DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!

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10 years 7 months ago - 10 years 7 months ago #36108 by SOC
DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!! was created by SOC
First of all I want to say, I do not advise anyone to attempt to load ANY ammunition beyond the pressure levels recommended by reputable component/ammunition manufacturers.

Even if you are watching brass and chronograph readings to estimate pressure you are getting only an estimate ie a good guess as to what pressures you are dealing with.

So now to the fun stuff.

I started with min loads and worked up just like anyone should when developing a load.

I used Lake City brass 1.759" max length

Rem 7 1/2 BR primers

8208XBR

Berger 77gn OTM .224

I debated using a LFC to crimp but I had good neck tension while loading the Bergers into the cases and I had no setback during testing in spite of my test rifle having a 2X power buffer spring, heavy buffer and mil spec weight bolt carrier assembly.

My barrel is 16.125" 1/7 twist with 5.56 chamber, gas system is adjustable and was tuned for optimum operation with Black Hills white box "seconds" 77gn 5.56 Match.

SAMMI uses a min spec chamber and barrel for .223 for pressure testing and place a strain gage at the mid point of the chamber.

NATO calls for a min spec 5.56 chamber and measures pressure at the case mouth.

I used Black Hills MK262 MOD1 and its Nato Max Pressure spec of 58700psi to calibrate my strain gage located 0.25" closer to the breech from the case shoulder on my rifle.

I fired 5 known rounds of BH MK262 MOD1 and used the difference between the highest reading and Nato Max to weight my pressure readings.

I also fired 2 more that I got from a "friend" that were rumored to be second hand from actual mil inventory but I have know way to confirm or deny the claim nor would I due to legality issues. I assume they were just more of the BH seconds...

Since my chamber and bore are not NATO min spec actual pressure should be slightly lower than the readings I got. Now for some pretty graphics.

First 5 rounds are BH Seconds last 2 are Rumored MK262 MOD1

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NOTE THE BOOK MAX FOR 8208 and 77gn SMK is 23.2gn!!!

My strain gage (adjusted with the goal of duplicating SAMMI pressure data from a min spec test fixture) confirms Loads above this point are over 55,000psi!!! SAMMI MAX for .223

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With a minor adjustment + .1-.2gn this load would duplicate MK262 in my rifle with less pressure.

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The following load produces about 50 more fps than MK262 with similar pressure.

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The last pic is the fired brass, 5 of each load left lowest right highest, last row of 5 is BH MK262

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Last edit: 10 years 7 months ago by SOC. Reason: Corrections
The following user(s) said Thank You: MrMarty51, OleCowboy, Siscowet

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10 years 7 months ago #36112 by MrMarty51
Replied by MrMarty51 on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!
Graffs all look real purty and all.
What types of software and pressure sensors are You using ???

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10 years 7 months ago #36118 by LebbenB
Replied by LebbenB on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!

NOTE THE BOOK MAX FOR 8208 and 77gn SMK is 23.3gn!!!

What was the source of your load data?

Berger 77gn OTM .224

Small error here. If the intent was to make a Mk 262 Mod 1 clone, the bullet used is a 77 gr OTM bullet with cannelure, so that the case mouth can be crimped. The Berger 77 gr OTM doesn't have a cannelure, so what you have is a Mk 262 Mod 0 clone.

Good write up, though. Thanks for posting it.

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10 years 7 months ago #36120 by SOC
Replied by SOC on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!

MrMarty51 wrote: Graffs all look real purty and all.
What types of software and pressure sensors are You using ???


Using a Pressure Trace II from Recreational Software Inc, don't recall off hand what company he said makes the strain gage itself other than he has never received a bad one, I also have the full RSI ballistic lab software as well.

LebbenB wrote:

NOTE THE BOOK MAX FOR 8208 and 77gn SMK is 23.3gn!!!

What was the source of your load data?

Source for load data.
bulletin.accurateshooter.com/2009/10/imr...ta-available-online/

Correction, Hodgdon lists 23.2gn as max.

Berger 77gn OTM .224

Small error here. If the intent was to make a Mk 262 Mod 1 clone, the bullet used is a 77 gr OTM bullet with cannelure, so that the case mouth can be crimped. The Berger 77 gr OTM doesn't have a cannelure, so what you have is a Mk 262 Mod 0 clone.

Good write up, though. Thanks for posting it.


Yes, in review I see I did not specify what "Mod" my clone is.

Mill spec lists SMK for both MOD0 and MOD1 specifically as well as crimping.

Word from friends of mine using actual non seconds MK262 is that Hornady TAP 75gn bullets have better terminal effect on "soft tissue" though they give up some long range accuracy, not an issue for the guys using it in 10.5" barrels.

Some say Nosler 77gn is better but these opinions are mixed on accuracy.

The Berger 77gn OTM Tac is a Hybrid of Tangent and Secant Ogive and seems to give better accuracy, tolerates being off the lands and gives better terminal effects.

