Just finished a 300 build and it fires well. Ejects/loads next round, does not lock when empty. tested two mag brands and same thing. It also easily ejects/locks manually. brass is not going far. Parts were decent. MAS Defense 8.5 nitrided barrel. it looked great, good reviews. St. Croix BCG, NiB coated, also good reviews. Decent Upper and lower mil spec receivers. Anderson lpk. Buffer tube kit is cheap Ebay but went by LGS and the spring and buffer seemed to be by look and feel (placing in their guns, etc) identical to their stuff. They do a lot of builds and spent a lot of time looking over mine. Nothing obvious. Logically either in buffer system or gassing problem. It’s Remington 220 grain with a slight hollow point. They are subs. Saw another post that Rem 220 subs were not even feeding the next round so thought I was doing pretty good then by feeding without any suppression for subsonic loads.
Decided to try some hotter rounds and see how it did and if worked ok might address subs with drilling gas port, KaK, etc. I picked up some Remington supersonic 120 grain OTFB. I put one round in and fired and was thrilled the bolt locked back. Much more recoil noticed. I put two rounds in to test feeding and thrill left me. Spent casing is consistently sideways with the newly fed round underneath it on the feed ramp or nose almost in the chamber, both wedged up front. It appears that the new round is what has the spent casing wedged, not the BCG since its grabbing the new round. changed the cheap silver buffer from the Ebay kit with another carbine buffer from LGS and tried different mag. Feeding problem with super is pretty consistent. Extractor problem?
I didn’t try a lot of subs, just a couple of pairs in the mag at a time to check feeding, so at this point subs appeared to be feeding, just not locking bolt, supers stove piping.
Maybe I shouldn’t have yet but went ahead and drilled the gas port to 7/64 which is about .110. It was already 3/32 or about .095 so that’s only 3mm difference. Subs now lock the bolt but now they have extraction/feeding issues also. Both subs and supers spent casings are now laying straight inside on top of the new round (new round was grabed by bolt but obviously didn’t get far) instead of stove pipe. The rims have mild scratches from the extractor but seems normal, no deformity, doesn’t appear any more than usual. They do have scratches down the length of the case on all sides as if maybe chamber is not smooth or polished but been that way since day one. Maybe it is an extractor problem.
It appears the symptoms before were short stroking, now there’s more gas but not extracting. There’s a you tube video a guy claiming a cheap non mil-spec ebay buffer tube kit was causing him problems. Buffer kit and BCG only variables not changed. I don’t really see how I’ve added that much more gas. Subs seemed to work when supers were stove piping. Now subs and supers have same problem. It seems gas should be about right now but maybe not and causing a timing issue. They eject with singles but doubles can’t get out the spent casing before jaming on the new.
I just received my order for the Springco/BCM BCG ejector and extractor spring kit. They say this can sometimes rip the rim off a casing they are so strong. I also ordered another St Croix BCG in Crome (on sale) to build a 16in 300 upper. Thought I can try the original BCG after spring kit, plus the different BCG and see what happens.
I Have not installed springs yet but was shocked to find that the new BCG was getting stuck on the gas tube. Would only go about half over. I called st croix and they said they would ship another, try both and ship back what didn’t work, they would include a shipping label, no cost. Thought that was pretty good service.
Coincidentally, the next day I received a new gas tube that I ordered for the 16in build. I ordered the old and new tube from ebay. Old included a gas block. Both stainless. New was just a tube, advertised as made in usa etc.
The new tube slid into the new st croix just fine. When I slide the new tube into the gas key of both the original BCG and the new that won’t slide over my old tube, they feel the same. Very little play, can’t tell any difference. So the new BCG is obviously thousandths under from the old tube or the original BCG is thousandths over to fit over the original tube. Yet new tube goes in both and feels the same.
Replacement BCG is not here yet, maybe today. This is why I shouldn’t do stuff like this because if it’s going to happen, it’s going to happen to me! I also bought a new good quality buffer tube kit from the LGS. My old tube is slightly shorter then the new but so is the spring when all parts are compared. My plan is to try the new buffer kit, then BCG spring kit since the original BCG is all that goes over the old gas tube, then maybe the new gas tube and different BCG. If that doesn’t work I’ll try a .223 barrel. If that works I’ll sell everything and get out of building AR pistols, especially in 300 blk.
Vox600
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