Some help to tune my AR rifle

A little background to kick this off... I decided to build two AR's from scratch rather than buying completed uppers/lowers or a completed rifle. These are the first two that I've built (and owned). I did tons of research before I even went down this path and felt I was capable of building a safe firearm (I purchased what I think are the correct tools along with go/no-go Clymer gauges). They both fire safely, however I'm trying to figure out how to tune them. Normally, I like to figure things out on my own but I seem to find some contradicting info online and wanted to share here and see if the experts could point me in the right direction before I start buying things that I don't actually need. I'm not on a tight budget, but I'm also not in need of top of the line stuff either, and I hate spending money on things I don't actually need.

For the purposes of my testing, I tried to keep as many parts consistent so I used the same exact magazines in both along with the same BCG, AIM surplus nickel boron. I was using Tula range friendly 55gr ammo (I know, it's crap ammo but it was cheap when I purchased it a couple months ago :/ )

I used the same lower to test both uppers as well. Anderson receiver, PSA lower parts kit (Magpul MOE kit) and upgraded to the RA Rave 140 drop in trigger.

Upper #1 - 16" mid-length "US manufacturer" heavy barrel, BCM upper receiver, odin works A2 flash hider
Issue - Occasionally I'll get a failure to feed. Maybe once or twice per 30rd mag. It hasn't jammed at all, it just randomly doesn't pick up a round (no consistency on how often it happens). When I rack it, it will start firing again for a bit.
Thoughts - Not too sure, but I'm thinking a heavier buffer may help send the BCG back with a little more force to pick up the round?

Upper #2 - 16" carbine BCA heavy barrel, BCM upper receiver, odin works A2 flash hider
Info (not really an issue) - This one has some extra kick (recoil) to it. Everything cycles fine, no FTF's or any actual "issues". However, I'm looking to bring the recoil down a little so I'm thinking a lightweight BCG may help reduce the recoil. But, would it better to start with an adjustable gas block to tune the rifle rather than changing out the BCG? I was looking at the odin works adjustable gas block.

This should be good on several levels

Wish I wasn't at work right now...

I had a similar problem with a similar upper as your “Upper #1”. I was able to fix it by removing the extractor spring and donut O-ring. and replacing the spring with a Colt copper colored extractor spring. I did not use a o-ring with the new spring. I would use a gold Colt spring or sprinco brand 4 coil extractor spring and not use the o-ring.

On rifle #1, make sure it's not undergassed. Make sure the gas block is not canted.

Rifle #1, BCA barrels tend to be a little rough= tougher extraction, some have out of spec or poorly drilled gas ports=possible undergas, add in steel cased Tula ammo that tends to be hard to extract and have low pressure, and even a decent build can short-stroke.

Rifle #2, more gas+ longer dwell = more recoil and more reliable with light ammo. There is a balance to be had between gas pressure/dwell time and reciprocating mass, and it needs to be within a certain tolerence to be reliable. Lightweight carriers/buffers work with adjustable gas blocks to reduce gas and keep a reasonable cycle speed, which reduces recoil, but they are more prone to jamming if there is any resistance from temperature changes or fouling. Full weight M16 carriers and H2 or rifle buffers have the mass to plow through dirt, and keep consistent cycle speeds with a wider variety of ammo and gas pressures in a wider range of conditions, but need more gas to do so. To reduce recoil, easiest thing to do is add a brake.

teratos said:

On rifle #1, make sure it's not undergassed. Make sure the gas block is not canted.

Click to expand...

Or just misaligned in general. Might need a camera to do it.

teratos said:

On rifle #1, make sure it's not undergassed. Make sure the gas block is not canted.

Click to expand...

Originally, I kind of thought it might be undergassed with the recoil being very similar to my M&P 15-22. I tightened the set screw in the dimple before tightening down the other set screw on the block, assuming that would've kept thing in-line. I will check this again.

alucard0822 said:

Rifle #1, BCA barrels tend to be a little rough= tougher extraction, some have out of spec or poorly drilled gas ports=possible undergas, add in steel cased Tula ammo that tends to be hard to extract and have low pressure, and even a decent build can short-stroke.

Rifle #2, more gas+ longer dwell = more recoil and more reliable with light ammo. There is a balance to be had between gas pressure/dwell time and reciprocating mass, and it needs to be within a certain tolerence to be reliable. Lightweight carriers/buffers work with adjustable gas blocks to reduce gas and keep a reasonable cycle speed, which reduces recoil, but they are more prone to jamming if there is any resistance from temperature changes or fouling. Full weight M16 carriers and H2 or rifle buffers have the mass to plow through dirt, and keep consistent cycle speeds with a wider variety of ammo and gas pressures in a wider range of conditions, but need more gas to do so. To reduce recoil, easiest thing to do is add a brake.

