So I'm building a rifle for a friend, and that also somehow devolved into spare parts becoming the start of a new upper for myself. Crazy how that happens, huh...

Anyways. The original plan, to help get as low recoil as posisible, was a rifle gas 16in running a Brownells lightweight BCG (8.2oz) with a Taccom ultralight buffer system (0.6oz) and their -10% reduced spring, for only 8.8oz reciprocating mass for not only low recoil but to more easily ensure the rifle would function.

Well, that idea got nixed because we decided that weight was more important than recoil, and that's a med/heavy fluted barrel so it's nothing crazy, but still heavier than optimal. Instead, I'll be stepping down to a mid length for her build while the rifle gas found it's way over to mine (RCA BCG, 9.5oz reciprocating)What I'm wondering about, is running an adjustable gas block, would the lightweight carrier/buffer still work on the mid-length? Or would I end up over-gassing the system for that little reciprocal mass even with the adjustable?

These are both my first forays outside of non-adjustable carbine gas on full-mass parts (have an H3 in my current rifle), so I just want to make sure I'm getting everything right.

Oh, thanks @ghostjoe319, this answers absolutely nothing!

Unless you're making some magical lower that can affect the gas flow and resulting forces on and from the BCG/Buffer system, in which case I'm thankful for the myriad of details provided on this system, that really would be exceptional and intriguing. Except you've now fully nuked any possible interest I may have had. There's plenty enough companies out there that provide good parts along with good customer interactions that I can work with rather than ones that shill out through irrelevance and nuisance.

Not to mention the part where I already have lowers and uppers for each build. And the just slightly major part where I was asking specifically about the gas, bcg, and buffer systems.

So for any non-shill accounts, the original questions still stand.

There are many competition setups that are on mid-length gas systems 14.5 - 18 inch barrels.  The adjustable gas system will allow you to dial in the amount of gas that will allow the rifle to cycle properly.  I don't think you have to worry that it won't work.  You may not be able to get it perfect depending on the adjustable gas block type, but you will find that the reduction in recoil and scope shake will be pleasant compared to your conventional rifle in addition to the weight saving.

Remember that your gas setting will be ammunition dependent, so a setting with weak .223 ammo may not be ideal for a full power 5.56 NATO round (and visa versa).  Also as the gun gets dirty, you may need a little more gas to cycle the action.  In my experimenting with my lightweight SBR, even muzzle devices can cause differences in gas settings.  These effects can complicate the reliability of the firearm, so this is why many here would not consider using such a firearm for a battle rifle.  3 gunners tune their rifles for a match and keep them clean.  They know they will be able to maintain their rifles between matches or even between runs in a match.  It's not like they will be in the "sandbox" in a 24/7 fight for their lives.

I actually had fun experimenting.  I found it amazing how sensitive the action is to many, many factors.  I found an ideal setting for the current configuration of my SBR and the ammunition I use and stick with that now.  I just keep the SBR clean between range sessions, and I know I can rely on it if I had to.

I'm going to be putting an SLR Sentry 7 on there, think that it'd be fine? I'm just worried that I'd be overgassed even at the lowest setting, as that'd somewhat negate the point of it all. It's not going to be a battle rifle, it'll be her first gun. It'll just be getting range duty, if I was building a fighting rifle we'd be running some very different parts. She loves my AR so much that I decided to build one for her, but my 8.#lb unloaded M4gery running an H3 buffer and still a bit overgassed is a bit much for someone her size. So we're dropping 2+lbs, and though the recoil isn't near as much a problem for her, figured I'd keep that as low as possible for more fun shooting and so she could handle it a bit better.

Sounds like it'll probably be alright, so that should be good. Thanks!

I have a SLR Sentry 6 on mine.  I'm six clicks open without suppressor on 556 NATO ammo.  I'm 3 clicks open with suppressor on the same ammo.  My dwell time is a lot shorter than a 16" midlength barrel, but my gas port is a lot bigger.  My educated guess is that the Sentry 7 will be just fine.  You have 15 clicks full closed to full open, so your setting may not be "perfectly ideal", but since weight is more important than recoil, a little more recoil or scope shake won't mean much to you.

