M855A1 Accuracy and Velocity

[Molon]

M855A1 Accuracy and Velocity

M855A1 ammunition is manufactured at the Lake City Army Ammunition Plant near Independence, Missouri. The lot of Lake City M855A1 ammunition that was evaluated for this article was manufactured in January of 2021. There were no malfunctions of any kind for this ammunition in any of the four barrels that were used in this evaluation.

M855A1 is packaged in kraft boxes with 30 rounds in each box. The rounds are on stripper clips with 10 rounds per clip.

The M855A1 cartridge has a nominal over-all length of 2.250”. This over-all length gives the A1 projectile a jump of 0.132” to the lands of a Colt 5.56mm NATO chamber.

M855A1 is loaded in Lake City brass. The brass cases have the annealing iris still visible. The headstamp for this lot reads:”LC 21” along with the NATO cross. The case-head stamp exhibits the octal station identifiers used on Lake City SCAMP machinery. The primer pocket has four “stab” crimps and a minimal amount of sealant. The case mouth has a generous amount of asphalt sealant and is crimped into a cannelure on the bullet.

Lake City M855A1 ammunition is charged with the St. Marks Powder SMP-842, which is a flattened ball powder. Sampled powder charges had an average weight of 26.4 grains.

The M855A1 bullet is considered a 62 grain round, however, sampled bullets had an average weight of 62.6 grains. The M855A1 projectile is constructed from three different components; a solid copper core, an exposed steel penetrator and a reverse-drawn copper jacket that holds the other two components together. Since this bullet does not have a lead core, the only thing that fragments upon terminal impact is the copper jacket.

It has been reported that with early lots of M855A1, it was possible to “spin” the steel penetrator inside the copper jacket with your fingers. This was not the case with any of the current rounds that I sampled.

The M855A1 projectile has a lower specific gravity than conventional lead-core, copper jacketed bullets and is significantly longer than the legacy M855 projectile. The A1 projectile has a nominal length of 1.00”. According to Ballistic Performance of Rifle Bullets by Bryan Litz the G1 ballistic coefficient of M855A1 is 0.291. The same reference states that M855A1 has a nominal gyroscopic stability factor of 1.41 when fired from a barrel with a 1:8" twist and 1.85 when fired from a barrel with a 1:7" twist.

Velocity


I chronographed the Lake City M855A1 ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered, 20” Colt A4 barrel with a 1:7” twist.

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 fired and then utilizes its onboard computer to analyze the data to determine if there is any statistically significant abnormality in the readings. If the readings are suspect, the chronograph “flags” the shot to let you know that the data is invalid. There was no invalid data flagged during this testing.

The velocities stated below are the muzzle velocities as calculated from the instrumental velocities using Oehler’s Ballistic Explorer software program. The strings 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: 76 degrees F
Humidity: 47%
Barometric pressure: 30.09 inches of Hg
Elevation: 950 feet above sea level

The muzzle velocity for the 10-shot string of the Lake City M855A1 ammunition fired from the 20” Colt barrel was 3131 FPS with a standard deviation of 18 FPS and a coefficient of variation of 0.59%.

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 mil-spec for M193 allows for a coefficient of variation of approximately 1.2%, 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%.

I also chronographed the Lake City M855A1 ammunition from three different 14.5” barrels in the same manner as described above for the 20” Colt barrel. Chronographing of the 14.5” barrels was conducted immediately after the chronographing for the 20” barrel.


A 10-shot string of the Lake City M855A1 fired from a 14.5” Hodge Defense barrel had a muzzle velocity of 2939 FPS with a standard deviation of 23 FPS.

A 10-shot string of the M855A1 fired from a 14.5” Colt M4A1 SOCOM barrel had a muzzle velocity of 2949 FPS with a standard deviation of 17 FPS.

A 10-shot string of the M855A1 fired from a 14.5” Bravo Company ELW barrel had a muzzle velocity of 2966 FPS with a standard deviation of 19 FPS.

The muzzle velocities for the Lake City M855A1 are summarized in the table below.

