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Old September 7, 2020, 03:03 PM   #1
45flaco
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correct amount of stock contact for bull barrel

I'm working on a 375 H&H mosin with a 1.25" bull barrel, 22 inches long.
Inletting the stock for the barrel, I seem to recall my mentor telling me not to do a full free float on 1"+ bull barrels, but instead to pillar and glass bed the action and rear 10% of barrel, because heavy barrels need a little more support.
Problem being, this was a long time ago, I might be remembering wrong, and I've never done it. Actually, I don't do stock work barely at all.
I'm only doing this because when I first inlet the stock, the barrel was touching in some places, and had both horizontal and vertical stringing when it heated up. Glass and pillar bedding are already on my list of things to do.

So my question is, do I free float the entire thing?
Free float except for a few inches in front of the receiver?
Do I glass bed the part of the barrel in front of the receiver?

This is a personal project, so I don't mind getting creative, but I'd prefer to have some advice before attempting.
Thanks
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Old September 7, 2020, 04:40 PM   #2
Bart B.
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Totally free floating the barrel with at least 1/16" clearance from the receiver forward is best. More clearance at the tip if the stock fore end is flimsy and barrel is heavy. The decades old dollar bill test (often done wrong; rifle not horizontal resting on stock toe and fore end tip) is one of the oldest myths on billboards by the highway to best accuracy. The barrel whips and wiggles before bullets leave the muzzle; there needs to be clearance so it's repeatable from shot to shot. Fore ends resting on anything bend up from the rifle's weight.

99% of all barrels that change point of impact as they heat up are improperly fit to the receiver. Receiver face wasn't squared up to the barrel tenon thread axis.

Conventional bedding done right works as well as pillar bedding. Some match winners and record holders prefer conventional methods. Few people know why pillar bedding was first used. It started with the original synthetic stocks made by Lee Six that had cores softer than wood stocks.

Last edited by Bart B.; September 8, 2020 at 06:33 AM.
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Old September 8, 2020, 12:28 PM   #3
Don Fischer
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I don't know abut bedding bull barrels but have done a number of sporter barrels over the years. First one I did was a Skao L61 in 7mm mag. Hadn't heard of free floating yet at that time so bedded the action and barrel solid all the way. Great shooting! Then heard about floating and back then the though was to float the barrel from just in front of the chamber area of the barrel out Have done several that way and they shot very well. Then got to the float from the reciever all the way. Do that now and rifle's do very well. I think important to know is that I also always bed the action. I don't believe an action can be bedded by machine or hand as well as by using something like JB Weld, I love the stuff! I might suspect that hanging a bull barrel could create a problem with the reciever, pretty heavy chunk of steel. I think were it me I'd solid bed the whole thing first and see how it goes. Then if it doesn't satisfy, simply sand out the bedding under the barrel to float it. Maybe first time to just in front of the chamber and if that doesn't work, them all the way. Something I didn't mention is the recoil lug. I always remove material from that area and bed it also. But I put a couple layer's of tape on the side's and bottom to keep them from touching the bedding. If you float the barrel all the way first, I believe you'll get a better bed on the action. But if you do, I recommend it, before setting the barrel action back in the stock with wet bedding, tape around the front of the barrel so it won't weight down the stock and pull up on the rear action screw. The tape need's to stop the barrel from pulling down in the stock. Then when you remove the whole thing the barrel will be floated. You float it, don't use bedding, simply refinish the wood. I don't care for the dollar bill test either. If your gonna float, float! With dollar bills I fold the bill into four layers but these days I simply use a piece of printing paper folded in half. Yu can't float to much but you can not enough.
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Old September 8, 2020, 09:47 PM   #4
Bart B.
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What's the size of the biggest 10 shot groups you get with full length bedding under the barrel?

Don't care about the smallest groups because they're mostly luck and seldom repeatable.

The main reason some clearance between the barrel and fore end is there has to be room for the barrel to wiggle (mostly in the vertical plane) without touching the stock while the bullet goes through it. Depending on how the rifle's held, clearance between barrel and fore end will change.

