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Mike_G
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Posted: 2/12/2008 4:48:44 PM
[Last Edit: 2/13/2008 9:30:19 AM by Mike_G]

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Assuming use of a heavier load e.g. Mk262 or Hornady TAP 5.56 75gr and a 1/7 twist rate how do a 10.5" and a 16" barrel compare in:

*effective range
*terminal ballistics / fragmentation
*How does shooting with a suppressor affect performance +/-
*Reliability

I supect the 16" barrel would be better than the 10.5" in each category, but is the difference significant? At what range would you put down the SBR and pick up a carbine or rifle with 16" + barrel?

Are there any websites that explain the differences?
12_gauge
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Posted: 2/12/2008 4:50:43 PM

Originally Posted By Mike_G:
Assuming use of a heavier load e.g. Mk262 or Hornady TAP 5.56 75gr and a 1/7 twist rate how do a 10.5" and a 16" barrel compare in:

*effective range
*terminal ballistics / fragmentation
*How does shooting with a suppressor affect performance +/-
*Reliability

I supect the 16" barrel would be better than the 10.5" in each category, but is the difference significant? At what range would you put down the SBR and pick up a carbine or rifle with 16" + barrel?

Are there any websites that explain the differences?


At any range where maneuverability of the 10.5 wasn't MANDATORY. I would pick an SBR'ed PS90 for close up before I would a 10.5" AR anyways.
sed6
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Posted: 2/12/2008 10:39:03 PM

Originally Posted By Mike_G:
Assuming use of a heavier load e.g. Mk262 or Hornady TAP 5.56 75gr and a 1/7 twist rate how do a 10.5" and a 16" barrel compare in:



*effective range


The Ammo Oracle


*terminal ballistics / fragmentation


again The Ammo Oracle


*How does shooting with a suppressor affect performance +/-


Check out my recent thread here


*Reliability


A great read on barrel length, ballistics and reliability on ChuckHawks


I supect the 16" barrel would be better than the 10.5" in each category, but is the difference significant? At what range would you put down the SBR and pick up a carbine or rifle with 16" + barrel? Are there any websites that explain the differences?


The Ammo Oracle
I also suspect a longer barrel will offer better performance in almost every measurable catagory. But size isn't everything. My SBR is good out to 120+ yards with my ammo of choice. Outside of that I'd reach for a dedicated distance rifle in at least .308, not a longer barrel 5.56...

If you haven't done so yet the Ammo Oracle is a must read, then read it again and then a third time for good measure. It'll answer 95% of your questions.
God and the soldier, we adore; in time of danger, not before. The danger passed, and all things righted; God is forgotten, the soldier slighted.
Mike_G
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Posted: 2/13/2008 1:13:19 AM
[Last Edit: 2/13/2008 8:53:30 AM by Mike_G]
Thanks to sed6 - Question: Do you think switching to a heavier round would extend the effective range of your SBR?

What I got from the Ammo Oracle (and the B&T Ammo labs site reference by ammo oracle) and Hawks article:

-Muzzle vlocity of the 77gr and 75gr 5.56 rounds is around 2624 fps from a 16" bbl
-You lose about 20 fps for each 1" of barrel length reduction
-Based on the above I am estimating a muzzle velocity of about 2500 fps for 77gr 5.56 from a 10.5" barrel
-The 77gr. 5.56 round will still fragment at velocities less than 2100 fps

So how do I calculate how far the77gr 5.56 will travel before reaching a velocity of 2100fps?
12_gauge
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Posted: 2/13/2008 2:39:15 AM
[Last Edit: 2/13/2008 2:40:41 AM by 12_gauge]

I really wonder, would a Nosler BT come into it's own here? They seem to work VERY well from the 5.7 pistols and rifles, 2100-2500fps is roughly their operating range from said weapon. Nosler claims that the BT will expand down to 1600fs. From what I have seen, 12"+ and fragmentation can be expected near the 1800-2400fps range using the FN 5.7x28 as a case study.
Combat_Jack
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Posted: 2/13/2008 3:03:19 AM
[Last Edit: 2/13/2008 3:05:00 AM by Combat_Jack]
The velocity will be around 2500 fps. Fragmentation will be partial below 2300, nonexistant below 2100.

The guns are more finicky but certainly capable of 100% percent reliability. Use Magpul followers or PMAGs for best results. And an O-ring in the extractor.

Suppressors will typically make a short gun act more like a long one, but you may need to play with buffer weights to make it work 100% others will be able to comment more.

I wouldn't feel undergunned with an SBR to 300M. Never tried it any farther.