For comparison, the next two tables show the muzzle velocities for legacy military 5.56mm ammunition that also uses 62 grain projectiles: M855 and MK318 Mod 0.

continued . . .

 

[Molon]

Accuracy


I conducted an accuracy (technically, precision) evaluation of the Lake City M855A1 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.

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 used. 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 accuracy 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 Lake City M855A1, I fired a 10-shot control group using match-grade hand-loads topped with the Sierra 77 grain MatchKing (without a canelure). That group had an extreme spread of 0.56”.

the control group . .

Three 10-shot groups of the Lake City M855A1 ammunition were fired in a row with the resulting extreme spreads:

1.78”
2.65”
1.78”

for a 10-shot group average extreme spread of 2.07”. 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 0.63”.


The smallest 10-shot group . . .

The 30-shot composite group . . .

In the category of useless trivia, the M855A1 bullet cuts the cleanest holes in paper targets of any 5.56mm/223 Remington that I’ve ever tested. It’s like wad-cutters for the AR-15.

I also fired a 10-shot group at 100 yards off of sand-bags from each of the 14.5” barrels that were used in chronographing the M855A1 ammunition.

A 10-shot group fired from the 14.5” Colt M4A1 SOCOM barrel had an extreme spread of 1.85”.

A 10-shot group fired from the 14.5” Bravo Company ELW barrel had an extreme spread of 2.15”.

A 10-shot group fired from the 14.5" Hodge Defense barrel had an extreme spread of 2.51".

Lastly, for any Internet Commandos in our viewing audience today, here’s a pic of a sub ¾ MOA group of the Lake City M855A1 ammunition fired at 100 yards. The group has an extreme spread of 0.59”.

Part 2

Hand-Loaded M855A1 Accuracy


When M855A1 was introduced, we were told by people with “inside information” that this new load produced “match-like” accuracy, yet none of these people where ever able to show statistically significant data to support this claim. The test results that I obtained with M855A1 certainly didn’t show “match-like” accuracy.

The Crane Naval Surface Warfare Center has done extensive testing with M855A1 fired from AR-15s mounted in a heavy, sliding machine-rest test fixture. The Crane Naval Surface Warfare Center is involved in developing special munitions and weapons for our warfighters. They’re not interested in sales hype and propaganda; they’re only interested in facts. They’re not driven by profit margin; their goal is providing our Special Operating Forces with the best tools for accomplishing their missions. When it comes to evaluating the accuracy of ammunition Crane uses 10-shot groups.

With newly barreled upper receiver groups mounted in the heavy sliding machine-rest test fixture, M855A1 was only able to produce a 10-shot group average extreme spread of 2.74” at 100 yards with an average mean radius of 0.85”. With a round count of 3,600 rounds through the barrels, M855A1 was only able to produce 10-shot groups with an average extreme spread of 3.84” at 100 yards with an average mean radius of 1.10”.

The Lothar Walther barrel that I used to test the M855A1 for this evaluation had approximately 3,350 rounds through it at the beginning of my M855A1 testing and as we saw it produced an average 10-shot group extreme spread of 2.07” at 100 yards. A 30-shot composite group of the M855A1 from the Lothar Walther barreled AR-15 had a mean radius of 0.63”.

People are often quick to point out that the lack-luster accuracy of legacy M855 manufactured at Lake City is due among other things to the fact that M855 is composed of three different components; the lead core, the steel penetrator and the copper jacket, yet people seem to gloss over the fact that M855A1 is also composed of three different components; the copper core, the exposed steel penetrator and the copper jacket.

We know that the M855A1 that the US Army based their accuracy claims on was not manufactured on the SCAMP machinery at Lake City, but rather the slower BAM machinery. The speed of the SCAMP machinery is significantly faster than the older BAM machinery.

The M855A1 that I evaluated was produced on the SCAMP machinery. These M855A1projectiles themselves showed quite a bit of variation. As an example, the base to ogive measurements were all over the map.

