7.62 x 40 WT vs. .300 BLK

olddawg · Feb 3, 2012

BenL said:
In the interest of complete disclosure...

"rsilvers" = Robert Silvers, AAC Research and Development Director

He birthed this beautiful baby.

Pretty cool that he's hanging with us and sharing his expertise. :thumbsup:

Russ D · Feb 3, 2012

My whole estimate on the 40% is due to the fact that almost everyone who wants an ar15 right now already has one or two. When these people are getting back into the market for their next rifle, the 300 BLK will already be established with lots of options and cheap ammo. Then the only decision will be another 556 or a more capable hunting/sbr cartridge. I cannot see the 300blk not doing well in that scenerio.

AwesomeBill · Feb 3, 2012

I really need to stop reading these threads. Now i want to build a suppressed .300 BLK. My wife is going to kill me!!!

rsilvers · Feb 3, 2012

erwos said:
If you're truly the project manager, you'll have the sales projections. Are you genuinely telling me that it's 40%+ of the AR-15 market in the next two years?

No. I would not forecast that much. I do think it will be the #1 alternative centerfire rifle AR cartridge within the next year.

rsilvers · Feb 3, 2012

Forest said:
The bigger issue was the chamber & case drawing screwup.

It was bad enough the Remington submitted design had less freebore and a much sharper angle where the neck transitions to the freebore, than the original chamber of the 5th SFG; but if you look at the drawings you can have a conditon where a case 'in spec' to the max dimensions would not fit in a chamber that was 'in spec' to the minium dimensions.

That is the popular perception. Western Powders did a study and it was determined that the free bore being shortened only accounted for 1000 psi typical (1500 psi max) additional pressure and 20 fps typical (30 fps max) lost velocity. The greater problem were bores that had chrome plating without accounting for their thickness. Being under SAAMI minimum cross-sectional area is a big problem.

erwos · Feb 3, 2012

rsilvers said:
No. I would not forecast that much. I do think it will be the #1 alternative centerfire rifle AR cartridge within the next year.

I'll buy into that prediction.

rsilvers · Feb 3, 2012

Rusty Shackleford said:
rsilvers, is the only difference between .300blk and .300WT the cartridge length. What is there to recommend one over the other?

7.62x40mm is not a SAAMI round, so larger companies won't make products for it. There is one or maybe a few companies working on it, while 300 BLK has about 90 companies. 7.62x40mm has less of a taper, so it has to be fire-formed to make the brass in-spec if you start with 223 or 5.56mm brass - a very costly step for reloaders as it requires firing a bullet. The cartridge is not compatible with standard magazines unless you download them to lower capacity. It has a very short neck length, so there is, in my opinion, not enough bullet support. And while it is claimed to be 200+ fps faster than 300 BLK by some users - that is only if you load it to well over 55,000 psi. If loaded to the same 55,000 psi pressure as 300 BLK, then it is more like 85 fps faster with 125 grain bullets. While fans of it have said it is better if you want just supersonic ammo, I don't see it that way - for the reasons listed - even for just supersonic use.

Markp · Feb 3, 2012

Just curious, what would be the implications for a small (85 grain) pistol bullet or 100 grain rifle bullet. Would this be practical for a supersonic load with increased velocity in the .300 blkout?

Just curious (and a little stupid).

Lex Armarum · Feb 3, 2012

rsilvers said:
7.62x40mm is not a SAAMI round, so larger companies won't make products for it. There is one or maybe a few companies working on it, while 300 BLK has about 90 companies. 7.62x40mm has less of a taper, so it has to be fire-formed to make the brass in-spec if you start with 223 or 5.56mm brass - a very costly step for reloaders as it requires firing a bullet. The cartridge is not compatible with standard magazines unless you download them to lower capacity. It has a very short neck length, so there is, in my opinion, not enough bullet support. And while it is claimed to be 200+ fps faster than 300 BLK by some users - that is only if you load it to well over 55,000 psi. If loaded to the same 55,000 psi pressure as 300 BLK, then it is more like 85 fps faster with 125 grain bullets. While fans of it have said it is better if you want just supersonic ammo, I don't see it that way - for the reasons listed - even for just supersonic use.

Thanks! That was the info I was looking for. Good to know. Looks like I am going .300blk for my new build.

Lex Armarum · Feb 3, 2012

AwesomeBill said:
I really need to stop reading these threads. Now i want to build a suppressed .300 BLK. My wife is going to kill me!!!

Welcome to the jungle baby! This place will feed your addiction.

BradMacc82 · Feb 3, 2012

Rusty Shackleford said:
Welcome to the jungle baby! This place will feed your addiction.

Yes it will, I just got done putting together my lower - minus buffer tube/stock - for my 300 Blk build.

Still haven't decided on barrel length - 10"pistol/sbr, or 16", decisions, decisions.

rsilvers · Feb 3, 2012

Markp said:
Just curious, what would be the implications for a small (85 grain) pistol bullet or 100 grain rifle bullet. Would this be practical for a supersonic load with increased velocity in the .300 blkout?

Just curious (and a little stupid).

The bullet would be too short to feed. 2.1 inches is the shortest OAL that is very reliable in an AR - same as 223. You can go shorter if reliability is less important, or if you are using a single shot or bolt-action rifle.

Markp · Feb 3, 2012

rsilvers said:
The bullet would be too short to feed. 2.1 inches is the shortest OAL that is very reliable in an AR - same as 223. You can go shorter if reliability is less important, or if you are using a single shot or bolt-action rifle.

Awesome, thanks... I plan on running only heavier sub-sonic loads, but it's nice to know 2.1 is the lower limit for reliable feeding!

Mark

teratos · Feb 3, 2012

This has turned into a great thread. I have a lower I was wondering what to do with.....now I know. Looks like more paperwork off to the BATF......

Kingjamez · Feb 3, 2012

Once I saw how easy it is to convert .223 brass into .300BLK, I too knew that my next AR will be 30 caliber.

-Jim

robmints · Feb 3, 2012

If you look at the barrel group buy thread, look at how many blk barrels are being asked for. Kind of amazing to me. I have tried to avoid all the AR hype but I can't. First time AR buyer, 300blk for me, just waiting on the lowers to come in.

reynolds25 · Feb 4, 2012

One more vote for 300 blackout. Easy to convert and quiet when suppressed

Forest · Feb 4, 2012

AwesomeBill said:
I really need to stop reading these threads. Now i want to build a suppressed .300 BLK. My wife is going to kill me!!!

I'll second this. I was planning on a SBR 6.8 to go along with my SPR, but the allure of using a smaller/lighter 9mm handgun supressor is tough to ignore.

7.62 x 40 WT vs. .300 BLK

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