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Posted: 3/7/2017 3:11:20 PM EDT
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I'm in the process of my first SBR build and looking for a little input. I wanted to start with a blank slate so I ordered a stripped RRA upper and away we go.
Here are a few questions: 1) I've looked/considered the following with a standard single stage trigger: RRA, CMMG, BCM and maybe a few others. Besides the trigger assembly is there much difference in a most lower part kits? Is there one you would recommend or one that you would stay away from? 2) I want a good quality Mil-Spec buffer tube and assembly. I've been reading about the KAW Valley Precision buffer kit w/ a heavy tungsten buffer (4.3 oz). Is says the benefits include: increased reliability, reduced wear and tear of critical internal parts, reduction in felt recoil, reduction in bolt bounce, as well as eliminating the annoying "rattle" of standard carbine buffers. What are your thoughts on a heavy buffer? Or should I stick with a standard carbine buffer kit for about the half the price? |
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I like CMMG lpks with ALG triggers.
Aero Precision receiver extensions are cheap and gtg. 7075/dry lubed interior/ milspec sized. I run H buffers and enhanced springs from Damage Industries.Smooth and quiet. H 3 buffer may be nicer on SBR.? Good luck. 
Edit: spelling 
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Generally - aside from the trigger - an LPK is an LPK.
I have used CMMG, PSA, RRA, and whatever comes in Red Barn Armory's Build Your Own LPK and have not had any issues. PSA's come with a film on them that I don't really like, but once parts get oiled and shot enough that film comes off. With an SBR, you should probably get an H2 buffer (if you are having bolt bounce with an H2 then I'd buy an H3, or you can just buy another tungsten weight to put in the H2 buffer which would bring it up to H3 weight). It appears that the Kaw Valley Heavy Buffer weighs slightly less than an H2 buffer (H2 is 4.6 oz, Kaw Valley's Heavy Buffer is 4.3 oz). By "mil-spec", but you mean mil-spec dimensions or mil-spec materials and dimensions? If you want mil-spec materials and not just dimensions then you should look for a buffer tube that uses 7075-T6 aluminum and not 6061-T6 aluminum. Kaw Valley doesn't list on their website what material their buffer tube is so you could call them and ask if mil-spec materials is something you want. |
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Quoted:
Generally - aside from the trigger - an LPK is an LPK. I have used CMMG, PSA, RRA, and whatever comes in Red Barn Armory's Build Your Own LPK and have not had any issues. PSA's come with a film on them that I don't really like, but once parts get oiled and shot enough that film comes off. With an SBR, you should probably get an H2 buffer (if you are having bolt bounce with an H2 then I'd buy an H3, or you can just buy another tungsten weight to put in the H2 buffer which would bring it up to H3 weight). Good advice right here. You don't know how much gas pressure the rifle will have until you build it. It appears that the Kaw Valley Heavy Buffer weighs slightly less than an H2 buffer (H2 is 4.6 oz, Kaw Valley's Heavy Buffer is 4.3 oz). By "mil-spec", but you mean mil-spec dimensions or mil-spec materials and dimensions? If you want mil-spec materials and not just dimensions then you should look for a buffer tube that uses 7075-T6 aluminum and not 6061-T6 aluminum. Kaw Valley doesn't list on their website what material their buffer tube is so you could call them and ask if mil-spec materials is something you want. +1 7075 is much stronger than 6061. I bought a BCM tube from Aimsurplus last month (http://www.aimsurplus.com/product.aspx?item=XBCMMILSPECRE). The BCM trigger is also pretty good for the cost. I have them in 2 of my SBRs. |
| BCM reciever extensions are good. I would also look at the Larue MBT trigger. You can get it for $99 with a few week wait or $125 for immediate ship and it is one of the best value triggers out there. The RRA 2 stage isnt bad for the money either, but prefer the Larue |
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Thank you. Yes when I said 'mil-spec" I was referring more to sizing and not taking into consideration the actual material of the item; I will defiantly look for 7075-T6 aluminum though.
