Thinking about 10mm AR again - RMW Extreme - what barrel length

[sstewart]

Thinking about ordering this:

http://www.rmwxtreme.com/#top

Should I do the 16" barrel or a pistol length? He offers 8 to 16 inch barrels. I probably would do the Sig brace if shorter than 16"
Opinions desired, but I am not real interested in MechTech or Just right carbine as I am not a Glock Guy. Glock Magazines are not an advantage over the 30 round grease gun mags Ron offers.

All my rifles are 20" barrels. (one AR .223, one .308 Remington 700)

[Rich10]

I think you receive diminishing return for anything more than 10"-11". 

I would either do a 10.5" pistol or 10.5" barrel with a permanent 6" muzzle attachment for a carbine. 

[ShadeTreeVTX]

Wrong!!You have to start thinking carbine or rifle powders when loading instead of pistol powders. I found 2400 to be a great powder for my 16" M-T and I'm looking at some other slower powders to compliment the longer barrel of my M-T.

Doug

[Rich10]

Wrong!!You have to start thinking carbine or rifle powders when loading instead of pistol powders. I found 2400 to be a great powder for my 16" M-T and I'm looking at some other slower powders to compliment the longer barrel of my M-T.

Doug

Yes, if you reload. 

[ShadeTreeVTX]

If your a shooter not a collector - for 10mm - its almost a must - start adding up the price of commercial amo and if your a serious 10mm shooter - you'll have at least a single stage on your bench.

Doug

[sqlbullet]

Wrong!!You have to start thinking carbine or rifle powders when loading instead of pistol powders. I found 2400 to be a great powder for my 16" M-T and I'm looking at some other slower powders to compliment the longer barrel of my M-T.

Doug

Ummm....

Several studies have shown that with rare exception, the best powder for a given cartridge/bullet weight at a given barrel length will be the best powder for that cartridge for all barrel lengths, speaking to velocity. 

Accuracy may be a different story.

There was an article in, I think, Precision Shooting many years ago where the author empirically tested this across a bunch of calibers.  He went the other way, starting with long barrels, developing a max velocity load, then shortening the barrel and working up a new max velocity load.

In every case he found the same thing.  The best velocity load in long barrels was also the best load in short barrels for a given bullet weight.

OP...

You may want to review the Ballistics by the Inch data:

http://www.ballisticsbytheinch.com/10mm.html

For 170 grain bullets and up, 14-15" is the sweet spot for 10mm.  Lighter bullets appear to benefit a bit more from an extra few inches beyond that.  Since you plan to use it like a rifle, I would get the 16" barrel, rather than mess with the admittedly cool sig brace.  The velocity they show lost to 'coast' with heavy bullets in these barrels really amounts to little more than statistical error.

[10mmfan]

Thanks now I want an ar pistol in a 10mm.

[sstewart]

Wrong!!You have to start thinking carbine or rifle powders when loading instead of pistol powders. I found 2400 to be a great powder for my 16" M-T and I'm looking at some other slower powders to compliment the longer barrel of my M-T.

Doug

Ummm....

Several studies have shown that with rare exception, the best powder for a given cartridge/bullet weight at a given barrel length will be the best powder for that cartridge for all barrel lengths, speaking to velocity. 

Accuracy may be a different story.

There was an article in, I think, Precision Shooting many years ago where the author empirically tested this across a bunch of calibers.  He went the other way, starting with long barrels, developing a max velocity load, then shortening the barrel and working up a new max velocity load.

In every case he found the same thing.  The best velocity load in long barrels was also the best load in short barrels for a given bullet weight.

OP...

You may want to review the Ballistics by the Inch data:

http://www.ballisticsbytheinch.com/10mm.html

For 170 grain bullets and up, 14-15" is the sweet spot for 10mm.  Lighter bullets appear to benefit a bit more from an extra few inches beyond that.  Since you plan to use it like a rifle, I would get the 16" barrel, rather than mess with the admittedly cool sig brace.  The velocity they show lost to 'coast' with heavy bullets in these barrels really amounts to little more than statistical error.

I read this post when you posted it a while ago. And I agree with the article completely. But I think the context is rifle. Like the difference between 20 inches and 26 inch barrels.
I do think that this will breakdown at some point, like is that 3.6 inch compact pistol as accurate as a .26 inch rifle.

[sstewart]

I guess I was thinking of another article about the myth that longer barrels are more accurate. Not the velocity one referenced above.
There are some other factors. Like 16" barrel is classified as a rifle.
Less is a pistol. And I don't pretend to understand the process of licensing a short barrel rifle. (Sounds complicated and long cause the ATF is involved)

[sqlbullet]

Depending on where you live, it can be easy or hard.  Where I live, it is pretty trivial.  The process is long though, as at present it is taking about 18 months for the ATF to approve suppressor and SBR requests.

Most guys that are set on having a true SBR build the gun up as a pistol, submit the paperwork and then put a stock on it when the paperwork finally clears.  The advent of the sig arm brace and ATF ruling that it doesn't constitute a stock even when used as one largely subverts the whole process in my mind.  Why pay 200 and wait 18 months just for a different piece of nylon that functions the same as the sig brace?

As far as barrel length and either accuracy or powder burn rate/velocity, there is no point at which, in testing, shorter barrels have been at any disadvantage other than velocity drop due to less time under the accelerating pressure.  Pick the shortest barrel that will meet your velocity objectives.

[Pinsnscrews]

Taken from page 169 "The Complete Reloading Manual for the T/C Contender"

PLEASE NOTE: "The following loads are for the Contender pistol only." 

Use the below information at your own risk. This information is provided for informational purposes only. This is Published Load data circa 1991.

