quote:

Originally posted by offgrid:

quote:

Originally posted by IndianaBoy:

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Originally posted by offgrid:


I would like to see a gas block manufacturer come out with a drill to size block. Ship with a gas hole as small as .050, drill to size....

There was a guy who had a captive detent sliding plate system that could be drilled with three different port sizes.

It was a smart design. Guy had a death in the family and other priorities took him away from it I think. Can't remember the name.

I am half tempted to pull my 3-gun rifle apart today just to inspect the adjustment screw in my most heavily used rifle that as an adj gas block.

MicroMoa

Smart, simple design.

Found several of his post regarding gas port size. He still has a few videos on youtube. https://www.youtube.com/channe...RTBMGsZVXJBnPfk8VabA

That's the one!

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Originally posted by offgrid:

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Originally posted by MikeinNC:

I’ve never had a problem with an adjustable gas block. I have a JP and one I made....once I get them set to run nato ammo with the suppressor and without, I lock it down and never fiddle with it again.

How many rounds?

At least 1k thru both...with and w/o the can thru both carbines

Did some accuracy testing and re-chrono'd with the 12.5". Have 200rds on it now, velocity has settled. This thing is hauling ass. Not sure the midlength gas has anything to do with the velocity? Went up to 24.0/8208/77smk/2640 had slight ejector swipe. 23.7/2600 shoots very well. Will keep in mind it 45 degrees outside today. Things might change when hotter! Cycles great with the can, very soft shooting, port size is working out great. Throws brass in a nice pile at 3:30-4:00. Fun when things work out! Did try cycling w/o the can. One round in mag tried it three times. One the bolt locked back, other two did not eject the case. Hopefully next week shoot it at 4-500yds, see what magnification I need to spot misses/impacts on steel, go from there on a scope choice.

I ended up not using the Noveske NSR handgaurd. The .800 gas block just barely cleared the handgaurd. Put a little pressure on the handguard gas block will touch. Had a JP handgaurd laying around, plenty of room with it.

As mentioned above had two barrels cut from the same blank. Game time decision went with a 11.5" for the second barrel, .063 gas port, carbine +1 gas system for 100% suppressed. Put the barrel on a older Sun Devil upper. Same procedure as other barrel, heated up the barrel extension.... nice tight fit. It ain't coming off w/o heat.

Shot 200rds though it yesterday, red dot sight, 25yds. Functioned great with all the loads. Slightly snappier compared to the 12.5", not bad though. Chrono'd the last 15rds. Interesting the difference in velocity between the 11.5" and 12.5", about 70fps. Once again barrels cut from the same blank, all components the same.

XBR8208/77SMK/CCI450/LC Brass

23.3-2490
23.5-2510
23.7-2530 No pressure, a bit over gassed

quote:

Originally posted by offgrid:
Interesting the difference in velocity between the 11.5" and 12.5", about 70fps. Once again barrels cut from the same blank, all components the same.

I don't see that much change per inch of barrel for my longer barrels, but it does make sense that that MV change is greater as SBR lengths are compared. Good to hear that your barrels are working out nicely.

*****
So....which barrel/upper do you like better?

This message has been edited. Last edited by: fritz,

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Originally posted by fritz:

So....which barrel/upper do you like better?

12.5", slightly smoother recoil pulse.

A friend gave me some MK262. Shot it through the 11.5". Stuff is scooting. No doubt these two barrels are on the fast side.

Swapped the grip to a Magpul K2+, puts my finger on the bang lever at a perfect 90.

2526 fps for a 77 grain in an 11.5" barrel is moving. That SD is uber impressive.

MVs for my 14.5" LWRC, with factory ammo:
2470 fps -- Hornady 75 HPBT match
2533 fps -- Hornady 75 HPBT Black

MVs for my new 14.5" Wilson Combat, with factory ammo:
2477 fps -- Hornady 75 HPBT match
2613 fps -- Hornady 75 HPBT Black

FWIW, that 2613 MV with Hornady 75 Black is comparable to the MV from my 16" barrels.

Thank you for referring me to this thread, offgrid. One comment; four questions:
I didn't know custom gas tubes were a thing. Thank you for that. I was recently pondering something between mid and rifle length, for a suppressed build. Not sure if it's worth messing with though.
What do you mean by carbine+1?
Why do you not want to use light buffers? I though a lot of match-shooters liked low reciprocating mass for quick follow-ups. You thinking reliability and cutting through grime with more weight? My recent project working out with a regular spring and carbine buffer is something I perceived as a lucky bonus.
Did you use a Lantac enhanced BCG in this build? You mentioned you picked-up Lantac BCGs, but didn't really elaborate.
Have you shot these guns in matches? I am curious about the gas-to-the-face performance, once higher round counts and a quicker cadence were employed.

Carbine +1 is in between carbine length and midlength. In between gas systems are nothing new. Noveske, KAC has been doing it with their intermediate gas systems for years.
Use a heavy buffer, full mass BCG for reliability. The Lantac BCG's are enhanced. Not sure how much the enhanced matters? Have not A-B enhanced vs non-enhanced to know. Less gas to the face on the 12.5".

I was aware that some manufacturers employ unique gas system lengths. I was not aware that similar components were available to and utilized by builders, but I learn more and more every day about how deep the rabbit hole goes.

The Lantac enhanced carrier employs a vent aft of the gas rings, which is something I believe is effective. That's why I inquired.

As to gas system tuning, these look pretty slick.
https://blackrivertactical.com...e-Gas-Drive-c6464009

These look look pretty nifty too.
https://www.riflespeed.com/RIF...s-Controls_p_12.html

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Originally posted by powermad:
As to gas system tuning, these look pretty slick.
https://blackrivertactical.com...e-Gas-Drive-c6464009

I exchanged a couple e-mails with the owner regarding ports size, he was very helpful, believe he has a good handle on all that stuff.