The picture below shows two M855A1 bullets that I pulled from the lot of ammunition that I tested. The bullet on the left shows a properly shaped base. Notice the beveled heel and the flat base. The bullet on the right has a “ridge” running around the bottom of the bullet and the base is recessed. Apparently, the speed of the SCAMP machinery comes at a cost.

To be continued . . .

…

 

[the monk]

As always thank you for your time in putting all this together.

I was surprised by the accuracy or lack thereof of the Hodge.

 

[Clayman]

Hodge the slowest 14.5 with the largest group. Interesting, a lot of hype around those barrels about being faster. Clearly not in your case.

 

[db2000]

Excellent review.
These are a couple targets I found in my pic collection of 855A1 through .223 Wylde chambered Seekins ARs w/ Magnetospeed V3. 3037 fps from the 16 Proof. Haven’t chrono’d the 20” yet unfortunately.
Proof CF 16” 1:8 85F that day
Criterion SS HBAR 20” 1:8 (pic is mislabeled at 22”) 70F that day

 

[Molon]

I was surprised by the accuracy or lack thereof of the Hodge.

https://www.snipershide.com/shooting/threads/colt-m4a1-socom-barrel-accuracy-another-look.6991100/


https://www.snipershide.com/shooting/threads/bravo-company-14-5”-elw-accuracy-a-quick-look.6989951/


Hodge Defense 14.5" barrel: A quick look





...

 

[Molon]

Hodge the slowest 14.5 . . ..

some additional data on that topic . . .

Originally Posted By DevilDoc602:
Proven, repeatable velocities of common off the shelf 855 (from Hodge rifles) . . .

Proven, repeatable velocities of two different lots of common, off the shelf M855, chronographed from five different Colt barrels.

Originally Posted By DevilDoc602:
Black Hills MK262 (from Hodge rifles)

Black Hills MK262 chronographed from three different Colt barrels.

…..

 

[346ci]

Great detailed write up, thanks for sharing.

Anyone have a source for this ammo? Can PM if needed.

 

[Huskydriver]

Great detailed write up, thanks for sharing.

Anyone have a source for this ammo? Can PM if needed.

 

[TheOE800]

Hodge the slowest 14.5 with the largest group. Interesting, a lot of hype around those barrels about being faster. Clearly not in your case.

They are mass produced by FN and not QCed by Jim in his basement. Hodge is what it always was: hype.

 

[bfoosh006]

Very informative post !

As always Thank You for your time and posting. And Thanks to whomever supplied the ammo ! ( I can't remember at the moment )

I always enjoy reading Molon's "just the fact's" posts.

So much for the original USGI claims of " Match like accuracy " .... Lol

 

[gxer]

Did they reduce the load on recent production M855A1? Early report on this round suggested it was loaded super hot

The M855A1

We have discussed doing a video on the M855A1 cartridge for quite some time. Looking over all the information it seemed to make more sense to do it in a blog article where it could be articulated...

smallarmssolutions.com

 

[Molon]

Did they reduce the load on recent production M855A1? Early report on this round suggested it was loaded super hot

The M855A1

We have discussed doing a video on the M855A1 cartridge for quite some time. Looking over all the information it seemed to make more sense to do it in a blog article where it could be articulated...

smallarmssolutions.com

I chronographed a lot of this ammunition from 2014 that was within 10 FPS of the 2021 lot tested for this thread.

...

 

[gxer]

It has been reported that with early lots of M855A1, it was possible to “spin” the steel penetrator inside the copper jacket with your fingers. This was not the case with any of the current rounds that I sampled.

Just tried one, I can't spin it freely but I can definitely feel it rotating in the jacket... maybe less than 1 degree

 

[DeathBeforeDismount]

This is a round that concerns me. Its making its way around outside of the military and guys who have plates, you better have a ST or A1 rated plate. This is a NASTY round that is designed to defeat most body armor.

It makes M885 look anemic.

 

[TapRackBang]

Appreciate the time you took to write this up.

 

[TonyTheTiger]

I was surprised by the accuracy or lack thereof of the Hodge.

