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50 BMG, M2HB barrel quandry for custom build

mrwatson

Plastic
Joined
Feb 24, 2021
Hi Folks

I've been a member for a whole 90 seconds and I'm off to the races already...

Seems I tickled the fancy of a retired machinist friend of mine when proposing the notion of building a 50BMG from scratch (mostly). In a haste to grab some barrels when I saw them, I've ended up with a couple of brand new, M2HB barrels that were part of the Sabre Defence liquidation. They weren't finish treated yet (parkerized) but otherwise are finished/chambered. What I didn’t realize was some very important details when I ordered these barrels. My quick-to-act ASSumption was they would be 41V50 steel, parkerized, have a 1.5”L x 1.5”D x 12 tpi tenon, and… well, that’s basically it.

Well… they’re just so, so much more. They’re made from MIL-S-46047 steel, have a 0.770”L x 1.450”D x 8 tpi tenon (that turns out is just the end of a threaded, steel, chamber insert, screwed in to anchor the stellite as well as form the chamber), and are stellite and chrome lined. Wowza. Needless to say my plans to “simply” cut an inch or two off the chamber end and re-chamber, re-thread, re-profile are now vaporized. Or have they…

I also own a decent bore scope. Lemme tell ya, I am thusly conflicted by what I saw. Now the stellite section isn’t anything to get all goose-bumpy about. Its not bad and is still more uniform and slick than most off the shelf, under $1,500, button rifled barrels I’ve seen. Cool enough. But the chromed section of the bore… Lordy, Lordy… now that portion is some slick looking bore’ness.

I have some pretty decent barrels in my collection that shoot solidly in the 2’s and these barrels are every bit as nice “looking” as the nicest of them. Its bore’ing to look at it with the borescope (gun-pun for effect) as the whole length of the monstrosity of a barrel is just completely “unfeatured”. No chatter, no hashing, no rolls, burrs, tooling marks, divits, diggers or Buick’s. Just monotonous, monochrome, symmetrical, uniform, featureless, land-groove, land-groove, etc. I did manage to read, post-purchase, about the innovative bore consistency quality that Sabre Defence developed for their M2 barrel. Granted I’m referencing off the limits of capacity of my naked vision through the borescope, but all indications are it wasn’t snake oil they were selling. Their claim to produce a 5 tenths or better bore/rifling/land consistency isn’t a hard swallow by looking at the bore.

A uniform, consistent, in-spec bore that is additionally chrome lined… what’s not to like for the shooting and longevity aspects. I have a mil-spec M4 barrel (yes, “M4”... as in is M16, M4 variant, chrome lined, with the anemic Govt profile, and ever-so-necessary grenade launcher relief cut...) that is one of my 2’s barrels (slow fire) with the good ammo. The wheels are turning…

Now, the stellite only protrudes 12” down the bore. I could still cut the barrel there and start fresh from that point. But then I’d have to have a carbide reamer to get through the chrome… in 50 bmg. Those are EVERYWHERE and CHEAP I’m sure. I’ve never turned with a carbide reamer either, and thereby, never through chrome. My friend seems to think that undertaking might be a proposition in expensive learning as to how to use such a large reamer in carbide on hard chrome. I have to very seriously consider his 55+ years of experience. We are considering a boring bar to rough it and finish with a HSS reamer, but the boring bar will only get the body up to the neck. The nose of the HSS reamer would still take it hard.

So, all the above rambling converging on these queries I’m hoping some can shed light on:
1. is it possible to ream a 50 BMG “match chamber”:
---a. in a chrome lined bore?
---b. with a carbide reamer?
---c. without breaking the reamer?
2. what will the long term effect of throat erosion look like at the exposed junction of hard-chrome and 41v50 that will be in the throat?
3. decent, long range accuracy being my objective ,should I:
---a. cut my losses and suck up the shipping and return these and buy Lilja, Green Mountain, or other blanks?
---b. keep my patience in check and head engaged and develop something novel that is entirely possible?
---c. file for divorce now because when the war department realizes what I’ve already spent on this “save money by making it mysef” project I’ll just have the paperwork done under less stressful conditions?
---d. some combination of the above?

