7.62 x 40 WT, A few snags.

[Hickok]

Have a 7.62 x 40 WT barrel installed now on an AR flat top. 16" stainless, carbine gas, from X-caliber barrels.

The barrel wont pick-up and feed with H110 or IMR 4227 powder, behind a Nosler 110 gr Varmigeddon bullet or Sierra 125 gr Pro hunter. (Using Wislon load data)

It will cycle, feed and lock bolt back with IMR 4198 and the Nosler 110 and the Sierra 125gr bullets, with charges from 20 to 24 gr.

24 gr/ Imr4198 is the absolute max I can get into the case, using a drop tube and jiggling the case to settle the powder.

Haven't had a chance to chronograph the loads yet.

It is pretty obvious that I need to get some AA 1680 powder, as this seems to be the "perfect" powder as to burn rate for this cartridge. AA1680 is "unattainium" every place I have checked. So for know I will use the 4198.

Also, this carbine barrel/upper is being used on a lower with a rifle length buffer/tube stock set up, could this be the fault with under gassed cycling with the faster powders? Is this a mismatch?

I see you can get a lighter buffer for the rifle length stock set up, and was just wandering if this would help with the "under gassed" problem and let the bolt move faster and pick up cartridges from the mag.

Enlarging the gas port hole might be a fix, but I don't want to attempt that operation myself.

[Patricklaw]

Oh man, does this ever sound familiar.

Is your barrel manufactured by Wilson or Noveske? My Noveske, built to Wilson specs, was under-gassed as I received it from them. I don't remember the numbers but I can find them if I look back. Mine is mid-length gas system so I'd say you're fortunate in that yours is carbine. I'm not sure that my numbers will help you much given the different system lengths.

I generally load 147 grain M80 pulls and have had good luck with 4198 but they chrono 2-300 fps slower than with 1680. I've been working with a Lee C309-180-R and 4198 but need a few more trips to the range to perfect it. I've been really pleased with the 312-155-2r but if I coat it with anything, paint of pc, the nose of the bullet is too large for the throat of the barrel.

In any case, you're right, 1680 is the holy grail.

[runfiverun]

1680 is around here.
2400 and red-dot not available.

the 1680 would be the right powder for this application but you then have one single option.
lightening the mass of the bolt or the resistance [spring] would for sure help.
doing the gas hole would need some research but I don't think it's all that difficult.

[Hickok]

My barrel came from X-Caliber barrels. http://www.x-caliber.net/

It is working perfect with a compressed load of IMR 4198 and the Nosler 110 and Sierra 125. I have to get out and set up the Chronograph to see what velocity I am getting. I know it wont be near what AA1680 gets, but if I can run a Sierra 125 @ about 2300 fps, with the IMR 4198, I would be very happy.

I have powdered coated a few Lee 312-155-2R ad then wiped the coat off the nose/ogive area and they will chamber fine, but like you said, if I coat the entire boolit, it is too tight in the leade/throat.

RunFiverun, I have checked with several gun shops, and even asked if they would order a couple of pounds of AA1680 with their next powder order, but "no joy." I get some of the lamest excuses.

May have to save up and eventually pay through the nose, (hazmat levy,)and have a couple pounds delivered to my door.

Really contemplating a reduced mass buffer, and/or a reduced weight recoil spring.

These AR's do get touchy when you start messing with dwell time of the locked bolt and recoil velocity of the bolt carrier group/ buffer.

[Hickok]

Popper, thanks for the info and the pointers on drilling the gas port. Wood dowel is a very good idea, to protect the bore.

Mine is a 1/12" twist, and it has a short throat, (very little freebore). Quality seems A+.

The Nosler 110 Varmegedden is seated to 2.240" COAL, just clearing the lands, and it fits the mag with about .020" length to spare.

The Sierra 125 Pro-hunter, seated to clear lands by .010" is 2.195" COAL.

[Hickok]

Popper, I removed the gas block and gave it a check a couple days ago. Looks good to go.

You might have something with the running wet. I'll try that. I use Mobile 1 on all my firearms, glad to here you recommend it!

I am going to work with the Lee C312-155-2R and see what I can do.

"My kingdom for a horse!".....Heck with the horse, I want some AA1680!:wink:

As for now, it is IMR 4198!

[runfiverun]

if you happen to be looking for a mold for the X40.
a couple of us drew this one up and Tom is cutting the first mold right about now.
it'll be good in other stuff like the 0-6 and 308 too.


http://accuratemolds.com/bullet_detail.php?bullet=31-155W-D.png

[temac]

Had a762-39 upper that was under gassed drove me crazy opened gas port quite a bit runs great now.