Why? I've always heard them described as mil-spec++, so super tough but with no pretensions of being more accurate or in any way a precision rifle.

 

[the monk]

Why? I've always heard them described as mil-spec++, so super tough but with no pretensions of being more accurate or in any way a precision rifle.

I have a 12.5 Hodge that generally runs fast and is typically sub moa (5 shot groups with 77 OTM Match). Just seemed odd to me that a 14.5 would be less accurate around a round Hodge said the barrels were built for.

 

[WindstormSCR]

This is a round that concerns me. Its making its way around outside of the military and guys who have plates, you better have a ST or A1 rated plate. This is a NASTY round that is designed to defeat most body armor.

It makes M885 look anemic.

possibly, though I think a good subset of folks are more worried about the guy with grandpappy's deer rifle and anything that will handle that will also handle 855A1 pretty well. My minimum has always been multiple hits of M80 which is usually the ST stuff or straight up IVs

 

[DeathBeforeDismount]

possibly, though I think a good subset of folks are more worried about the guy with grandpappy's deer rifle and anything that will handle that will also handle 855A1 pretty well. My minimum has always been multiple hits of M80 which is usually the ST stuff or straight up IVs

The AR is the by far the most prolific rifle in America and people who try to get into gun fights with grandpapies deer rifle, won't live long enough to get well aimed shots unless its an ambush situation. Its not the movies.

 

[the monk]

The AR is the by far the most prolific rifle in America and people who try to get into gun fights with grandpapies deer rifle, won't live long enough to get well aimed shots unless its an ambush situation. Its not the movies.

I take it your not in the mountains much. As someone that is pretty good with an AR and taken numerous classes I am very worried of the guys with deer rifles that could set up an ambush and block off whole sections of land that you need to get around.

 

[DeathBeforeDismount]

I take it your not in the mountains much. As someone that is pretty good with an AR and taken numerous classes I am very worried of the guys with deer rifles that could set up an ambush and block off whole sections of land that you need to get around.

LOL, litterly spent half the day hiking up in the mountains.

Have you seen the average to above average hunter/shooter? We see them come out and try PRS all the time, its a shitshow.

 

[FatBoy]

Usage Probably should have it’s own thread.

On point, I have never shot this but have very good first hand account about some group guys taking this stuff to 1k with their 14.5”/ATACR guns and doing daily well. Was talking about it yesterday with another guy who worked in Astan after he retired and he got to shoot some. Said it’s good shit compared to most issue ammo and also mentioned it’s very accurate, considering what it is. He is a national rifle team coach and one of the best prone shooters I know.

I wonder how this round is going to treat barrels? For the assaulter, probably not a big deal. If we get back to a DMR situation with 5.56 this concerns me some, though I was quickly reminded that the majority of big Army only shoots twice a year. Can’t argue with that, but I am wondering how long a stainless barrel will stay accurate with this round. My mk12 is opening up at 600y at 2200 rounds with just handloads 77s going 2600. Can we expect to lose distance accuracy in 2000 rounds or less?

I guess if the Army was worried about it the new Sig round wound have never been considered. That shit is going to tear through barrels like a hot 22-250.

 

[db2000]

Usage Probably should have it’s own thread.

On point, I have never shit this but have very good first hand account about some group guys taking this stuff to 1k with their 14.5”/ATACR guns and doing daily well. Was talking about it yesterday with another guy who worked in Astan after he retired and he got to shoot some. Said it’s good shit compared to most issue ammo and also mentioned it’s very accurate, considering what it is.

I wonder how this round is going to treat barrels? For the assaulter, probably not a big deal. If we get back to a DMR situation with 5.56 this concerns me some, though I was quickly reminded that the majority of big Army only shoots twice a year. Can’t argue with that, but I am wondering how long a stainless barrel will stay accurate with this round. My mk12 is opening up at 600y at 2200 rounds with just handloads 77s going 2600. Can we expect to lose distance accuracy in 2000 rounds or less?

Not sure why this would be shot past 600 yards anyway. Seems like a moot point or just mental masturbation.

