Built another 9mm AR tonight :)

Nice build Mildot

I figure I have about 5k through mine. Mostly 125gr lead with 231. I haven't cleaned it in 2k if not more its filthy inside (mostly due to powder and blowback operation) but its still ticking if its stops shooting I'll clean it lol..

I broke a bolt catch on mine at about 3500 round mark - did some research and it seems that it is due to bolt bouncing.

Got a heavy 9mm buffer from heavy buffers and so far so good.

I also ramped the bolt and removed the 9mm hammer for standard AR hammer.
Now the hammer pin don't get hammered as much. With non ramped bolt the hammer would be cocked at about 1/2" of bolt travel now its more like 1-1/2"

Its got to be one of my fave AR's accurate to 75m no problem - reliable and 10 round magazines are nice....
 
Deckard said:
That plastic bar? Isn't that for A2 stocks?
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No. The Colt 9mm system is notorious for breaking bolt stops. This is because if you use a standard Colt or RRA heavy 9mm buffer, which is the same length as a standard CAR buffer, the bolt can go 1.25" past the bolt stop and builds enough forward momentum that it gives the bolt stop a good "whack" every time it engages.

Over time this will either break your bolt stop or deform your lower or both.

It's not a problem with DI guns due to the retarded blowback system, but the Colt-style SMG is a direct blow-back, so this problem is unique to the 9mm SMG.

In the US on AR15 . com, for years guys just advocated putting $2.25 worth of quarters into the base of the buffer tube, then some custom AR guys started making a slightly longer tungsten powder filled stainless buffer to control the length or stroke of the 9mm bolt.

Spikes builds a stepped aluminum buffer spacer the same height as $2.25 in quarters you install on the back of your spring to do the same thing for guys (like me) who already have the RRA 9mm buffer.

It ensures your bolt only just clears the bolt stop so that when the mag is empty the bolt only slams forward a couple of milimeters before hitting the bolt stop, which lowers the momentum and thereby the force with which your bolt strikes the bolt stop and lowers the probability of that part failing in your AR.

It's not a necessary part, but a definite "nice to have".
 
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Ref bolt ramping, I always understood that if you run a dedicated 9mm hammer, you don't have the hammering issues on the hammer pin - it was only if you ran an M16 or DPMS hammer with an un-ramped bolt (aparently no 9mm bolts work with a notched AR15 hammer).

What I have read is that if you do full-auto or run a suppressor, it's a good idea for reliability to switch to a DPMS hammer and a ramped b9olt, but for semi-auto un-surpressed there's no advantage to switching out your 9mm hammer and un-ramped bolt - apart from easy changes to a 5.56 upper, which I never do, because this is a dedicated 9mm lower ;)
 
Got a heavy 9mm buffer from heavy buffers and so far so good.
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This sounds like some good preventive medicine, what weight did you get? ;)

5000 rds, how the hell do you get that much shooting in? :eek:
 
Claven2 said:
Ref bolt ramping, I always understood that if you run a dedicated 9mm hammer, you don't have the hammering issues on the hammer pin - it was only if you ran an M16 or DPMS hammer with an un-ramped bolt (aparently no 9mm bolts work with a notched AR15 hammer).

What I have read is that if you do full-auto or run a suppressor, it's a good idea for reliability to switch to a DPMS hammer and a ramped b9olt, but for semi-auto un-surpressed there's no advantage to switching out your 9mm hammer and un-ramped bolt - apart from easy changes to a 5.56 upper, which I never do, because this is a dedicated 9mm lower ;)
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The way I understood the issue it was how soon the hammer was cocked by the bolt. Un-ramped bolt was cocking the hammer with only 1/2" of bolt travel vs ramped of about 1-1/2"

Only cost me fex bucks to get it ramped and I had the hammer in the parts bin.

I'll report when I have 10k through the gun.

So far so good...
 
mildot said:
This sounds like some good preventive medicine, what weight did you get? ;)

5000 rds, how the hell do you get that much shooting in? :eek:
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I got the standard 9mm buffer.

When comparing to RRA 9mm buffer the heavy buffer is longer silimar to what Claven explained.

Well worth the 100 IMHO.

Lots of casting and re-loading lol brings the cost of ammo down....
 
Fascinating. That travel limiter makes sense now. Is there any issues about buying and receiving a heavy buffer from Heavy Buffers? I was thinking about the 11.5 oz. Comments? It is longer and theoretically slows things down.
 
Slowing things down isn't important in a semi - it's for controllability in FA mode. Limiting travel is, however, useful. You can do so either by putting a spacer in the buffer tube, or using a longer buffer. Both work equally well.
 
Claven2 said:
Ref bolt ramping, I always understood that if you run a dedicated 9mm hammer, you don't have the hammering issues on the hammer pin - it was only if you ran an M16 or DPMS hammer with an un-ramped bolt (aparently no 9mm bolts work with a notched AR15 hammer).
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The factory Colt / RRA etc pattern 9mm bolt has a very abrupt and goofy two step ramp. As already mentioned, the ramping allows a far more gentle cocking of hammer regardless which hammer you have

The reality is this wouldn't bother me ( more wear on pins etc ).

The reason I ramped my bolt is I wanted to run all my lowers ( Geissle Hi Speed, RRA 2 Stage, CMC modular etc ) on the uppper. The factory RRA will lock up so solid first time bolt goes forward that you need to remove BOTH pivot and takedown pin to !

For a dedicated lower I wouldn't have bothered

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After 5deg Ramp
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Hello, anyone know where I can purchase a AR 9mm bolt new or used in Canada? Also having FTE problems, seems to b an ejector problem, it's failing to eject the last spent casing causing a double feed, some really bad stove pipes. Has anyone encountered this problem? Thanks for any info.
 
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