EDIT: Fragmentation range will be less than 50M.
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jhud
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Posted: 2/13/2008 9:55:55 AM
I guess this forum should be a giant ammo oracle link.
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Mike_G
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Posted: 2/13/2008 10:06:08 AM

Originally Posted By jhud:
I guess this forum should be a giant ammo oracle link.


Maybe, maybe not. I may be missing it but I'm not seeing seeing info with figures (or how to calculate) effective range of the 75 gr and 77gr, 5.56 rounds from a 10.5" barrel.

I got a lot of good info from the Ammo Oracle and B&T Ammo labs, but I am having trouble finding that one last piece of info i.e. How far out in yards / meters will a 75gr or 77gr. 5.56 round effectively fragment when fired from a 10.5" barrel
sed6
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Posted: 2/13/2008 4:43:39 PM
Referring back to my results here question 3 shows a drop of about 200fps per 100 yards. So if you are getting 2500fps at the muzzle, you'd be down to 2100fps by 200 yards. Your question addresses a heavier bullet than the 62gr M855 I tested, though a heavier bullet will go faster farther than a lighter one.

I was full of what if's before I built my SBR. Some research, like you're doing, helped clear things up a bit. I didn't, and you won't, get any absolutes here. The only way to be sure is to build the rifle you want, then go test fire it like I did. My research let me to suspect I'd get decent velocity at intermediate ranges, it was my range time that confirmed this for me though. But until I actually put some rounds in 10% gelatin at those ranges I cannot be 100% positive on the fragmentation. I can though be sure that if I'm shooting at you at that range you will a) duck for cover b) bleed when shot c) die if you loose enough blood. My AR fits my intended purpose, yours should too.
God and the soldier, we adore; in time of danger, not before. The danger passed, and all things righted; God is forgotten, the soldier slighted.
Molon
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Posted: 2/13/2008 5:29:57 PM
[Last Edit: 5/7/2008 2:19:32 PM by Molon]

Originally posted by Mike_G:

-Muzzle vlocity of the 77gr and 75gr 5.56 rounds is around 2624 fps from a 16" bbl


Incorrect. The velocity will be more like 2715 FPS.






Originally posted by Mike_G:

You lose about 20 fps for each 1" of barrel length reduction



Invalid. There is no valid equation to determine the change in muzzle velocity across a spectrum of barrel lengths and a variety of ammunition loads. The change in muzzle velocity will depend on a variety of interactive variables such as the barrel length spectrum involved (e.g. 20” to 16” versus to 16” to 14.5”), the operating velocity spectrum involved (e.g. a 20” barrel firing a load with a MV of 3,000 FPS compared to other barrel lengths versus a 20” barrel firing a load with a MV of 3,250 FPS compared to other barrel lengths) and the bullet weight spectrum involved (e.g. a 40 grain V-MAX versus a 75 grain OTM.) The particular powder used in the loads will even cause variations between the spectrum of barrel lengths used.

Examples

An average difference in muzzle velocity between a 14.5” barrel and a 16” barrel using a 75 grain OTM load is approximately 86 fps. This gives you a difference of 57 FPS per inch of barrel.

An average difference between a 20” barrel and a 16” barrel is 108 FPS for a difference of 27 FPS per inch of barrel.

An average difference between a 20” barrel and a 24” barrel is 79 FPS for a difference of approximately 20 FPS per inch of barrel.







Originally posted by Mike_G:

Based on the above I am estimating a muzzle velocity of about 2500 fps for 77gr 5.56 from a 10.5" barrel



Your estimation is far too high. Actual chronographs of MK262 have shown the muzzle velocity to be approximately 2360 PFS from a 10.5” barrel.






Originally posted by Mike_G:

The 77gr. 5.56 round will still fragment at velocities less than 2100 fps



A much more realistic threshold for reliable fragmentation with the 75-77 grain OTM loads is 2,250 FPS. From your 10.5” barrel, this will give you a fragmentation range of approximately 48 yards.






Originally posted by sed6:

My SBR is good out to 120+ yards with my ammo of choice.



If by “good” you mean effective and reliable fragmentation with adequate penetration, please tell me where I can purchase some of this magical ammunition. The 75 grain 5.56 TAP load has the best terminal ballistics of any commercially available load for the 5.56mm platform and as shown above it only has a 48 yard fragmentation range when fired from a 10.5” barrel.




All hail Jeanne Assam!
Mike_G
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Posted: 2/13/2008 6:06:27 PM

Originally Posted By Molon:

Originally posted by Mike_G:

-Muzzle vlocity of the 77gr and 75gr 5.56 rounds is around 2624 fps from a 16" bbl


Incorrect. The velocity will be more like 2715 FPS.