Last edited by Bart B.; September 9, 2020 at 03:47 PM.
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Old September 9, 2020, 09:23 PM   #5
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The correct amount of stock contact on the barrel is NONE. Any contact will cause shot stringing.
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Old September 10, 2020, 01:41 PM   #6
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Floating a barrel is about whether or not the rifle likes it. It guarantees nothing either way. The only way to find it if your rifle likes it is to try it. Putting a pressure point back in isn't difficult.
"...and rear 10% of barrel..." It's out to under the chamber area. You must seal the inside of the barrel channel either way.
"...horizontal and vertical stringing when it heated up..." That indicates inconsistent bedding. Probably caused by the barrel touching in some places. Likely the action isn't straight or sitting correctly in the stock.
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Old September 10, 2020, 04:13 PM   #7
Bart B.
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Quote:
Originally Posted by T. O'Heir View Post
"...horizontal and vertical stringing when it heated up..." That indicates inconsistent bedding. Probably caused by the barrel touching in some places. Likely the action isn't straight or sitting correctly in the stock.
I and other top ranked competitive shooters have had the receiver face squared up then their their free floating barrels quit stringing shots firing 10 shots in 1 minute. Some actions were not perfectly straight, just repeatable from shot to shot.

How are actions measured for being straight? What's the measurement unit of error?

Last edited by Bart B.; September 10, 2020 at 07:46 PM.
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Old September 11, 2020, 02:00 AM   #8
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Quote:
How are actions measured for being straight? What's the measurement unit of error?
Actions are measured in thousandths of an inch deviation from bolt journal centerline and deviation from perpendicular to centerline. If done properly truing an action can make the deviations very small. Factory actions, for example, often show deviations from bolt journal centerline of .005"-.010", runout on action face of .010". Remingtons, for ecample, are pretty good as they come off the CNC, but they are then heat treated and can warp. due to more metal on one side of the action than the other (ejection port). An hour on the lathe truing them up really makes a difference.
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Old September 11, 2020, 09:27 AM   #9
Bart B.
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Quote:
Originally Posted by Scorch View Post
Actions are measured in thousandths of an inch deviation from bolt journal centerline and deviation from perpendicular to centerline. If done properly truing an action can make the deviations very small. Factory actions, for example, often show deviations from bolt journal centerline of .005"-.010", runout on action face of .010". Remingtons, for ecample, are pretty good as they come off the CNC, but they are then heat treated and can warp. due to more metal on one side of the action than the other (ejection port). An hour on the lathe truing them up really makes a difference.
How much does the receiver bend vertically from the weight of a heavy free floating long barrel?

Is the receiver's threads axis for barrel shank always aligned with the bolt journal centerline?

