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Page AR-15 » Ammunition
AR Sponsor: bravocompany
Posted: 6/21/2016 11:19:53 PM EDT
Anyone use PMC-223 & PMC-556 Xtac equally?

Could use some advice from guys who shoot alot of this ammo.

I have nearly equal amounts of "PMC- (55gr) 223 Bronze" and "PMC-(62gr) 556 XTAC" at the moment, and plan to precisely zero both ARs (rifles mentioned at very bottom) using both rounds and hoping they will be very similar in POA/POI (atleast enough to be considered "fine tuned" for a 50/200 zero with each round) although I know it may vary at further distances.  

Well, I've had my eye on the another XTAC variant which is "PMC- (55gr/ XM193) 556" and wish I had of gotten that rather than 223 bronze originally, although didn't know the difference back then. Would like to try out the 55gr 556 Xtac being it's 556, but being I have a decent amount of the other 2 PMC offerings, I prefer not to have 3 diff variations stocked for sake of zero *especially if its not much different than the 223 Bronze unless considerably better.*

If familiar with this ammo, would "PMC (55gr) 556 XTAC" likely be closer in it's Trajectory/Zero to the "PMC- 223 (55gr) Bronze", OR closer to the "PMC-(62gr) 556 XTAC"??? Guess I'm asking if I am missing out on anything if I just get more 62gr Xtac and/or PMC 223.

At one point thought of selling the "223 55gr Bronze" to fund the "556 55gr Xtac. I will admit, the packaging and the 556 factor alone makes it appear superior.

May also vary between rifles, using an "M&P-15 Sport 16" Carbine (early version with the good Melonite-Nitrided "1/8 5R twist Barrel") and also use a "Spikes (Middie) LE" (w/ Heavy Carrier and 1/7 twist- Chrome lined Barrel.)

Sorry for lengthy post, all advice would be appreciated!
Link Posted: 6/21/2016 11:36:09 PM EDT
[#1]
No experience with the Xtac, but the PMC Bronze is some pretty good stuff. There will more than likely be a POI shift due to the different bullet weights. I like to use the PMC Bronze to get my AR on paper and near the point of aim, then use some good stuff, Black Hills, Hornady etc for groups.
Link Posted: 6/22/2016 12:14:35 AM EDT
[#2]
I would think the PMC would be closer to the 55gr XTAC because of the bullet weight.
Link Posted: 6/22/2016 12:55:25 AM EDT
[#3]
55 grain yes, 62 grain no.
Link Posted: 6/22/2016 1:20:54 AM EDT
[#4]
I bought 2K of the PMC-(62gr) 556 XTAC a while back.

I like it a lot. High quality looking, good accuracy (~2") and pretty clean shooting.

I would buy it again.
Link Posted: 6/22/2016 1:40:20 AM EDT
[#5]
I love X-Tac ammo, both 55g and 62g.  Great stuff.
Link Posted: 6/22/2016 4:49:37 PM EDT
[#6]
Ever compared the 2 Xtac offerings? If so, ever compared 55gr Xtac to 223 Bronze (non xtac)?

To others, thanks for advice, and I know all rifles are different but is there normally a drastic difference in the zero using 55gr 223 VS 62gr 556?

Want to do a 50yard zero opposed to the 25 it was on, I know the the 62gr will likely hit higher or lower than the 223 further out, but hoping at 50-100yards it will be only an inch or so different. Then again, not sure if this ammo is the type to stay super tightly grouped but have always heard great things and seemed great everytime I've used it at a 25yd indoor range.

Will check myself when I find a nice outdoor range but figured I would ask in advance, I like things to be compatible and especially if buying more, I'd like to use the 2 that are the most consistent with each other.
Link Posted: 6/22/2016 7:20:33 PM EDT
[#7]
Link Posted: 6/22/2016 10:17:44 PM EDT
[#8]
I've shot about 5K of X-Tac M855 from 2011 and you're not going to do anything precisely with it.  It's 3-4MOA ammo tops.  

I've had much better results with Federals XM stuff.
Link Posted: 6/23/2016 1:10:02 AM EDT
[#9]
PMC 5.56mm 62 Grain X-TAC Ammunition







PMC’s 62 grain X-TAC ammunition is loaded in brass cases that have the annealing iris still visible.  The 62 grain projectile  has a copper jacket construction with a lead core and a steel insert in the ogive.  The tip of the bullet is painted green.  The case mouth is taper crimped into the cannelure of the bullet and the case-mouth is sealed with asphalt sealant.  















The boxer primers are sealed and crimped and the load is charged with “ball” powder.









(The individual squares in the red grid below are 1/10th of an inch.)






After reading the above description of this PMC ammunition, some of you might be thinking, “I wonder how this ammunition compares to M855?”  So, let’s compare!


The US mil-spec for M855 (MIL-C-63989C [Amendment 4]) states that the average velocity of the cartridges “shall be 3,020 feet per second (fps) plus or minus 40 fps at 78 feet from the muzzle of the weapon. The standard deviation of the velocity shall not exceed 40 fps.”  This specification is for a 20” barrel and depending upon variables equates to a muzzle velocity of approximately 3105 FPS (plus or minus 40 FPS.)

