My 9mm DI AR

[kiwicollectorar15]

Hey Guys
Been messing around with my 9mm DI AR that I started building a week ago and its coming along, will post pics when its done.

I'm interested to know how much lead in or chamfer is put on the breech face as some of my rounds show a crease in the case about half way down from not quite entering the chamber smoothly enough and getting hung up and stopping the bolt from seating.

Also when extracting an empty case it wants to turn and eject while still coming out of the barrel extension and ends up jaming against the back side sharp edges of the barrel extension.

I'm using uzi 9mm magazines, standard AR carrier, opened up bolt, copy of RRA modded magazine block to feed from the center position in the mag well.

Any thoughts

Thanks

 

[kiwicollectorar15]

OK I got to spend some more time on the build and while thinking about the feeding issue I found the ejector pin is causing the problem.

I put a slight bevel on the ejector's end and the problem is gone, feeds nice and smooth.

So one problem gone but what about the ejection of the spent case getting caught on the backside of the barrel extension lugs when I manual rack the bolt ??

Should I smooth out the sharp lugs on the backside of the barrel extension ??

Cut the ejector spring a little as its only ejecting a case a 1/4 of the length of a 5.56 case ??

 

[HMC710]

You can take a dremel with small rotary stone and bevel the back of the lugs. A little bit does wonders. There's another guy that drills the extension in front of the lugs and puts in a small pin to act as a shim so the case can't rotate into the lugs. Keep us posted!

[kiwicollectorar15]

That was the decision I came up with last night and decided on beveling the back side of the lugs a small amount and it did make a huge difference in not grabing the cases, so good to know others came to the same conclusion as well and I'm on the right path.

The pin idea is interesting I might have to look at that

Tryed some hot test loads today after work with the gas system not drilled yet into the bullet trap and the case's came out good so should be able to wrap this up soon before the weekend and go play with my new toy hopefully and do some load developement.

[kiwicollectorar15]

Got home from work and got an hour to carry on with the project so I drilled the gas port and fitted the gas tube and block that I made a few days ago and it now functions under its own steam.

Screwed the suppressor on pointed it into the bullet trap and it loads and ejects untill the magazines empty.

Tryed a few loads that I use in my 9mm rifles and pistols and some are abit weak and others work fine.

I need to have a play with some subsonic loads.

Can the DI system run on both subsonic loads and super sonic or is an adjustable gas block required to work with a larger gas port to run subsonic

Or just play around with super sonic loads that only give enough gas pressure to function

[kiwicollectorar15]

Had an interesting day at the range today, I didn't get as much time to shoot the 9mm DI as I wanted because the IPSC match went nearly all day.

However I did get to run some loads that I brought along to test for function without the suppressor and I found some of the loads short stroked when I filled the magazine to 30 rounds.

Fitted the suppressor on and it went alot better so I think I will increase the gas port size a bit more.

There is not much response on these forums to this subject so not sure if there is much interest in my project, but I will throw this question out there 

Those guys with pistol DI carbines do you set the port size when it locks the bolt back with a standard ar15 magazine, and keep going bigger untill you obtain that

[HMC710]

Hey Kiwi,
True, not the response on the forum we've had in the past, must be the day jobs have taken its toll. If you are reloading, tailor your loads to fit. The issue is not getting the DI 9 to work, its getting it to work on factory loads. You've figured out running the suppressor helps you out so you've kinda figured out your own question. If you can get a big enough gas port in there with an adjustable block, go for it. Where is your port dia now? The gas tube itself is also going to limit gas flow. Keep at it and keep posting!

[kiwicollectorar15]

Hello Tim
Good to hear from you,

Been playing around with the rifle and fine tuning it yesterday and got it running quite good, gas port at the moment is quite abit less than the gas tube size of 0.125 so I have room to play with.

I reload all my ammo except .22 so loading the rounds to suit is not a problem,the rifle will be fed 100% reloads so not concerned about getting it running on factory ammo.

Have been playing with vihtavuori 3n37, blue dot, ADI AP100 and winchester autocomp to see what it likes, these powders give good gas volume.

I'm looking to choose a powder the gives the least amount of dirt and crap back into the bolt and receiver and try and get a subsonic load that functions, almost there.

Do you have any sugestions of other powders that I should be looking at trying

Do you set up your gas systems so they lock back on a empty magazine

From the 300 odd rounds that I've shot while testing and just playing around I must say that its very smooth and light recoiling and way better than the B/B 9mm. 

 

[HMC710]

Hey Kiwi,
Just keep doing what you are doing. Gas makes the system run and running is the key to success. Doing that for yourself is fine but if you want to market something, it has to run on factory ammo. Dirt is one of the issues with the slower powders as you have found out. Faster powders (factory loads) don't generate the gas needed to run the system. What we did was take a whole different approach to the DI with a piston system that we designed to work around the issues with the small 9. The DI system for factory ammo is just too narrow for everything we wanted to do from fast and light to slow and heavy. Keep at it, its all good info!

[kiwicollectorar15]

Spent the day at the range today and consumed over 600 rounds of 9mm reloads finding out what the DI likes and dislikes in quantity and accuracy, everything was going good untill the extractor started slipping and not extracting the rounds.

The extractor is due to be replaced anyway as it has been on an SP1 carbine since 1980 with many thousands of rounds down the pipe.

Some powder's seem very dirty and others not bad, between each test load I cleaned the rifle and bolt to get a starting point of how dirty each load was.

At this point I going to call the project done, it shoots very well with a few differant powder loads and bullet weights and runs, it feels very smooth and soft when firing and stays on target very well, there is no gas in the face even with the suppressor on.

It is a toss up what I like better the DI 9mm AR or my 9mm AK that I built many years ago. 

Thanks Tim for your encouragement, I will post pictures in the next few days of the finished rifle. 

[kiwicollectorar15]

My 9mm DI AR15, 12.5" s/s barrel and muzzle brake

[HMC710]

Great Job!
So, what's next?.......

[kiwicollectorar15]

Not sure what I'm wanting to build next, still have a bunch of stuff I have yet to complete, but I need to want to do them or they just sit untill I'm ready.

Still not got all the answers to the 9mm DI AR, so still messing around with it trying different things with loads and powders, It seems to have a mind of its own running great one day then not so great other days, the fouling in the bolt is amazing with some powders. 

It is suprising that my 45acp DI that I built a couple of years ago can run with a powder that is alot faster than the slower powder that I'm running in the 9mm and runs clean.

Should I run the port at .125 and try and use faster powders that may consume all the powder and give less crap or am I risking gaining nothing but more crap in the bolt because the 9mm needs slower powders to run no matter what. 

I may end up scrapping this barrel playing around with it untill I figure out some answers to my questions.


  

[HMC710]

I had a larger port than that on one of mine with a simple inline adjustable gas block.

[kiwicollectorar15]

Hi Tim
What sort of powder were you running, Longshot ? and how many grains or were you able to run a faster powder with the bigger port.

I'm running 9mm major loads with about the same powder burn rate as longshot but I have quite abit of port diameter left to play with. 

I'm not sure if I open it right up I will get into the faster powders to make it run clean enough to keep the bolt functioning and may just end up with a bigger problem stuck with using slow powders and a large port that allows to much crap into the bolt.