Not sure if I am undergassed or overgassed. Using carbine buffer, tube and spring. AIM v2 nitrided bcg, 8" nitrided barrel with .093 port. std set screw lp gas block.

The bcg work great in a 5.56 rifle so dont think it could be gas key or rings. Gas block alignment has been checked 3 times and is correct.

I load single round in pmag and from a locked bolt, will pick up round and fire but wont lock back on the empty mag. It wont pick up the next round if I use a mag with multiple rounds.

My brass is ejecting at at about 3 oclock at a distance of abt 5 feet.

Can I be overgassed and the bolt not able to lock back? I have read it my be too fast. I am getting some roughness on the edge of the spent rounds. Wonder if there is too much gas and extractor is pulling on case early.

Using Fiocci 150 fmj brass case. The barrel was completely cleaned but haven't polished the chamber. Using pmag 30 round gen 2.

I will get an adjustable gas block if that would help. Want to set it up for range and maybe hunting so No subsonic or supressors.

I have a pic of the 6 rounds I have shot to show the edges.

Thanks for any assistance.

JBL121

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IMHO, your rifle is "undergassed".  I hate these terms.

I suggest you try the following in some kind of sequence that suits your wallet or technical skills.
1.  Replace your buffer spring with a Wolff reduced power buffer spring
2.  Install a "standard" carbine buffer (approx 3.0 oz.) if you are currently using a heavier unit.
3.  Open the gas port to 0.106"

Thanks Russ for the suggestions.

I will order a reduced spring.

The current buffer is a carbine AT 2.95 OZ.

I can open the port up but will try the spring replacement first. The barrel is nitrided so wonder if I need a special bit.

Springs are cheap and the one in the effected gun is at the max of length, 11.25". Do you think if I trim it to the minimum which I think is 10.125", do you think that may get it to cycle to lock or pick up the next round?

Thanks again for the response.

JBL121

I'm interested to hear what solves your problem.
Keep us posted.

A short barreled .300 was meant to use a standard spring and an h2 or similar buffer.  I have heard the fiocci ammo is underpowered.  I have not had any issues with it, but it has come up several times.  Try some different ammo before you go tinkering.

I would try other ammo first, I've been seeing reports of issues with Fiocchi .300BLK ammo.

UPDATE:

Went to range today and this is what happened. Took the carbine spring out of my 5.56 rifle that is 10.75" and the carbine buffer. Shot single round and no lock back. Tried 2 rounds in mag and now it will pickup second round and chamber it. I also tried the original carbine buffer with the 10.75" spring with results, no lockback but will pickup round off mag.

The spring that I started with that wont do either, is 11.25" which is the max length for a carbine spring. I think I have it down to the dpring being too powerful. I will order a Wolff reduced power spring and wonder if in the meantime can I cut down this spring to 10.25" which is 1/8" over minimum.

If decreasing the length 1/2" is getting me able to chamber a new round, I wonder if another 1/2" down to 10.25" will give me a quick fix until I get the Wolff spring.

I would like to try different ammo but its hard to come by. I read that Wallyworld in certain areas is carrying Remington UMC/Barnes 120grain but not in this area.

If I cut down the buffer spring, is there any tips? I have heard to put the cut end into the tube first so the factory end is by the buffer.

Thanks for any responses.

JBL

Does it lock back if you retract the bolt manually with the empty mag in place? Does this lower lock back when shot with a different upper? Be sure to eliminate mag and/or bolt catch issues.

Yes it will lock back if I pull back on the charging handle with an empty mag in.

I also attached the pistol lower to my rifle upper and it functions fine.

I cut the extra long spring from 11.25" down to 10.375" which is a 1/4" above minimum.

Will test it out tomorrow.

I will order a Wolff spring if this doesn't work.

The bcg I am currently using is a full auto cut bcg. AIM V2 nitrided. When I get around to getting a dedicated bcg for this pistol, do you think a ar15 cut carrier would help?

Will post results from tomorrow.

JBL

SOLVED

I got different ammo, Barnes/Rem 120gr and it was doing the same thing.

Was at a gun show last weekend and a vendor had a NEMO 300 blk spring. He said it was a reduced power spring and picked it up for about the same as a Wolff.

Installed today and runs like a champ with both the Barnes 120 and Fiocci 147.

For reference if anyone is building a similar pistol:

7.25" pistol buffer tube, reduced carbine spring. Carbine buffer 2.95oz. full auto bcg, AIM nitrided V2. Law-gun 8" nitrided barrel with .093 port. KAK flashcan.

Thanks for all the assistance.

JBL