As an aside, after reading the above specification, some of you may be wondering, “Why 78 feet from the muzzle?”  The answer to that question is that this specification is simply an historical hold-over from the days when “circuit” chronographs (e.g. Le Boulenge Chronograph and the Aberdeen Chronograph) were used at Aberdeen Proving Ground, Frankford Arsenal and Springfield Armory.  These types of chronographs required a significant distance between their first and second screens to produce accurate results.

As an example, when using the Boulenge Chronograph, the first screen of the chronograph was placed 3 feet in front of the muzzle and the second screen was placed 150 feet beyond the first screen.  For those of you who might not be aware of the following fact; chronographs determine the velocity of the bullet at a point that is midway between the first and the second screen (i.e. not at the location of the first screen).  Therefore, with the above spacing, the velocity of the bullet is determined for a point that is 75 feet from the first screen.  So, add the three feet (from the muzzle to the first screen) to the 75 feet (the midway point of the screens) to obtain the “78 feet from the muzzle” distance.














I chronographed the PMC 62 grain X-TAC ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered 20” Colt M16A2 barrel.









Chronographing was conducted using an Oehler 35-P chronograph with “proof screen” technology. The Oehler 35P chronograph is actually two chronographs in one package that takes two separate chronograph readings for each shot and then has its onboard computer analyze the data to determine if there is any statistically significant difference between the two readings.  If there is a difference, the chronograph “flags” the shot to let you know that the data is invalid.  There was no invalid data flagged during this testing.

The velocity stated below is the muzzle velocity as calculated from the instrumental velocity using Oehler’s Ballistic Explorer software program. The string of fire consisted of 10 rounds over the chronograph.














Each round was single-loaded and cycled into the chamber from a magazine fitted with a single-load follower. The bolt locked-back after each shot allowing the chamber to cool in between each shot. This technique was used to mitigate the possible influence of “chamber-soak” on velocity data. Each new shot was fired in a consistent manner after hitting the bolt release.  Atmospheric conditions were monitored and recorded using a Kestrel 4000 Pocket Weather Tracker.









Atmospheric conditions

Temperature:  78 degrees F
Humidity:  54%
Barometric pressure:  29.99 inches of Hg
Elevation:  950 feet above sea level


The muzzle velocity for the 10-shot string of the PMC 62 grain X-TAC ammunition fired from the 20” Colt barrel was 3073 FPS with a standard deviation of 14 FPS and a coefficient of variation of 0.46%.  For comparison, IMI M855 chronographed from the same 20” Colt barrel had a muzzle velocity of 3110 FPS with a standard deviation of 21 FPS and a coefficient of variation of 0.68%.

For those of you who might not be familiar with the coefficient of variation (CV), it is the standard deviation, divided by the mean (average) muzzle velocity and then multiplied by 100 and expressed as a percentage. It allows for the comparison of the uniformity of velocity between loads in different velocity spectrums; e.g. 77 grain loads running around 2,650 fps compared to 55 grain loads running around 3,250 fps.  

For comparison, the US mil-spec for M855 allows for a coefficient of variation of up to approximately 1.3%, while one of my best 77 grain OTM hand-loads, with a muzzle velocity of 2639 PFS and a standard deviation of 4 FPS, has a coefficient of variation of 0.15%.









….





The accuracy specification from the US mil-spec for M855 (MIL-C-63989C) states that the average vertical standard deviation and the average horizontal standard deviation shall be “no greater than 1.8 inches at 200 yards using an indoor range.”* The accuracy testing is conducted using machine rested, bolt-action, heavy test barrels.  All other things being equal (which of course they seldom are) this accuracy specification equates to an average vertical standard deviation and an average horizontal standard deviation of 0.9 inches at 100 yards (the distance at which I evaluated the accuracy of the PMC 62 grain X-TAC ammunition.)


I conducted an accuracy (technically, precision) evaluation of the PMC 62 grain X-TAC ammunition following my usual protocol.  This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any Group Reduction Techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Also, a control group was fired from the test-rifle used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrel. Pictures of shot-groups are posted for documentation.

All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.









The Wind Probe.






The test vehicle for this evaluation was one of my semi-automatic precision AR-15s with a 20” stainless-steel Lothar Walther barrel.  The barrel has a 223 Wylde chamber with a 1:8” twist.  Prior to firing the 62 grain X-TAC ammunition, I fired a 10-shot control group using hand-loads topped with a 62 grain OTM bullet.  That group had an extreme spread of 0.83”.














Next, three 10-shot groups of the 62 grain X-TAC load were fired in a row with the resulting extreme spreads:

2.76”
2.24”
3.07”

for a 10-shot group average extreme spread of 2.69”.  The average horizontal standard deviation was 0.66” and the average vertical standard deviation was 0.76”.  The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group.  The mean radius for the 30-shot composite group was 0.88”.


The smallest 10-shot group . . .







The 30-shot composite group . . .






….

* There is also a 600 yard accuracy specification for M855, that is greater than the mathematical equivalent of the 200 yard specification.


....
Link Posted: 6/23/2016 6:05:31 PM EDT
[#10]
Awesome info and tests!!!

How does M855 differ in the first few paragraphs explaining the Iris, tip being painted, and ball powder?

Any pics of comparison?
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