AR15.Com Archives
 M855 M193 Muzzle Velocity Report -- Does this sound right?
MedCpt  [Member]
8/25/2010 5:45:45 AM EST
A guy is claiming with his M4 16" barrel AR his muzzle velocity (15 feet away) is

1) 3450 fps with M193 (BC .243)
2) 3350 fps with M855 (BC .304)

Doesn't sound right to me...Anybody got any numbers they've recorded themselves? I think this guy is little off on his numbers...
Paid Advertisement
--
CAR-AR-M16  [Team Member]
8/25/2010 5:53:42 AM EST
Look here: http://www.ar15.com/content/page.html?id=213
Eric802  [Team Member]
8/25/2010 6:00:27 AM EST
Yeah, those look a few hundred FPS high from a 16" barrel.
Zhukov  [Moderator]
8/25/2010 6:41:51 AM EST

Originally Posted By CAR-AR-M16:
Look here: http://www.ar15.com/content/page.html?id=213

That Ammo FAQ dude is way cool for putting that up.
MedCpt  [Member]
8/25/2010 7:02:13 AM EST
Thanks for chart. I think his Ballistic Coefficients are off, I know these vary with Muzzle Velocity and I've seen those at lower velocities in other places. Wondering if he's making it up?

Anybody got 16" AR barrel chrono they've done themselves (at muzzle, 15ft, or 78ft) for these 2 rounds (i.e., the M855, M193) and the calculated ballistic coefficients you got at those velocities?..
steven_uk  [Team Member]
8/25/2010 7:17:53 AM EST
I doubt his 16" M855 figures are correct.

It depends on the barrel but i'd say sub 3000fps.

My Chrono results with M855:

14.5" 2900fps
20" 3150fps

reelserious  [Team Member]
8/25/2010 8:09:59 AM EST
M855 will give you about 3000 fps from 16 inch and M193 about 3100 fps. That's what I get in FL at sea level on a 95 deg day. Have tested it many times.
Forest  [Moderator]
8/25/2010 8:10:07 AM EST
Originally Posted By MedCpt:
Thanks for chart. I think his Ballistic Coefficients are off, I know these vary with Muzzle Velocity and I've seen those at lower velocities in other places. Wondering if he's making it up?

The BCs are fine. The M193 BC is the one I use, and the M855 one you have listed is VERY close to the one I use.

Anybody got 16" AR barrel chrono they've done themselves

Plenty of us have run 10 to 30 round strings of those rounds through the chrono. His MVs are WAY WAY over spec, but the BCs are fine.
MedCpt  [Member]
8/25/2010 8:41:31 AM EST
Correct me if I'm wrong but the Ballistic Coefficient (BC) will vary according to muzzle velocity. The BC for M855 in a 20" barrel should be different than in a 16", due to shorter barrel length and lower muzzle velocity. I've seen that BC for a 20" not 16" barrel...
WayOutWest  [Member]
8/25/2010 8:50:12 AM EST
Originally Posted By MedCpt:
Correct me if I'm wrong but the Ballistic Coefficient (BC) will vary according to muzzle velocity. The BC for M855 in a 20" barrel should be different than in a 16", due to shorter barrel length and lower muzzle velocity. I've seen that BC for a 20" not 16" barrel...


You are wrong. BC is constant regardless of velocity.

http://en.wikipedia.org/wiki/Ballistic_coefficient
Market_Garden  [Member]
8/25/2010 8:59:15 AM EST
Originally Posted By WayOutWest:
Originally Posted By MedCpt:
Correct me if I'm wrong but the Ballistic Coefficient (BC) will vary according to muzzle velocity. The BC for M855 in a 20" barrel should be different than in a 16", due to shorter barrel length and lower muzzle velocity. I've seen that BC for a 20" not 16" barrel...


You are wrong. BC is constant regardless of velocity.

http://en.wikipedia.org/wiki/Ballistic_coefficient


Actually, you're wrong. Do a little more reading. BC definitely changes with velocity.
Forest  [Moderator]
8/25/2010 9:03:11 AM EST
Originally Posted By MedCpt:
Correct me if I'm wrong but the Ballistic Coefficient (BC) will vary according to muzzle velocity.