 

[FatBoy]

Not sure why this would be shot past 600 yards anyway. Seems like a moot point or just mental masturbation.

Maybe. Certainly not it’s wheelhouse. That said, if it could perform like m262 as general issue ammo that really would be something. As hard as it is I wonder about any kind of wound channel past maybe 300y but the 77SMk is pretty anemic last 400 so…..

 

[the monk]

LOL, litterly spent half the day hiking up in the mountains.

Have you seen the average to above average hunter/shooter? We see them come out and try PRS all the time, its a shitshow.

I get that but I think you are talking about (may be wrong) their gun handling in somewhat close combat say within 100 yards. Which I would not disagree that they are clueless. That being said, it's not very difficult for a few guys to block roads with cars or trees and sit out 6-700 yards away. Its an effective way to block off whole areas of land especially in rural communities where you may have to drive an hour or more to go around a roadblock, especially if you are not familiar with the area.

Edited to add: Us being on opposite coast may have something to do with this. My rednecks may shoot a little better than yours.

 

[smoothy8500]

I wonder how this round is going to treat barrels? ... but I am wondering how long a stainless barrel will stay accurate with this round. My mk12 is opening up at 600y at 2200 rounds with just handloads 77s going 2600.

Unfortunately, most match barrels start to show dispersion at 600 yards around 2k rounds regardless of which projectile used. Typically, Highpower shooters switch out their barrel at 2k to avoid an issue.

 

[FatBoy]

Unfortunately, most match barrels start to show dispersion at 600 yards around 2k rounds regardless of which projectile used. Typically, Highpower shooters switch out their barrel at 2k to avoid an issue.

Yup, depending on caliber. In this case, 5.56 you’re exact right. I shot SR for years and still shoot prone matches.

“If” these rounds are harder on barrels is it something like a hot double based powder like The VV N5 series or pressure, or both? I wouldn’t think the tungsten would ever get close to the barrel so it would be just liken a normal copper jacket, or even a solid I suspect.

It is starting to look like the military is much more accepting of high pressure rounds, some very high pressure. The SIg bi-metal case being the current extreme. That is if they ever field it. Serviceability of not just barrel, but bolts and other hard parts will suffer. Time will tell if it pays off.

 

[WindstormSCR]

I’d be curious to see what the performance/accuracy is like out of an 11.5-12” barrel, since that’s the direction several “pdw” designs are leaning in recent years, all the way down to 9” as an extreme low.

I know most of us would rather use 300blk or something more purpose-built at that point, but some of the ideas are being floated as a revival of the backline PDW concept that spawned the P90 and MP7

 

[sinister]

Yup, depending on caliber. In this case, 5.56 you’re exact right. I shot SR for years and still shoot prone matches.

“If” these rounds are harder on barrels is it something like a hot double based powder like The VV N5 series or pressure, or both? I wouldn’t think the tungsten would ever get close to the barrel so it would be just liken a normal copper jacket, or even a solid I suspect.

It is starting to look like the military is much more accepting of high pressure rounds, some very high pressure. The SIg bi-metal case being the current extreme. That is if they ever field it. Serviceability of not just barrel, but bolts and other hard parts will suffer. Time will tell if it pays off.

I think out of a chrome-lined SOCOM barrel you'll see close to 3,000 to maybe 5,000 rounds for best precision. M855A1 does very well to 400 with an ACOG, and tolerable (E-type) to 500.

I don't know if it's a double-base like N540. It's spherical, with bismuth for copper-fouling eraser. The penetrator is steel vice tungsten.

 

[Molon]

fired cases.

left: from a 5.56 Colt M4A1

right: from a 223 Wylde

....

 

[FatBoy]

Seeing some pressure for sure. How deep is the ejector flow? Swiping, I may try to reload with that much swiping but it’s certainly more than I get with hand loaded 77s in a Wylde chamber. I have gone to mostly longer gas systems though.

