heated to 400F first, the as-welded hardness would be a lot less, due to slower cooling of the weld zone. If I weld on my mini bolt, I will use er100s with preheat to about 200f.

And Kinganothing, I love the vortex scope. I am getting another one for my 270.
 

Attachments

·
Registered
Joined
·
1,117 Posts
thanks. think I'll get it then.
 

·
Registered
Joined
·
10,469 Posts
It has been discussed before that shutting off the gas block and shooting the rifle in a single shot mode increases accuracy. The harmonics of the gas system around the gas block causes about 1/2 the accuracy problems and I believe and have tested that mag feed lip angles cause the other 1/2. I think the bolt and receiver are fine and will only hurt the reliability of the gun if tampered with. It's your gun to do with as you please and maybe your on to something one has thought about. Good luck!
 

·
i like the details
Joined
·
254 Posts
Ill throw my $.02 in too. Im sure you are aware but hardness isnt the only measure of strength, there is a metric of toughness that must be met and additionally these are cast parts that could have specific grain pattern in the metal in increase toughness in certain directions. I believe the rem 700 bolt lugs are this way. I dont have any reason to say they do have this but you just never know. At any rate the heating and cooling of the weld will be uneven no matter how you do it, there will always be a boundry to the heat affected zone until you normalize the temper by doing the whole bolt.

Why dont you set the barrel back a revolution of threads and re cut the breech and chamber and maybe face the back of the locking lugs? Thats how you true up a bolt gun.

I cut a champfer in the OD of my bolt and matched it on the breechface to aid in a true lockup.

In any case GO FOR IT! It might turn out to be a great idea, you never know.
 

·
Registered
Joined
·
494 Posts
Why dont you set the barrel back a revolution of threads and re cut the breech and chamber and maybe face the back of the locking lugs? Thats how you true up a bolt gun.

I cut a champfer in the OD of my bolt and matched it on the breechface to aid in a true lockup.
.
Now that is the right way to go about it. It is much more work than adding weld though...
 

·
Registered
Joined
·
494 Posts
You are right, except the entire angled ramp doesnt need to be built up, just the flat spot on top.
With respect, you are mistaken about this. The entire ramp area bears bolt thrust with the Garand type action - this is different from a Remington 700 type bolt action, where the thrust faces of the lugs are flat with a short ramp to help cam the bolt shut - the equivalent of the latter in a Garand action are the radii at the lug edges.

I have been looking for some photos to ilustrate my point and found some good ones at this thread on M14 lug lapping: Lapped a TRW bolt to a 2009 Polytech yesterday.

The bright area on the right lug shows how large the contact area should be; and on the 2 degree slope - or whatever the helix angle is.



 

·
i like the details
Joined
·
254 Posts
With respect, you are mistaken about this. The entire ramp area bears bolt thrust with the Garand type action - this is different from a Remington 700 type bolt action, where the thrust faces of the lugs are flat with a short ramp to help cam the bolt shut - the equivalent of the latter in a Garand action are the radii at the lug edges.
I think he was refering to the "in battery position" as the "flat spot" even though it may be at a 2* angle, and the ramp as the radius.
 

·
Registered
Joined
·
494 Posts
I think he was refering to the "in battery position" as the "flat spot" even though it may be at a 2* angle, and the ramp as the radius.
Perhaps we are all in a greement, but this is what got me concerned, along with the conversation around it:

Since there is at most .015" excess clearance, it will require only a small dot of weld.
The "dot" of weld would need to build up the entire lug contact area by a little more than 0.015" to dress it back down.
You are right, except the entire angled ramp doesnt need to be built up, just the flat spot on top.
My point being that you want near to full possible lug contact area, so trivializing it as needing only a spot that is required sounds like "point loading" to me...

Perhaps Scott will clarify what he meant :)
 

·
Registered
Joined
·
80 Posts
Discussion Starter · #18 ·
Thanks guys. OK I did what I should have done in the first place. I put a live round in the chamber and closed the bare bolt on it. With Federal american eagle, it had .003" clearance at the back of the lugs. With Remington umc it had .004". With the extractor and spring in, it had zero clearance with either round, meaning the extractor is holding the shell off the bolt face by .003" plus. A target bolt-gun shooter would crap himself over that, but I'm not going to worry about it. Also all welding plans are cancelled.

But I still think the bolt should lock up tight with no round in it. Then on my gun at least, the chamber would need to be about .038" deeper for proper headspace. If the rest of the gun were more accurate, proper bolt lockup would make a noticable improvement.

There is plenty of other stuff to do though. I spent a couple hours yesterday with a set of small files, deburring and detailing the bolt and extractor. I used wear marks in the bluing to id rough spots on the moving surfaces, and just cleaned up machining burrs and tool marks all around. Today I gave them a light bead-blasting, then dropped them off at Robar for the NP-3 Plus plating treatment (free upgrade this month from regular np-3!). Here is a pic after bead blasting.

While I am waiting for the bolt to be plated, I am going make a fluted sleeve, and thread the barrel for a flash hider to hold it on. I will try a strut if the sleeve doesnt help it shoot better.
 

Attachments

·
Registered
Joined
·
80 Posts
Discussion Starter · #19 ·
Here is a handy trick, useful on the 10-22 also - I drilled a hole in the back of the reciever for a cleaning rod. I did this a few years ago and it lets you clean the barrel a lot better without worrying as much about the rifling.
 

Attachments

·
Registered
Joined
·
494 Posts
I drilled a hole in the back of the reciever for a cleaning rod. I did this a few years ago and it lets you clean the barrel a lot better without worrying as much about the rifling.
I contemplated this idea and decided the reason Garand didn't incorporate such an obvious barrel cleaning aid was: If a cartridge case head failed on firing, gas would jet into the receiver and out of all the holes - including the one pointing straight at your eye. Otherwise, it is a brilliant plan.

Perhaps a little sliding cover could be added...
 
1 - 20 of 82 Posts
Top