Originally posted by Mike_G:

You lose about 20 fps for each 1" of barrel length reduction



Invalid. There is no valid equation to determine the change in muzzle velocity across a spectrum of barrel lengths and a variety of ammunition loads. The change in muzzle velocity will depend on a variety of variables such as the barrel length spectrum involved (e.g. 20” to 16” versus to 16” to 14.5”), the operating velocity spectrum involved (e.g. a 20” barrel firing a load with a MV of 3,000 FPS compared to other barrel lengths versus a 20” barrel firing a load with a MV of 3,250 FPS compared to other barrel lengths) and the bullet weight spectrum involved (e.g. a 40 grain V-MAX versus a 75 grain OTM.) The particular powder used in the loads will even cause variations between the spectrum of barrel lengths used.

Examples

An average difference in muzzle velocity between a 14.5” barrel and a 16” barrel using a 75 grain OTM load is approximately 86 fps. This gives you a difference of 57 FPS per inch of barrel.

An average difference between a 20” barrel and a 16” barrel is 108 FPS for a difference of 27 FPS per inch of barrel.

An average difference between a 20” barrel and a 24” barrel is 79 FPS for a difference of approximately 20 FPS per inch of barrel.







Originally posted by Mike_G:

Based on the above I am estimating a muzzle velocity of about 2500 fps for 77gr 5.56 from a 10.5" barrel



Your estimation is far too high. Actual chronographs of MK262 have shown the muzzle velocity to be approximately 2360 PFS from a 10.5” barrel.






Originally posted by Mike_G:

The 77gr. 5.56 round will still fragment at velocities less than 2100 fps



A much more realistic threshold for reliable fragmentation with the 75-77 grain OTM loads is 2,250 FPS. From your 10.5” barrel, this will give you a fragmentation range of approximately 48 yards.






Originally posted by sed6:

My SBR is good out to 120+ yards with my ammo of choice.



If by “good” you mean effective and reliable fragmentation with adequate penetration, please tell me where I can purchase some of this magical ammunition. The 75 grain 5.56 TAP load has the best terminal ballistics of any commercially available load for the 5.56mm platform and as shown above it only has a 48 yard fragmentation range when fired from a 10.5” barrel.






Thanks for your input. What source(s) does your data come from? Not that I don't trust you, I'd just like to read for myself. My proposed SBR represents a sizeable investment (for me) and if the effective range is less than 100 yards with the best available ammo, then I'd have to rethink my build.

Molon
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Posted: 2/13/2008 6:11:27 PM

Originally posted by Mike_G:

Thanks for your input. What source(s) does your data come from? Not that I don't trust you, I'd just like to read for myself. My proposed SBR represents a sizeable investment (for me) and if the effective range is less than 100 yards with the best available ammo, then I'd have to rethink my build.



Here's a good place to start: click here
All hail Jeanne Assam!
jhud
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Posted: 2/13/2008 7:04:24 PM
I will bet a lower that it will still hurt at 150 yards, maybe more
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seahorse
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Posted: 2/13/2008 7:23:26 PM
As the barrel gets shorter, 1" becomes a larger percent of the total length. Thus the larger velocity drops at shorter lengths. The post by Molon bears this out.

Personally I can't see going below 14.5" unless the gun is dedicated for CQB.

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Combat_Jack
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Posted: 2/13/2008 7:43:18 PM
Effective range is dictated mainly by how far you can hit something.

If you want a compromise, get a 12.5.
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Posted: 2/14/2008 2:29:42 AM
When discussing terminal ballistics, "effective range" (also known as maximum effective range or maximum performance distance) has a specific meaning. From Hornady's Ammunition Test Report and Application Guide;

Maximum Performance Distance: This is based on bullet-retained velocity at distance and the associated expansion, fragmentation and penetration at that velocity. The distance given indicates the point out to which the terminal performance will closely match that as shown in the test results. (performed at close range)
Combat_Jack
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Posted: 2/14/2008 2:32:58 AM
That's a crock of shit. That means the effective range of M118LR is 0, since all it does is poke holes in shit.
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Mike_G
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Posted: 2/14/2008 9:26:11 AM

Originally Posted By seahorse:
Personally I can't see going below 14.5" unless the gun is dedicated for CQB.



Whats the average engagement range in yds/meters/feet of a CQB or urban combat scenario....no offense, but I'm looking for empirical data not opinions
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Posted: 2/14/2008 10:32:48 AM
[Last Edit: 2/14/2008 11:48:35 AM by DevL]
I know its not a 10.5" but it gives some insight...

Chronoed my LWRC 5.56 cold hammer forged, chrome lined, 11.75" barrel with 75 grain 5.56 TAP for two ten shot strings suppressed and unsuppressed.

Average muzzle velocity unsuppressed was 2450, suppressed was 2485 fps.

