Okay, fellas, I called one of the three companies that will be making the 6.8mm uppers to ask some general questions.  The tidbit that peaked my interest the most is that one of the manufacturers stated that they will be using stainless barrels for the time being, not chrome lined barrels.  He further stated that not having a chrome lining isn't really necessary because the type of stainless steel barrels (i.e. Compass Lake) that they will be using has been holding up very well even under full auto.  But I was always under the impression that CHROM LINED barrels resisted rust and lasted longer than stainless barrels and that's why military weapons had chrome lined barrels.  Any takers on this?

Edited to add:  The individual who I spoke to also stated that the barrels do loss some accuracy after sustained fire, but that after cooling off a bit, accuracy is regained.

One last thing:  Does having a SS barrel mean that we MUST clean the barrel right after a day at the range?  I'm used to leaving the barrel dirty for a couple of days after a stint at the range if I'm too busy to clean right after...

There has been some research for awhile now into better stainless steel alloys for machinegun barrels.

I'm not sure who is doing it or how it is paying off; but I wouldn't be surprised to see some it working its way out to the market.

I was meaning to ask this as well, What again is the reason that SS is not a good idea for M-16 barrels (for instance the ADCO SS 18inch SPR style barrel).  What if anything is the reason why it is not a good idea for at least limited full auto and suppressed use?

It's contour is .75 forward of the post and .82 rearward and larger in the chamber region.

I know SS might not be a good candidate for thin M4 barrels but how or why would the barrel be any weaker than a gov't profile 1/7 20inch barrel?

[b]By the way this is one of those areas where I totally dissaggree with conventional thought, in that Chrome lined barrels are more rust resistant than SS barrels.

The bore? possibly. But the external surface of the SS barrel is far more rust resistant than the outer surface of a chrome moly barrel. and given that URX hasn't come out, and cleaning under the FF RAS is a pain, why not use SS that you don't have to worry about?[/b]
                   

I'm curious as well.  A lot of folks seem to want midlength systems and barrels that will stabilize the heavier bullets but still reliably handle milsurp ammo.  

Seems like the RRA 16" SS barrels with 1:8 twist, 5.56 chamber (or is it Wylde?) meet these reqs nicely.  Not a sub-MOA system, but the complete upper is well under $500 (maybe ad few more dollars to dull the finish.)

So what is the downside of stainless?  How does it handle heat compared to 4140 or 4150 steel?  Is there a big difference in the stainless steels used among the various barrel makers? Douglas and Wilson come to mind.

Regards,
Randy

Wes,

But if the military does pick up this cartridge and it becomes standard issue, they would probably require chrome-lined barrels, right?

I've heard that stainless, while softer than 4140 or 4150, has a better wear pattern, or wears more evenly.   Thus it keeps its accuracy, longer.   So the throat erosion is not as big a deal, especially if you can chase.

What about 16inch barrels with 77grain ammo? the round is probably traveling at 2650FPS does that mean that it will have a longer lifespan than 55grain at 2900FPS?


Does anyone have a link to a PDF detailing SPR barrel testing procedures and results?

I had a 11.5in SS HBAR M-16 upper and got rid of it in favor of chrome a while back, but in firing it was very cool (didn't heat fast) and I didn't have any problems with it. I always wondered how much truth lay in this no SS for M-16's argument.

[b]I always thought the SS held pressure better at higher temps (hence use in suppressors) what is the difference like? %wise.

If I could get a 3/4 inch straight taper SS barrel to hold out to limited FA use It would be perfect since no-one makes a heavy contour 1/7 with a rifle gas tube. (I know I could cut-down a 20in gov't profile but the accuracy would probably be no where near 3/4MOA.)

2750

OKay guys - I am in the dark,  6.8mm spc?  I have been living under a rock - fill me in on this new round that is being tested by the military.

Wes,

Roger the BH Mk262 Mod 1
The 16" using it was faster than the 20" using the HSM 77gr SMK loading

Barrett will be offering 4150 chrome lined barrels...

-Cap'n

Have you heard if there will be a pre ban version and what contours are they going to be?

Thanks Kris

"AS A SIDE NOTE, WE CHRONO'D THE RBCD AMMO. 3870 FPS OUT OF A 20" GUN AND ZERO SIGNS OF OVERPRESSURE. OK, IT WAS A HOT DAY, BUT THAT IS MOVING OUT."


3870 out of 5.56! with 77grain SMKs? if that ammo is safe it must be the most desirable round on the market. (that should easilly hit 2800 out of a 10.5.)

"One last thing: Does having a SS barrel mean that we MUST clean the barrel right after a day at the range? I'm used to leaving the barrel dirty for a couple of days after a stint at the range if I'm too busy to clean right after..."

[b]Hell no.[/b] This I do have ananswer for.  In my experience I rarely cleaned the outside of a SS barrel even after rain and didn't see any rust ever, My BM barrels will rust within a couple days after rain without attention.

As for the inside of the bore, SS is far more rust resistant than chrome moly steel, while it may not be quite as good as (the "magical" couple thousandths of hard chrome people worship) it is deffinitely not chrome moly.

The Marine Corp switched to SS in M40A1 barrels and never experienced rust problems again. (In Vietnam M40 barrels were rusting bad, that is why they switched.) If I had to guess I would say SS is at least 10times more rust resistant than Chrome moly if not 20times more.

Green0
The RCBD is 37gr IIRC