ETA: Don't put a brake on it.  They make a gun loud and you feel the concussion that might scare her.  If you do use a brake, put a blast shield over it.  That blast shield may increase the back pressure enough that you need to close the block a click.  It allowed my SBR to lock back on 5 clicks open on 5.56 NATO ammo.   Blast shields tend to reduce the effectiveness of the brake, though.  Have fun with it.

Already discussed brake/comp/FH with her, she seemed fine with it. If it does cause problems then I'll switch her over. She was standing between my 13.8" and a 30/06 last time we went shooting and didn't have much trouble. She's pretty tough, but she's also like 5'2" which is why we're trying to keep weight and recoil down.

I may go ahead and pick up a comp, and we'll use whichever one she prefers and the other will go on the upper I'm putting together for myself.

My small contribution is=  lower reciprocating weight will lower recoil but lowering the overall weight of the rifle adds to recoil. Reciprocating recoil and blast recoil are both contributors to the overall felt recoil. Good to keep both in mind.

Yup. If I can keep recoil where my gun is after dropping 2lbs, she'll do just fine. If I can drop 2+lbs and get recoil lower than mine is, then we're reaching grail territory.

I just picked up a BCM Mod 0 off the EE, which should be significantly less blast than the Arson Machine I was planning while still giving a bit of recoil help. Once the build is together we'll get out to the range with some crush washers and find out which she does better with, then get it properly mounted up back home.

My build is just happening because I had an extra barrel after deciding the rifle gas was too much weight and work for her, and then ALG has their V0-E on closeout, one thing led to another and now I'm cheating on my M4gery.

Thanks for the help! It'll be the end of the year before the build is finished but she's already hyped.

I run a SLR Sentry 6 Titanium with an RCA Competition low mass BCG and H1 buffer with a LW Larue PredatAR barrel. No issues, runs well on the 6th setting with my 55, 60 and 62 grn reloads.

I have 2 LW/ULW builds.  One uses a full-weight BCG and carbine buffer, the other uses an AP Custom lightweight (steel) BCG with an empty carbine buffer.  The ALG single-chamber brake is a godsend with felt recoil, even though both have adjustable gas and are tuned WAAAYYYY down to just lock the bolt back on bulk 55FMJ ammo.  Neither one has much felt recoil, but the full-weight BCG version (DD .625 barrel) with the SCB has CONSIDERABLY less felt recoil.  Yes it's louder, but that's the trade-off.

As inexpensive as the SCB is, it may be worth a try if you need some additional recoil mitigation.  That or maybe the FSC556.  I've heard exceptional opinions about those but haven't tried one myself.

I'll add some photos later (after work) if you'd like.

Interesting, would you say this is because of the SCB, or because of the full-mass parts?

I have an SCB actually, but it's a CWTX2 Privelige part so that's staying with me unless I can get her to attend a Cola Warrior.

She'll either end up with the BCM, or an Arson Machine Mk4A based off whichever she prefers. I'll put the remainder either on the LW precision upper I'm building, or I'll steal the SCB off my 22/45 for that.

Definitely because of the SCB.  For shits and grins i tossed it on the lightweight BCG rig, and it was like shooting a rimfire (minus the noise of course).  between the two, the full-mass rifle does have more recoil, but it's extremely relative.  The full-mass rig still has CONSIDERABLY less felt recoil than my GWOT m4 clone, without rds/vfg/ras panels.  and the M4 has probably 2-plus pounds over the LW, even with all that ancillary stuff removed.

Just adding a photo as promised. It's an awful one and includes a light-up gentleman's vegetables but they're tactical so it's okay.


20181017_182458 by Armed Ferret, on Flickr

Tossed it on the scale and 5 lbs 7.5 oz as is (without the ornament). Full mass m16 bcg (psa premium) and standard buffer.

Shoots like a dream.