Am I missing anything here?

[justapod]

I was wasting time at the gun shop and asked about an AR pistol. Out from behind the counter comes a gently used 10.5 inch 1 in 7 AR pistol with a tacticool paint job (I don't care!). I am wanting to play with it using a Sig brace and save the time on SBR paper work. The little thing has some pretty nice parts in it: a carbine length gas system, a Fail Zero M-16 BCG and hammer, KNS anti-walk pins, MBUIS, quad rail forend with a mount and light, a little Weaver red dot (it won't be staying), a tacticool looking muzzle break with sawtooth design on muzzle. The price is right and with the upgrades and extras is far cheaper than what I could build it for and it shows little to no wear. I am a little suspicious about what caused it to be sitting in the gun shop but I figure I have time to experiment now that I am retired. Off to the range and load it up with a known good 30rd Magpul magazine of Win 64gr Ranger PP. Bang stovepipe. Clear, bang, stovepipe, clear, bang, stovepipe. Now I know why it was at the gun shop. The compensator works well at least but the side blast is pretty formidable.

I head to the house strip it down and wipe the dripping oil out of it. Why do gun plumbers think if it is not running put more oil on it? I start with looking over the bolt and I notice that I can open and close the extractor with moderate thumb pressure. I am not an expert but I am pretty sure this is a problem. I check the extractors on a couple of other bolts and they cannot be moved by squeezing them at all. I remove the extractor and find it has only a 4 coil spring (very weak), rubber buffer, no o-ring. I replace the extractor spring with a BCM extractor upgrade kit: new 4 coil CS spring, rubber buffer and mil spec o-ring. I was going to be very scientific and only make one change at a time and test to see exactly what it takes to get it running reliably but I broke my rule and pulled the ejector and found that spring was about an 1/8" shorter than a new CS ejector spring so I changed that also. I check the buffer and spring and find a standard carbine buffer (2.95 oz) and spring that is 1 1/2" short and suspiciously weak but I leave them for now. A little bit of TW25B on the right parts and it is ready to go again.

I am back to the range the next day and start with the same magazine and ammunition: bang.......bang...bang, bang bang bang....bang bang. It is running right now. I try a magazine loaded with the cheapest 55 gr FMJs I could find at Academy and it runs fine fast or slow. Both magazines lock back on last round fired. The action spring is pinging away so I replace it with a Wolff extra power action spring with the stock buffer and it runs fine with a bit less noise from the action spring but still a noticeable ping. I put in a BCM H2 buffer (the heaviest I have) and test some more. It runs fine the bolt locks back on an empty magazine with all the ammunition I feed it. The muzzle seems to come up less and the spring is not pinging anymore. I try another 200 rounds made up of all the odd bits of .223 and 5.56 ammunition I could find laying around the bench and this little pistol is running perfectly. I know the guy who originally built this rig and he builds pretty nice stuff. I am pretty sure he is not responsible for the weak and or cut springs I found in this pistol. I cannot for the life of me figure out why some nimrod would think using a weak extractor and ejector spring on the bolt would be a good idea or improve anything let alone cutting the action spring.

I am no expert on short barreled ARs so do I leave it alone or would I gain more recoil reduction and reliability by going to an H3 buffer or one of Slash's heavy 5.5 oz. buffers? I kind of like the little thing and I have to admit it looks pretty good. The function and reliability is most important. From what I have heard and read the heavier buffers and or adding weight to the BCG improves function and reliability with the short barrels. I am going to keep it and I will be switching out the compensator for a Noveske KX3 to make it a bit easier to be around and to stop the dust storm in my face when firing prone. I appreciate your input.

 

[Javelin]

I would look at lessening the weight of the bcg before messing with the buffer.

 

[jasonfaz]

Who knows, the guy who sold it may have just thrown a bunch of spare parts in it that didn't work and traded it in.

I'd leave it how it is unless there's something that becomes an issue. A heavier buffer would be good if you plan on shooting heavier loads. DEFINITELY don't lighten the BCG. The heavier your BCG is the longer your bolt will stay locked equating to less gas in your face. An M16 carrier is a very good choice for that short of a barrel. Hell, I'd personally go even heavier. I use a PWS Enhanced DI carrier (about 10.2 oz compared to the Fail Zero's 9.7oz) in my 10.3" and the brass comes out shiny and no gas in the face even when shooting suppressed. All in all, I think you're gtg.

 

[justapod]

Thanks Jasonfaz. I don't see me going to heavy bullet loads with this. I see it more as a much more effective defensive weapon than a handgun. Sort of like an M1 carbine.

It is running well no gas in the face and yes the brass is pretty darn shiny. I have not tracked down the builder and probably won't he and I used to be in the same line of work but he left it before retirement. He got a few backers and opened up a firearms manufacturing company for a while and this is one he built. He was just big enough to have his own receivers built with his company name on them. He knew what he was doing but has always had trouble keeping drama out of his life. I think this is one he built on special order for somebody three or four years ago who then got to messing with it. They had no idea what they were doing and got rid of it.

I am not an expert on the AR platform other than shooting them enough to have a pretty good idea how they work and what parts should be like. I sort of enjoyed having the time to check it out and see if I could figure it out one step at a time. I just want to be sure I have not missed something. Thanks for your input.

 

[charvey9]

Those can be finicky, it sounds like someone was having some problems and just started tinkering beyond their ability and/or knowledge. Sounds like you know what you are doing, so if you like to tinker there is no harm in trying to improve performance through either of the ways you suggested. Sounds like a good little project.

 

[justapod]

Thanks charvey9. I just wanted some folks with more experience to warn me off if I am going the wrong way. I don't want to go so far the other way I get back to it not running again.