You're right it does, but not to the exent you think.

The BC for M855 in a 20" barrel should be different than in a 16", due to shorter barrel length and lower muzzle velocity. I've seen that BC for a 20" not 16" barrel...

The BC can vary depending on the velocity of the projectile (at the specific velocity/moment in time). The difference in the BC between a 20" barrel and a 14.5" barrel at the muzzle isn't enough to worry about. The difference is absolutely meaningless for all practical purposes.

Now if you want to build a 24" upper and shoot some whiz bang bullets loadded REALLY hot, then we'll talk about adjusting the BC for that situation. But for the ammo/rifle combinations we're discussing the BC is fixed for all practical purposes.
WayOutWest  [Member]
8/25/2010 9:04:04 AM EST
Originally Posted By Market_Garden:
Originally Posted By WayOutWest:
Originally Posted By MedCpt:
Correct me if I'm wrong but the Ballistic Coefficient (BC) will vary according to muzzle velocity. The BC for M855 in a 20" barrel should be different than in a 16", due to shorter barrel length and lower muzzle velocity. I've seen that BC for a 20" not 16" barrel...


You are wrong. BC is constant regardless of velocity.

http://en.wikipedia.org/wiki/Ballistic_coefficient


Actually, you're wrong. Do a little more reading. BC definitely changes with velocity.


So can you tell me why in every reloading book I own, the BC for each bullet is listed without reference to velocity?
Forest  [Moderator]
8/25/2010 9:05:54 AM EST
Originally Posted By WayOutWest:
Originally Posted By MedCpt:
Correct me if I'm wrong but the Ballistic Coefficient (BC) will vary according to muzzle velocity. The BC for M855 in a 20" barrel should be different than in a 16", due to shorter barrel length and lower muzzle velocity. I've seen that BC for a 20" not 16" barrel...


You are wrong. BC is constant regardless of velocity.

http://en.wikipedia.org/wiki/Ballistic_coefficient


Did you read more than the first couple of sentences? Check further down:

The BC changes during a projectile's flight and stated BCs are always averages for particular range-speed regimes.
Market_Garden  [Member]
8/25/2010 9:07:47 AM EST
Originally Posted By WayOutWest:
Originally Posted By Market_Garden:
Originally Posted By WayOutWest:
Originally Posted By MedCpt:
Correct me if I'm wrong but the Ballistic Coefficient (BC) will vary according to muzzle velocity. The BC for M855 in a 20" barrel should be different than in a 16", due to shorter barrel length and lower muzzle velocity. I've seen that BC for a 20" not 16" barrel...


You are wrong. BC is constant regardless of velocity.

http://en.wikipedia.org/wiki/Ballistic_coefficient


Actually, you're wrong. Do a little more reading. BC definitely changes with velocity.


So can you tell me why in every reloading book I own, the BC for each bullet is listed without reference to velocity?


Because most places don't bother to calculate the BCs for velocity ranges. Check out Sierra's website and look up bullet BCs, they actually take the time to list the BCs for velocity ranges. Also, if you're using a drag profile like G7 that more accurately models the flight of the style of bullet we're actually shooting then you will find that the multi-BC listings aren't as important as when companies use G1 drag profiles to model modern bullets. Most bullet companies are still using G1 profiles to list BCs for their stuff, some places like Berger and other specialty manufacturers are using G7 now though, which is a good thing. I think some of the resistance to using G7 comes into play from a marketing standpoint where people who don't understand how it all works see G7 numbers, which are lower than G1 numbers and think that the bullet listed with the G7 number isn't as good as one listed with a higher (but likely less well suited G1 number.)
WayOutWest  [Member]
8/25/2010 9:08:44 AM EST
Ok, so they change, just not enough to statistically matter. Does that really make a difference?
Forest  [Moderator]
8/25/2010 9:09:00 AM EST
Originally Posted By WayOutWest:
.
So can you tell me why in every reloading book I own, the BC for each bullet is listed without reference to velocity?


Because you don't read the Sierra Reloading Book? Sierra publishes the BC for bullets for a variety of velocity ranges - go check it out on their website.

However as pointed out for practical purposes you use the BC as a fixed 'average' for the flight.

