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jumbopanda
10-31-2010, 7:58 PM
A little while ago I posted a thread about how I'd have a small amount of gas irritate my eye while shooting my AR. I had also noticed that there was some gas hitting my Eotech at the front of the receiver, where the gas tube enters. After going to the range again today, I couldn't help but feel that the recoil impulse is a bit jerkier than it should be. On top of that, I keep getting the impression that the rifle is become dirtier than it should be with my Varget reloads. I clean and lube this rifle after each range trip, but after shooting only 200 rounds, the bolt carrier group begins to feel sluggish.

Here are the relevant details of my build:

16" BCM mid-length
KAC Triple Tap brake (maybe this is increasing gas pressure a little?)
Rifle length buffer tube and buffer
David Tubb CS flat wire buffer spring


I also shot someone else's 14.5 BCM mid-length with a FSC556 brake today, and the recoil felt noticeably less violent than that of my rifle.

From what I have read, there is nothing wrong with using a rifle length buffer with shorter gas systems, but I tend to think that carbine buffer systems, with their stiffer springs, would be more appropriate. I know that rifle buffers are heavier to compensate for this, but in this case I don't think it's doing enough.

I'm not sure what to think right now, so I could really use some help.

OutlawDon
10-31-2010, 8:47 PM
I'm no expert but if everything's installed right, it sounds like it's overgassed with your loads. It's recoiling harder than you think it should and it's also getting dirtier with gas spraying out. Have you shot just factory, off the shelf loads? How hot are your own loads?

Try some of these...

-Use an LMT enhanced bolt carrier that delays bolt unlocking
-Install a gas tube with regulator screw that lets you turn down the gas flow
-Install a regulated gas block that lets you turn down the gas flow
-Install a bushing in the gas block to reduce gas flow

jumbopanda
10-31-2010, 8:56 PM
I have shot factory loads, including weak Brown Bear ammo. What I'm really wondering right now is whether or not the rifle buffer system is appropriate for this upper.

OutlawDon
10-31-2010, 9:00 PM
I have shot factory loads, including weak Brown Bear ammo. What I'm really wondering right now is whether or not the rifle buffer system is appropriate for this upper.

Hmmm, well you're using the David Tubb CS flat wire buffer spring now, right? I've ran them before and if I'm not mistaken, a carbine and the rifle both use the same spring model.

What buttstock are you running?

If you plan to change to a carbine stock, that will require not only a new buffer tube along with buffer (obviously), but also a new carbine buttstock.

jumbopanda
10-31-2010, 9:10 PM
Hmmm, well you're using the David Tubb CS flat wire buffer spring now, right? I've ran them before and if I'm not mistaken, a carbine and the rifle both use the same spring model.

What buttstock are you running?

If you plan to change to a carbine stock, that will require not only a new buffer tube along with buffer (obviously), but also a new carbine buttstock.

The stock shouldn't matter since there's only one type of rifle buffer tube, but it's a Cavalry Arms A1 length stock. I already have a carbine stock assembly on a different lower, but the one I'm currently talking about is a featureless build.

Omega13device
11-01-2010, 11:27 AM
Who built the upper?
What load are you using (powder amount, bullet weight, brass, primer)?
Are you using the Tubb spring to fix some other problem or ???

I'm not sure what you mean by your bolt carrier becoming sluggish...do you mean it starts to drag? If so how much lube are you putting on it?

jumbopanda
11-01-2010, 3:07 PM
Who built the upper?

BCM

What load are you using (powder amount, bullet weight, brass, primer)?

I've fired several different kinds of loads, including Brown Bear, Ultramax remanufactured, and my own loads with 27gr of Varget and a 55gr or 62gr bullet. But honestly I don't think it should matter.

Are you using the Tubb spring to fix some other problem or ???

No, it was just what I decided to try after my old spring wore out.

I'm not sure what you mean by your bolt carrier becoming sluggish...do you mean it starts to drag? If so how much lube are you putting on it?

It becomes sticky and doesn't chamber rounds with as much force. I apply a medium coat of CLP on my BCG. Not dripping wet, but certainly not dry either.



:sleeping:

Omega13device
11-01-2010, 5:17 PM
Isn't 27gr of Varget pretty hot? I don't reload rifle so correct me if I'm wrong but Hodgdon says the max load for 55gr is 27.5 and Nosler says it's 25.0. I'm looking at their online reloading tables.

That said...A BCM upper should shoot any .223 or 5.56 factory ammo. So as long as your ammo is in spec I'd look at lube and spring.

Lube: CLP works fine but burns off relatively quickly. It sounds like that's what's happening if your BCG is getting sticky so after 200 rounds it's probably time to re-lube. Make sure you get all four carrier rails on the inside of the upper, and put a drop in each of the carrier's exhaust ports. Dirty shouldn't matter if you've got enough lube. Don't skimp. A little too wet is better than "medium". The excess will just drip off. Also, consider switching to Slip 2000, it lasts a lot longer.

Spring: Try a standard rifle spring. It's a good rule of thumb with ARs to use standard parts unless you're having a problem.

jumbopanda
11-02-2010, 6:32 PM
Isn't 27gr of Varget pretty hot? I don't reload rifle so correct me if I'm wrong but Hodgdon says the max load for 55gr is 27.5 and Nosler says it's 25.0. I'm looking at their online reloading tables.

That said...A BCM upper should shoot any .223 or 5.56 factory ammo. So as long as your ammo is in spec I'd look at lube and spring.

Lube: CLP works fine but burns off relatively quickly. It sounds like that's what's happening if your BCG is getting sticky so after 200 rounds it's probably time to re-lube. Make sure you get all four carrier rails on the inside of the upper, and put a drop in each of the carrier's exhaust ports. Dirty shouldn't matter if you've got enough lube. Don't skimp. A little too wet is better than "medium". The excess will just drip off. Also, consider switching to Slip 2000, it lasts a lot longer.

Spring: Try a standard rifle spring. It's a good rule of thumb with ARs to use standard parts unless you're having a problem.

My load is fine; it is well within .223 pressure levels and my brass does not show any signs of excess pressure. My rifle DOES shoot anything I feed it, and has been 100% reliable so far. My only concern is that it MIGHT be slightly over gassed. If that's the case, a stronger spring wouldn't hurt. The CS flat wire spring is probably slightly stronger than a standard rifle spring, so I kind of doubt switching back would help in this case.

I will try adding more lube before the next range trip and see if that helps the sticky BCG.

Omega13device
11-02-2010, 8:26 PM
I didn't say your loads were unsafe, just that they're at the hotter end of the spectrum. When you shot the other person's 14.5" midlength, was it with your ammo or his?

OutlawDon
11-02-2010, 9:55 PM
If it's truly overgassed, then you need to rectify the front chain of the issue and not the back chain. Changing to heavier spring/buffer might reduce the recoil, but doesn't take care of the dirty bolt/gas in your face/optic problem.

Omega13device
11-03-2010, 10:21 AM
If there's really something wrong in the gas system then BCM needs to fix it. There's no excuse. But... I'd be very surprised if an out-of-spec gas port got past their QC.

Before getting BCM involved I think a good diagnosis step would be to try this upper with a known, good-quality, factory load (not Russian...a good brass .223 load, M193, M855 or whatever) and a lower with a carbine stock. Then put a second, similar upper on the same lower and shoot the same ammo. If the OP's upper runs significantly different from the second upper in that test then there's something odd going on. I have a BCM 16" middy and an LMT 14.5" carbine and the recoil is almost identical, with the LMT being just a touch more sharp, so you shouldn't see a big difference across uppers with setups that are close.