FSB flew off

[jbanzai 113]

After getting the FSB and GB on my rifle, I went to the range for a quick function check. I debated whether or not to use the '74 brake. I decided to use it. After about 12 rounds, I noticed the FSB was a little canted, but it was cycling fine so I decided to take a few more shots. After 2 more shots, the FSB flew off the end about 3 feet down range.

 

I believe I read a post a while back with someone with this concern and the response was.....it's not like its gonna fly off the end.

 

I had to pound like Casey Jones with a rubber mallet to get the GB on, but the FSB went on ALOT easier than I expected. In fact, after I just got it back on, I could have indexed it by twisting with my hand if I could control the pressure. VERY light tapping is all it took to get it to drift.

 

My concern now is that when I drill the pin holes, that I will push the FSB out of alignment and have canted sights.

[bigdust80 10]

I just did the '74 FSB conversion on my .223. I was concerned about using my new Bulgarian 74 brake w/o pinning the FSB in place. Was yours surplus or one of the new Dinzag units? Mine went on easily, but I lightly buffed the inside of mine to remove some of the mill marks on the inside, used a little oil and tapped it on with a 5lb maul with a piece 1/2" rubber to deaden the blow. I have a new Dinzag unit.

I guess when I take it out to check alignment I shouldn't use the brake.

[jbanzai 113]

My brake is from a kit... surplus. Sounds like yours went on about as easily as mine. I did very light polishing on the barrel....didn't even remove any mill marks. I think the diverted pressure inside the brake caused the fsb to fly off but don't really know.

 

I wish I went with my instinct and left it off, but the GB was solid and it cycled fine which was what I was really checking anyway.

[thebuns1 4,323]

dont let this deter you. after pinning it to the barrel, you shouldnt have to worry about it ever. that is odd though. the one i just did, my FSB is a bulgy unit, and was kinda a pain in the ass to get seated and indexed. im glad to hear yours went on much easier, but that sucks that it actually came off that easy.

[Agent Lemon 157]

It flew off? Secondary projectiles are awesome.

 

Well you WERE shooting with barrel components not pinned. 13 shots is too much.

 

I read somewhere on the AK forum that when a 74 style brake is installed, that the forces push the barrel towards the front and also up. A 74 style brake is attached directly to the FSB, so it makes sense that gas pressure against the brake also affects the FSB directly!

 

If you had an AKM FSB on there with a threaded barrel and a slant brake, then it would not have came off, and you could have confirmed zero with it even (if it did not move too much).

 

I usually just use a quality boresighter at 30 yards to make sure that the FSB is on straight.

 

Drilling the FSB should not be a problem unless your work is not correctly aligned with the drill.

 

The easiness with which the FSB moves also sounds somewhat off. Perhaps you got one of them .223s with a slightly different barrel diameter?

[mancat 2,368]

Lightly polished mine before installing, and FSB still required some firm smacks from dead blow hammer before it went on. Normal.

 

Took mine to the range after aligning, shot five rounds dead on, without brake, and it had already started to move a touch. It doesn't take much between heat and shock.

 

Assuming you install the pins tightly, the FSB will not be moving.

Edited September 8, 2012 by mancat

[jbanzai 113]

13 shots is too much.

 

My plan was 15...didn't seem like alot. The brake shoulda been left off for sure.

[Agent Lemon 157]

I honestly would not want to shoot it unpinned, or maybe do no more than a 3 shot group to make sure that its shooting in the correct genenral location, and leave the fine tunning to later.

 

I also doubt that the FSB will move on you while drilling. The pin holes are touching the barrel (duh), so its like trying to spin a wheel by forcing the part closest to the axle, instead of applying forces to the easier to move outer part. Maximum is you'll have to make a quick little wooden jig to hold everything straight or something. I find that once everything is lined up in the drill press, that drilling fast and lowering the bit very slowly gives best results.

 

 

How did the rest of the conversion go?

Edited September 9, 2012 by Agent Lemon

[jbanzai 113]

Hindsight being 20/20, it's obvious now that I shot way too much and installing the brake was borderline retarded. Although I'm kinda glad in a way because I know the FSB is definitely on the loose side. It went on easy at first, but I froze the barrel and heated the FSB to 350F and used oil so I figured this was why.

 

I hear what you're saying about the unlikeliness of it moving while drilling, but I was planning on using a hand drill. AND, the most gentle of taps will cause it to drift. There's a sticky at AKfiles about intalling barrels/components that warns it's hard to keep the fsb/gb straight while pinning if they are loose fitting. I definitely think it's time for a drill press and extreme care when proceeding.

 

Rest of the conversion was ok. Not flawless (BG drill/tap slightly off center, barrel gouged during FSB/GB removal) but should turn out if I don't seriously fuck up this last step. I know what to do to make the next one better at least.

[Agent Lemon 157]

I would advise against pinning components with a hand drill, unless you have done this in the past and/or are comfortable with it. I have seen some horror images of improper freehand pin drilling before.

 

I bought a cheap 150 dollar drill press off Harbor Freight Tools once and it works well enough for most AK building (I wouldn't use it to pin a barrel to the trunnion). It was a good investment.

 

If you think that the FSB might move on you, then it should be easy enough to fabricate some kind of holder out of wood. Just some piece that is high enough to let the FSB rest on it perfectly, or maybe a little lower, so that it only stops movement in the event that the FSB actually moves. Some kind of holder of this type sounds ideal to me, especially if your work is clamped down to a sturdy flat surface (which it would be, ideally). I think that maybe alternatively, you could use some threadlocker stuff in there to keep it from moving. I forgot what the stuffs called, but loctite makes a compound that keeps slidy things from sliding.

 

The first time is the hardest when doing a complete conversion like this, because you never really know what to expect. My first one had a couple extra un-needed scratches as well. I hit the barrel a little bit during removal of components as well, but these barrels are really tough and can take a beating. Nothing that some paint cant fix.

Edited September 9, 2012 by Agent Lemon

[rs51085 136]

don't feel borderline retarded. it is a learning process. when i built my psl kit i did the same thing. i didn't put the retaining pin in the break because i had to pound the heck out of it to get it on the barrel and it wasn't lined up exactly so the pin wouldn't fit. i shot it a grand total of 2 times before i noticed i was missing it. i luckily found it about 25 yards down range. i got to put it on again and got it lined up properly that time. no problems after that. good luck

[thebuns1 4,323]

yeah the first time is always a learning curve. the knowledge gained is priceless though. and i agree with lemon that these things can take a good ass bangin without compromising anything.

 

i look forward to seeing the end result.