5.56 in a short barrel-MK262 clone GTG?

[atomic41]

I did search and found related talks but not exactly what I'm looking for.

I'm finally building up a lower that I've had sitting around and I'm pretty sure I'm going 5.56. I'm wondering where the sweet spot is for reliability, terminal performance, short barrel length, and ammo.

Plan is for a fun gun that will double as defense if needed at short ranges. I know that too short and it's just a loud obnoxious flamethrower, so I'm thinking somewhere in the 10-11.5" range. Let's say I go 11.5"...is one of the clone MK262 options a good choice? I already shoot IMI 77gr Razorcore out of a 20" and keep some in inventory. How about for a shorty...good choice?

Before I get the "what about better caliber" comments, I'm curious about 5.56 options. I have other calibers including .300BLK. So what about the 77gr options and what (short)barrel length works best?
?

 

[redneckbmxer24]

I’ve run a good bit of IMI Razorcore 77gr from my 10.5” LMT. It’s been very accurate and it was in the mid-high 2600’s when I chrono’d it which I thought was great considering the barrel length.

If I was going to load and make a MK262 clone then I would just forget about the whole MK262 thing and load a 77gr SMK or whatever with a better powder for shorter barrels than what MK262 uses.

 

[RyanScott]

Barrier blind is better but if you aren’t using it professionally and you already have 77s in inventory, rock on.

 

[Yondering]

IMO - thumbs up for 11.5-12.5" when matched with a reasonably short flash hider or comp.

Also IMO - I'd way rather have a 12.5" with a short flash hider than a 10.5" or shorter with one of those long/heavy blast diverters that seem popular in some circles now (like a Flaming Pig or one of the many knockoffs). For about the same size package, you get better performance from the 12.5" with no downside that I can percieve. Others will disagree of course.

 

[Docsherm]

Real MK262 is too hkt for short barrels. I have seen way too many broken BCGs. And this is in the MIL issued stuff.

If you want to properly use MK262 a 12.5 barrel is as short as you want to go.

 

[Docsherm]

I did search and found related talks but not exactly what I'm looking for.

I'm finally building up a lower that I've had sitting around and I'm pretty sure I'm going 5.56. I'm wondering where the sweet spot is for reliability, terminal performance, short barrel length, and ammo.

Plan is for a fun gun that will double as defense if needed at short ranges. I know that too short and it's just a loud obnoxious flamethrower, so I'm thinking somewhere in the 10-11.5" range. Let's say I go 11.5"...is one of the clone MK262 options a good choice? I already shoot IMI 77gr Razorcore out of a 20" and keep some in inventory. How about for a shorty...good choice?

Before I get the "what about better caliber" comments, I'm curious about 5.56 options. I have other calibers including .300BLK. So what about the 77gr options and what (short)barrel length works best?
?

See above..... i forgot to quote your post.

 

[Matches Malone]

I did search and found related talks but not exactly what I'm looking for.

I'm finally building up a lower that I've had sitting around and I'm pretty sure I'm going 5.56. I'm wondering where the sweet spot is for reliability, terminal performance, short barrel length, and ammo.

Plan is for a fun gun that will double as defense if needed at short ranges. I know that too short and it's just a loud obnoxious flamethrower, so I'm thinking somewhere in the 10-11.5" range. Let's say I go 11.5"...is one of the clone MK262 options a good choice? I already shoot IMI 77gr Razorcore out of a 20" and keep some in inventory. How about for a shorty...good choice?

Before I get the "what about better caliber" comments, I'm curious about 5.56 options. I have other calibers including .300BLK. So what about the 77gr options and what (short)barrel length works best?
?

Velocity run off on a 5.56/.223 is pretty severe on sbr’s. Especially with a 77gr bullet. If you want short but practice, 16in barrel might be the compromise. Mk12’s were 18in and military m4s are 11 to 14ish inches. I’m not talking about velocity run off for a long range shot either, I’m more or less talking about the over all lethality when considering tissue destruction.

 

[RyanScott]

Real MK262 is too hkt for short barrels. I have seen way too many broken BCGs. And this is in the MIL issued stuff.

If you want to properly use MK262 a 12.5 barrel is as short as you want to go.