My apologies and thanks for your reading through this, and especially if anyone cares enough to offer anything constructive for me to consider.

-w
 
I had considered that, using as is, but I'm fairly certain I wouldnt get the precision I'm looking for. Although these barrels are the most accurate M2 barrels by far apparently, I think that trying to make one of these shoot "rifle-precision wise" with the original chamber/stellite is not going to produce a "precision" rifle. Two main reasons being 1) the stellite liner has a gap between where it ends and where the barrel bore starts, and 2) the throat of the M2 chamber is overly generous and sloppy relative to the convention of a precision throat. It may shoot well enough for some though, depending on the precision objectives of the individual. If I dont come up with a feasible way to use these to fit my objectives, I'd be happy to sell you one or both at a loss to me.
 
My opinion:

---a. cut my losses and suck up the shipping and return these and buy Lilja, Green Mountain, or other blanks?

You'll spend way more than a new barrel's price in tools and labor trying to polish and coax that barrel into being something it wasn't meant to be, than it'll ever be worth, which would be true if it were free.
 
My opinion:



You'll spend way more than a new barrel's price in tools and labor trying to polish and coax that barrel into being something it wasn't meant to be, than it'll ever be worth, which would be true if it were free.

Absolutely agree that this would be a futile project if the economy of it were a prime objective, although household management may end up dictating that regardless, LOL :) It would never have the expensed value to another as well. Even at the peril of disregarding the lack of economy if it, I am at least temporarily stuck on considering the prospect of having a precision barrel AND one that is exceedingly durable. That has some intrinsic value to me beyond the direct cost. It will have to be within a plot intersection of time/cost/result though, for sure. Where that boundary is what I'm hoping to flesh out here via technical insight as to what some options might be.
 
Chrome-lined barrels are optimized for durability, not repeatable accuracy.

I used to think that too. Both in the military and since, I have shot/owned some amazingly accurate, chrome lined barrels. Many of them far better capable than 99% of shooters. Get some trigger time on one of Criterions [i.e. Krieger] offerings thats set up right with good ammo if you have a chance. Sabre Defence broke some very innovative ground on the big bores, much like Criterion did on small bore. It's really a shame they went down the path they did.
 
As far as establishing the performance criteria of this barrel... I'd be happy if it would hold sub-moa when done
 
I've made up my mind after allowing myself a moment of post-mistake-realization reality and the rational thought process to kick in. I was just so enamored by what I read about the quality/innovation of those barrels and the beauty of that chromed bore that I just WANTED it to work.

Despite the risk if reaming, the bigger hangup for me being the transition of partial chrome/steel in the throat. That will likely wear, and even cut, in a less than desirable way and that's just too dynamic a place for uncertainty. Would the throat cut well enough and still last longer than in a stainless barrel... who knows.

Had I been a pre-informed purchaser, I would've known better and passed... but man, they sure are a beautiful piece of work inside once you see one. If only I had an M2 receiver or was willing to risk just how well an unaltered one would shoot. Im thinking I'll gauge the chamber dims before I make the final move to move them on... just cuz.

I'll ask this last ditch question... is anyone aware of anyone having built/fired-for-accuracy one of these specific barrels, new, in a rifle, in the native chambering? Other than that, I'll just say I paid $700 ea including shipping/tax/etc
 
Well, the deal is sealed. I measured the throat diameter before the leade angle began and it was .5172". Much too much for what I want the barrel to do. I will be returning these unless someone here wants them. Now... to find a great quality blank that's IN STOCK... any leads on that from anyone here?
 
Well, the deal is sealed. I measured the throat diameter before the leade angle began and it was .5172". Much too much for what I want the barrel to do. I will be returning these unless someone here wants them. Now... to find a great quality blank that's IN STOCK... any leads on that from anyone here?

I have a few new match grade 50 BMG Montana Rifleman (no longer around) 4140CM Blanks set aside for projects. I think they are 1.625 dia x 32" long - no chamber. I would be interested/willing to trade for M2HB barrels as you describe.

Let me know by PM

Chris
 








 
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