View Full Version : AR15 conversion to 5.45X39mm

Hebrew Battle Rifle
July 21, 2007, 23:55
SUCCESS!!! Well, it is running anyway. I was going to build it as a mid length, but Rock River Arms* is not being co-operative, so since I already had the parts for it, I built it as a carbine.
I got the barrel** and all of the other parts that I had to make machined and as blind luck would have it, they all fit. I got the upper assembled and attached to my lower. My 30 rd AR mags that I bought from Brownells will hold 29 rounds of 545 just like it was made for them. YEAH!
I measured the existing gas port and the closest reading that I could get was .076.( I was using number drill shanks as feeler gauges) Since I was setting the gas block back about 4 inches closer to the chamber, I deducted 25% (this is a SWAG figure)from the measurement and the closest reamer that I had to that figure was .059.
With this gas port size, the cartridges would fire and eject, but the bolt would not strip a new round from the mag. I opened the port up to .076 and I got about 50% eject/feed. So, I opened the port to .082 and out of 29 rounds, I had one Failure to extract about half way through the mag. A quick pull on the CH and I ran through the rest of the mag in about 10 seconds or so. So, I am going to run it like this for a while and see things loosen up a bit.
Actually, for a training only rifle, having 1 round out of 29 Fail to extract is not a bad thing. Quick reaction drills would be a regular thing. Regular enough that they would become automatic I suspect. The extractor is not modified and is for 223. It has not failed to grip the rim nor has it failed to pull an empty from the chamber. I set the bolt face back about .010 so that the extractor would fully seat every time. So far, it has.
I am not sure why the port needed to be bigger when the gas port is closer to the chamber than the original. It may have to do with the volume of gas needed to operate the DI gas system VS a gas piston. It could also be that my measurment is off and the FSB is partially obstructing the gas port. I just thought of that so I will give that look tommorow.
I am planning to do some accuracy tests tomorrow. I'll post the results if I do.

Some of you may be thinking, Well big fat hairy deal. Who Gives a Fat Rats Eyelash about shooting 545 ammo. It is corrosive and made by communists.
Well, here are a couple of reasons that it is a big fat hairy deal. While the prices of our beloved calibers of ammo are currently racing each other into freakin orbit, the price of 545 ammo is insanely cheap. The former Warsaw Pact countries are dumping their stores of this caliber on our shores and it is raining 545 ammo. While the current ammo market is a barren desert, the flood of 545 ammo is like manna from GOD.
The ballistics are comparible to 223 and the cases are made of steel. So, when my range time is o'r, I quick sweep with a speaker magnet on a string and my mess is cleaned up. And all of this for the silly sum of .11c per round delivered. Um, yeah, I consider that a big fat hairy deal.

* Rock River Arms has been very disappointing. This is the first time that I have attempted to do business with them and I am underwhelmed so far.

** I bought a NIW AK74 barrel from K-VAR out of Las Vegas NV. It is chrome lined bore and chamber.

July 22, 2007, 06:05
sounds pretty cool to me, good work!

is all 545 surplus really corrosive? weird.

even so, 1 conversion upper for me please! LOL

July 22, 2007, 09:59
Sounds like a good deal to me - cheap ammo is good ammo! I was actually considering buying one of the '.20 Genghis' conversions some time ago, but like everything else that Alexander Arms sells, it's insanely expensive! :cry:

Can you provide any details about your barrel? Source, cost, etc.? How about the bolt - did it require opening the face up?

July 22, 2007, 10:50
Originally posted by TerryN

Can you provide any details about your barrel? Source, cost, etc.?

Originally posted by Hebrew Battle Rifle
I bought a NIW AK74 barrel from K-VAR out of Las Vegas NV. It is chrome lined bore and chamber.

Originally posted by TerryN
How about the bolt - did it require opening the face up?

Originally posted by Hebrew Battle Rifle
I set the bolt face back about .010 so that the extractor would fully seat every time.