That’s a good point. I’m glad I have a KAC and not a BCM. LOL

 

[Sogan]

Real MK262 is too hkt for short barrels. I have seen way too many broken BCGs. And this is in the MIL issued stuff.

If you want to properly use MK262 a 12.5 barrel is as short as you want to go.

AGB?

 

[atomic41]

I’m not talking about velocity run off for a long range shot either, I’m more or less talking about the over all lethality when considering tissue destruction

I'm curious about this as well, is this effective out of a short barrel at short range. I did go search and found gel testing done that showed it to perform well. This gun will be a pistol so I'm wondering specifically about options for 5.56 in 11"(ish) length.

The reason I am wondering about the IMI Razorcore is that I keep it on hand since I shoot it a lot out of a long barrel and want to keep things simple.

 

[atomic41]

For about the same size package, you get better performance from the 12.5

If you want to properly use MK262 a 12.5 barrel is as short as you want to go

Interesting and thanks. I was wanting something closer to 10 or so but both of you say 12.5. Can you expand a little on that? I appreciate the replies!

 

[RyanScott]

12.5 is a sweet length. Carbine +1 would be a good gas system for it. You lose a lot of velocity after 11.5. A lot. And SBRs are very hard on bolts as Doc pointed out, especially with Mk262 which was the hottest issue ammo before M855A1.

 

[redneckbmxer24]

Real MK262 is too hkt for short barrels. I have seen way too many broken BCGs. And this is in the MIL issued stuff.

If you want to properly use MK262 a 12.5 barrel is as short as you want to go.

Uhhhh, what?

Please explain to us how having less barrel out in front of the same length gas system increases pressure to the point of breaking bolts... That makes precisely zero sense. The load is also optimized for a longer barrel with slower powders than ideal which would also decrease pressure out of the shorter tube.

 

[RyanScott]

Because a 12.5 port is substantively smaller which reduces bolt unlocking force. Would you say a Mk18 and M4 have similar bolt, extractor and barrel life? No, we know they don’t, from numerous studies.

 

[Greg Langelius *]

Velocity run off on a 5.56/.223 is pretty severe on SBR’s. Especially with a 77gr bullet. If you want short but practice, 16in barrel might be the compromise. Mk12’s were 18in and military m4s are 11ish inches. I’m not talking about velocity run off for a long range shot either, I’m more or less talking about the over all lethality when considering tissue destruction.

Lethality aside, this is the reasoning I've grasped. My M4gery uses a 16" 1:7" lightweight Upper, and the 77 IMI as an effort to retain range, accuracy, and energy.

I'm still not in a position to do significant testing, but the equipment is ready.

The intended application is Two-Gun Comp. The handgun is the Ruger American Pistol 9 Pro, the current companion Carbine is the Ruger PC Carbine, which accepts the same magazines.

The M4Gery will only supersede that if/when it proves to be significantly superior at the task.

The intent would be to achieve batter reach than the PC Carbine shooting 124gr. It should, but I'd rather test the theory than adopt it without that.

Greg

 

[redneckbmxer24]

Because a 12.5 port is substantively smaller which reduces bolt unlocking force. Would you say a Mk18 and M4 have similar bolt, extractor and barrel life? No, we know they don’t, from numerous studies.

Yeah, gas ports are spec'd to the barrel length. What does MK262 have to do with any of it though? A round that is optimized for longer barrels with slower powder. I don't buy it.

 

[RyanScott]

More rounds of it has been fired through SBRs than SPRs. Are you asking why someone would do it or why a longer barrel would be easier on a bolt even if the gas system was the same length?

 

[redneckbmxer24]

I'm aware more has been shot through SPR's. I'm not wondering anything, just pointing out it's bullshit.

 

[DJL2]

I went with an 11.5 inch tube when I put mine together, though a lot of folks like 12.5 inches. To me, those two work - shorter or longer and you're getting into the "why bother" zone. That 10.5" tube is cool...and that 3.3% reduction in overall length has a significant performance impact that just isn't worth it to me. Alternatively, while I find my 14.5 inch tube from work to be a useful length...do I really wanna go through the SBR hassle for 1.5 inches? Nah.

