15.7 inch vs 20 inch Diemaco

highspeedlowdrag said:
Yes please. An answer either way would be appreciated (I also haven't heard anything back from Colt Canada or Korth since e-mailing them early last week). Thank you in advance.
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I won't discuss pricing here, perhaps when our own forum is up. I'm new here, but I get the feeling that hijacking threads is in poor form.

I'm sorry I have not yet responded. Please understand I get hundreds of emails a day, and there is only me to deal with commercial sales concerns. I manage several separate projects. I have responded to several such emails in a very positive manner. I'm not sure about your particular email, but I also leave the rude offensively emails in the junk bin. My job is to deal with any technical, warranty or escalated customer concerns. If you have a concern with pricing it should be addressed to your dealer, or in the case of IOP purchases to Korth directly. I'm military myself with operational experience in Bosnia and Afghanistan, and I have a good grasp of the issue. I know Korth is working on something and we'll get the information to you in an appropriate manner.

To the OP, sorry for the sideshow, I hope I addressed your technical questions.
 
d1ce said:
That extra 4" of barrel gives a bit velocity to make the 5.56mm FMJ fragment reliably upon impact at 150m. For combat purpose, I would choose nothing less than 14.5" or velocity at muzzle no less than 2850 fps. The rifle/carbine must capable to maintain 2700+ fps at 50m at least. For range toy I don't mind any barrel length, I love em all.
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As civilians, we are not limited to FMJ rounds.....I always find that barrel length vs fragmentation argument on US boards silly.
So many better options that are more accurate and more effective.
 
Matt K said:
I won't discuss pricing here, perhaps when our own forum is up. I'm new here, but I get the feeling that hijacking threads is in poor form.

I'm sorry I have not yet responded. Please understand I get hundreds of emails a day, and there is only me to deal with commercial sales concerns. I manage several separate projects. I have responded to several such emails in a very positive manner. I'm not sure about your particular email, but I also leave the rude offensively emails in the junk bin. My job is to deal with any technical, warranty or escalated customer concerns. If you have a concern with pricing it should be addressed to your dealer, or in the case of IOP purchases to Korth directly. I'm military myself with operational experience in Bosnia and Afghanistan, and I have a good grasp of the issue. I know Korth is working on something and we'll get the information to you in an appropriate manner.

To the OP, sorry for the sideshow, I hope I addressed your technical questions.
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You've answered them all and more. Thanks for all this information. I'm buying the 15.7. My son is getting the 20. I can see why the 15.7 is more costly now.
 
Matt K said:
Small arms barrels have a number of different nodes of vibration. These vibrations cause the muzzle to move. If you shorten a barrel 1 mm at a time and graph the accuracy, results vary in a pattern of larger and smaller groups. The smaller group sizes along that graph are the accuracy nodes.

When you combine the accuracy nodes, with customer requirements, functional requirements such as dwell time and terminal requirements such as stability and velocity, you get what we found to be the ideal carbine length - 15.7 inches.

This is not an inexpensive test to conduct, as you might imagine. This required firing thousands of rounds in a number of samples to be statistically relevant. Further, the C8 has a choke hammer forged into it to improve accuracy and barrel wear. That means this was not a hack saw test, but that each set of test barrels needed to be hammer forged specifically for a pre-determined length.

15.7 inches (as measured from the breech face to the muzzle) is one of the accuracy nodes. 16" is not an accuracy node (though it may be for some steel and some profile), it is an arbitrary legal requirement in the US just as the Canadian 18" length restriction has nothing to do with accuracy or function. With the flash hider, the barrel is just slightly over 17". I suspect the M203A1 sleeve also enhances accuracy just as barrel tuning weights have an effect on group size.
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That sounds like a whole lot of range time - which would be great at first, but I get the feeling someone probably went to work thinking 'not again' during that testing. Shooting from a fixed rest is like shooting, but with all the good parts removed.
 
Matt K said:
This is also just not true, there are very definitive and measurable results between the two. Nor is it that true that we don't know how to measure barrels.

Small arms barrels have a number of different nodes of vibration. These vibrations cause the muzzle to move. If you shorten a barrel 1 mm at a time and graph the accuracy, results vary in a pattern of larger and smaller groups. The smaller group sizes along that graph are the accuracy nodes.

When you combine the accuracy nodes, with customer requirements, functional requirements such as dwell time and terminal requirements such as stability and velocity, you get what we found to be the ideal carbine length - 15.7 inches.