July 22, 2007, 11:17
I've always thought the 5.45 would be an improvement to the AR system.

very nice.

July 22, 2007, 14:21
Glad to hear it is working. Please keep us posted.

Hebrew Battle Rifle
July 22, 2007, 20:24
I ran about 75 rds though the rifle today. I had 7 dud rounds and 4 failures to extract. The bolt went to the rear without pulling the expended casing from the chamber.

Accuracy was nothing special. However, I will re evaluate once I have thinned the front sight post down and remember to bring my glasses along.
But, for close quarter battle training or for use in the popular carbine classes offered now, it would be more than adequate. Head shots out to 100 yrds would be easy and upper torso shots out to 300 could reasonably be expected.

Master Blaster
March 29, 2008, 13:47
You might want to consider the Noveske Krink Flash Hider before drilling your gas port further. They designed it to improve the 5.56 carbine reliabilityand I'm told that they were successful in that endeavor. Neat project though, I hope you can get it sorted out.

March 29, 2008, 23:34
Oh dang...something else for me to think about building.

Damn you!

March 29, 2008, 23:55
So you traded a .22 round for a .21 round, I don't see it. Now a 762x39 would be OK.

March 30, 2008, 12:49
I'm still going to get one in 762x39

March 30, 2008, 13:26
Originally posted by stimpsonjcat
Oh dang...something else for me to think about building.

Damn you!

You build one, you build one for me as well!

The russians got it right with this round. I consider it heads and shoulders above the 62 grain Nato steel penetrator round. It beats it at wounding ability and it beats it in ballistics. And the round is a lot lighter than the 223, which was one of the main reasons the 5.56 ever came to be.

Now don't tell me some super duper match 75 grain load will outshoot it, because that's not what the average grunt is going to carry.

Hellion Productions
April 01, 2008, 22:26
Tagged for future reference. Good job, HBR.


April 09, 2008, 13:51
Got my parts...never realized the AR bbl ext was threaded, makes this even easier for me to do.

But now I am wondering if I want to make it a piston-type upper while I am at it...to avoid gunking up the bolt/carrier.

Guess it is time to check the shop for spare FAL parts again!

April 10, 2008, 20:35
Why not just get a 74? I built two from mint kits and they are fantastic. I don't think I've ever had a malfunction with them. And they are plenty accurate to boot.

April 10, 2008, 22:13
Well...for me it comes down to the fact that I dislike AKs.

The ergonomics just do not work for me...too short, no BHO, charging handle is on the wrong side, so is the safety, sights suck.

Plus I have a lower I already use for 3-gun, this will make feeding it cheap again. Less than $200 of parts = new caliber. No new mags, gear, or manual of arms.

I plan to mod up the parts Sunday...I need to test new mag catch design for the 8mm, so maybe I can test both at the range on Sunday.

April 11, 2008, 11:43
Originally posted by stimpsonjcat
Well...for me it comes down to the fact that I dislike AKs.


i used to have an AK, along with 5000 rounds of cheetah 7.62X39

i sold the rifle, and doubled my $$$ on the cheetah, just because i did not enjoy shooting it.

its pointless to have a firearm thats not enjoyable to shoot.

now, i would REALLY like one of these AR conversions so i can start buying cheap ammo again...

April 11, 2008, 17:39
Another project, just what I needed. What would be the optimum barrel length be for this caliber?

April 12, 2008, 03:14
this is interesting...


although, i wish model1sales or someone abit cheaper would put an upper together.

April 15, 2008, 11:25
Originally posted by jaykden
this is interesting...


although, i wish model1sales or someone abit cheaper would put an upper together.

Gadzooks! I bought all the parts and 6k of ammo for that price!!!

April 20, 2008, 22:34
HBR, hope you don't mind me posting this here!

I have a few feed issues to deal with with the magazines as they don't like to feed properly when loaded above 25 rounds or so, but overall the new upper works just fine. Who is making the custom followers?