Again, great info guys. Thanks! This will be my first build from total parts and I'm figuring out real quick that building the one you want is not necessarily the cheapest route. haha. In the past I've bought a complete upper (used) then upgraded the parts I wanted. |
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Quoted:
BCM reciever extensions are good. I would also look at the Larue MBT trigger. You can get it for $99 with a few week wait or $125 for immediate ship and it is one of the best value triggers out there. The RRA 2 stage isnt bad for the money either, but prefer the Larue |
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I dont see the Larue MBT in a single stage? Are you putting a 2 stage trigger in an SBR? There is nothing wrong or illegal with using a two stage trigger in an SBR. I have a Geissele SSA in mine but the Larue MBT, Geissele G2S, or RRA 2 Stage trigger would all be good choices. If you want a single stage trigger, check out the Geissele SSP. |
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There is nothing wrong or illegal with using a two stage trigger in an SBR. I have a Geissele SSA in mine but the Larue MBT, Geissele G2S, or RRA 2 Stage trigger would all be good choices. If you want a single stage trigger, check out the Geissele SSP. Quoted:
Quoted:
I dont see the Larue MBT in a single stage? Are you putting a 2 stage trigger in an SBR? There is nothing wrong or illegal with using a two stage trigger in an SBR. I have a Geissele SSA in mine but the Larue MBT, Geissele G2S, or RRA 2 Stage trigger would all be good choices. If you want a single stage trigger, check out the Geissele SSP. I guess I was thinking a 2 stage trigger would be used more for long range precision?? Am I thinking about this wrong? |
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I guess I was thinking a 2 stage trigger would be used more for long range precision?? Am I thinking about this wrong? It really depends on the break weight of each trigger stage, IMO. Geissele Automatics - who as you probably know makes a variety of high quality triggers - recommends the SSA-E for Precision & Bench Shooting as well as target shooting but recommends the SSA and G2S for a LE duty trigger or for a home defense rifle. The SSA-E stage break weights are ~2.3 lbs break in the first stage and ~1.2 lbs in the second stage. Geissele believes that is too light for an HD or duty rifle trigger. The SSA and SSA-E triggers are functionally very similar except for the trigger stage break weights. The SSA has a first stage break weight at ~ 2.5 lbs and a second stage break at ~ 2 lbs. While there are arguably better triggers than the SSA or better values in triggers than the SSA, I'd say that if you used a 2 stage trigger with similar stage break weights that the SSA has, that trigger would be appropriate for an HD or duty rifle. |
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I've been reading a few other threads out there and don't want to be guilty of hijacking someone else's thread but have another question. As i mentioned above this will be my first SBR. I have a half-dozen other full length (16") AR's all in 5.56, so when I first started this process I was going to build a ~10" barrel in 5.56 since I already have the ammo. I also plan to suppress it too.
So here's my question. I've had people tell me that I don't want a 5.56 with a barrel less than 12". I've had people tell me that a shorter barrel in 5.56 will shoot a 6ft fire ball out of the end of the barrel. I've heard that a shorter barrel wont cycle 5.56 that well. With all those things in mind I started moving towards the direction of 300BLK. I understand that for starters a 300BLK should be easier to shoot subsonic than a 5.56? Are there any other significant advantages in a 300BLK over 5.56 in a SBR? If you guys are shooting a shorter barrel in 5.56 (less than 16") what seems to be the sweet spot? Thanks in advance! |
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I've used LPKs from RRA, Delton, DPMS, and Aero Precision. So far the kits that have gone together the smoothest have been RRA. Their roll pins are the coiled type vs the split type and just seem to install easier than other kits from my personal experience. I've also been pleased with the quality of the Aero Precision kit. It has the best single stage mil-spec trigger of the group, followed by the RRA.
I am in the middle of a 10" pistol build. I chose 300 blackout for this one because it was designed around shorter barrels and I didn't like the performance loss 5.56 would take. |
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Quoted:I've been reading a few other threads out there and don't want to be guilty of hijacking someone else's thread but have another question. As i mentioned above this will be my first SBR. I have a half-dozen other full length (16") AR's all in 5.56, so when I first started this process I was going to build a ~10" barrel in 5.56 since I already have the ammo. I also plan to suppress it too.
So here's my question. I've had people tell me that I don't want a 5.56 with a barrel less than 12". I've had people tell me that a shorter barrel in 5.56 will shoot a 6ft fire ball out of the end of the barrel. I've heard that a shorter barrel wont cycle 5.56 that well. Quoted:I've been reading a few other threads out there and don't want to be guilty of hijacking someone else's thread but have another question. As i mentioned above this will be my first SBR. I have a half-dozen other full length (16") AR's all in 5.56, so when I first started this process I was going to build a ~10" barrel in 5.56 since I already have the ammo. I also plan to suppress it too.
