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Discussion Starter · #1 ·
I am new to the forum and I wanted to bounce some gunsmithing ideas/questions off some of the members, especially those with rebarreling experience. First, the rifle is a 188 series ranch rifle in .223"

I am machining a steel gasblock to accommodate the larger diameter barrel. I have bored the barrel hole in the gas block and am now locating the bore for the gas tube. Before I bore it, I noticed that with the original gas block installed, when I pull the op-rod back, as the op-rod slides back off the gas tube, the op-rod block drops down into the stock channel about .035" (measured by using a single feeler gauge under the op-rod block) and when the op-rod is closing the bolt, it picks up the gas tube and uses it as a pilot in the opposite manner.
That gave me the thought that I could locate the gas tube bore about .020" (did not want to use the complete .035") farther away from the barrel bore, thereby giving me a little more "meat" between the barrel bore and gas tube bore. Using the above extra .020" I figured the wall thickness between the gas tube bore and the barrel bore would be about .058" at its narrowest point. I feel that should be sufficient. Any thoughts?

The additional benefit of this would be that I would have to remove .020" less off the op-rod block barrel channel to gain the clearance necessary for the larger barrel. The only downside that I can see is a possible small angular difference between the angle of the gas pipe entering the op-rod bore.

The other issue I am debating is machining the op-rod. My plan was to use a .750 carbide ball endmill and machine the barrel groove to roughly match the barrel with about ".010 or so extra play to give the op-rod room to work. Currently, a factory op-rod has about .113" of material between its narrowest point between the gas tube bore and the barrel channel. I feel this should leave a sufficient wall thickness in that area for the intended purpose. The gas tube is not an air tight seal and should be able to easily handle the momentary gas impulses before the rod moves. Any thoughts?

I welcome any thoughts or ideas. I had considered plugging the op-rod gas port and relocating it and with it the bore in the gas block. Does anyone have any idea how ASI does their gas system?

I have not turned down the barrel yet and have only progressed about 1/2 way on the gas block and bored the barrel bore to .749"

I am sure the op-rod has some sort of hardness to it, but was wondering if I would need to send it out to have some sort of case hardening or nitride coating applied where I machine out the clearance for the barrel.

Ok, let me hear what you think about my ideas. Thanks
 

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Re-barreling a Mini

Jetfixr:

I think the op rod cut a little thinner would be no problem and another option is to make a new gas pipe with two changes.

The grooves in the gas pipe are designed to create a "gas dam" utilizing the turbulence (with the gas flowing in and out of the grooves) to be somewhat of a seal.

What I did was make a new one adding an extra groove to four. If three grooves were OK on the factory GP, I figured four would seal a little better. Does it???? Who knows? Also created a smaller start to the taper for the gas pipe to receive the op-rod. Even rounded it a little because I was concerned about alignment under high speed cycling.

On the op-rod hardness, is it stainless steel? If so it should be hard throughout and is machinable although tough, and no need to anneal prior to cutting or reshaping. If blued, I would only guess it is also OK to do the same process while watching for a possibility you cut through the hard surface. IMHO it should be OK.

My barrel was 1.25" before initial turning down to 1" at the chamber end (wanted it to fit under the top shroud) and chose .800" where the op-rod contacts because of the same measurement snafu that you are considering. Leaving a step up to .900 at the front of the gas block I made, which created a stop taking the responsibility off the gas bushing to keep the gas block in place in recoil and the heavy op-rod slamming forward. I use a 1911 buffer here with no issues at all but one could thin a little if so inclined.

I wanted a 20" barrel but when I got through with chambering and crowning, it came out 19.25". Longer than the factory which was about 18.25" IIRC.

Next is something you should consider. As the op-rod moves away from the center of the bore due to a larger barrel, the alignment at the rear may need adjusting if that makes some sense. Just a word of caution.

I made my own receiver truing device, a bolt truing guide that uses a PTG bolt face cutter, to use after lapping the bolt in using a spring tension tool I also made.

My web site has not been updated lately but you can see all these in the Mini 14 tools section. Updating is on the calendar for this month.

