As mentioned on another thread I finished up a frankengun in .300 Blackout.

I have to have the headspace checked Sat by a shop not too far away.

How often do they go together and two different manufacturers barrels and bolts not headspace correctly?

Mike

P.S.

If I start doing this on a somewhat regular basis will buy my own gauges I guess.

Mike

Not sure about the 300BO barrels but quality .223/5.56 bolts and barrels headspace correctly 99% of the time. I measured fired cases from 6 different barrels once and all headspaced within .002". Thats pretty darn tight tolerances considering all were mixed and matched.

That is impressive!

Mike

the black out uses a 5.56 bolt, whose barrel did you use?

Very rarely, especially if you are using mainstream brands IMLE. Unless you need match level tolerances, shouldn't be an issue.

I used a JSE barrel and Palmetto bolt and carrier.

Mike

64

it's a fun gun to plink and play

Mike

I'm sure that it won't be too far out to deal with by adjusting your sizing die.

Mike - I doubt you will any problems with the PSA BCG, they seem to hold up well.

I have had an issue with one JSE barrel in 6.8 SPC. Over-gassed and a rough chamber that took some work to get right. Data point of one, and I haven't had any issues with anything else I have ordered from them.

Good news after I ordered it I have seen they have mixed reviews.

Mike

Barry

I don't want to even fire the thing without checking it. The shop is a 30 minute drive to and we are going there this weekend anyway so I want to ere on the side of caution.

Mike

Do you have a gauge?

No, the shop I took it too said they used a gauge for the first hundred or so rifles they assembled without any of them ever being bad and quit checking them!

Mike

Went to the range after work and put 4 rds through the rifle by headlight!

Brass filled out perfectly, did not have enough umfff to drive the bolt back far enough to pickup the next round, had to cycle by hand.

Guess I need to find a weaker spring or lighter buffer. Just using standard carbine stock parts.

16" unsuppressed, Rem factory 125gr loads. Brand new upper and bolt carrier group so still not the slickest yet.

Mike

#31 drill bit through the gas port

Will it hurt later when shooting suppressed?.



Mike

Don't drill your gas port yet. That's always a last resort because it's permanent.
Try a lighter buffer, more lube on the BCG, make sure your existing has block is aligned.

Nonsense, #37 drill, 5-44 tap and set screw, allen key, lock-tite, and your back to no port at all...doesnt take too much imagination to guess what has to happen after that.

Then again, the shortest distance between too much gas and the perfect gas pulse is an adjustable gas block.

PRI makes a nice one.

Thx for all of the help men, I will get back to the range with a decent amount of time this time and try some spare parts.

Mike

Well almost a year later swapped the upper onto a well used lower and swapped bolt carrier groups with one that didn't have the M-4/M-16 bcg and had previously loosened the gas block to check for port to port alignment and it appeared to have been aligned.

It went from never feeding to 4-5 hiccups out of 20 rds, will order a Nemo buffer spring specifically engineered for .300 blackouts and hopefully that will get me to 100% reliable.

Mike

They are interesting for idiots like us that know little about them. They are beginning to grow on me.

I was going to build a 6.8 SPC as a wet weather deer rifle, have to have some excuse you know, but once this round was commercialized and the fact it uses standard mags sold me real quickly on it over the SPC.

Will post results once I get the spring in.


Mike

late to this party... don't drill... get a couple hundred rounds through the gun first...

New gas guns typically need things to smooth up a bit, and keep the BCG and upper lubed well as it breaks in.

Then, if it doesn't work, IMHO an adj gas block is by far smarter than drilling a hole... especially if you are going suppressed and different ammo later.

BUt as noted you can drill, then tap, plug and redrill like a redneck. Could even put jb in the port hole and drill smaller...

10-4, I appreciate it, I don't think it will be necessary to drill it now.

The rifle has 40 rds through it, last year at this time I was crippled up with bulging discs in my back and didn't/couldn't do much.

