I have a Radical Firearms RF-15 chambered in 7.62x39mm. It will eat steel all day. I also have some Sellier & Bellot brass (124 gr soft point) and the bolt will not go fully into battery when using this ammo. I can drop a brass round in through the ejection port and the round will seat under it's own weight. I can then release the bolt and the weapon will fire, but then the next round won't seat properly when the weapon cycles. This only happens with brass. I use the same mags that work with the steel (dura mags). What gives?

Is this weapon bought from a mfg or custom built?

If bought from a mfg then you need to call them. I'm certain they'll be most helpful.

If you built this you need more examples before finding a conclusion to your issue.

In other words you need to try a couple more mfg's of brass case ammo and then you'll know more.

If you own a dial caliper you can probably find a difference between the loaded steel case and the loaded brass case. Dimensional difference.

Last thing...many times in posts like these there's always just a little more to the story.

Anything else you can remember to offer up would be most helpful

Upon further review it appears to me this company might be Mickey Mouse.

#1 no phone number on their site...


#2
right off the bat they talk about a $40 return charge...non negotiable, non refundable

#3
Their site doesn't work right with an android phone.

#4
They announce in BOLD , DO NOT USE REMINGTON UMC AMMO in any of our weapons.


Uuuhhhh....


I know in the last decade a lot of these smaller mfg's have started making AR's but this place seems like it's completely amateur hour.

Good luck my friend

Clean the crap out of your chamber and bore with a bronze bristle brush.

Lube the hell out of your bolt carrier group.

The only 7.62x39mm magazines I will call reliable are the 17 round Duramags.

I have never achieved reliable feeding and function with 25 round mags.

Only a few manufacturers make reliable magazines in 6.8 SPC, 6.5 Grendel and 7.62x39mm for AR-15's. The smaller capacity option is always the safer bet.

I will try to contact the manufacturer. Yeah I noticed the thing about UMC ammo. Makes no sense. I've kept up with the trouble shooting and i t almost seems like the soft point is getting hung up on something when stripped from the mag. Thanks for your comments.

borderpatrol, a friend suggested the same thing. If it is the soft point that is getting hung up, then your suggestion might just do the trick.

'nuff said.

out of my lane here, but trying to offer some second-hand insight...
Several years ago a friend of mine had a 7.62x39 AR.  He liked the shooting characteristics of the cartridge, but never could get it to feed reliably, despite trying every 7.62x39 AR magazine brand that was available at the time.  After some research, he concluded (as someone has already mentioned in this thread) that AR compatible magazines for the 7.62x39 cartridge don't have a very good reputation for reliability.  With that in mind, your rifle may be fine but your magazines may be the issue.  Consider:

• both CMMG and PSA spent considerable time and money to develop proprietary AR-ish rifles that reliably feed the 7.62x39 using AK magazines, not AR compatible magazines.
• the .300 BO cartridge exists to give ballistics similar to the 7.62x39 in a *reliable* AR platform using AR magazines.

My apologies if I'm incorrect on the above points, but this is my basic understanding of the issue.  

My first 7.62x39 upper was a Colt with "Frankenmags" (straight sided AR sheetmetal tower welded onto the bottom half of a AK mag). The barrel extension was a standard 5.56 one. I  noticed that when the round didn't fully chamber, when extracted and ejected, there were two grooves running from almost the tip of the bullet all the way to the base. The 7.62x39 round has a larger diameter than 5.56X45. So the bullet rides at the top of the feed ramps in the barrel extension and has a sharper transition from the mag into the chamber. I used a Dremel to round off the sharp top of the feed ramps and and polish the surface. I also made the ramps deeper into the upper. Again as 7.62x39 is larger in diameter, the center of the top round in the magazine is lower to the bore axis than 5.56X45.

Check the rounds that didn't chamber.  Do they have two gouges down the length of the round? Extra drag tends to cause malfunction. A stronger spring will help chamber, but too strong a recoil spring can cause other issues. Especially in full auto a stronger recoil spring ups the cyclic rate.

Scott

might consider deburring the sharp edges on the barrel extension feed ramps.  and a quick polish job.

https://www.ar15.com/forums/Precision-Rifles/Hellbender-s-a-k-a-Lostinthewoods-Guide-to-the-Ultimate-AR-fixed-/4-6919/

might also consider deburring the mag feed lips, sometimes the stamping mfg process leaves sharp edges that gouge and grab hold of the round as it gets pushed forward out of the mag, perhaps preventing the round from smoothly going up the feed ramp.

Clean chamber with wire brush
Debur , lube
I removed the oring from extractor
Helps go in battery easy , when broke in good, try replacing the oring, I don’t
Load only 4-5 rounds
See if that helps
The coating from steel Ammo can gum up brass some time

Sorry for late post, just saw this.
Contact RF. I had failure to fire due to excessive headspace. I counted up the rounds and it was at least 5000, I wore the barrel out. Lots of mag dumps LOL.