Slowest unsuppressed round was 2419
Fastest suppressed round was 2499

With a fragmentation velocity threshold of 2200 FPS that would be reached at 105 yards unsuppressed and 120 suppressed

Fragmentation threshhold is between 2250 and 2150 for the 5.56 T2 TAP. Worst case scenario would be unsuppressed 2419 and 2250 threshhold and just over 70 yards till fragmentation would not occur. Best case would be suppressed 2499 velocity and a threshhold of 2150 for 150 yards till fragmentation would not occur.

The barrel and ammo combo displayed a rather large velocity variation between rounds in each string. Ambient temp was 60 degrees F. Warmer weather would increase the range of fragmentation and colder weather would reduce it. Rounds were fired in 3-4 second intervals with a propensity for the rounds increasing in velocity as the chamber warmed but there were several slow rounds at the end of the strings and fast rounds in the beginging.

If you care about the range of fragmentation at all I would highly suggest a 11.5" or even a 12.5" barrel for a general purpose rifle. Shorter barrels also cause more bullet yaw as the bullet leaves the barrel. I had to stop testing of the above rifle when I had a 55 grain bullet yaw and bounce off the blast baffle, plow through all my baffles, and self destructed in the end cap. I am still waiting on my suppressor to return from a rebuild. This is a very rare occurance to be sure but it is more likely with shorter barrels (this comes from AAC).

I had my barrel made to give the absoloute shortest upper possible when combining a 9" midlength rail and an AAC SPR/M4 suppressor... thus the odd 11.75" length. It is only about an inch longer than a 10.5" M4-2000 combo unsuppressed or suppressed but I have a lot more railspace, much lower back pressure, and less noise and blast suppressed and unsuppressed with enough added range/velocity that the 1" extra length is totally worth it.

Past the fragmentation range the approx 1" long bullet still yaws and would give about the same performance as an AK74U (5.45x39 Krink) at the same range. The max effective range of the AK74U is listed at 300m... whatever that means.

I hope you realise you will NOT get 2500 fps from a 10.5" 5.56 chambered, chrome lined barrel. Heck it required a warm barrel, comfortable temps, a suppressor, and 11.75" of barrel to get ONE shot to 2499.
Mike_G
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Posted: 2/14/2008 2:37:44 PM
Thanks for all the info guys. I'd love an SBR for the fun and for a good CQB / SHTF tool. I aleady have a 16" AR. All of this discussion has led me to question whether to build an SBR and whether to stick with the 5.56 platform at all. Though the things that attracted me to the platform to begin with are low recoil, lighter weight, the ability to carry more ammo and the modularity (is that a word?) and availability of accessories. Maybe I should consider switching to the 6.8SPC.
HermanSnerd
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Posted: 2/14/2008 2:44:59 PM
Taggage

I wonder if the ballistics for a 10.5" would be about the same for a 10.3" like
the SEALs Mk18 Mod0 rifles?



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Mike_G
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Posted: 2/14/2008 3:20:31 PM

Originally Posted By HermanSnerd:
Taggage

I wonder if the ballistics for a 10.5" would be about the same for a 10.3" like
the SEALs Mk18 Mod0 rifles?





Thats what I was assuming. If the ballistics data I'm getting from this thread are accurate, why do the Navy Seals use the Mk18?
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Posted: 2/14/2008 3:56:02 PM
Maybe because there's more to killing people than the exact distance a given load is supposed to fragment/not fragment at.....
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Posted: 2/14/2008 4:02:36 PM

Originally Posted By Gunwritr:
Maybe because there's more to killing people than the exact distance a given load is supposed to fragment/not fragment at.....
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Mike_G
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Posted: 2/14/2008 4:55:11 PM
How about if Combat Jack and Molon wrestled for it. If Molon wins I don't build an SBR is Cactus Jack wins I build it.
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Posted: 2/14/2008 5:45:42 PM
[Last Edit: 2/14/2008 5:51:32 PM by ma96782]

Whats the average engagement range in yds/meters/feet of a CQB or urban combat scenario....no offense, but I'm looking for empirical data not opinions



No offense.......so........

That kind of "Talk"..........gets you a free trip to Iraq on the US Tax Payer's buck. Feel free to Join Up.

Don't forget to, e-mail us......."arm chair folks." Then again, it may not be "scientific enough" for you.

There is always someone screaming for, "REAL WORLD DATA." And, don't bother looking at the LE data cause..........I doubt they have much. Or, at least not enough to make firm statements as to, "effectiveness," with the stated weapon and ammo. Not to mention: bullet placement, environmental conditions, clothing worn and size/health/condition of the person who is shot. Then, you could also throw in the EMS and Hospital's efforts, that skewed the results.

Aloha, Mark
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