Boy, Bill Ruger would turn over if he got wind of all these modifications. LOL.

Ed
 

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The beefier gas block will definitely improve the mini performance. If you could utilize 6 bolt gas block instead of 4, the reason being the pounding it takes and bad harmonics created from the pounding. I believe if the gas block is completely true and solidly secured, it will improve accuracy. I have an Amegaranges rail on my 196 skinny barrel, I have lapped the gas block halves, tried to true the roundness of the barrel at the gas block for best fit.
It sounds very interesting on what your doing, keep us posted!
 

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Discussion Starter · #4 ·
Thank you for the inputs. Its nice to bounce ideas around before the chips begin to fly.
The mini is a blued ranch rifle. I missed that when I posted.
I bought a Douglas XX barrel blank a while back, but have since picked up a Remington 700 short action and I am going to convert it to .223. I just bought a Green Mountain 1" barrel blank in 1/9 that I will use for this project. I was not sure I would get the noticeable difference between the two barrels and figured the bolt gun would benefit more from the better barrel.
I think I will make my barrel the same diameter at the breech as the factory barrel which is .903" I believe. I will extend this for about 5" or so and then down to .750" to conform to the contour of the op rod.
I am going to make the barrel 18" long and thread the end 1/2"x28 for an AR flash hider. When its all done I think I will try and make a clamp on winged front sight with possibly a bayonet lug underneath. It will be a .223 Wylde chamber.

I had thought about the angle of the operating rod, but then I thought that after leaving gas pipe, the op rod drops down into the channel in the stock and rides the metal liner back to the receiver, so I think things should not change much in that aspect. I guess my biggest concerns were about the gas system and reducing the wall thickness of the op-rod gas pipe bore. The gas block should be fine I would think because it is actually clamped to the barrel at its weakest point where the barrel bore to gas bore dimension has been reduced.

I upgraded the gas block screws to a #10-32 screws which should be about 20% percent stronger screws and allow an increase in gas block torque. I think I will upgrade the O.D. of the gas bushing to give more surface area to locate the gas block on the barrel and neck it back down where it enters the gas pipe.
One thing I never understood is the gas block having an affect on accuracy to a great extent. My thought is that after the cartridge is fired, the bullet has, for the most part already exited the barrel by about the time the op-rod even begins to move or shortly thereafter. By the time the op-rod slams back home to the gas block,the bullet is long gone. I think the greatest influence is barrel diameter followed by bolt to barrel fit and stock bedding/trigger pull, etc. Not sure if I am off the mark on that statement.

I had planned to try and closely match the bolt nose to the barrel recess leaving a cutout for the extractor as the factory barrel has.
The factory mini bolt seems very loose. I would think a couple of thousands difference should allow a nice tight bolt lockup when the bolt is in battery and still have the reliability. Any thoughts?

How did you attach your handguard? I was thinking about bending the factory spring clip but not sure how that will hold up.

How does your rifle shoot Ed? It sounds like you have done a great job on it.
I would imagine you have found a very noticeable difference in accuracy. Would you consider the reliability to be similar to a factory rifle?

I have been wanting to do this mod for a very long time. I have probably spent close to what it would cost to have someone do it, but I always wanted to do it myself.

Many thanks for the input gentlemen.

Chris
 

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Re-barreling a Mini

On the op-rod - you may discover that the clearance sliding onto the gas pipe is not as loose as it appears. Don't be surprised if this happens and realigning is necessary. Also with the fatter barrel, there will be less room in the "channel" for slop. One of the reasons I chose to reduce to .800" where the op-rod rides the barrel.

On the counterbore for the bolt - I chose to stay with the factory contour but keep headspace to the minimum. Lapping the lugs and truing the bolt face helps keep true alignment when a round is chambered.

Hand guard. Yea...... it got spread a little and stays in place unless i grab it by mistake.

Bedding - The Mini is notorious for responding to bedding. In my opinion, it suffers from rounded receiver roll out under recoil. Thus bedding helps.

