new 300 whisper cycling problems

[GaryM]

I just finished building my first whisper on an AR15 platform. I range tested it and ran into this problem.
It chambered and fired great, I see a lot of potential accuracy in it too. it would eject the fired brass properly too but it wouldn't chamber the next round. I am 100% sure it isn't running the bolt back far enough.
I remember seeing a fix for this but since I can't seem to find it again I wanted to make sure. I believe it was simply swapping the rifle type buffer and spring for a carbine buffer.. or maybe it was a carbine buffer and spring. Can anyone tell me which it was or maybe an even better fix?
Right now I have a .125 gas port with a standard gas tube. (An adjustable gas tube is on order but won't be here for a few weeks)
The ammo I was testing was
1. 150gr fmj/8grs wc680 (fired, ejected, wouldn't reset trigger)(should be subsonic)
2. 150gr fmj/9grs wc680 (fired, ejected, wouldn't reset trigger)
3. 150gr fmj/10grs wc680 (fired, ejected, DID reset trigger)(supersonic)
Thanks in advance!

[Spook]

Gary, I had a similar problem with a 458 socom loaded light. I ran it for a hundred rounds supersonic to get the parts meshing together and then loaded heavier bullets for my subsonic loads... it ended up working that way.

[kurtz]

Gary,

I have found in my sub-sonic AR builds that when using a fully loaded mag they were a little sensitive to magazine spring tension until everything is worn in as Spook mentioned....if the bullet stack puts too much drag on the bolt carrier it can slow the cycle down enough to cause a short stroke....an inexpensive experiment is to cut a couple coils at a time off the mag spring then try it with a fully loaded mag....or try putting only two or three rounds in the mag with a full length spring to see if it cycles fully...

I usually end up cutting two to four coils of my mags used in my sub-sonic AR's.....

kurtz

[libertyswiss]

Originally Posted by GaryM

I remember seeing a fix for this but since I can't seem to find it again I wanted to make sure. I believe it was simply swapping the rifle type buffer and spring for a carbine buffer.. or maybe it was a carbine buffer and spring. Can anyone tell me which it was or maybe an even better fix?

Hello Gary

Another user wrote this to me, maybe this can help you:

Are you using a CAR or A2 stock?
If A2 & it doesn't want to cycle, get a CAR buffer & spring they are lighter.
Model 1 Sales has a 300-221 buffer & spring but DO NOT use it w/supersonics!

Regards from Switzerland.

[redtazdog]

These buffer springs fixed my short stroker

ACTION SPRING - reduced power
Stock No. 16505 - AR-15, M1-6 and Sporter.....$ 14.99 ea
Stock No. 16502 - CAR-15, M4 and 9mm SMG....................$ 14.99 ea

http://www.gunsprings.com/1ndex.html

[GaryM]

I am using an A2 stock and spring/buffer assy. I will be going to the range again tomorrow and will bring along one of my CAR clones, if I can't get the heavier (200gr) rounds to cycle properly I will "borrow" parts from the CAR and see if that fixes it.
Once I get it to work with the subsonics I will have to pick up an adjustable gas tube and try out supersonics.

[Garrett]

Originally Posted by GaryM

I am using an A2 stock and spring/buffer assy. I will be going to the range again tomorrow and will bring along one of my CAR clones, if I can't get the heavier (200gr) rounds to cycle properly I will "borrow" parts from the CAR and see if that fixes it.

DANGER!

Don't use your carbine buffer in the A2 buffer tube. It's not long enough, and will allow your bolt carrier to travel too far. The gas key will slam into the back of the receiver where the buffer tube screws in. You'll end up with a cracked receiver after a while.

[GaryM]

Originally Posted by Garrett

DANGER!

Don't use your carbine buffer in the A2 buffer tube. It's not long enough, and will allow your bolt carrier to travel too far. The gas key will slam into the back of the receiver where the buffer tube screws in. You'll end up with a cracked receiver after a while.

Wow, ok, gotcha. Thanks for the info, I don't wan't to destroy my reciever this quickly.
I did hit the range today. Using 9grs of WC820 and a hardcast 200gr bullet I was getting in the neighborhood of 1180fps, but not cycling even with the CAR buffer spring. So what do I do now? I have to drop the powder charge, I will be trying 8grs next but what about the cycling? Do I get an extra CAR spring and cutting coils?

ETA,
I just took apart and removed the internal (rifle type) buffer weights, just over 3 1/2 ounces. Do you think if I run it this way it would help cycling with subsonics? Of course for supersonics I would have a standard buffer to drop in.