I plan to tune this "CLONE" for proper velocity. From there I'll be tweaking it to my rifle. Along the way I hope to get in some good accuracy and terminal ballistic testing.

My end goal is to have a round that Duplicates the external ballistics of the MK262s but with less pressure, more accuracy and better on target effects. So far this experiment looks promising.

Maybe I should call it MK262 MOD3?
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10 years 7 months ago #36121 by SOC
Replied by SOC on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!
Something I think should be taken as caution.

Even my hottest load tested did not show signs of excessive pressure in the brass or primer. All showed less sign than the Black Hills seconds. If someone were working up a load in the "traditional" manner using the components I used, looking only at brass sign for pressure and not using a chronograph or was trying to get velocities quoted from a longer barrel than they were using. They would be way up there in pressure by the time the primers were as flat as the BH Seconds.

NATO Max for 5.56 is 62,000psi (Spec for MK262 is lower)

During loading I got very close to compressed loads. I may continue in the direction of the NATO Max with my gage calibrated as is. I think I will be compressing before I reach that pressure level. Something I DO NOT want to do with the 8208.

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10 years 7 months ago #36124 by Siscowet
Replied by Siscowet on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!
Thanks for the write up. I am going to develop a load for 75 gr Hornady TAP this spring, and you have given me a lot to research before I start. Not interested in nearing maximum pressures. I was surprised that the BH stuff was so high in pressure. I will be working up slowly since I am not interested in going that high. Good write up.

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10 years 7 months ago #36126 by OleCowboy
Replied by OleCowboy on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!
WOW, just WOW. Some of you guys on here really are on top of the game. This is as good as it gets for real information from folks who clearly know what they are doing. Wish other forums were as good as this in the regards.

While I am not or ever have been into reloading I certainly appreciate the information... :twothumbs:

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10 years 7 months ago #36129 by LebbenB
Replied by LebbenB on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!
"Mill spec lists SMK for both MOD0 and MOD1 specifically as well as crimping."

The original 77 gr OTM bullet from Sierra did not have a cannelure (Hence the Mod 0 nomenclature.) The cannelure was a requirement from NSWC Crane so that the case mouth could be crimped. Sierra balked at this requirement, fearing a loss of accuracy in the bullet. When Crane told them that Hornady was willing to provide a similar bullet WITH a cannelure, Sierra bent to Crane's spec. I suppose the one thing Sierra feared more than a loss of accuracy was a loss of contract.
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10 years 7 months ago #36134 by jtallen83
Replied by jtallen83 on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!

SOC wrote: Something I think should be taken as caution.

Even my hottest load tested did not show signs of excessive pressure in the brass or primer. All showed less sign than the Black Hills seconds. If someone were working up a load in the "traditional" manner using the components I used, looking only at brass sign for pressure and not using a chronograph or was trying to get velocities quoted from a longer barrel than they were using. They would be way up there in pressure by the time the primers were as flat as the BH Seconds.

NATO Max for 5.56 is 62,000psi (Spec for MK262 is lower)

During loading I got very close to compressed loads. I may continue in the direction of the NATO Max with my gage calibrated as is. I think I will be compressing before I reach that pressure level. Something I DO NOT want to do with the 8208.



I've been shooting some of the BH out of my PM400 and haven't noticed any signs of excessive pressure on the brass. Does that have something to do with the 10 inch barrel?

Let me know when you have a commercial version for sale,the SMK, Nosler, or the Berger would all work for me.
I'd just as soon keep my ammo allowance in the family if I can. :usa:

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10 years 7 months ago #36169 by SOC
Replied by SOC on topic DANGER EXPERIMENTAL MK262 DUPLICATION BY SOC!!!

jtallen83 wrote:

SOC wrote: Something I think should be taken as caution.

Even my hottest load tested did not show signs of excessive pressure in the brass or primer. All showed less sign than the Black Hills seconds. If someone were working up a load in the "traditional" manner using the components I used, looking only at brass sign for pressure and not using a chronograph or was trying to get velocities quoted from a longer barrel than they were using. They would be way up there in pressure by the time the primers were as flat as the BH Seconds.

NATO Max for 5.56 is 62,000psi (Spec for MK262 is lower)

During loading I got very close to compressed loads. I may continue in the direction of the NATO Max with my gage calibrated as is. I think I will be compressing before I reach that pressure level. Something I DO NOT want to do with the 8208.



I've been shooting some of the BH out of my PM400 and haven't noticed any signs of excessive pressure on the brass. Does that have something to do with the 10 inch barrel?

Let me know when you have a commercial version for sale,the SMK, Nosler, or the Berger would all work for me.
I'd just as soon keep my ammo allowance in the family if I can. :usa:

Save your brass. If you send it I can load it and return it and am not required to pay ITAR tax on it so I discount tax and brass from cost.

Also barrel length has almost no effect on pressure. The exception is when unburnt powder goes down the bore and ignites or detonates causing a second pressure spike.
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