Here is where some may be critical with my mods. I chose to square up the recoil areas of the Mini receiver. I had seen the recoil lug idea on a Rem 700 and how it worked. So welded up and milled almost square allowing about 1 to 2 degrees angle so the receiver could angle out of the stock. Then bedded completely. Really solid.

Shooting - When I got it together, I experienced the first shot off syndrome. First shot low and left about an inch or more then 4 touching. Frustrating. Sent the barrel off for CRYO and when I got it back loaded some test rounds.
Only loaded 5 rounds each so not a lot of wiggle room for re shooting for groups. I did get one load to shoot 5 shots under .600" at 100 yards and that was 18 months ago. Had not shot it since except to test a new firing pin I made with 4340.

A coincidence but now in process to assemble new loads this week and with a new quality scope, head out to record the results. Am expecting 1" to be little problem with the right loads and will be happy with .5" consistently all with 5 shot groups. I have several loads that showed promise and will start with those and vary as needed. The difference will be keeping better records.

Spending - Yea again ......... could have bought a ________ (fill in the blank)

I am curious as to how you will cut the extractor relief? I know what I did, but that is another story...................

Ed
 

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Hi Jetfixr,

While the oprod doesn't move far while the bullet is in the barrel, it is being accelerated by the force provided by the bled off gas. After the bullet leaves the barrel, gas pressure drops to ambient quite fast, so the oprod impulse is gained almost completely before the bullet leaves the barrel.

In other words, the reaction force applied to the oprod is also applied to the gasblock before the bullet leaves the barrel. The shock of this impulse probably bends the barrel a little because the gas pip is below the barrel line. The magnitude of this deflection and "twang" should be reduced significantly by using a heavier barrel.

The oprod cuts easily with a carbide mill at appropriately slow speed and feed. Do not lighten the oprod by more than a few percent or reliability and part life may suffer.

Instead of turning the barrel down where the oprod runs underneath, you could just mill a flat to accommodate the oprod. That way you don't loose all of the barrel mass and stiffness. The downside is that the barrel may warp, although the Green Mountain barrels are button rifled, so I don't think this is as big a risk as with hammer forged rifling.

You could mill one or two grooves in the underside of the barrel and mill (or attatch) a corresponding tab or tabs on the oprod so that the oprod front end is guide more positively, left to right before it picks up the gaspipe going forward. This way, less material is cut from the barrel and you end up with one wide and deep flute under the barrel instead of reducing its diameter before the gasblock as much, or cutting a huge flat on the barrel. Don't use a ball endmill for this, nor a flat one. Use a radiused corner endmill so that the barrel does not end up with a 90 degree inside corner in it to start a crack from.

You could fill in the front of the oprod or cut it off and weld on a new one and drill that for the new gaspipe location. I would use a piece of pre-hard 4140, such as this, although it will probably be OK in the annealed state:

McMaster-Carr

McMaster-Carr

McMaster-Carr

McMaster-Carr

In any event, you need to ensure that the tabs at the rear of the oprod remain near level with and parallel to the receiver grooves throughout the oprod's travel. The same can be said for the recoil spring channel - keep the spring lined up with its position when the oprod is all the way back in recoil, or binding will result.

Bolt slop is actually much smaller than it appears when you have a loaded round in the chamber that cause the bolt lugs to contact the receiver lugs. This also presses the rear of the bolt up into the receiver "ceiling' and acts as a third softer alignment point for the bolt that does not prevent both locking lugs from accepting full load during firing. Understand that the slop is to allow reliable functioning and to accommodate dirt through most of the bolts travel; constraining it only as it goes into battery on a loaded round.

Cutting the cone in the barrel that accepts the bolt nose and leaving more metal should help align the bolt more consistently with the barrel, but some clearance must be left or the bolt won't be able to rotate into full lockup - the bolt's lugs have a helix angle and "screw" the bolt forward as it rotates, unlike a Remington 700 action that has flat lugs.

Carry on.
 

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I wonder if a longer spring guide rod would improve accuracy and remove some of the play in the oprod movement.
 

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Discussion Starter · #8 ·
Many, many thanks for the wonderful replies. My barrel arrives tomorrow.