@redneckbmxer24 - I stepped away, might have been answered in the interim. I believe what he was referencing was running higher port pressures and the challenges with tuning the operating system for adequate versus excessive BCG velocity when the dwell time gets tiny. Too many folks just go nuts on gas port size chasing reliability with predictable effects.

 

[RyanScott]

I'm aware more has been shot through SPR's. I'm not wondering anything, just pointing out it's bullshit.

You didn’t hear about the time ARSOF did train ups with Mk262 and broke guns like crazy? Doc was there man.

 

[Yondering]

I'm aware more has been shot through SPR's. I'm not wondering anything, just pointing out it's bullshit.

I believe the bolt failures mentioned were a result of an over-gassed system run with hot loads (which the 262 load is). While maybe that was necessary for a military application, it doesn't have to be that way for a personal gun. Tune the gas right for that Mk262 load, and you'll get decent bolt life regardless of barrel length. Square the receiver for even bolt lug contact and it'll last even longer.

IMO this is an example of why military rifle data doesn't always translate to civilian useage. As a civilian, I don't care about mass producing 1,000 rifles that all are reliable with a certain configuration in extreme environments; I only care about setting up my rifle for the way I want to use it.

 

[Constructor]

You can run a mid gas system with a 12.5" barrel.

 

[Docsherm]

AGB?

For what?

 

[Docsherm]

Uhhhh, what?

Please explain to us how having less barrel out in front of the same length gas system increases pressure to the point of breaking bolts... That makes precisely zero sense. The load is also optimized for a longer barrel with slower powders than ideal which would also decrease pressure out of the shorter tube.

I am pointing it out becuse i have seen it many times. At least 10 or so. And only from the people using the MK262.

Also, the 12.5 barrel lenght was started to be the shortest barrel length to utilize the MK262 round.

 

[Docsherm]

I'm aware more has been shot through SPR's. I'm not wondering anything, just pointing out it's bullshit.

What do you think is bullshit?

 

[Docsherm]

You can run a mid gas system with a 12.5" barrel.

I have a 12.5 carbine and Mid gas set up. The middy is a bit softer and it is a SS barrel and my 12.5 carbine is a CHF.

I like them both.

 

[atomic41]

Thanks for the replies. Parts landed on my porch today to build the lower, now I need to decide on the upper. I'm leaning towards 12.5 based on what I'm reading here.

 

[Docsherm]

Thanks for the replies. Parts landed on my porch today to build the lower, now I need to decide on the upper. I'm leaning towards 12.5 based on what I'm reading here.

What 12.5 barrel are you thinking about?

 

[slothlacrosse]

You can run a mid gas system with a 12.5" barrel.

What gas port size?

 

[Constructor]

What gas port size?

Depends on the buffer weight, type of spring and if you run full power ammo(58k) but .089" works unsuppressed or if using a 30 cal can. .086" may work better with a 5.56 can if it causes an increase in backpressure.

 

[RyanScott]

@Constructor 16.5 RLGS with OPS can in 5.56... what port? Rifle receiver extension. Have you tried such a thing?

 

[atomic41]

What 12.5 barrel are you thinking about?

I'm not sure, haven't got that far yet.

 

[Constructor]

@Constructor 16.5 RLGS with OPS can in 5.56... what port? Rifle receiver extension. Have you tried such a thing?

I have not but I'm sure it will work but may be a little more finicky about loads. A slightly lower pressure load may barely cycle and a slightly higher pressure may be over gassed so it will be important to choose the ammo you want to shoot first then adjust the gas port to fit or go big and use an AGB. A RG 16 has apx the same dwell time as a mid gas 12.5. An 18" RG will run with a .093" port. I think you would need to increase the port size apx .006 depending on how much back pressure the can creates. You could start with a .096 and if doesn't lock back go to a .098.

 

[Longshot85]

If using for defense or even hunting I would look at other options than using 77grain bullets out of a short barrel. If you have the option and defense really is a priority there's several things to consider.

I keep IMI 77 grain and IMI 69 grain on hand to shoot when I don't have time to reload. It's good ammo and shoots lights out of my SPRish build with a WOA 18 in SPR barrel. I understand wanting to have common ammo to run across multiple platforms.