 

[db2000]

This isn’t very scientific, but for my own records I call the left “mild” pressure signs and the right “moderate” since it made a full circle. Next level will be cutting into the brass where you can feel an edge raised up. That can interfere with chambering next time it’s reloaded. The pressure level after that is blown primers. I can’t imagine anything past “moderate” is very good for the gun and even that is pressing it probably.

 

[Forgetful Coyote]

Anyone know the BC 855A1? Aparrently the Marines are putting it to good use at quite a distance from their M38 DMR's..?

 

[Molon]

According to Ballistic Performance of Rifle Bullets by Bryan Litz the G1 ballistic coefficient of M855A1 is 0.291. The same reference states that M855A1 has a nominal gyroscopic stability factor of 1.41 when fired from a barrel with a 1:8" twist and 1.85 when fired from a barrel with a 1:7" twist.

 

[Count VonFuhrman]

Question: is just the bullet available for reloaders. If not closest bullet that matches it.

 

[bfoosh006]

Question: is just the bullet available for reloaders. If not closest bullet that matches it.

I have seen the M855A1 bullets for sale once. Many years ago.... and those were pulldowns.

If you mean a BC match... quite a few 62ge bullets are a "close" BC match according to the various manufacturers webpages.

 

[Molon]

.....

 

[WindstormSCR]

.....

beautiful bit of macro photography there.

 

[db2000]

 

[Molon]

I think out of a chrome-lined SOCOM barrel you'll see close to 3,000 to maybe 5,000 rounds for best precision.

NSWC Crane has done extensive testing of M855A1 fired from 10.3” M4A1/RIS II upper receiver groups mounted in sliding-rail test fixtures. When new, those barrels produced 10-shot groups that had an average extreme spread of 2.74” at 100 yards (a mean radius of 0.85”). With a round count of 3,600 rounds these barrels produced 10-shot groups with an average extreme spread of 3.84” at 100 yards (a mean radius of 1.10”).

The Lothar Walther barrel that I used to test the M855A1 had approximately 3,550 rounds through it at the beginning of my M855A1 testing.

 

[WindstormSCR]

I do wonder sometimes if there is any appreciable difference in ballistic coefficient on the 855A1 vs regular 855, I would think not, and searching has turned up none, but it's still something I wonder about.

 

[Molon]

I do wonder sometimes if there is any appreciable difference in ballistic coefficient on the 855A1 vs regular 855,

M8555: G1 = 0.300

M855A1: G1 = 0.291

...

 

[Frank Green]

Hodge the slowest 14.5 with the largest group. Interesting, a lot of hype around those barrels about being faster. Clearly not in your case.

Not picking on you but using your post to bring something up…..

Unless you (this means anyone reading this) know each barrels bore and groove size to the 4th decimal place and the same chamber reamer spec was used for all…

your velocity readings etc…can be skewed. I’m not saying your velocity readings are incorrect but to say one brand is faster or slower than another can be skewed.

I’ve seen factory barrels a full .002” undersize and I’ve seen them way oversize. Same goes for chambers. Min spec and production spec!

 

[WindstormSCR]

M8555: G1 = 0.300

M855A1: G1 = 0.291

...

thank you sir, now I just need to figure out an adjustment table for A4 type irons from a 14.5" and a 20"

come to think of it, I should probably do that for Mk262 (and equivalents) as well

 

[TheHorta]

I have 3-4K rounds of the stuff. Not easy to get, but not hard either. Plenty available on Gunbroker. Price is a bit… steep.

 

[Molon]

Unless you (this means anyone reading this) know each barrels bore and groove size to the 4th decimal place and the same chamber reamer spec was used for all…
your velocity readings etc…can be skewed.

Different companies do have differently dimensioned reamers, or no reamer at all is used with some cold hammer forged barrels, and different companies do have differently dimensioned bores at the 4th decimal point, especially with chrome-lined barrels. There is nothing “skewed” with the velocity data that I posted for M855A1.

.....

. . . to say one brand is faster or slower than another can be skewed.

