LAR-8 Variant: Zig or Zag?

[Hoot]

Given Tripledeuce's recent success adapting a DPMS .260 Remington barrel to his LAR-8, I am pondering my 2012 project caliber, based upon my LAR-8 Predator HP rig. I dearly love the 6.5mm bullet, so my immediate goal is either a 260 Rem or 6.5 CM.

Here's my decision factors regarding one over the other:

260 Rem:

I already own a Savage Model 12 Thumbhole Varminter with a 26" EA Brown bull barrel that is boringly accurate, so I already have dies, brass, load workups, etc.

I like that the 260 Rem chamber reamer is based upon a 2.80 COL and has a shorter leade/throat designed in than the Creedmoor's chamber reamer. I like seating at or real near the lands, but have to live within the confines of my FAL magazine's COL.

I like the 6.5 CM shoulder angle better and its shorter case length. The latter again, being to work with the magazine limitations, though it has a longer leade/throat by design. I would have to buy dies, brass and work up load data, but then the last part is what I enjoy as much as anything about shooting. It's always entertaining, breaking new ground.

Barrels cost the same, regardless of which way I go. Unfortunately, I thought I had a line on an affordably priced DPMS 24" bull 260 Rem barrel based upon a web site, but when I called to verify availability, they had just sold the last one. So there went the economic advantage in terms of barrel cost. In terms of reloading, I'm not the guy agonizing over milking the remaining few fps from a cartridge at the cost of accuracy, so each caliber's upper velocity limit claim is not as important as inherent accuracy with a wide range of bullet brands and weights.

If you're wondering about dimensional difference specifics, from the SAAMI site:

260

Chamber length 2.045

Case length 2.035 -.020

Leade/throat .221

6.5

Chamber length 1.9408

Case length 1.92 -.020

Leade/throat .361

Anyone care to wade in?

Hoot

[planeflyer21]

Hoot, since I teach with my guns we focus on caliber commonality.  Therefore I would say build it in .260, like your Savage.

New ground is good also!  Who'da thunk I'd enjoy that little .25-20 could be so much fun...from heavy hitting .22LR levels to WELL past .22 Magnum, up into .22 Hornet and even beyond.

Hey!  Look how muddy the water got when I waded in!  <lmao>

Jon

[Hoot]

This is kinda funny in an odd way. In my intro thread, I detailed the travails of removing and reinstalling the RRA handguard, which on the Predator HP serves also as the barrel nut, in order to send my barrel out to have the muzzle threaded. I knew it was going out on the mail truck today and since the truck does not come until around 5 PM, while the post office is open at 9 AM, I had them hold the barrel and drove the mile from my house to pick it up at 9, so that I'd have the day to play with it. It's back on and good to go, but my wife came home this evening from shopping and carried in a box from the front porch that the mailman left at 5 PM. In it was my DPMS 260 Remington Barrel that the place where I ordered it from had told me it was out of stock and I left it backordered since the price was significantly less than DPMS' recommended price. I wish the lady at the post office had told me that I had another box in the push cart to go out on the truck when I was there at 9 this morning, but so it goes.

So, now I have my Zig barrel after having wrestled the 308 barrel back on earlier today. I did a headspace quick check using a freshly resized 260 Remington case and just like Terry (tripledeuce) observed, the chamber, when used with the RRA bolt, is a skosh short. Not more than a few mils I'd wager.

I say that because despite the fact that a freshly resized 260 Remington case will not allow the lugs to fully engage, on a hunch, I tried a freshly resized 243 Winchester case and that case does.

Back when 260 Remington cases were in short supply, folks were fireforming 243 Win cases to make them. Now I almost wish I hadn't discovered that fact as it leaves me in a quandary.

I can do like Terry did and kiss the chamber with a 260 Remington reamer, enough to achieve the proper headspacing using the RRA bolt. That's going to leave me with a barrel that is no longer to DPMS spec, or in other words a custom barrel only suitable IMHO for mounting on an RRA LAR-8. If in the future, I no longer want it, the only person I could sell it to in a clear conscience would be an LAR-8 owner, though the minute, additional chamber length would not really compromise performance.

I could however, buy some 243 brass, fireform it to my chamber condition and leave the barrel unchanged, or I can try to set up my 260 die to bump the shoulder back the mil or two it'll take to get the brass to work. Or, I could purchase an additional LAR-8 bolt and lap the lugs, leaving the barrel unchanged.