I don't normally recommend stuff that I or friends don't have lots of rounds on... but!

For a 12.5 mid would consider this barrel.

https://www.ar15performance.co.../sdetail/38010/14399

For a fixed gas system would consider the gas tube powermad linked, go with hole size the owner suggest based on your info.

With my barrels only shooting handloads that are a little less pressure then factory BlackHills MK262 or 77TMK's, my fixed gas/buffer system is easy to get right. I'll never shoot anything but those handloads or BH factory ammo.

The JP silent spring system is very nice running supressed, it's quiet!

Starting with the correct gas port size to begin with would be nice.
It seems nearly everyone makes the gas port big enough to stub a cigar out in though.

I've read a few posts from the guy at Black River Tactical on m4carbine and he seems to know his stuff when it comes to AR gas systems.
Their line of barrels look to be sized properly. The recommended buffer for a 14.5-16" un-suppressed barrel is a Vltor A5H0.

I'm using a Faxon 16" mid length with a gas port size of .081"
That by most accounts is pretty big, seems .076" is about the largest he likes to see.
With an A5H2 buffer and a 2oz law folder adapter it's dumping brass in a pile at my 3:00.

I removed the folder and will probably need the A5H4 I have.
That's more mass than necessary though and the gas tube would bring that down to an A5H0 or H1.

A JP system would be slick, I'm running a green spring and it's sproingy to say the least.
For now I'll try a Tubbs spring instead.

powermad, going from a green spring to a Tubbs is probably going to be a linear move.

I tried the Vltor A5/H2, Tubbs/H2 and the JP on these uppers. All function great, I preferred the JP by a wide margin shooting suppressed.

Had some simple goals putting together the 12.5' upper.
Reliability, cycle smooth w/o adjustable anything and accurate.

It's been 100% reliable. Don't know the exact round count I've gone w/o cleaning, maybe 300rds? The full mass BCG and the H2 buffer smashes through that grime.
The time/thought put into getting the gas system right was well worth the effort, cycles very well.
Accuracy is outstanding. Need that accuracy competing against other quality stainless barrels in the hands of guys like fritz. Not competing against minute of something chrome lined barrels!

Shot this last month when checking to see if changing lots of XBR powder mattered. This barrel is the most accurate AR barrel I've shot. Because how well it cycles, watched the trace into the target on these shots shooting prone, bipod, rear bag at 15X.



Can see the the velocity at the target at 445yds. Station pressure 21.5'ish, what's the 77TMK velocity at the muzzle?

After shooting both these uppers. I regret not having two 12.5" barrels chambered from that blank. Live and learn!

quote:

Originally posted by offgrid:
The JP silent spring system is very nice running supressed, it's quiet!

I'm moving towards JP silent spring systems on all my lowers. I notice the reduced "sproing" sound more on rifle-length systems than on carbine-length systems.

More importantly is noticeably smoother cycling and less evidence of over-gassing. This is based on shell ejection pattern and the occasional gas on the check. I ordered special H3 versions from JP. This requires a phone call, as H3 versions aren't on their website.

About 10 months ago I signed up for a email notification for BlackHills 556 77TMK when back in stock. Surprised to get a in stock email a couple weeks ago, picked some up. Got lucky, 10 minutes later it was gone!

Shot the new lot through both barrels to check velocity. No difference from the other lot that's a couple years old.

We've all read about the predicted velocity difference with barrel length. Here's some real world velocities from two barrels cut from the same blank, new lot of BH 77TMK's. Fun stuff!

11.5"



12.5"



11.5"
23.5/XBR/Hornady 75BTHP/Rem7.5. It's the 75bthp load that shot the best through the 12.5", no where near the accuracy of the handload 77TMK's. Loaded my remaining stash of 75's for practice ammo. Interesting how much faster they fly!



I'll shoot 5-10rds of the new lot of BH on paper at 450yds, see what I see. The other lot is a little over MOA at 450yds.

From my experience with these two barrels, gas port size, gas length.... moving forward on a 14.5" intermediate gas for suppressor only. Pin/weld a TB flashhider on it.

Is that 77TMK the MK262 bullet? I read an article a while back about their great terminal performance out of SBRs, and my interest was rekindled in a recent conversation with a pig hunter. He also mentioned a 62gr soft point "FBI load". Is this a loading y'all are familiar with? I struggle with this: deciding whether or not I should make an effort to stock ammo that performs better than M193, and train enough with it to know it's trajectories out of my favorite guns, in an effort to be better prepared. The mindset would be that the majority of my practice is done with M193, but if SHTF I have better-performing ammo, and know how it shoots out of my gun(s). I practice enough though, that I think the M193 trajectories would be rather ingrained, and difficult to forget about. Does that make sense?

MK262 uses the 77SMK.

I shot 10rds of XM556FBIT3M FBI 62 grain load out of the 12.5 barrel, prone, bipod, rear bag, 15X at 100yds. Shot just over 3". I want better accuracy then that. I can't let go of my tons of rounds shooting LR bolt rifles/AR's and the accuracy required to be competitive. For the SHTF scenario does accuracy matter? Let the SHTF expert debate that! My HD AR is loaded with BH 77TMK's. YMMV and all that stuff.

I think accuracy always matters. The only exception being a strictly CQB use-case. In that case, your accuracy as a shooter still matters, but your ammo need not be held to strict standards of accuracy; just terminal performance. Maybe that's the mindset that drives design and production of those "FBI loads".