They took great care of me and I can’t recall, I don’t think I even had to cover shipping costs. Came back with new barrel.
Before and after this incident this was my do-all gun, mag dumps, 90% comblock and the hornady sst and PPU BRASS and bear subsonic all fired reliably and grouped about 3” @ 100 yds. Took 5 deer with it out to 200 yards.
(Subsonic was not able to cycle the action, which I expected).

So don’t listen to the bashers, they don’t know. You start trying to figure this thing out, you are in for at least $100 for headspace gages, minimum.
Cheaper to send back to RF, if it comes to that.

All I can say is, I did not like the traditional AK rifle and sold the FEG I had since 1996. I had an AMD65 and I was able to get that to a degree of accuracy but ended up selling that too. A few years went by and although I got a Zastava AK pistol that I liked a lot, I still missed the full-sized rifle in 7.62x39 - plus, I had a lot of ammo. So I took a chance on a Radical 16" AR after reading up on the changes they had made to get more reliability. I put some flip sights and a dot sight on it, bought a bunch of mags and went to the range. After sighting in, I was blowing the center out of the target at 25 yards and there was not a single operational glitch. The thing has become my favorite rifle. I did change out the ignition set that worked fine but was a little rough - I got an inexpensive Nickel set that was very much like an ALG-ACT I had once.
I think the OP's problem has to be related to the soft-nose cartridge which must be getting jammed in the feed ramps. The quick answer is to quit shooting that but you want to be able to shoot any reasonable ammo. I have some 154 gr soft nose I want to try in mine but I'll just try loading them at home before taking to the range. On second thought, I doubt if there is anything you can reasonably do to use that particular ammo in the rifle so you probably should just shoot the ammo that works.

BTW, I have since re-zeroed at 50 yards which is a much better trajectory.

I own two 7.62x39mm AR-15's. One has a 16" barrel, the other is an A2 with a 20" barrel. Both are reliable and accurate.

I have switched to 17 round (maybe 20 round?) Durafeed magazines and the reliability finally became acceptable. I have never been able to get ASC magazines to work and the larger capacity (28?) were hit and miss. Going with a slightly lower capacity made all the difference in the world.

I also prefer 20 round magazines in AK's, not because of reliability concerns, AK's just run. I like them because I can lay flat on the ground when shooting and they allow me to practice mag changes more often. They also work better off a bench.

I am a rare individual because I reload for this caliber.

24.5 grains of H4198 with a 123 grain Hornady or 125 Sierra Pro-Hunter bullet, seated ar 2.190" is accurate and reliable. Both have exposed lead tips. I use CCI-200, CCI-250 or Remington 9.5 standard large rifle primers. All of these primers are considered "mild" when it comes to pressure.

You can substitute 28.0 grains of H322 with these bullets and OAL" with excellent results as well.

Magazine feed angle is critical to reliability. The AR-15 was never designed to run a cartridge this size. Gas port location and gas port diameter are critical to running the gun. My 20" rifle gassed barrel from DPMS would not function when I built the upper. I had to open the gas port (if I remember correctly, it was around .090" from the factory"). I used one step at a time, both SAE and metric drill bits to open the port up. I didn't know how big it needed to be and didn't want to overshoot the process. I ended up with a 1/8" (.125") gas port before the upper would feed and function 100% of the time.

IMO a mid-gassed or carbine gassed upper will be more reliable that any rifle gassed upper in this caliber. 7.62x39mm uses faster burning or at least medium burning powders that are normally used in .223. The actual powder charges are not that much larger than .223 rounds using 55 grain bullets. Because of the powders used and the larger bore diameter, pressures drop off dramatically the further away you get from the chamber.

A .125" gas port is about as large as you can get in an AR-15 because the gas tube internal dimension isn't much different than that. Of course, you can drill the gas big as you want, but the gas tube will only pass so much gas.

AK-47 rifle gas ports are huge! I have never measured one, but looking at them once you remove the gas tube reveals an over gassed system that is part of the reason they are so reliable. The shape (tapered case and gentle angle of 17.5 degrees on the case shoulder) allows for easy insertion and extraction. The 7.62x39mm case shares the same shoulder angle as .30-06 and .50 BMG.

IMO the 7.62x39mm round really shines in an AR-15 if it runs reliably. The accuracy is much better than "good" AK's, usually producing groups under 2" at 100 yards. It is also a better option for hunting pigs and deer at short range. It hits harder and is still a mild recoiling option.

I won't suggest it for self-defense, because I won't accept anything less than 100% reliability in that arena. If you miss a deer or feral pig, no big deal. If crackheads are at the door, I want something that has never let me down.