[RU shooter]

You can lighten the existing buffer you have rather than getting a new one . That worked for me when I had a BO with the rifle stock /buffer assembly . Drive out the roll pin that holds the plastic cap on and there should be a couple metal "slugs" in the buffer take one out and replace it with a piece of plastic tubing the same length

[Hickok]

Good idea, RU.

[Hickok]

I did get out this afternoon to the range.

Using 125 gr Sierra and 24 gr IMR 4198 I chronographed 2319 FPS. I was happy with that.

After zeroing, I shot a series of 3 groups of three shots each at 100 yards. The average for the 9 shots came out to 1.21". Again happy with that.

Perfect functioning, no FTF, or eject, and have lock back on empty.

Groups could have been better, but had a 30 round mag, and because it extended so far below the rifle, I had to use a bull bag, and then a sandbag on top of that to clear the mag on the bench. Didn't have any support on the butt of the rifle. Stock trigger was a little gritty also.

Need to get a shorter 20 round mag, or use a regular 20 rd AR mag when bench shooting, so I can bag the rifle butt.

But I am happy with the results, as I am getting 7.62x39 velocities with the 125 gr jacketed, and that is what I wanted. Good for deer.

Now on to working with the Lee C312-155-2r boolit. Don't know if I can make it work with the bulky 4198 or not. Not much room in the case for a heavy boolit and a bulky powder.

Sometime I will find some AA1680, hopefully.

Still may try the lighter buffer and a few other things to see if I can get faster powder to cycle properly.

But I am happy that I can load up a mag of Sierra 125's and shoot accurate and reliably.

[runfiverun]

Popper:
the lube groove will just be covered and the gas check will be right at the base of the neck.
the nose should just snuggle right into the throat with a little clearance.
the angles for the throat are cut at 1.6* instead of the 1.5* the bigger 30 cals have, but this will allow just a bit more engraving and support.

I don't think it will be a good mold for the 300 B.O. or the 7.5 Swiss Rifles, as the throats are cut differently.

[GooseGestapo]

I recently built a .300BO with an assortment of parts. My barrel is a mid length gas. It originally had a .090 or so port. Opened it up incrementally to .125 (max).
It will never run subsonic, but that wasn't my desire. It runs with 4198, 1680, and my favorite to date, RL7. H110 gives best speeds (125gr Speer), but 1680 best function.

My primary load however is the Lee 155gr PtGC. My recently acquired 6 cav mold "pours" bullets. Back about 20yrs ago, I used a single cav. I still have to feed a SKS. It gets ~1,950 fps with 155 and powder to bottom of neck. 20.5gr irrc. My notes suggest I can drop the charge a little and still get function. Accuracy, however is quite good. It will do 2,100 with 1680, but accuracy is starting to fall off.

I'm considering a rechamber to -40, for the increase velocity potential with jacketed bullets.
The only problem I've had with the 155's, (other than earlier under gassing) is a few case necks being oversized preventing chambering. I plan to use it with Lee 150gr FNGC which it also feeds well to hunt pigs with this fall.

with a mid length gas system, you'll likely need to go all the way to .125" gas port to get the function you desire.

[Hickok]

Good info from all you guys! Any and all ideas,/ experience is appreciated.

Goose, I tried loading some Lee C309-150- FN and also the Lee C309-170-FN and cycling from the mag to chamber, and my AR wont feed them. The FN hits the lug area of the barrel extension and it wedges the boolit solid.

Patricklaw hit it right on the head, AA 1680 is the Holy grail for this caliber.

[runfiverun]

it's tops in many of the super mag cartridges too.
and in the little 25-20 sized cases it works like it was made for them too.

[scb]

I had the same problem as you're having but I'm not sure my fix would be applicable to your situation. I built mine with a Wilson barrel and an Adam Arms gas piston system. I had to open the gas port hole in the barrel significantly. I'm using H4198 and Speer 125gr. TNT's. When it became available I purchased an Ares SCR lower (living here in the peoples republic of ny). At the time there was no gas piston bolt carriers available so I fitted a direct impingement to it and it worked fine. I did however modify a Sadlak Industries gas block to take care of the over sized hole in the barrel. I don't know if this is of any help.

[timberhawk]

I bought a Wilson barrel. Mounted it in a Rock River and am going to start reloading this weekend.
Bought a Lee 312-155R and max OAL in my chamber is 2.075". Not happy about the Lee fit, but the mold was only $15.00, so I guess I can't complain too much.
I'm PC coating my bullets and will probably try to load to an OAL of 2.070" to give it a little jump. Just going to use them to fire form brass.
I've got AA1680 and 296 to try.
I read the post from last spring regarding the loads of AA1680 and the Lee.
Do you think a 10% reduction in the charge of AA1680 is enough for the shorter OAL?
Has anyone tried 296 with this bullet?