ETA: Whoops looks like someone covered that already.
Market_Garden  [Member]
8/25/2010 9:11:51 AM EST
Originally Posted By WayOutWest:
Ok, so they change, just not enough to statistically matter. Does that really make a difference?


It definitely matters if you're shooting longer distances. Anyways, my pointing out that the BC changes was just to make sure people are reading correct information.
WayOutWest  [Member]
8/25/2010 9:16:43 AM EST
.006 is what I found the variation from 0-3000+ fps to be in most .224 bullets. If that makes a difference to you, you must be a much better shot than me.

ETA I think that a nick in the jacket would have more of an effect.
MedCpt  [Member]
8/25/2010 9:22:26 AM EST
Yes I've seen references where they will list 3 different BC's for the same round and it does vary with velocity. Not sure the Sierra website has the military round BC's. Yes with the G7 noticed they are lower which throws some people.

Reelserious and Steven on your MV's how far is that from the muzzle? 15 ft, 78ft or at muzzle? Thanks
Market_Garden  [Member]
8/25/2010 9:22:56 AM EST
Originally Posted By WayOutWest:
.006 is what I found the variation from 0-3000+ fps to be in most .224 bullets. If that makes a difference to you, you must be a much better shot than me.

ETA I think that a nick in the jacket would have more of an effect.


You must not have looked hard. Here's Sierra's numbers for the 77SMK

.372 @ 3000 fps and above
.362 between 2500 and 3000 fps
.362 between 1700 and 2500 fps
.343 @ 1700 fps and below

That's a little more than .006 variation.
MedCpt  [Member]
8/25/2010 9:32:17 AM EST
Was referring to the 62 grain M855 . Will recheck but IIRC was not on the list when I looked... 77 grain yes as would be expected with their SMK BTHP, thanks..
mathecb  [Team Member]
8/25/2010 9:58:19 AM EST
Originally Posted By Market_Garden:
Originally Posted By WayOutWest:
.006 is what I found the variation from 0-3000+ fps to be in most .224 bullets. If that makes a difference to you, you must be a much better shot than me.

ETA I think that a nick in the jacket would have more of an effect.


You must not have looked hard. Here's Sierra's numbers for the 77SMK

.372 @ 3000 fps and above
.362 between 2500 and 3000 fps
.362 between 1700 and 2500 fps
.343 @ 1700 fps and below

That's a little more than .006 variation.


From Bryan Litz's Book:

77SMK
1500fps G1=.338
2000fps G1=.372
2500fps G1=.381
3000fps G1=.394

Average G1 = .371
Variation G1 = .056

Average G7 = .190
Variation G7 = .006


G7 is what I go by.
Forest  [Moderator]
8/25/2010 9:59:42 AM EST
Originally Posted By Market_Garden:
Originally Posted By WayOutWest:
.006 is what I found the variation from 0-3000+ fps to be in most .224 bullets. If that makes a difference to you, you must be a much better shot than me.

ETA I think that a nick in the jacket would have more of an effect.


You must not have looked hard. Here's Sierra's numbers for the 77SMK

.372 @ 3000 fps and above
.362 between 2500 and 3000 fps
.362 between 1700 and 2500 fps
.343 @ 1700 fps and below

That's a little more than .006 variation.


Yes from the most extream to the least extream. However reality is you won't see that in 99.999% of shooting an AR. I've never seen someone push the 77gr SMK to 3000fps from a 5.56 AR (don't think it's possible, you'd have to wildcat to get those numbers in an AR).

With M193 & M855, the rounds the OP was discussing is a known finite amount. Between accuracy and typical issue weapon limitation you're really looking at a max range of 600M or so for a point target. We're not talking really long range shooting or high accuracy with those rounds.
steven_uk  [Team Member]
8/25/2010 11:03:47 AM EST
Originally Posted By MedCpt:
Yes I've seen references where they will list 3 different BC's for the same round and it does vary with velocity. Not sure the Sierra website has the military round BC's. Yes with the G7 noticed they are lower which throws some people.

Reelserious and Steven on your MV's how far is that from the muzzle? 15 ft, 78ft or at muzzle? Thanks


Chrono was 10ft from the muzzle
Paid Advertisement
--