This is not an inexpensive test to conduct, as you might imagine. This required firing thousands of rounds in a number of samples to be statistically relevant. Further, the C8 has a choke hammer forged into it to improve accuracy and barrel wear. That means this was not a hack saw test, but that each set of test barrels needed to be hammer forged specifically for a pre-determined length.

15.7 inches (as measured from the breech face to the muzzle) is one of the accuracy nodes. 16" is not an accuracy node (though it may be for some steel and some profile), it is an arbitrary legal requirement in the US just as the Canadian 18" length restriction has nothing to do with accuracy or function. With the flash hider, the barrel is just slightly over 17". I suspect the M203A1 sleeve also enhances accuracy just as barrel tuning weights have an effect on group size.

These rifles are not permitted to be sold to the US, nor is it legal to export them because of US export and import laws and our licence agreement with the US state depts. The lengths have nothing to do with US laws. The barrel length was determined exclusively based on performance for a military customer requirement.

Cheers,

Matt
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Just out of curiousity why did you guys not go midlength gas instead of carbine gas?
 
Matt K said:
This is also just not true, there are very definitive and measurable results between the two. Nor is it that true that we don't know how to measure barrels.

Small arms barrels have a number of different nodes of vibration. These vibrations cause the muzzle to move. If you shorten a barrel 1 mm at a time and graph the accuracy, results vary in a pattern of larger and smaller groups. The smaller group sizes along that graph are the accuracy nodes.

When you combine the accuracy nodes, with customer requirements, functional requirements such as dwell time and terminal requirements such as stability and velocity, you get what we found to be the ideal carbine length - 15.7 inches.

This is not an inexpensive test to conduct, as you might imagine. This required firing thousands of rounds in a number of samples to be statistically relevant. Further, the C8 has a choke hammer forged into it to improve accuracy and barrel wear. That means this was not a hack saw test, but that each set of test barrels needed to be hammer forged specifically for a pre-determined length.

15.7 inches (as measured from the breech face to the muzzle) is one of the accuracy nodes. 16" is not an accuracy node (though it may be for some steel and some profile), it is an arbitrary legal requirement in the US just as the Canadian 18" length restriction has nothing to do with accuracy or function. With the flash hider, the barrel is just slightly over 17". I suspect the M203A1 sleeve also enhances accuracy just as barrel tuning weights have an effect on group size.

These rifles are not permitted to be sold to the US, nor is it legal to export them because of US export and import laws and our licence agreement with the US state depts. The lengths have nothing to do with US laws. The barrel length was determined exclusively based on performance for a military customer requirement.

Cheers,

Matt
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Now that is a rebuttal! I have amended my previous statement to reflect that you know far more about the subject than I do. Clearly a very great deal of work and thought has been put into what most would disregard (myself included) as just a very odd choice in measurement. The vast majority of shooters do not have the resources to fire thousands of rounds to find an accuracy node 1mm of barrel at a time. Even the greatest benchrest shooters don't do that, but they also (if permitted) generally employ a tuner to achieve the same effect. I will say this, the dedication to quality displayed here does wonders to justify the price of the rifles against your competitors. A choked barrel is the holy grail of barrels, and is right up there with gain-twist for the ultimate in barrel quality. Does the C7 rifle length have the same type of choked barrel as the C8 carbine?

As for the US angle, my implication was not that they would be sold in the US, but rather Canadian owners may want to take the gun to the US to shoot. As such without the muzzle device being permanently attached a Canadian would not be permitted to temporarily import the rifle as the barrel is less than the 16" minimum length. This is my understanding of how the US system works, and it may be a flawed or incomplete understanding. However, if, as you say, they are banned from import/export; that nullifies my point entirely and unfortunately is a point against the 15.7 should someone want to shoot stateside. Is the 20" also not permitted to enter he US?
 
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Matt; I would also like to add that on the Colt Canada/Diamaco webpage, the wight of the SA15.7 has been entered incorrectly.The SA20 is listed accurately at 3.31kg (7.29 lbs) but the lighter SA15.7 is listed at 2.97kg (7.96lbs), which is 1/3kg lighter than the SA20, but 1-1/2lbs. heavier at the same time.
 