Anyway, any advice you have regarding loading for this cartridge will be greatly appreciated.

[Hickok]

You can lighten the existing buffer you have rather than getting a new one . That worked for me when I had a BO with the rifle stock /buffer assembly . Drive out the roll pin that holds the plastic cap on and there should be a couple metal "slugs" in the buffer take one out and replace it with a piece of plastic tubing the same lengthRU, I took your advice and took my buffer apart and removed one of the metal slugs and replaced it with a piece of hardwood, made to duplicate the size of the slug.

Worked perfectly with IMR 4227, feeds and logs back on empty mag. Case rims look good, no ripping or tearing from the extractor.

RU, thank you for the info/advice!

[RU shooter]

Glad it worked and I could help . Yes when I built my BO it was not standard by any means ie : rifle stock and buffer 20" 12 twist barrel and carbine gas system and every one on several different AR forums told me it wouldn't work and was all the wrong set up blah blah ! Well it worked very well with cast as that is what I wanted it for mainly . Got it to cycle with loads and powders no one ever thought would work like RE 15 and 4895 and even faster powders like unique and 2400 worked once I got things sorted out . Again glad you got her running the way it should .

Tim

[Hickok]

Thanks Popper for the link. I need to study up.

I really am a bit afraid of messing around with H110 in this cartridge. Just me, but I am leery of that powder.

And Tim, I give you a big thumb's up![smilie=s:

[Hickok]

As an added note to anyone removing any of the metal slug/cylinder in a rifle length buffer to lighten the mass. When you make a new replacement slug/cylinder, make it the same length as the original. I took out the hard wood slug I used to try out my buffer, and worked down a piece of hard plastic from a screw driver handle, works great.

You need everything the same length, as this type AR rifle buffer is designed to have a "rattle". Has to do with the harmonics of the bolt carrier group, and bolt bounce back.

Other type buffers may have powdered tungsten or bb's and the above does not apply.

Just don't replace the inner parts of the buffer and try to make it nice and tight and quiet. It was not designed to be made this way.

The buffer may well work with parts fitted tight, but just saying it was not in the design to be used as such.

[Hickok]

Went out and shot some 110 gr Nosler Varmegeddons with Imr4227 and it went perfectly, Cycled, locked bolt back on empty mag, and dropped them in a nice tight group at 100 yards.

All my empties are dropping in one nice pile at 3 o'clock, with the lightened buffer, so all seems well.

[timberhawk]

if you happen to be looking for a mold for the X40.
a couple of us drew this one up and Tom is cutting the first mold right about now.
it'll be good in other stuff like the 0-6 and 308 too.



http://accuratemolds.com/bullet_detail.php?bullet=31-155W-D.png


I bought this mold and loaded to 2.130",it feed flawlessly in my barrel with M4 feed ramps and a modified PMag.

[Kfisch]

I was running a 300BLK for a couple of years and found the 7.62x40 and have not looked back. I don't care about subsonic living in NY so my loads are for hunting, 125gr Nosler BT and 147-150gr anything for practice. I built a 20" , mid gas rifle with a WT barrel and an Ares Defense lower that I just love. The best powders I have found are the Accurate 1680 for the 125's and 5744 for the 150's. Both bullets are doing well over 2500 using loads around 1gr OFF max., again 20" barrel.
Sub 1" groups for the 125's and with Hornady 150 fmj, pulled 147's shoot around 1.250" or so with perfect functioning. The A5477 is a great powder if you want to load hotter or heaver bullets and you can't really get in trouble with A1680 because of case capacity, problem is around here in NewYorkastan you can't find it but if you want to take a day trip I found it from Pa. to Fl. no problem.
The cartridge is great for deer and hogs out to 200yds or more, burns half the powder of a 308 Win. and because of normal throating (Not using 220gr bullets) you can shoot cheaper, normal bullets ............... win,win.

[Hickok]

Thanks for the info Kfisch, and welcome to the best site on the web!

[Hickok]

Just like to say this. Would I recommend an X-Caliber brand barrel?

Yes I would, as the barrel is of high quality, well made and shoots excellent. I am getting more "feel" for shooting the light weight AR Carbine off the bench, and the barrel will do MOA @ 100 yards with monotony with a older 4x Burris scope and Sierra bullets.

Will be working with some more cast load development in the future.