So here's my question. I've had people tell me that I don't want a 5.56 with a barrel less than 12". I've had people tell me that a shorter barrel in 5.56 will shoot a 6ft fire ball out of the end of the barrel. I've heard that a shorter barrel wont cycle 5.56 that well. Two things are at work here, reliability and shootability: 1. Plenty of people run 7.5-11.5 bbls on ARs. If it's a DIY build, yeah, getting reliable/good cycling make require a little tuning. Gas port size (or adjustability), buffer weight, spring strength, BCG weight, ammo type etc. are all factors in how well a gas gun cycles. A minor amount of experimentation may be required, but like I said, plenty of people do it and have reliable guns. 2. 556 was designed to be shot out of longer bbls (longer than 11.5 anyway). It's case capacity means that factory ammo is gonna have a lot of flames / still-burning powder when you shoot it out of a SBR. Some people like this. There are times when I WANT some fire-breathing / loud-shooting action, it's fun. If you don't want that, a really good flash suppressor, 'flash can' type of muzzle device, or linear compensator will help with the fire / felt concussion. Alternatively, if you love side ported muzzle breaks, they often amplify the fire/concussion effects for the shooter and especially for anyone nearby...so most people prefer not to use them on SBRs. With all those things in mind I started moving towards the direction of 300BLK. I understand that for starters a 300BLK should be easier to shoot subsonic than a 5.56? Are there any other significant advantages in a 300BLK over 5.56 in a SBR?
If you guys are shooting a shorter barrel in 5.56 (less than 16") what seems to be the sweet spot? Thanks in advance! I love love love 300blk, especially in short bbls. Having both super / sub reliability was a design objective from day 1 with that caliber, so by and large it 'just works'. I've got 8.5" 300s, 10.5" 300s and a 16" 300, and all of them worked out of the box with both supers and subs with no tuning or adjustments or anything else. I plan on building a 6.5"-ish 300 pistol soon as well. It has much smaller case capacity, so you get way less fire/concussion, all else being equal, compared with 556. You can load heavy bullets in it that make subsonic 'worth doing', which is pretty much impossible with 556 simply because the bullets are so small/light. 300blk isn't the perfect caliber, most subsonic loads don't have great terminal ballistics, mainly because they use bullets not designed for that purpose. There are alternatives that do, however, if you really wanted to use it for a SHTF caliber. The most fun I've ever had with an AR is a 300 blk SBR with subs and a silencer. Pretty epic. 
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| OP didn't mention the purpose of building the SBR, but assuming you're building it for more than just a range toy, then you should also research terminal ballistics in 5.56 short barrels. Short barrels reduce velocity, making round selection even more critical. How far you want to go down that rabbit hole may help determine barrel length selection. |
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Thank you JekBrown, that's great info. I've heard a 5.56 SBR will shoot a fire ball 5-6' out of the end of the barrel. And I plan to use a suppressor to help quite it down a little, but I've also been told that after a few rounds the can will all but be glowing red. Everything I've read so far kind of points to a 10.5-11" barrel as being the minimum length for the 5.56 round....with less "tuning" required?? My thoughts were that if I could keep the barrel in the 10.5-11" range then when I add the can my total barrel length would still be ~16". If I cant do that then I probably wouldn't wast the $$ on a 5.56 upper.....just apply those funds toward the 300 upper and/or ammo.
My ultimate goal would be to have a 300 and 5.56 upper in SBR. The 300 would be for shooting sub and ultimately more of the go to. However, I was hoping to build a 5.56 first since at this point this is what I have in ammo supply; then as I build my supply in 300BLK I would primary use it and have the 5.56 as a spare or just for plinking. Mike to answer your question, yes this is more of a toy than a tool; especially as for the 5.56. Just something I've wanted to do for a while but just haven't ventured out with it until now. As for the 300BLK I would use it for hog hunting, plinking and personal defense if ever needed. Thanks again for your help guys! |
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Fireball size depends on the ammo and muzzle device type, but yeah with certain combinations that can be pretty large and all else being equal shorter bbls will result in bigger ones. There are plenty of 10.3-10.5 AR barrels available, but for practical use I think 11.5" or 12" is the sweet spot SBR bbl length for 5.56. That still gives you some decent fps and yet more manageable OAL with a can attached.
As much as I like 300 blk, I am glad I have other uppers in 556 to shoot as well. Even if you get cheap ones, factory 300 blk subs are going to run about $500/case. That makes a day of shooting pretty $pendy. 
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11.5" Would be my suggestion if you are looking for a reliable yet shortest barrel.
12.5" is just a pleasure to shoot... Whatever you do, do not get 7.5" unless you are just going for shits and giggles....
I have 10.5, 11.5 (x2) and 12.5 for my 5.56 SBR. 8.75 for 300AAC I shoot 11.5 the most. |
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