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"Small arms barrels have a number of different nodes of vibration. These vibrations cause the muzzle to move. If you shorten a barrel 1 mm at a time and graph the accuracy, results vary in a pattern of larger and smaller groups. The smaller group sizes along that graph are the accuracy nodes"

Matt..thanks for the info....so barrel whip is a large factor in AR accuracy? Is it the most important factor? I was under the belief that the shorter barrels didn't suffer enough to make a difference unlike a 24" hunting barrel..
 
Jarvy said:
That would be the case with any carbine ...except the C8A3. It is ridiculously heavy. OP, If you're set on a Colt Canada, I'd get the 20". With a collapsed stock, it's as short as the carbine with the stock extended.
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C8A3 "ridiculously heavy" ? You need to get some gym time then since its lighter than a C7A2

Collapsed C7A2 is 36.6inch VS extended C8A3 34.5in. So a fully extended C8 is 2 inch shorter than a fully collapsed C7 and a full pound lighter...

OP: whatever floats your boat, both model are very accurate combat rifle. I personnaly prefer the "C8" and we've used them up to 400m and 500m with no modifications and back up sights and punched holes accuratly in our beloved Figure11 :p

The only way I'd consider a "longer than 16inch barrel AR" would be if it was non-restricted at 18.5inch. If you're into CQB/3 guns the C8 variants is what you're looking for. And if you're into AR accuracy shooting, its still the C8 you are looking for (between the 2 colt variant). And as a bonus it smaller and fit in a smaller gun case :p
 
Matt K said:
This is also just not true, there are very definitive and measurable results between the two. Nor is it that true that we don't know how to measure barrels.

Small arms barrels have a number of different nodes of vibration. These vibrations cause the muzzle to move. If you shorten a barrel 1 mm at a time and graph the accuracy, results vary in a pattern of larger and smaller groups. The smaller group sizes along that graph are the accuracy nodes.

When you combine the accuracy nodes, with customer requirements, functional requirements such as dwell time and terminal requirements such as stability and velocity, you get what we found to be the ideal carbine length - 15.7 inches.

This is not an inexpensive test to conduct, as you might imagine. This required firing thousands of rounds in a number of samples to be statistically relevant. Further, the C8 has a choke hammer forged into it to improve accuracy and barrel wear. That means this was not a hack saw test, but that each set of test barrels needed to be hammer forged specifically for a pre-determined length.

15.7 inches (as measured from the breech face to the muzzle) is one of the accuracy nodes. 16" is not an accuracy node (though it may be for some steel and some profile), it is an arbitrary legal requirement in the US just as the Canadian 18" length restriction has nothing to do with accuracy or function. With the flash hider, the barrel is just slightly over 17". I suspect the M203A1 sleeve also enhances accuracy just as barrel tuning weights have an effect on group size.

These rifles are not permitted to be sold to the US, nor is it legal to export them because of US export and import laws and our licence agreement with the US state depts. The lengths have nothing to do with US laws. The barrel length was determined exclusively based on performance for a military customer requirement.

Cheers,

Matt
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Thanks for the very informative post. I know Diemaco had enjoyed a stellar reputation when it came to build quality, especially their barrels. Obviously, their attention to detail played a major role in creating that reputation as evidenced by the testing you described above. I for one am glad to see Colt Canada join CGN and finally enter the civilian firearms market in Canada. :)
 
FYI-wolverine is selling 1799 for 20 inch and 1999 for 15.7! Hope I am not the last person found that out! Much better than 2299 few month ago!
 
r34skyline said:
Just out of curiousity why did you guys not go midlength gas instead of carbine gas?
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There is no MILSPEC mid-length system. To keep the logistics simple, there are as few parts as possible. I could get parts for my C8 at nearly any FOB or base in Afghanistan. An M4 gas tube will work just fine. The rest of the military world uses carbine length tubes, hand guards and accessories.

I have a few myself, and while they are nice, the C8's are the most reliable and accurate rifles in test after test. The improved chamber and the other changes we made have a greater effect on system reliability than anything like that. So for us, the mid-length was a solution with no real problem.

That said, if a military customer asked for it, we could do it.
 
Blastattack said:
Matt; I would also like to add that on the Colt Canada/Diamaco webpage, the wight of the SA15.7 has been entered incorrectly.The SA20 is listed accurately at 3.31kg (7.29 lbs) but the lighter SA15.7 is listed at 2.97kg (7.96lbs), which is 1/3kg lighter than the SA20, but 1-1/2lbs. heavier at the same time.
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Thanks. I'll check it out - any errors are entirely my fault. I'm drinking from the fire hose here.
 
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