I was swamped with other things in life and my bolt gun (6.5CM) was in between a chassis swap and several other parts this past fall so I took my SPRis build out for deer season. The ammo was IMI 77grain Razorcore. I ended up shooting a buck at 26 yards (verified with sig kilo 2000). The shot was absolutely perfect behind the left shoulder in the money spot for the lungs/heart. The deer started to run after impact and immediately fell flat on its face after 2 steps, then got right up and hauled ass out. I waited for it to bleed out and after about 45 minutes I got down from my stand. The terrain was very steep (knobs in KY) with a ton of gullies as well. The sun had gone down and it was now dark. I had 5 other people come to assist with a goal of a fast recovery and 3 out of those 5 were experienced trackers (so 4 experienced trackers including me and 2 others to total 6.) One is my father in law that has been hunting this property for 30+ years to include a lot of squirrel and raccoon hunting (he knows the terrain.) We have multiple game cams up and are VERY intimate with where the deer travel, where they bed, and can notice a general shift in activity from week to week starting in August when we start gathering info on them. With all that said.......despite finding some blood that night (which was NOT much) we did NOT recover the deer. I went back out at sun up and got on a blood trail which took 2 hours to track 186 yards worth since the drops (more like specks) were so small. Eventually the blood stopped and depsite 2 other people looking for an additional hour we did not find it. We knew exactly where the game trails, water, and thickets were but still had no luck. The next weekend my father in law was out hunting and was able to recover the head off of the remains due to buzzard activity.

With all that said........I had watched every video that's out there (IMI's testing, BARFcom TMK etc) on any terminal ballistics for the 77 grain SMK and 77 grain TMK. I was confident that at short range the bullet would perform. It did NOT perform anywhere near how I thought it would. I will never shoot another deer with ANY 5.56 round/rifle. The only exceptions
would be:
-I was in danger of starving and 5.56 was my literal only option
-i was doing population management
-even in those situations I would place a head/CNS shot

A lot of people have had other results and I believe a true hunting bullet would have performed better than the SMK.

That's just my $0.02 and others have expertise on others aspects like the BCG issues.

Deer and humans are clearly different with anatomy. Standing broadside on 4 legs vs a person upright presents 2 totally different types of exposure. Even still, if I'm choosing a rifle/caliber to save my life and my families life.....its not 5.56 out of an SBR based on my personal experience.

I'll finish off by leaving a picture of an EXIT wound at 632 yards out of my 6.5CM as food for thought ....147 ELD handload moving 2858 fps (no typo and yes it's a hot load)

 

[RyanScott]

When I had a 17” RLGS at .093” it cycled slowly unsuppressed but my M4S can with its two baffles restored it right to unsuppressed carrier velocity. I’m going to try .08 and drill up from there.

Longshot, SMKs can be finicky. Try TSXs or a bonded bullet next time.

 

[Longshot85]

Thanks for the TSX recommendation, I've heard and read a lot of good results from them.

I've had great performance from Hornady SST 129grain, old 140 AMAX and 147 ELD-M.

Back to the 77 grain discussion, the 77 grain SMK and later TMK fit a good spot in the military because it presented a good option in the already in use M4 platform. (We all know this)

When going to a dedicated an up close defense setup....other options are better.

I'm excited about the 8.6BLK/8.6 Creedmoor that will run out of an AR10 setup. That will be my next AR build.

 

[atomic41]

What 12.5 barrel are you thinking about?

I've been shopping around. KAK has 12.5", mid gas for $103 which is a low cost risk and should be fine for this gun. Most other barrels have carbine gas and cost on some is way more than I want for this gun. I would rather put the money saved into a AGB. Sometime later it will have a can.

 

[Docsherm]

I've been shopping around. KAK has 12.5", mid gas for $103 which is a low cost risk and should be fine for this gun. Most other barrels have carbine gas and cost on some is way more than I want for this gun. I would rather put the money saved into a AGB. Sometime later it will have a can.

If you get a good barrel you won't need an adjustable gas block. Bad barrels and poor setups require them. They are fixing an issue and they do not address the underlying problem that makes it necessary to have one. I shoot all of mine with and without a can and have no issues. I shoot all kinds of ammo and under all kinds of conditions.

