I may have missed it, but is there a reason that BCG is not staked?
I am impressed by the amount of time and research that went into this. What is that? 4.10lbs suppressed? Wow!
Jerry, using an adjustable gas block will greatly reduce the amount of gas coming out of the receiver end of a suppressed AR. I’ve never tried it, but using an adjustable gas block with the adjustable gas key should allow you to make gross adjustment of the gas flow at the block and a fine adjustment at the key. In any case, the adjustable gas block will work much better than siliconing the charging handle.
I found your post interesting and informative. Thank you for taking the time to share it with us
Thanks. You know, it is more the challenge of it and the systems approach to building the “perfect” build than actually needing such a lightweight rifle, call it a hobby I guess. That said, my 6lb Noveske is quite nice and I have become accustomed to its lack of heft.
The .750" V7WS titanium gas block is .8oz and a Syriac or SLR Rifleworks gas-block is about 1.4/1.5oz. So about .7oz difference, maybe not much but it didn’t fit the strategy of compounding weight, so I was willing to experiment with the adjustable key to use the V7WS piece.
SLR Rifleworks is said to be making a titanium version of their adjustable gas-block which would be ideal, IMO, and likely the same weight as other Ti gas-blocks. Who knows when they will be available though or if they will be available in black (hopefully in black and also .625").
Originally Posted By SLRrifleworks:
Titanium Sentry 7’s are coming.In production now.
22 grams for the .750 Set Screw Sentry.
Eventually all versions will be available in Ti.
They are about 50% Lighter. We are talking about a half once. Its not noticeable! -that said they are pretty neat.
But I keep getting hammed to make these so its happening.
These 7-S should be available in a few weeks in raw and melonite finish.
They will be moar expensiver.
I’ll have more info after Shot Show.
Heading out in about 5 hrs.
Todd
Thanks. It was kind of an underlying parameter to use high quality parts. It also adds to the flexibility of the rifle, since I can swap out the internals and have a pretty standard, robust configuration without carbon fiber parts.
Good eye! Sort of, I installed the gas-key myself and I do not have a staking tool (the stock Boomfab key is staked). SunDevil Mfg gas-key instructions say to use red loctite to install the key, staking not necessary. Not sure if that is the best idea since a gas-key surly gets over 412*F but since I didn’t have the staking tool and 'am testing out the RCA gas-key I figured red loctite is good enough until I decide if the part is staying permanently. I may go back to the Sun Devil key and I also have my eye on what 2A Armament is doing with an adjustable carrier with modular tail sections (http://www.ar15.com/forums/t_2_493/258846_A_few_images_of_one_of_TWO_lightweight_carriers_coming_out_soon_.html&page=1)
but, really, I would prefer a black Ti adjustable gas-block all around.
76.9oz=4.8lbs suppressed
63.7oz=3.98lbs unsuppressed
The rifle actually feels balanced unsuppressed because it is so short. With the can, however, it is inevitably front heavy, but still very light.
Thanks for viewing! I would prefer an adjustable gas-block but I am interested to see how this adjustable gas-key/carrier regulation shakes out. A few companies are working on these products, Gemtech’s is even called the “suppressed bolt carrier.” Having both would certainly be interesting maybe if SLR Rifleworks releases their Ti adjustable I will mess with that combo. I am just not sure if regulation at the gas-key is on the same par as keeping the extra-gas from entering the gas-tube in the first place. Certainly less gas comes out of the carrier vents, but as far as timing is concerned I am curious if the gas-tube is still pressurized when the gas-key uncovers it. If so, it would stand to reason this method of regulation, while successfully reducing cyclic rate, will do very little for reducing blowback into the upper from the gas-tube. But if carrier velocity is reduced, chamber pressures should also drop more before the bolt unlocks than if the it was moving faster, which should reduce blowback coming out of the chamber as the case is extracted. I am just not sure which variable is more a factor in blowing gas out the upper.
https://www.m4carbine.net/showthread.php?150517-New-Drop-in-adjustable-gas-system
Yes, there is pressurized gas in the tube when it separates from the gas key. The adjustable gas key will slow carrier speed, giving the bore more time to vent before extraction, so it will help some there. But the suppressor slows the velocity of the gas escaping from the muzzle increasing the time the bore and the gas tube need to vent down to atmospheric pressure. That means the gas flow through the tube will be regulated by the gas port.