I like the idea of an adjustable gas block and once I get it reliable and broken in will decide on final configuration.

Mike

I don't think going with a can you could do it any otehr way and be able to tune, to cylce, and then flip to super sonic and without the can and so on. IMHO.

First 100 rounds through a top line barrel like a Krieger sometimes will even have a few hiccups, much less over time since they pretty much figured everythign out, but still you never know. Though I did set a range record once on about the round count of 150/200 or so range...

An adjustable gas block won't do a thing on an undergassed barrel. You'd need to drill the hole out too big first, then the adjustable block would be effective.

I disagree that he needs to just keep shooting it. If it won't cycle at this point, it's undergassed and needs to have the gas port opened up a little. If you go in small steps, you can get it tuned perfectly that way.

I would drill instead of messing with special buffers. Some of that "special for 300 Blk" stuff is just marketing snake oil; just tune it right, same as you would a 5.56.

Carbine std buffer just a different spring.

Mike

http://www.brownells.com/rifle-part...out-carbine-buffer-spring-prod56149.aspx

Headspace checked on an AR lol...I must be one lucky SOB I have built around 60 plus ARs not one has ever been checked. Barrel can only go so far back and the bolt can only go so far forward. If it chambers a round and ejects it's good to go.

All I can say is having went through a LOT of barrels in competition, it was not unusual to have a gun barely function or not function quite right until everything was slicked up some.
Generally on totally new uppers.

Its easy to put an Adj block on. And wide open if it doesn't cycle after 100 rounds, then open it some. Goign subs and with a can you may have to open it even more.

But its VERY rare to have a factory tube undergassed. I wonder if the base for the block is not lined up with the port completely?

If you use good parts you are ok. Bolt with barrel.

If you don't, you can have enough headspace to make brass life very short if you don't understand headspace or reloading.

If just making it go bang is the desire its fairly hard to mess up.

If you are putting em together for others and don't have 60 plus of your own and you are not not overly smart about that part. Its one thing to have a possible mistake for you, but for others....

In ARs, proper headspace happens with chambering, not with bolt selection.

yes,and I"m not sure who you are replying to, but if you buy a bolt headspaced to the barrel you are fine. Thats what I was saying.

OTOH you can swap bolts back and forth and find minor changes in headspace at times, just due to bolt tolerances.

The cheap way out, put one together, fire a few cases and read them on an RCBS headspace gauge for fired brass.

Just a general observation for the OP. If he thinks he's going to fix headspace with a new bolt, he's schitt out of luck. Ain't happening.

Just grab a bolt out of that box of 1,000 and slap it in. It will work as good as any other bolt in a box of 1,000.

Easy to do, but completely useless on a barrel that's already undergassed.

Being undergassed is not that rare when you get away from 5.56, especially if his 300 barrel has carbine gas. Someone may have just used the same port size as a 5.56 barrel, which would explain the issues he is reporting.

No way in heck you would use same gas port as 5.56

But maybe in this day and time folks are generally stupid I guess. It well could be.

Never seen mass makers drill ports to small in the day, always to big.

For 300/221 you shoot it sub sonic at some point, its the whole reason for the round, and for that, you need to open the port up big enough, then when going back to supers, you need to close it. Hence eventually needing an Adj gas block even after the initial problem is solved.

I bet, and I don't recall because I've had the Rock barrel around so long, that a Rock barrel for 300/221 is not undergassed nor does it have a 5.56 port size( which are generally to big to start with anyway IMHO)

Spring came in today, noticeably softer, smaller wire and less pressure to compress, wider coils, feels like it will be great, hope to test tomorrow at lunch or at least after work.

Mike

Got the new spring in and finally got a chance to test it, had a minor magazine problem then it ran like a top.

First 5 shot group at 100, I don't have a clue about the stray round, I put 2-3 rds on paper at 50 yards prior to this group and it sat while I went down and hung the target





Mike