View Full Version : Adams Piston Question/Realization

03-02-2012, 9:11 AM
Hey everyone,

I wanted to relay an experience I had last weekend regarding my carbine Adams Arms piston setup, and then maybe ask a few questions.

My friend was going out of town and we both went in on a new Chronographer. I was going to the range last weekend and wanted to try it out. It worked great and I was able to successfully test all my reloads. My friend also wanted me to test his reloads because he wanted to see how fast the 77 gr Sierra's were moving out of a 16" barrel. So I said okay (I know, I know what you're thinking....but I trust him). Anyway, my quick reloads were consistent enough for plinking, about a 75 FPS spread from the mean. But then I get up to his reloads....they were all over the board! Anywhere from 2025 to 2650. THAT is terrible. I talked to him and asked about what might have happened. He found out that his powder measure was in way too far when he made some of them. He has since fixed the problem and it is consistently pulling pretty accurate charges.

Anyway, the reloads were not my question....this is about the Adams Arms piston setup. What I would have expected from the VERY soft reloads that were going barely over 2000 FPS was that they would not be near powerful enough to cycle my gun. For informational purposes, my gun has the David Tubb flat wire buffer spring and a Spikes ST-T2 Tungsten buffer....which together should require quite a bit of pressure/force to cycle. But what I found was that even with the extremely low pressure rounds, they cycled PERFECTLY without a hitch and felt WAY MORE SMOOTH than my other reloads.

That got me thinking: Is my rifle overgassed? I always thought it was the piston OpRod hitting the carrier that made the harder "impulse/recoil" feeling, but I was wrong.....It's not the OpRod hitting the carrier: It's the back of the carrier hitting the end of the buffer tube! If I were to tune my rifle by putting in an even heavier carrier that will counteract the higher pressured rounds to get the perfect amount of rearward movement in the carrier, I SHOULD have a smoother firing gun, right?

Has anybody experienced anything like this with a piston gun? Does it take much less pressure to cycle the action? Or is it possible that my barrel's port hole is just way too big?

Thanks for any insight.

03-02-2012, 9:56 AM
If it's a high round count rifle then the gas port size may have increased. So you'll want to use the right spring and buffer combo to compensate. Basically you just want the buffer to barely touch the buffer tube during recoil for the load you use and you'll have a very smooth running gun.

I'd try a Springco Red spring and a Spikes T3 on your rifle.

03-02-2012, 10:13 AM
I think you have hit on an often overlooked positive of a gas piston AR. Not being as ammo sensative as a DI AR. I have both types of AR gas systems.
The carrier should not ever be crashing into the buffer. Spring/buffer weights need tweaking.
Adams has a 3 position regulator. Full, Suppressed and Off.
Try it again on Suppressed.

03-02-2012, 11:46 AM
Thanks guys. For the record, I should say that, even though the rifle may be over gassed, it has NEVER ONCE failed to fire or extract in the 2000+ rounds that have gone through it. Now I know that's not statistically significant as 2000 rounds isnt much. But if it is over gassed, then it is t really much of an issue other than wear and tear, and recoil impulse. I'm thinking I am goIng to have to experiment with buffer weights.

Too bad, I really liked the ST-T2's quietness.....

Droppin Deuces
03-02-2012, 12:56 PM
I had some really weak reloads that cycled perfectly in my Adams Arms gun as well. They are definitely overgassed, but it's not always that obvious as you're also pushing a lot of weight. It's when you shoot really hot loads(that's what she said) that you really notice how overgassed those guns are. I have a DI midlength upper that kicked abnormally hard, so I put an adjustable gas block and a Surefire muzzle brake on it, along with a standard carbine buffer. Now it literally kicks like a .22 when shooting 55 grain.
You can take weight out of your operating system when you have a finely tunable gas system. Since the Adams Arms only has two cycling settings, you can really only add weight if you want to slow the action down. I really liked my Adams Arms upper, but the inability to fine tune it was what ultimately made me sell it.

send it_hit
03-02-2012, 2:04 PM
It's when you shoot really hot loads(that's what she said)


03-03-2012, 11:32 AM
Okay, so I did some weighing this morning. Here's what I found:

- My Spikes ST-T2 weighs 4.13oz

- My Full Auto Adams BCG+B weighs 11.59oz

- David Tubb CS Flatwire Buffer Spring.....claimed to be as strong as the "Extra Power" AR-15 buffer springs without the extra weight. I cannot confirm how much extra opposing force this is putting on the action cycle, but it's got to be more than the standard.

So the total is 15.72 oz action weight with the equivilent of an Extra Power spring.

And yet based on the recoil impulse (carrier hitting the stopping point hard enough), I believe the system is STILL "over gassed" when using full speed, high pressure 5.56 rounds. How much more do you think the system can take?

At this point, I only have two options to "fine tune" the rifle without ditching the AA Piston: Add weight to the system, or buy a barrel with a smaller port hole. I am looking into adding more weight to the buffer and the BCG. Here is one product that looks promising: http://www.midwayusa.com/product/598476/tubb-ar-15-cws-bolt-carrier-weight-system . And I am also looking into the Spikes ST-T3 for additional oz's.

Then again, I suppose I could try the Suppressed mode and decrease the weight in the action parts and see what happens.....This would actually be free because because I have all the parts necessary already (old std spring, 2.96oz carbine carrier).

I guess we'll see what happens.