C4IGrant talks about his experiences getting a shorty AR to run reliably both suppressed and unsuppressed (https://www.m4carbine.net/showthread.php?33743-Best-Suppressed-SBR-Ever). He discovered that, not only did having the right gas port size (which regulates flow) important to reliable function, but drastically cut down the gassing a shooter experiences when using a suppressor. If you plan to run your AR suppressed, I think it’s worth weighing the utility of the adjustable gas block against it’s extra weight.
It’s also worth exploring how the adjustable gas key would work protecting the shooter from noxious fumes. It may be that it will work delaying extraction long enough for most gas to be vented through the muzzle
Thanks for confirming. Perhaps blowback while suppressed is a weak point of regulation at this point in the system. It would be nice if a manufacture working with products on this front would drop by but unlikely they would divulge testing results in the parts race. I do intend to shake it out suppressed and will update. You are likely right about the adjustable gas block being the way to go. Most people running .300blk don’t bother with adjusting the gas but then they are not using ridiculously lightweight reciprocating assemblies. To that end, I did some looking around at SLR Rifleworks found the .750 Ti gas-block has been released. I don’t know for how long, 'never saw an announcement.
http://slrrifleworks.com/index.php?route=product/product&path=57_125&product_id=496
Thank you for sharing this project, an amazing amount of time, attention to detail, and $$$ went into this.
Very nice project gun. Curious to see how you like it over time.
i like it! great writeup/information; especially all the weights. thanks for posting it.
This^^^
Awesome build Jerry!
Cheers
Shannon
Very nicely done Sir - and a great write-up !!
This is what the custom build forum is supposed to be…thanks for the effort!
Great build and parts review. I have bought or am planning on buying a few of those parts myself, so it was good to have your take on them. I just paid for and sent off paperwork on a SiCo Omega this week. They are definitely amazing cans. It is almost unbelievable how a can that small and light will handle up to .300 Win Mag. I am also planning on getting the Spikes rear sight. I need a very low profile option to clear the ocular housing on my scopes (I mount mine a little lower than most so I can have a solid cheek weld). Also, call me old-fashioned, but I like having an elevation-adjustable rear sight with consistent click values. I have two of the KAC 2-600s, and while I love them, they are too high profile to work on my scoped ARs. They will stay on my red dot equipped rifles. Also I am planning on an RM06 for a Glock.
I generally don’t get down on stuff like this for myself but it looks an awesome setup. I really think those receivers are something! Beautiful machine work; very FAL-esque lightening cuts.
Even though it isn’t exactly my cup of tea, I can seriously appreciate all the research and hard work that went in to this.
I am glad I found out about those receivers and the various low pro/light sights. Thanks for the effort.
Wow, outstanding job on the write-up. I thought I knew which direction I wanted to go with my ultra lightweight 5.56 build, but now I’m considering .300 Blackout…
Thanks for the great info!
Great Great Job… Makes me want to put one together.
.
How did I miss this in June? must be working too much.
Any updates?
Yes, thanks for asking. I meant to post earlier but haven’t had time to shoot it in its most current configuration, since you asked I’ll post the changes here before the range report.
I swapped some parts out. Some add weight but serve an improvement in function. Some save weight, and I kidd you not, the thing still weighs right at my target weight of 4.0lbs unsuppressed and is <5lbs suppressed. Overall I had a .37oz net weight gain doing the math on the parts weighed individually. With the .2oz NSR panel handstop not pictured in the original weight pic showing 63.5oz the gun weighed in at 63.7oz, with the new parts swapped in the scale shows right at 64.0oz, no trickery. I think I might still swap the V7WS titanium firing pin in place of the melonited steel pin to shave hopefully another tenth ounce and get down 63.9oz.