You seem to have completely missed his point about the Hodge barrel. Hodge barrels are claimed to be "designed for M855A1." It has been the Hodge fan boys that have carried on and on that Hodge barrels are significantly faster than other barrels yet none of them have posted velocity data from significant shot strings of M855A1 over the chronograph compared to other low round count barrels. If the Hodge fan boys' claims were true, the Hodge barrel should have easily produced higher velocities than the other barrels that I compared to the Hodge barrel with the M855A1, yet the exact opposite is what happened.

And there is definitely a statistically significant difference between the velocities from the Hodge barrel that I chronographed and the BCM barrel that I chronographed.

....

 

[Frank Green]

Different companies do have differently dimensioned reamers, or no reamer at all is used with some cold hammer forged barrels, and different companies do have differently dimensioned bores at the 4th decimal point, especially with chrome-lined barrels. There is nothing “skewed” with the velocity data that I posted for M855A1.

I'm not saying your velocity data is skewed at all.

What I'm pointing out to everyone in general is this...

When one guy compares velocity of his barrel to another guys barrel and then it comes up that this or that brand is slow or faster...is hard to compare/justify unless you know each barrels bore and groove dimensions and what the chamber was made to.

All is cool brother!

Later, Frank

 

[Molon]

Part 2

Hand-Loaded M855A1 Accuracy


When M855A1 was introduced, we were told by people with “inside information” that this new load produced “match-like” accuracy, yet none of these people where ever able to show statistically significant data to support this claim. The test results that I obtained with M855A1 certainly didn’t show “match-like” accuracy.

The Crane Naval Surface Warfare Center has done extensive testing with M855A1 fired from AR-15s mounted in a heavy, sliding machine-rest test fixture. The Crane Naval Surface Warfare Center is involved in developing special munitions and weapons for our warfighters. They’re not interested in sales hype and propaganda; they’re only interested in facts. They’re not driven by profit margin; their goal is providing our Special Operating Forces with the best tools for accomplishing their missions. When it comes to evaluating the accuracy of ammunition Crane uses 10-shot groups.

With newly barreled upper receiver groups mounted in the heavy sliding machine-rest test fixture, M855A1 was only able to produce a 10-shot group average extreme spread of 2.74” at 100 yards with an average mean radius of 0.85”. With a round count of 3,600 rounds through the barrels, M855A1 was only able to produce 10-shot groups with an average extreme spread of 3.84” at 100 yards with an average mean radius of 1.10”.

The Lothar Walther barrel that I used to test the M855A1 for this evaluation had approximately 3,350 rounds through it at the beginning of my M855A1 testing and as we saw it produced an average 10-shot group extreme spread of 2.07” at 100 yards. A 30-shot composite group of the M855A1 from the Lothar Walther barreled AR-15 had a mean radius of 0.63”.

People are often quick to point out that the lack-luster accuracy of legacy M855 manufactured at Lake City is due among other things to the fact that M855 is composed of three different components; the lead core, the steel penetrator and the copper jacket, yet people seem to gloss over the fact that M855A1 is also composed of three different components; the copper core, the exposed steel penetrator and the copper jacket.

We know that the M855A1 that the US Army based their original accuracy claims on was not manufactured on the SCAMP machinery at Lake City, but rather the slower BAM machinery. The speed of the SCAMP machinery is significantly faster than the older BAM machinery.

The M855A1 that I evaluated was produced on the SCAMP machinery. These M855A1projectiles themselves showed quite a bit of variation. As an example, the base to ogive measurements were all over the map.

The picture below shows two M855A1 bullets that I pulled from the lot of ammunition that I tested. The bullet on the left shows a properly shaped base. Notice the beveled heel and the flat base. The bullet on the right has a “ridge” running around the bottom of the bullet and the base is recessed. Apparently, the speed of the SCAMP machinery comes at a cost.

To be continued . . .

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[TheHorta]

I have 3 different variations of 855A1. If you’d like, I can send you a handful of each variant (maybe 20-30 rounds of each) “for the cause” to see how they differ. Reportedly, the Olin/Winchester variant is the best, but by far the least produced. It’s visibly different from the far more ubiquitous LC variant.