Accuracy issue after installing lightweight bcg

[munsonbw]

I recently installed a Cryptic lightweight bolt carrier group (8.2 oz) in my SPR that previously was tuned for a "standard" bcg (unknown weight). Prior to installing the LW BCG I was getting sub moa accuracy with my handloads. Afterwards I am seeing around 2 moa and this is mostly vertical stringing. Any ideas? I did not change the buffer or spring and I do not have an adjustable gas block. I gather from some digging that I need to retune the system. Does this sound right? Anyone have suggestions on what I should be looking at for changes?

Thanks
Ben

 

[Blazin]

The 3-Gun guys noticed if they went too light on the BCG/buffer/buffer spring with a fixed gas block that the gun would start unlocking too soon and affect accuracy.

 

[RTH1800]

I would look for a standard BCG

 

[jda2631]

I'd look at getting a heavier buffer and/or adjustable gas block and see if that helps. I've quit using non-adjustable gas blocks on all my builds, just run so much better when you can tune the gas, I prefer the SLR adjustable block, I like the "click" adjustments instead of just a screw.

 

[Bigjake83]

I recently installed a Cryptic lightweight bolt carrier group (8.2 oz) in my SPR that previously was tuned for a "standard" bcg (unknown weight). Prior to installing the LW BCG I was getting sub moa accuracy with my handloads. Afterwards I am seeing around 2 moa and this is mostly vertical stringing. Any ideas? I did not change the buffer or spring and I do not have an adjustable gas block. I gather from some digging that I need to retune the system. Does this sound right? Anyone have suggestions on what I should be looking at for changes?

Thanks
Ben

I'd put the old BCG back in and see if your groups come back, and if so leave it be. You will find out that this is how people fall down rabbit holes.

 

[Subwrx300]

Clear sign of early unlocking of bolt (and your fired brass may be growing slightly more than it did prior). You will need to retune gas block or go back to standard weight.

 

[munsonbw]

I'd put the old BCG back in and see if your groups come back, and if so leave it be. You will find out that this is how people fall down rabbit holes.

Yeah, that is the next step. The original bcg is back in, but its been raining constantly and I haven't had a chance to test the grouping out.

Thanks for the hints, gang.

 

[308pirate]

Why did you change to a non-standard bolt carrier?

The best part of AR-15s is that they are easy to tinker with. The worst part of AR-15s is that they're easy to tinker with.

 

[jljr23]

Sounds like the lw bolt is unlocking to early.

 

[munsonbw]

A friend is associated with Cryptic and got me a blem. It’s a cool piece for sure, but looks like i assumed a little too much “plug and play “.

 

[jljr23]

A friend is associated with Cryptic and got me a blem. It’s a cool piece for sure, but looks like i assumed a little too much “plug and play “.

No free lunch in that stuff. The barrel and BCG are heart and soul of a rifle. You change those and things can get wonky.

 

[Hellbender]

You'll need less gas now, you're moving less weight.

Get an AGB. When you do that you can get a CS spring and really tune it right, see my old post here....

http://www.snipershide.com/shooting/threads/11-how-to-ultimate-ar-buffer-spring-tuning.48536/