Weight 64.0oz/4.0lb:
I swapped the steel KMR clamp blocks (.35oz) for the V7WS titanium KMR clamp blocks (.2oz).
I swapped the original Magpul MOE-K grip (2.0oz) for an UCWRG G23 grip (2.35oz) because, as you can see in the photos below, the original moe-k grip and the 1st run 2A Armament Balios-lite lower didn’t interface well. The overhang of the trigger guard tore up my middle finger when shooting. The G23 is still one of the lightest grips, interfaces flush with the integral trigger guard and just feels better all around. I made this same decision on Noveske Ultralight yet thought I would get away with prioritizing the weight over comfort on this build but the flesh missing from my middle finger protested.
Original 2.0oz MOE-K grip:
2.35oz UCWRG G23:
I swapped the V7 Weapon Systems .750 Titanium gas-block (.8oz) for a SLR Rifeworks titanium Sentry 7 adjustable gas-block (.97oz) mentioned earlier in the thread. I had it cerakoted black. With the insanely lightweight reciprocation assembly on this experimental gun gas-adjustability is crucial. I have shot the rifle since my last post but prior to the adj gas-block. I successfully tuned the adjustable carrier back a little more to where subsonic rounds struggled to cycle the action without a suppressor but supersonic rounds still functioned unsuppressed. I am not sure how much margine is left to adjust and there are other variables involved, mainly ammo type and temperature, but that tune helped slightly (it is still a lot) with the intense blowback I was getting while shooting supersonic rounds suppressed on the previous tune (cycle but no lock back with subs unsuppressed; full function with supers unsuppressed). Since this gun is a part experimental I thought adding the ti Sentry 7 was a perfect match for the build because I now have regulation at both the more conventional location of the gas-block and at the carrier with the adjustable carrier key while still fitting with compounding weight savings by being made of Ti (even though it is slightly heavier than the non-adjustable V7 Ti block). Things should be real interesting now! I can mess with the settings of each and really shake out the concept of carrier regulation vs gas-block regulation and probably end up with a really nice tune at the end! Also, if I were to swap out the superlight weight reciprocating assembly for a more standard set-up I will still have reliable gas regulation (the SLR Rifleworks Sentrys are excellent!).
.97oz Titanium SLR Rifleworks Sentry 7 gas-block cerakoted black:
Did I mention this build was experimental? Some bad bolt wear is an issue that came up and I really don’t know what to make of it. The bolt looks like it is hitting the lugs of the barrel extentsion while slightly rotated counter-clockwise/ in the direction of locking. The deformation on the left side (facing muzzle-ward) of the bolt lugs indicates this. The only theory I have been able to work out is that the BCG being so light while traveling faster than designed with less gas venting from the expansion chamber (carrier key regulation), the BCG may be bottoming on the reciever extentsion hard enough to jolt the bolt and cam pin backward thus rotating the lugs a little toward counter-clockwise/locked. Then when the BCG accelerates fastly forward due to being extreamly light weight, it slams on the barrel extentsion lugs hard enough and at enough of an angle to deform the top left corner of the bolt lugs. This may be a big issue since I only have about 180rds down the pipe mixed supers/sub/suppressed. Against this theory is that there should not be much room inside the upper for the cam pin to rotate toward locked when out of battery and I don’t see gouging on the left side of the upper reciever interior from the cam pin. I do however remember that the boomfab bolt carrier had a slight amount more play than the JP Lowmass it replaced. Perhapse that is where the give is in the rotation of the bolt interfacing with the barrel extentsion lugs. Though I suppose it could also be an undersized cam pin or oversized cam pin track allowing for the bolt to rotate but that, I think, would have enough play in it to not wreck the top left corners of the bolt lugs like is happening.
Any opinions? This is new territory for me, I have never seen this kind of wear on a bolt before.
Unusual bolt wear:
Awesome thread, thank you sir. I appreciate all the info on lightweight parts!