Test Specifications:
Firearm:T/C Contender
Bbl. Length / Twist: 14" / 1-16"
Cases: Norma
Trim-to Length: .987
Primers: Federal 150

Sierra Bullets Used

150gr JHP                 
Powder    1300   1400   1450   1500   1550   1600
No.7           11.6   12.2   12.5   12.8   13.1   
Blue Dot   10.9   11.5   11.8   12.1   12.3   
HS7           11.7   12.5   12.9   13.2     
No.9              14.5   14.9   15.3   15.7   16.0
                 
180gr JHP                 
Powder   1100   1200   1250   1300   1350   1400
No.7          9.8   10.6   11.0   11.3     
Blue Dot    9.0   9.4   9.6   9.8   10.0   10.3
HS7           9.8   10.6   11.0         
No.9          12.5   12.9   13.2   13.5   
2400              12.3   13.1   13.5   13.9     
                 
190gr FPJ                 
Powder   1000   1100   1200   1250   1300   1350
No.7          9.2   9.8   10.5         
Blue Dot    8.6   9.2   9.8   10.1   10.4   
HS7          9.5   10.1   10.7         
No.9         12.5   13.0   13.4   13.7
2400                 12.0   12.7   13.3   13.6   14.0   


--Tables cleaned up a bit

150 gr JHP

Powder	1300	1400	1450	1500	1550	1600
No.7	11.6	12.2	12.5	12.8	13.1
Blue Dot	10.9	11.5	11.8	12.1	12.3
HS7	11.7	12.5	12.9	13.2
No.9	14.5	14.9	15.3	15.7	16

180 gr JHP

Powder	1100	1200	1250	1300	1350	1400
No.7	9.8	10.6	11	11.3
Blue Dot	9	9.4	9.6	9.8	10	10.3
HS7	9.8	10.6	11
No.9	12.5	12.9	13.2	13.5
2400		12.3	13.1	13.5	13.9	13.9

190 gr JHP

Powder	1000	1100	1200	1250	1300	1350
No.7	9.2	9.8	10.5
Blue Dot	8.6	9.2	9.8	10.1	10.4
HS7	9.5	10.1	10.7
No.9	12.5	13	13.4	13.7
2400		12	12.7	13.3	13.6	14

Please Note: the Data as noted is from 1991 and some of the powders have changed formulary in that time. please Cross Reference to other published data, and always work up to those max loadings. It has been pointed out that some of the data has changed.

[Pablo]

Thinking about ordering this:

http://www.rmwxtreme.com/#top

Should I do the 16" barrel or a pistol length? He offers 8 to 16 inch barrels. I probably would do the Sig brace if shorter than 16"
Opinions desired, but I am not real interested in MechTech or Just right carbine as I am not a Glock Guy. Glock Magazines are not an advantage over the 30 round grease gun mags Ron offers.

All my rifles are 20" barrels. (one AR .223, one .308 Remington 700)

That site seems rather sparse. What mags does that 10mm upper use? I assume it comes with a bolt, but what else? Does it even come with a 10mm magazine? Block for mag well.

How to order - email him?

Price is high, but may be worth it depending on extras.

Thanks!

P

[sqlbullet]

Thanks for posting up this data Pinscrews.

I have a couple of comments about the data though.

First, anyone thinking of using this data should be warned that the data for 2400 is well over the Alliant published max loads for 10mm in those weights.  Alliant lists 12.9 grains as max in 180 grain, and 12.5 grains as max in 190 grain.

Second, when looking at the data, it also stopped well short of max book loads for AA #9 with 190 gr.  Accurate lists 14.2 grains as a max load for that bullet weight.  I don't know if that means that is just where the authors stopped testing, or if they encountered pressure signs or velocity irregularities, or other issues that gave them pause.  Extrapolation would put the AA #9 a little ahead of 2400 if they had loaded to 14.2 grains.

Third, the velocities listed with AA#9 in 180 grain are low compared to other sources.  In fact, these velocities are more in line with a 8" test barrel than a 14" barrel.  Again, this could be evidence that they were experiencing velocity irregularities in testing #9 in their test gun.

Doug, you have the gun.  It would be great if you could test some loads and post up the raw data of the results in both your M/T 16" and a standard length barrel.

[sstewart]

Thinking about ordering this:

http://www.rmwxtreme.com/#top

Should I do the 16" barrel or a pistol length? He offers 8 to 16 inch barrels. I probably would do the Sig brace if shorter than 16"
Opinions desired, but I am not real interested in MechTech or Just right carbine as I am not a Glock Guy. Glock Magazines are not an advantage over the 30 round grease gun mags Ron offers.

All my rifles are 20" barrels. (one AR .223, one .308 Remington 700)

That site seems rather sparse. What mags does that 10mm upper use? I assume it comes with a bolt, but what else? Does it even come with a 10mm magazine? Block for mag well.

How to order - email him?

Price is high, but may be worth it depending on extras.

Thanks!

P

Yes every thing is by email. Definitely not a pushy sales type. His reputation seems good.
I am looking at an assemble it your self deal between 1,110 to 1,250. Upper is complete. lower has to be put together.
He uses grease gun mags - 30 round capacity (this actually is a good thing) most pistol caliber ARs use this type of magazine
YHM hand-guard is a $100 upgrade (in above amount)
The beauty of RMW's gun is that it is mostly standard AR parts, triggers, pins, etc and that it is gas impingement instead of blow back

[Pablo]

Thanks - duh on my part, you did say grease gun mags in your OP. I agree that's a good thing. Slight adjustment and they hold 10mm just fine - over 30 rounds!!

And bonus you answered my next question - gas impingement. 10mm does fine with a gas system from what I've seen.

I agree that 14-15" is a sweet spot with most powders and 16" will be great.

I have emailed him. I see he sells GG lowers. SweeT!!!

Thanks man!