I reread my post and it appears I may have not been as clear to a person reading it as it was to me writing it. lol
My plan is to have the barrel round in all areas. I am just going to have it at .903" at the breech for about 5" then taper it down abruptly to .750" for the rest of the way out to the muzzle. There is room on the op rod for a much longer breech area than the factory chose to utilize.

Subscriber, thanks for the links to McMaster Carr. I did not realize they had blocks of steel like that. I had bought other things, but not steel. They are great.

At the moment I don't have a tig welder, only a mig, so I think I will stay away from building the op rod block from scratch unless it becomes completely necessary, but in the near future I think I will break down and buy a tig. I am looking for a reason to turn this into a $4000 dollar mini project. lol.
I think once the barrel is mounted in the receiver and the gas block finished, I will slowly remove material from the op rod channel with a .750" ball endmill until I get a nice sliding fit with the action mounted in the stock. then I will polish the area for a smooth finish.

I honestly think the most difficult part of this build will be getting the radius's correct where the stock fits into the end of the gas block. I will be using a rotary table so it will be a bit of layout to get things correct.
On the original gas block I had made an adjustable setup where a threaded, knurled handle screw would adjust how far a pin slid over the gas port hole in the gas pipe and reduced the gas to the op rod. I am sure its similar to the ASI system, but mine just has a small knurled jam nut to lock it. I am going to incorporate that into my new gas block.

Ed, I visited your site and I don't think I can come up with a better way to do the relief for the extractor than what you did, mounting a tool post type grinding setup. I have a roto zip also and will make a mounting plate like you did.
I also saw all the mini tools you made. I am very impressed with your work.

I think I had read a post from you a year or two ago on what it took to rebarrel at mini in very detailed instructions and it was extremely helpful. I searched the internet to find it again and could never stumble upon it. I was just certain that it had been originally posted on perfectunion. If that was you or you know of it, Id love to read it again.

Tri70, once I get everything together, I will look into the spring guide rod. I think that's a good idea and had not thought about that aspect of it.

Again, many thanks to all. I think this coming weekend I will take a little time from my home addition project to work on something that's really important, my mini project.

I think its almost time to post some pics once I make some measurable progress. Hopefully this weekend I can either have the barrel turned down or the gas block finished.
I will keep you posted.

Chris
 

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I have a cheesy but well-used and durable H&R 223 that shoots 0.3", and my M700 (OK, ADL) does about 0.6" with match bullets. Handloads all.

What was the original question?
 

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I wonder if a longer spring guide rod would improve accuracy and remove some of the play in the oprod movement.
Probably not: The spring guide rod's front end picks up alignment from the oprod, not the other way around, while the spring guide rod's back end is free to pivot through a small but significant angle.

A longer spring guide rod may also crash into the front of the oprod spring channel when the oprod moves all the way to the rear. You could make a hole in the oprod's nlind hole for the spring guide rod to poke through, but that may be solving a non-existent problem.
 

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I have often thought that a guide rod, threaded into the receiver, and slipped into a snug hole in the gas block would do that job perfectly. Not sure I can make myself drill and tap my receiver.

If the rod were threaded into the receiver, that would hold it in place, and the reason for the slip fit at the gas block is to allow easy removal of the gas block.

You would then either have to drill the op rod or weld a guide loop onto it, with the guide rod slipped through the guide loops. This woukd eliminate about 99% of any slop. You could also machine the ears completely off the op rod, so as to prevent ANY contact with the barrel.

To the OP, if your gas block is machined the same size as the barrel diameter, you will be putting all the stress on the gas pipe to hold the gas block in place. If you didn't want to machine a recess in the barrel and the gas block to fit that, then you could make a pin recessed into the gas block, in FRONT of the gas pipe, and a matching recess in the barrel. That could serves as a recoil lug, of sorts.

Of course, if I checked mine correctly, it seems the bolt reaches full lock BEFORE the op rod contacts the gas block. Am I wrong on that?
 

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You could also make the oprod channel narrow to reduce the movement. I bent my liner in to just make a little contact going into the gas block.
 
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