Mk262 clone too hot?

[bluebird]

Hi everyone I've been looking at hundreds of posts around this forum and various forums to prepare myself to get into the community in the future because I currently don't have the opportunity to reload or even own a firearm unfortunately (This website is too addictive)

Anyways I've noticed people are saying that the Mk262 ammo used by some troops is currently the best way to utilize a shorter barrel (ex. 10.5 inch or even 7.5 inch) in a 5.56 rifle/pistol and they are trying to clone the ammo. However, lots of people are saying that duplicating the Mk262 is impossible as it uses non-cannister grade powder and it is very hot which makes it extremely hard and dangerous to clone.

The reason that it is dangerous to clone is because the SAMMI pressure for .223 ammunition is 55,000PSI. Duplicating this ammo will not only exceed commercial powder load specifications but also gets really close or possibly exceed the 55,000PSI limit.

Surprisingly, I don't see many people asking the following question:

What if a 5.56 brass is used instead of a .223 brass?

Since the 5.56's max pressure is 62000PSI instead of the .223's 55000PSI, would this make the Mk262 ammo easier and safer to reload? Of course I understand there are other concerns such as burning primers and blowing the casing apart with reused brass. But theoretically does this mean it is possible and safe to exceed the 55000PSI using 5.56 brass?

I understand my zero experience on reloading or even shooting a real firearm will not provide me enough knowledge to truly discuss this matter with experts like you. I'm merely trying to take a few steps ahead and eliminate some questions I might have in the future, and please enlighten me on this matter.

Thanks guys

[joelogic]

Its not the brass, its the chamber.
People duplicate loads all the time. I loaded up some M855 "clones".
People load SMK 77gr'ers all the time.

Maybe you should buy a gun instead of over thinking ammo questions.
Glocks are going for $500.

[GeoffLinder]

You need to jump into the water to swim with the sharks

[bluebird]

Haha thanks guys for the replies. I wish I can now go out and buy a gun right now but I can't. I'm still in school and yes...pistol is a no go for me because I'm under 21

I'm currently living in dorms and there is no way for me to keep a rifle until I move out next year (long story). My friends are anti-gun-ish so unfortunately I can't go out and rent a rifle because most ranges probably won't let me do that...

I'm studying hard so that I can get out of college asap and aiming at med school for now...my very first quarter just got 3.85GPA

Back to the topic, so the 5.56 vs .223 max pressure that i was talking about is actually the maximum chamber pressure for the 5.56 mil spec upper vs .223 commercial upper (not the brass itself)? If so, can I (literally) disregard the 55000PSI limit and use the 62000PSI limit if I have a mil spec upper? If so, can I theoretically clone Mk262 while exceeding the 55000PSI chamber pressure limit? Thanks.

[FLIGHT762]

Just a question. What kind of equipment are you going to have on hand in your reloading room to measure the difference between 55,000 PSI and 62,000 PSI in your reloads?

The point is, unless you have the equipment to measure the pressures, you actually don't know. When hand loading, you load to safe pressures in your rifle. Unless you have the lab equipment, you won't know.

Most if not all off the shelf AR-15 type rifles will have barrels chambered in 5.56 NATO or Wylde chamber. I don't think you're going to find an AR-15 upper chambered in .223 Remington. There were some made years ago, I had a upper in the 80's from Olympic Arms in .223 Remington. I know this because I tried the upper on an M-16 lower and the upper would cycle fine on semi-auto, but it would not cycle properly on full auto.

To make a MK 262 clone, you would need to know the velocity of the MK 262 fired in your rifle and then make a handload that can safely duplicate that velocity. That, you can easily do, using a chronograph.

[joelogic]

Sounds like someone is too book smart. Mix in some street smarts and you should be fine. Pressure is only one measuring component, it is velocity that matters. Who cares about that specific round, people can get .223 to shoot out to 1k. For that matter if damage is what matters, think about .300 blackout or 6.8spc or for that matter just buy the ammo you want to shoot.

[bluebird]

Flight762,

I forgot where I read it but there was a tool that is used for measuring chamber pressure with sensors and a laptop, but someone said it would be a bit complicated to put in an ar since it is not a bolt action rifle. However I also read that you can calculate the expected chamber pressure with a complicated equation based on bullet weight, seating depth, amount of powder, type of powder, etc (which is what I have in mind).

I understand the idea of duplicating MK262 is to match the real MK262's velocity while maintaining safe (chamber?) pressure. I'm just confused when people said that we cannot exceed the SAMMI specification (55000PSI) while the mil spec chamber is rated at 62000PSI.

If we throw away accuracy for a moment, can we just put as much powder as we want as long as we don't get too close to 62000PSI (or 55000PSI? I'm not sure)? When people say that MK262 is too hot, do they mean the round will create a chamber pressure close to 55000PSI, or are they worrying about something else like exploding brass and burnt primers? I don't understand why people are so nervous about exceeding 55000PSI IF (and only IF) the TRUE maximum is rated at 62000PSI. Thanks for your input!

JoeLogic:

I'm not sure if that is a compliment or a ridicule, but I'm not particularly intelligent comparing to lots of other people in college. I DO believe that I can get good grades if I study hard and work smart.

I understand that the goal is to match the velocity of the true MK262 round, but I am aware that I need to make sure the pressure is not dangerous enough to blow the rifle apart and cause injuries.

The reason I am interested in duplicating the MK262 if I have a chance is because the true MK262 is rare and expensive for a 5.56 round (comparing to XM193, for example). It also has a better performance than other 5.56 rounds in terms of impact energy and accuracy (especially in shorter barrels).

I really appreciate your suggestions on other calibers (especially the 6.8mm SPC), but I don't think it will be my first caliber nor the first caliber that I will reload. The 6.8 will probably be my second rifle caliber in the future.