Last edited by Bart B.; September 11, 2020 at 09:37 AM.
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Old September 11, 2020, 12:13 PM   #10
45flaco
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This seems to have very minimal bending when the action is in a vice, and barrel is hanging out, but there is some (I think about 0.005" vertical deflection).
The receiver face was not trued. I have access to a lathe, but was not sure how to dial in the receiver, as the outside diameter is likely not very concentric to the inside. I considered making a fixture to hold the action from the inside, but never got around to it.
If I did this, I was thinking of making a rod with the same thread as the barrel tenon that threads into the action from the front, but has a smaller diameter going forward. Then I could put that into the lathe chuck, and face the action off to be 90 degrees to the threads. I don't know about how to true the receiver locking surfaces or bolt lugs though. And I do realize I'd have to check headspace and likely cut the chamber a little deeper, if I faced the receiver and it was off by a lot. Not a worry, I have the reamer.
Any suggestions for truing surfaces other than the face of receiver?
Thanks!
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Old September 11, 2020, 12:14 PM   #11
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I was taught to bed the chamber area of the barrel, the large diameter section before the barrel taper begins. This was especially important with long/heavy barrels because of the pressure exerted on the rear action screw.
I have no idea if this is correct but it's worked on the 100+ plus actions I've bedded.
The exceptions being a few sporter barreled 700's that would only group with a light pressure point near the end of the stock and a model 7 I completely floated. Most hunting rifles are rarely shot more than the magazine capacity in a hunting situation and in a very short time frame, usually seconds rather than minutes.
The impact point of first shot out of a cold barrel is the most important one usually, when sighting in a gun like a 375 H&H this would be especially true. The magazine probably holds 3 so 4 shots as fast as you can shoot the gun accurately.
I had 35 whelen semi-auto that grouped very well with 4 fast shots, if shot slowly it strung the shots, my point is agonizing over the size of slow fired 5 shot groups from a benchrest might be off track unless it's a long range elk rifle.
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Old September 11, 2020, 12:17 PM   #12
45flaco
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I don't know how to check the bolt journal centerline, other than maybe turning a rod of the right diameter, and putting the action in the lathe using the barrel tenon jig, then running a dial indicator off of the rod in the bolt journal?
I really appreciate all the advice, there's a whole lot more to this than I thought.
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Old September 11, 2020, 12:25 PM   #13
45flaco
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Also, if I find the bolt journal to be skewed from the receiver/bore centerline, what can be done to fix that?
Time is no object, this is a learning experience. But that being said, I'm not sure I'm capable of TIG welding up a receiver and re-boring it, without massively warping it.
The only other way I can think of is boring out to a slightly larger size, correctly aligned, then making a new bolt body from bar stock with a slightly larger diameter. I'm capable of this, but would prefer not to do so.
Any other options to fix misaligned bolt journal?
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Old September 11, 2020, 01:51 PM   #14
Bart B.
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As long as the receiver and bolt faces are squared up to the barrel tenon thread axis a little misalignment is not an issue. They are repeatable from shot to shot.

More important is the receiver not twist out of good bedding contact from the barrel's torque shooting heavy bullets at high velocity in fast twist rifling. This issue was first observed in the mid 1960's with heavy bullets shot from 308 Winchester cases in rifles using Remington 700 actions. Gluing the receiver in aluminium flat bottom/side sleeves fixed this problem
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Old September 12, 2020, 06:59 AM   #15
Nathan
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My smith beds the action and the full diameter part of the barrel and any barrel lugs in big bores. Does yours have an extra barrel lug about 6” down the barrel?
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Old September 12, 2020, 01:11 PM   #16
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The heavy barrel's weight gives the action a large moment of inertia at the bedding. It's conceivable with a wood stock that this could tend to pull on the stock screws by trying to pry the action out of the stock when the stock torqued up under recoil, and do it hard enough that it compresses the wood a bit over time, especially if it's not particularly hard. I doubt a synthetic stock will care.
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Old September 12, 2020, 04:40 PM   #17
Bart B.
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Quote:
Originally Posted by Unclenick View Post
The heavy barrel's weight gives the action a large moment of inertia at the bedding. It's conceivable with a wood stock that this could tend to pull on the stock screws by trying to pry the action out of the stock when the stock torqued up under recoil, and do it hard enough that it compresses the wood a bit over time, especially if it's not particularly hard. I doubt a synthetic stock will care.
Some competitive shooters loosen receiver screws when wood stocks are used with conventional epoxy bedding only the receiver. They're torqued back to these typical inch pounds values:

* 20 to 25 for bolt action single shot 22 rimfire.
* 40 for Remington 700, 721, 722, 40X.
* 60 for Winchester 70.
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Old September 12, 2020, 10:00 PM   #18
45flaco
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Just gave a try to bedding the receiver, lug area, and chamber area of barrel. Will see how that turned out tomorrow, when the epoxy has set.
This rifle only has one recoil lug, on the front of the receiver.
I also checked the front of the receiver, it will need to be trued on the lathe. But first I have to make a mandrel.
Any recommendations? Just turn bar stock down on either end, with a middle section that threads into the receiver?
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Old September 12, 2020, 10:06 PM   #19
Bart B.
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Quote:
Originally Posted by 45flaco View Post
Just gave a try to bedding the receiver, lug area, and chamber area of barrel. Will see how that turned out tomorrow, when the epoxy has set.
This rifle only has one recoil lug, on the front of the receiver.
I also checked the front of the receiver, it will need to be trued on the lathe. But first I have to make a mandrel.
Any recommendations? Just turn bar stock down on either end, with a middle section that threads into the receiver?
Receivers are usually faced before bedding barrel are fit because they'll be angled different.