Click to expand...

I'm actually not sure who actually manufactured upper #1/mid-length barrel as it was listed on the site as "US Manufacturer". I've gone through the limited Tula I could find at the time and will likely stick to brass in this one.

I bought a muzzle brake initially but have not tried to use it yet. Wanted to keep things as consistent as possible to see how it works and then make adjustments. Initially, I didn't think swapping those out would be as big of an impact since the recoil between both uppers is pretty significant. Definitely worth a shot since I have a brake already.

outrider58 said:

Wish I wasn't at work right now...

Click to expand...

Uh oh. Somehow I feel like this is going to be like the equivalent to going to the principals office

Orawhaty said:

Uh oh. Somehow I feel like this is going to be like the equivalent to going to the principals office

Click to expand...

Don't mind him. He's a genius clown who loves google.

I do love me some clowns.

I ain't say'in nothin now...unless I have to call someone down to my office!

Sure clown...

Truth is OP, it cpuld.be a number of issues causing your problem....or a combination of problems.....Teratos is correct, it may be gas block alignment, it could be just shit ammo, bad mag, buffer/action spring, gas system issues besides gas block....I would run good brass cases ammo, kie Federal, with a good mag.....before doing anything....unless maybe Clandestine woukd be able to examine it.....he is the high authority on everything ARs.

3paul10 said:

Sure clown...

Truth is OP, it cpuld.be a number of issues causing your problem....or a combination of problems.....Teratos is correct, it may be gas block alignment, it could be just shit ammo, bad mag, buffer/action spring, gas system issues besides gas block....I would run good brass cases ammo, kie Federal, with a good mag.....before doing anything....unless maybe Clandestine woukd be able to examine it.....he is the high authority on everything ARs.

Click to expand...

This^^^
In the case of #1, mid length gas was developed to soften the shot impulse for shooting full power, NATO type ammo. That's why gun #1 feels gentler than gun #2). You try shooting powderpuff ammo through it, you can have cycling issues due to the shorter dwell time(length of barrel past the gas port), causing it, in effect, to be under gassed.


As for gun #2, that extra kick should be normal(relatively speaking). As long as it cycles, it should be fine.

Buffer systems can be touchy to play with. Too light a spring can increase bolt speed to the point of double feeding, FTF, FTE. Another problem with lighter springs, you can actually end up with a heavier impulse/felt recoil as the buffer slams back into the buffer. Too heavy a spring can have the same results with too slow a bolt speed/bolt short stroking.

Monkeying with buffer weight can have the same results.
You could tame the impulse a bit with an adjustable gas block, but if you're not running a suppressor, it's usually not worth the effort and expense, plus you would probably end up catering your ammo to such a setup.

#1 - stop using bottom of the barrel ammo. If it short cycles and fails to feed with good (M193 or M855) ammo it may be undergassed. Installing a heavier buffer is only going to make that worse. Given that your lower/buffer setup works with #2 also argues against playing the buffer game.

#2 - Extra kick? Compared to what? The one that short cycles? It's just a 223 so Cowboy up - if it working 100% it does not need to be "tuned." Stop looking for ways to spend $$ to make it fail.

I'd take a few steps back and do some basic checks.

Check the feed ramps, gas rings, look for gas leaks, etc. SOTAR has some good videos to get you started.

I believe that your rifle should cycle everything unless you have it set up for something specific.

Furious George said:

#1 - stop using bottom of the barrel ammo. If it short cycles and fails to feed with good (M193 or M855) ammo it may be undergassed. Installing a heavier buffer is only going to make that worse. Given that your lower/buffer setup works with #2 also argues against playing the buffer game.

Click to expand...

He absolutely should test with bottom of the barrel ammo.

A basic set up should be able to run everything.

omegared24 said:

I'd take a few steps back and do some basic checks.

Check the feed ramps, gas rings, look for gas leaks, etc. SOTAR has some good videos to get you started.

I believe that your rifle should cycle everything unless you have it set up for something specific.

Click to expand...

Now we're getting deep into the weeds. I was trying to hold off until we covered the basics. Gun #1 should cycle just about everthing. Let's see what it does with some 5.56, then go from there, maybe.

outrider58 said:

Now we're getting deep into the weeds. I was trying to hold off until we covered the basics. Gun #1 should cycle just about everthing. Let's see what it does with some 5.56, then go from there, maybe.

Click to expand...

I guess I take what we know for granted. I didn't think we were in the weeds....yet.

#1 could have bad feed ramps. Take a pen and see if it's catching or post a clear pic.