This is a great barrel and not much more, plus it has a pinned Gas Block. Ballistic Advantage 12.5

And there is this one: BA 12.5 ALSO

I built one for a guy using this barrel and he was taking it out to 600 plus yards and it ran fine.

@Eurodriver

 

[atomic41]

If you get a good barrel you won't need an adjustable gas block. Bad barrels and poor setups require them. They are fixing an issue and they do not address the underlying problem that makes it necessary to have one. I shoot all of mine with and without a can and have no issues. I shoot all kinds of ammo and under all kinds of conditions.

This is a great barrel and not much more, plus it has a pinned Gas Block. Ballistic Advantage 12.5

And there is this one: BA 12.5 ALSO

I built one for a guy using this barrel and he was taking it out to 600 plus yards and it ran fine.

@Eurodriver

Thanks, I did look at those. side note: I was entertained by one guy's 5 star review where he said he hasn't even shot it yet. I have a BA on my .300BLK and like it a lot so they are in the running.
Questions for you...the reason I started eyeing up the KAK was not just price but the mid length gas. Is it worth it to bump up the gas length or just go with carbine?

 

[Docsherm]

Thanks, I did look at those. side note: I was entertained by one guy's 5 star review where he said he hasn't even shot it yet. I have a BA on my .300BLK and like it a lot so they are in the running.
Questions for you...the reason I started eyeing up the KAK was not just price but the mid length gas. Is it worth it to bump up the gas length or just go with carbine?

I have no issues wirh the carbine gas. That is what i plan on going with in the future.

 

[Yondering]

If you get a good barrel you won't need an adjustable gas block. Bad barrels and poor setups require them.

Sorry but no, that is not an accurate statement and it's very misleading for someone new to this stuff.

Barrel quality has nothing to do with tuning the rifle for the load you're using. In turn, gas port sizing has nothing to do with barrel quality. You're acting like better quality barrels have smaller gas ports, which is not true at all.
In reality, almost all barrels (with a very few exceptions) are intended to function with milder 223-spec ammo unsuppressed, at minimum. Using hotter loads like Mk262 or similar level handloads creates an overgassed system, adding a suppressor makes it worse; sometimes mildly overgassed and sometimes severely. There's more to this than just whether the rifle cycles.

The comment about adjustable gas blocks not addressing the underlying problem is completely misleading about what an adjustable gas block does or how. Functionally it creates a smaller gas port above the barrel's gas port, the point being to restrict gas flow to the correct amount. It doesn't make any difference if that's done at the barrel port, or at the gas block - the functional result is the same, and it directly addresses the "underlying problem" of too much gas flow.

 

[RyanScott]

Quality barrels do tend to be ported smaller. Mostly because the people who buy shit barrels buy shit ammo.

 

[Docsherm]

Sorry but no, that is not an accurate statement and it's very misleading for someone new to this stuff.

Barrel quality has nothing to do with tuning the rifle for the load you're using. In turn, gas port sizing has nothing to do with barrel quality. You're acting like better quality barrels have smaller gas ports, which is not true at all.
In reality, almost all barrels (with a very few exceptions) are intended to function with milder 223-spec ammo unsuppressed, at minimum. Using hotter loads like Mk262 or similar level handloads creates an overgassed system, adding a suppressor makes it worse; sometimes mildly overgassed and sometimes severely. There's more to this than just whether the rifle cycles.

The comment about adjustable gas blocks not addressing the underlying problem is completely misleading about what an adjustable gas block does or how. Functionally it creates a smaller gas port above the barrel's gas port, the point being to restrict gas flow to the correct amount. It doesn't make any difference if that's done at the barrel port, or at the gas block - the functional result is the same, and it directly addresses the "underlying problem" of too much gas flow.

I completely disagree. There is no real need for an adjustable gas block, unless you don't have your rifle put together properly. That includes having all the parts that work together properly.

If you are new to the game and don't completely understand the process then yes, you may need one.

And quality parts do come into play in this selection. There is a greater probability of items not working in harmony if they sre not the truest they can be.