Isnít she cute?


standard AR parts except for an AK-74 bbl custom fit onto a standard AR bbl extension. Other necessary mods were sleeves to make up the difference in OD of the AK bbl to the standard AR front sight and some work on the bolt face to allow the 5.45x39 rounds to seat properly.

AR bolt - $35
AK bbl - $90
Bbl ext - $15
Gas tube - $10
Handguards - $18
Various pins - $5
Total = $173

And yes yes...the 8mm FAL got some loving today also...her new mag catch design worked...but got bent under recoil (don't we all?). I will make one out of tool steel now that I have a good design. She now functions on gas settings as low as 6...go figure.

April 20, 2008, 23:15
If your worried about corrosive ammo in an AR gas system you might try something like this.



you might also try GI mags with black followers this is what i am finding work the best by hand at least cycling by hang no range time yet......

April 21, 2008, 10:06
Near as I can tell the real problem with the mags is related to the fact that the AR cartridge is a bit longer from the rear to the shoulder and is also a bit less tapered. Theses two differences allow the 5.45 cartridge tip to dip down as more are added to the magazine (a similar issue occurs with 45ACP in extended 1911 mags).

The solution may be to build a custom follower that has a riser at the front, or possibly just has the protrusion angled to the rear.

Tonight I will try to lay out some 5.45 ammo on top of a GI mag, it should be pretty obvious at what point the taper will cause problems. Comparing this to the possible problems an angled follower will cause when the mag is empty should be pretty simple.

April 21, 2008, 20:26
HK mags can take 28 rounds of 5.45 and feed relaibly.

I never use more than 28 rounds in an AR 30 rd mag on general principals, even with 5.56 NATO.

PMAGs seem to also work well but I don't enough data points to verify reliability.

Standard GI mags are problematic in 5.45, but then again - they can also be problematic with 5.56

April 21, 2008, 21:31
Interesting, this is contrary to my testing, at least regarding PMAG and GI surplus.

I do not own any expensive HK mags.

Testing tonight with various magazines it seems there are several issues at play. The most important is the change between the taper on the 5.56 and the 5.45. I tested 5 AR mags mostly surplus in various condition and also a PMAG. The crappiest condition surplus mag handled the most ammo loaded and fed reliably (25 rounds). The failure of the other magazines was typically that the angle of the cartridges would tend to nose down as the number in the mag increased.

I took all the mags apart and the surplus that performed best actually had the shortest spring. The GI mags fed better than the PMAG also.

I noticed with the PMAG that the angle of the cartridge tended to fail much sooner than on the GI mags. Looking at this I think the blame lies with the fancy 'no rise' follower. The worst performing of all the GI mags also turned out to have a fancy follower.

Analyzing this data it occured to me that the plain ole followers have the ability to change their angle (assuming there is enough spring tension to do so) to support the front of the round better at higher capacities. As a test I tore apart some junky old steel AR mags someone gave me ages ago...horrible things...but the springs are very nice. I then trimmed one of these mags to the same length as the best performing GI mag spring and began tinkering with the angle of the coil at the top that engages the follower.

The results are interesting and I believe will eventually solve the issue. Initially I set the angle of the new spring to almost the exact opposite of how the standard GI spring fits at the top. Normally this is point down, I took it to point up. This spring seated rounds in the mag all the way to 30 rounds with perfect angle BUT as the mag emptied the cartridges tended to nose UP too much and I got bolt over base failures. Changing the angle changed the number of rounds before the failure occured.

At some point my hands really started to hurt (I have a nasty WECSOG cut on my trigger finger from Sundays testing) and so I stopped testing.

I think some combination of spring angle and maybe some mods to the follower will be the solution. The follower dimple is too wide at the front end and goes too far forward for the 5.45 round. This cause it to have to rock in the mag about a moment somewhere near the shoulder. I'll try grinding on the follower to relieve this as I think this is aiding the bolt over base issue.

Well there ya go...that's all I got for tonight.