Buy a mandrel from Brownell.

https://www.brownells.com/gunsmith-t...ters/index.htm

Last edited by Bart B.; September 12, 2020 at 10:18 PM.
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Old September 13, 2020, 07:24 AM   #20
Nathan
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It is my understanding that you hold the outside of the front ring of the receiver in the lathe. You adjust until a rod down the centerline of the bolt bore runs true. Then you face lugs, action face and single point cut threads. You might be better off to measure each of these before cutting as I’m not sure 0.001” or so would be worth cutting.

Then you hold bolt body (which can be hard). Some folks thread a custom cut block into the bolt shroud threads and then adjust in the lathe until the bolt body runs true. Then check/cut the front/back of bolt lugs until true and same for the bolt face.

There are fixtures available to make this all better/easier to setup.

BOLT

ACTION Mandral

ACTION Jig

Or ACTION/BOLT/BARREL Truing Jig

Last edited by Nathan; September 13, 2020 at 07:33 AM.
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Old September 13, 2020, 03:06 PM   #21
45flaco
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I'd considered buying the parts, but the reason I'm doing all of this is to learn. I don't actually need a superbly accurate mosin with 200 hours into it, I just felt like learning by doing. Since I work in a machine shop, I figured making the tools would also help me learn more about machining.
The other reason is that most parts are intended for Rem700 or Savage platform. Most of them don't work so well with a mosin action, except for the "universal" tools, which don't particularly fit anything well.
I did find some pictures of action mandrels, and they're almost exactly what I planned to make, so I'll just go ahead as planned.

The reason that I bedded the action and barrel before truing it is because I likely won't have time to true it for another few months, but I want to shoot it now. If just bedding the action gets me to 2 MOA or so, I'll be happy to hunt with it for deer season, and then redo the bedding job this winter when I true the action.
I really appreciate all the advice, I have zero experience with stuff like this, so it's good to be able to just ask questions!
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Old September 13, 2020, 04:12 PM   #22
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One thing you need to consider is what I posted is Rem 700 truing. I think Win 70 is similar.

Savage truing would be different. The bolt bore is ignored due to the bolt head floating. I’ll bet a Savage gunsmith has to built a jig to hold the bolt head.

I don’t know Mosin’s, what makes them accurate and what doesn’t matter. Somebody surely does.
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Old September 13, 2020, 06:49 PM   #23
45flaco
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The mosin has a floating bolt head, so I'm not super worried about that, it's more of a practice thing. I plan to true the back of the bolt lugs and the bolt face to the centerline of the bolt head. Then true the receiver face and lug abutments to the receiver threads.
Hopefully that will result in everything up front being close to perfect, and the rear will be mostly irrelevant.
I've also considered truing up the recoil lug, since I plan to redo the glass bedding this winter anyway. I haven't checked it on a lathe, but this gun is 100+ years old, so I doubt the recoil lug is square to the bore. Only one way to check.
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Old September 13, 2020, 08:59 PM   #24
Bart B.
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Quote:
Originally Posted by Nathan View Post
One thing you need to consider is what I posted is Rem 700 truing. I think Win 70 is similar.
The only things Winchester 70's ever needed truing up was first the receiver face squared up to the barrel thread axis, then the bolt lugs lapped to full contact and finally the bolt face squared up.

If the Winchester bolt axis ends up a degree or thereabouts off the barrel chamber axis, doesn't matter. Their receivers are over twice as stiff as the Remington.

Last edited by Bart B.; September 13, 2020 at 09:49 PM.
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