 

[RTH1800]

Lot of issues brought up in this thread.

1) What Mk 262 ammo are you planning on shooting? USGI issue? BH commercial? Other? Reloaded ammo with TAC? Not all generic so called MK 262 ammo is hot.

2) The folks who shoot SBR's in combat report no issues with Mk 262 in 11.5" as far as killing goes. I personally do not know. What I do know is that Mk 262 and every other round I have tried is a miserable killer in an 11.5" barrel. In 16" AR's it's fair. In 18" barrels it is excellent. I have a lot of history with it in guiding hunters and deer and varmint culling. I really like the 11.5" CAR uppers and have several. I do keep one handy for SD. Guess I am being an optimist but I think they will work fine but hopefully never will find out.

3) I simply have difficulty with the folks who have issues with the 77 grain SMK killing deer with an 18" barrel. Shorter barrels have issues and the 11.5's are miserable with any bullet. It is simply stunning to me the damage it causes with a 7 twist barrel and velocity over 2750. I guide a lot of hunters every year and no one has an issue with it. I require my hunters to use my rifle for several reasons including sighting, lack of recoil and blast etc. Many are kids and some adults with little or no hunting experience. We do place bullets exactly where they need to be.

 

[Docsherm]

Lot of issues brought up in this thread.

1) What Mk 262 ammo are you planning on shooting? USGI issue? BH commercial? Other? Reloaded ammo with TAC? Not all generic so called MK 262 ammo is hot.

2) The folks who shoot SBR's in combat report no issues with Mk 262 in 11.5" as far as killing goes. I personally do not know. What I do know is that Mk 262 and every other round I have tried is a miserable killer in an 11.5" barrel. In 16" AR's it's fair. In 18" barrels it is excellent. I have a lot of history with it in guiding hunters and deer and varmint culling. I really like the 11.5" CAR uppers and have several. I do keep one handy for SD. Guess I am being an optimist but I think they will work fine but hopefully never will find out.

3) I simply have difficulty with the folks who have issues with the 77 grain SMK killing deer with an 18" barrel. Shorter barrels have issues and the 11.5's are miserable with any bullet. It is simply stunning to me the damage it causes with a 7 twist barrel and velocity over 2750. I guide a lot of hunters every year and no one has an issue with it. I require my hunters to use my rifle for several reasons including sighting, lack of recoil and blast etc. Many are kids and some adults with little or no hunting experience. We do place bullets exactly where they need to be.

Some very good points. I am refering to the actual USGI Black Hills MK262 and not any of the other products when i refer to it. I use the other stuff for training but only the Black Hills for precision use.

Who shoots an 11.5 in combat? I think the only a few units i have seen use them in the last 20 plus yesrs. The majority of the Mil barrels are 10.5 amd 10.3. Was that a typo?

The MK262 in a 12.5 barrel has had no problems with getting the results required for combat use at distance.

I agree with you. The last time i went deer hunting i used my 18" Noveske SPR with MK262 and an AAC Mini4 can. Dropped them with no issues. It was only 120 yards, but had no problems.

 

[RTH1800]

The commercial BH in the red boxes is not the same as the USGI Mk 262. The USGI ammo has a flash suppressant and is hotter. It is in 20 or 30 round boxes that are the grey cardboard and on stripper clips in the 30 rd version. It is 50 fps or more faster in an 18" barrel and has a crimped in primer.

 

[atomic41]

1) What Mk 262 ammo are you planning on shooting? USGI issue? BH commercial? Other? Reloaded ammo with TAC? Not all generic so called MK 262 ammo is hot.

IMI 77gr Razorcore is my go to, that's what I'm wondering about for this gun. It shoots great from my 20" wylde barrel and I keep it in stock and I have a drive to keep things simple.

 

[RyanScott]

BH recently introduced bulk ammo that is supposed to be more like military issue ammo.

 

[RTH1800]

Anything over 2700 FPS in an 18" barrel is going to be a fairly hot load. At or over 2800 is in the true MK 262 USGI range.

 

[RyanScott]

Here’s ammo with 2 of 3 things that distinguish the issue ammo.

Black Hills 5.56 77gr MK262 MOD 1-C 460rd Ammo Can