I know that many people will tell me I should get a rifle and start shooting before I think about stuff like this, but I'm a person who love to be well prepared LONG before I get a chance to do something I guess that's just me

I'm still in a learning process, so please correct me if any of my concepts are incorrect. Thank you guys

[Chief-7700]

Question what powder are you planning on using?

[bluebird]

Question what powder are you planning on using?

I'm not sure yet. I am trying to understand what makes the MK262 more dangerous to load than other 5.56 ammo and how the 55000PSI chamber pressure will matter if mil spec upper can withstand up to 62000PSI.

I've read that Ramshot TAC seem to produce a good velocity with less powder btw.

[joelogic]

Where are you getting this dangerous stuff from? The MK262 is more effective because of the bullet not the powder. Asking questions about the minutiae of exterior ballistics before owning a gun (or shooting one, not sure if you have shot one) is like asking me about having tantric sex when you are a virgin. Not an insult, its just an odd quest. Match ammo > plinking ammo.

[GeoffLinder]

Shooting Software Systems

[bluebird]

JoeLogic,

http://www.calguns.net/calgunforum/showthread.php?t=54716

Originally Posted by ocabj
I've posted the one I developed for my 18" SPR when I still had it.

NOTE: The following data exceeds SAAMI specifications and can be dangerous to use in certain rifles.
Sierra Match King 77gr BTHP
25.3gr Hodgdon Varget
LC Brass
Winchester SR Primer

Developed in a White Oak Armament 18" SPR configuration with a Wylde chamber.

Note: At the time, I was using Winchester SR primers. I would recommend Remington or CCI instead.

Any load that will give you Mk262 performance will exceed SAAMI specifications for .223. Thus, you're not going to find any published commercial data that will meet Mk262 velocities.

Originally Posted by ocabj
If you want to make your own Mk262 clone ammo, you NEED to get a chronograph and work up the load appropriately. Don't kid yourself thinking you can just use someone else's recipe or the commercial data and guestimate the proper load to meet a specific velocity. The Mk262 pressures/velocities are pretty hot and you're going to need to carefully find the right load for your specific rifle. And when you do find the correct load for your specific rifle, you need to reconfirm the load everytime you go to a new lot # in bullets, powder, primers, or cases.

Originally Posted by FAB-10_Guy from ar15.com
I just finished building my SPR Mk12 mod0 and am in the process of discovering what her preferences in ammo are. First, I'm not all that impressed with Mk262 in my rifle. MV seems to vary quite a bit, and accuracy is sub-optimal. No, I'm not a champion AR shooter, so that may be part of it. Also, they seem pretty hot, and the case heads seem to get beat up with the first firing (ejector marks and burrs, as well as extractor marks). But, this is the ammo that was paired with the Mk12, so...

The above were just a few quotes. I can type MK262 clone on the search engine and a lot more information will pop up saying that a reloader will have to proceed with EXTREME caution when trying to duplicate this round. It is definitely "hotter" than other commercial .223 or even regular 5.56 rounds. The MK262 is effective not only because of the bullet weight and design but also its velocity. From what I understand, if we use the same amount of powder, different powders will produce different velocity with a different pressure and temperature, and we are trying to produce the highest velocity with the lowest pressure possible (since it's going to be hot anyway so it should cycle the bolt regardless).

I guess it's like college: you don't get an internship/job in a hospital if you have no idea how the immune system work, for example. Right now I'm just basically reading "the book" and asking a "professor" about something I don't really understand

[bluebird]

Shooting Software Systems

Thank you Sir. The articles on that website are very educational

Unfortunately my question is still unanswered

[GeoffLinder]

Actually your question has been answered very well. There is nothing inherently dangerous in loading to match a specific load specification (bullet type + velocity), there is only danger in doing things that will blow up in your face.

Proper load development is an incremental process that stops whenever the criterion point is reached or pressure signs are found.

As mentioned earlier, if you were actually shooting and reloading you would not have asked this question because the answer would have been obvious.

FYI, the answer is: Chrono some MK262 in your rifle, select a bullet weight and construction type that is the same, select a powder, prep some cases, start with reduced powder charges and work up in 2-3 tenths of a grain increments until the same velocity is achieved (in your rifle) or excess pressure sign is found. If you find pressure sign before desired velocity is achieved start over with a different powder and repeat until you get the desired velocity. End of story here.

Yes, there are reference tables on powder density and burn characteristics that allow a powder to be pre-selected that "should" perform as desired. BUT, thats what testing in the real world is all about, verifying the calculated data as actually working as expected

As to what if 5.56 brass were used in place of .223, nothing much. You are going to pierce the primer first when you get over-pressured, then you start getting cases sticking instead of extracting, then last of all the case head separates and the rifle blows up. The difference in construction between the two types of brass is small and won't effect this much. In fact, the extra case capacity of the .223 versus 5.56 will help keep internal pressure down a tad as the extra metal is all inside the case base and web which serves to reduce 5.56 internal case capacity a tiny bit. The stronger case construction is more about handling the abuse a too large machine gun chamber with excess headspace puts on a cartridge case already loaded to max velocity/pressure.

You can ask all the "what if" questions you want, but in the end, you will only become solidly educated about this by doing it.

[SVRider]

However I also read that you can calculate the expected chamber pressure with a complicated equation based on bullet weight, seating depth, amount of powder, type of powder, etc (which is what I have in mind).

Be careful to understand this is "expected chamber pressure". The variables are on the chamber/barrel side as much as on the cartridge side, and the theoretical calculations cannot take those into account as they vary from manufacturer to manufacturer and even barrel to barrel. This is why you always work up a load for your specific firearm and don't just rely on the data of others. May be safe, may not be. The only way to verify is to test.

Be safe....