If you knew me better, you'd know just how delicious a conundrum this is for me. I love challenges like this that take me outside the nine dots.

Lastly, I'm kind of a "in for a dime, in for a dollar" guy. If I decide the re-ream the chamber and have to rent a reamer (if I can't borrow one) I may opt to make the chamber a 260 AI chamber at the same time. The improvements afforded by the AI 40 degree shoulder are akin to the benefits afforded by the 6.5 Creedmoor and I'd gain a small amount of case capacity for my trouble. IE, if it's going to be custom anyway, might as well go all the way.

The winter is long up here and time is on my side. I will no doubt go to sleep tonight ruminating on the possibilities. Life is good...

Hoot

[planeflyer21]

<munch>

Jon

[Hoot]

This project just got a whole lot more interesting, though a little enigmatic.

I've seen my share of manufacturing tolerances going both in my favor and not through my shooting career and I'm wondering if tripledeuce's new DPMS 260 barrel, with it's need to have the chamber "kissed", maybe came down on the short end of the stick? Here's why.

I finally got some time to take my new barrel, clean it thoroughly and actually see how it interacted with both my PTG .308 Go gauge and a piece of sized, new, Remington 260 brass. Now keep in mind that my RRA .308 bolt has seen less than 50 rounds, so for all intent and purpose, the lugs are not even close to broke in. The new barrel is just that. Sharp edged and for all intent and purpose, a virgin.

Here's where it gets interesting. With the new barrel chucked in a barrel vise on one of my work benches, IE not mounted to the receiver, I can put the Go gauge in with just the bolt, minus the ejector and extractor and hand rotate the bolt into battery. Granted there is zero bolt slop when in battery, but I rotated it just using my thumb and index finger. When I try the same thing with the RRA .308 barrel the bolt originally came with, the degree of resistance to rotation is almost identical. IE, a nice, firm, lockup much like a match grade chamber.

Next, I took the fresh piece of new, sized and trimmed 260 brass and coated the shoulder with Dykem layout stain. I placed it in the new 260 chamber and rotated the bolt into battery once again using just my thumb and index finger. It exhibited the same amount of rotational resistance as the Go gauge did. When I carefully removed the case, you could see where the shoulder was engaging the chamber, marked in the Dykem and it was right at the datum point on the shoulder. I cleaned and re-coated the case and chambered it in my bolt action 260 which has a Match chamber cut in it. Upon removal, it had the same marking on the shoulder at the datum point as the new DPMS barrel did.

So what are the chances that tripledeuce's new barrel may have been cut with an older reamer, winding up on the slightly short end of the tolerance stick and normally it should have been able to chamber the Go gauge, had it not come from the factory a little tight?

I realize that I'm kind of in uncharted waters with regard to what I'm doing, as I haven't found any references on any other forums to someone trying a DPMS barrel in an LAR-8 other than tripledeuce. Has anyone else?

Any opinions? I'm thinking I have a nice, close toleranced fitting bolt / barrel combination, that will eventually get a little more smooth with wear and fall right in the sweet spot. Or, am I overlooking something, that you more experienced folks already know about from your own experiences chambering new AR barrels? I've only done this two other times and both were with Remington 700 bolt actions, where I knowingly bought a factory short cut, drop-in barrel that I knew I would have to do a final ream on. 

I don't want to assume too much on this project as that's where trouble comes from. Obviously, I'd love to not have to rent a reamer and "kiss" the chamber, but if that's what needs doing, I'm certainly up to the task.

Please feel free to chime in. I PM'ed tripledeuce the same question and if he doesn't respond here, preferring to do so in the PM, I'll share his opinion, if that's OK with him, in this thread.

This could wind up being very good news for us LAR-8 owners who want to try other calibers not currently available through RRA. Even if it winds up that a little touchup work is needed, it's still great news since RRA certainly hasn't chosen to admit the interchangeability of barrels, let alone any of the other more precise parts, with other brands.

Thanks,

Hoot

[Tripledeuce]

  It is extremly probable that my bbl was reamed with a different reamer.  many contractors "gang mill"  a batch of barrels, and some ream the chamber body with a body reamer, then finish chambering with a "pull-through" reamer and test bolt to set the headespace.

      As my friend the FBI sientist says. "  All I can say, with sientific certiny is that this works for me". LOL!!!!!!( the forward was mildly para-phrased,,,,LOL!!

  Respectfully

  Terry

[imschur]

I love it!