New builds, 7.62x39mmUSA kinda like a 300/221XL

[JFettig]

What velocities are you getting out of a 16" barrel?

Jon

[kurtz]

Hi Jon,

When I started out on the two builds I had 125 grain TNT target velocities of 2400fps for the 16" and 2500fps for the 20" in mind.....and hit both using right around 25grains of 1680.....there hasn't been much time to go to the range in the last couple weeks to try any loads other than what are listed in the thread for the 20".....

I've been spending most of my free time re-chambering a couple rifles for friends and another of mine.....I have now hand re-chambered a total of (4) 300-221 and 300 fireball rifles to 7.62x39mmUSA...this project was my first attempt at cutting chambers and have been pretty happy with the results.....it probably took more time to tool-up and cut the
receiver/T-handle bushings out of delrin than it has to cut the chambers.....polymer sucks to cut...maybe it's just my tools???

I have a new/unused chamber reamer and headspace gauge if anyone would like to join in the fun....fair price and no wait....

the reamer that I have been using is still sharper than woodpecker lips....PTG is the stuff...anybody have an idea how many barrels can be cut with a reamer before re-sharpening is needed...

Thanks for the interest and I hope to get to the range this weekend to be able to post more data....

kurtz

[JFettig]

Not sure what the problem with delrin is, its my absolute favorite thing to cut. A sharp tool goes a long way.

I'd almost be interested if I had the cash to do another barrel. This is kind of what I originally had in mind instead of a 300/221, maybe sometime in the future.

When you get around to getting those velocities, post them up, I'm interested in seeing what you get out of the shorter barrel.


Jon

[kurtz]

Got to go to the range this weekend to test a couple changes made to the 20" 7.62x39USA......I had PTG make me a new chamber reamer to try a couple new ideas.....I moved the shoulder forward .050", opened the neck up .001" and added .003" taper to the neck....The gas port that I had been trying was .093" and the rifle cycled ok but was a little slugish and would fail to lock open every once and a while on the last round with less than 25gr of 1680......

I went to the range with a bunch of 125 TNT's with 25gr of 1680, my drill press and numbered bits.....opened the gas port up .002 to .003 at a time firing 10 rounds between.....took a little time but ended up at .102 with very reliable cycling.....now that the shoulder is moved forward .050" I can now fit a little over 26gr of 1680 in fire formed brass....with more powder and a bigger gas port it brings the adjustable gas block back to use other than wide open....also noticed that opening the gas port around .010" took about 80 fps off the top-end of the 25gr loads now clocking around 2450.....

I can't say enough good about the 20" 1:12 Noveske on this rifle, rapid fire (10 rounds in about 8 seconds) from a bi-pod at 100 yards printed a group that could be covered with a quarter....very happy, thanks John....

now to work on load development for the 16"....hopefully this weekend...

kurtz

[kurtz]

went to the range to test a couple loads in the 16" and 20" 7.62x39USA


16" 1:8 Olmypic .078 gas port carbine length gas system, fire-formed brass, no signs of high pressure...

125 TNT 21.5gr 4227 = 2,230 fps
125 TNT 22.0gr 4227 = 2,350 fps
125 TNT 22.5gr 4227 = 2,440 fps
125 TNT 25.8gr 1680 = 2,430 fps


20" 1:12 Noveske .102 gas port rifle length gas system, fire-formed brass, no signs of high pressure....

125 TNT 21.5gr 4227 = 2,270 fps
125 TNT 22.0gr 4227 = 2,440 fps
125 TNT 22.5gr 4227 = 2,470 fps
125 TNT 25.8gr 1680 = 2,575 fps


I'm going to work up more loads for the carbine: 296, lil-gun, H110.......hopefully I'll have the data tomorrow...


kurtz

[kurtz]

went to the range to test a couple loads in the 16" and 20" 7.62x39USA


16" 1:8 Olmypic .078 gas port carbine length gas system, fire-formed brass...

125 TNT 22gr lil-gun = 2,540 fps
125 TNT 22gr H110 = 2,480 fps
125 TNT 22gr 296 = 2,475 fps


20" 1:12 Noveske .102 gas port rifle length gas system, fire-formed brass....

125 TNT 26.0gr 1680 = 2,606 fps


I think I've hit a stopping point with the 16" around 2500fps...my favorite loads have been with the 4227 and lil-gun around 2350 to 2450fps.....I can probably push it a little faster but I'm not sure if the additional velocity is worth the increased pressure (wear and tear on the rifle).....2350 to 2450 is comfortable to shoot....the additional power it takes to reach the 2500 to 2550 mark is pretty noticable in the BOOM factor....

The 20" rifle handled the 125's at 2600fps great.....I think the 1680 really shines in the 20" barrel.....it's funny, in the 16" barrel a charge of 22.5gr of 4227 and 25.8gr of 1680 produced almost identical fps (around 2440fps) ....but out of the 20" with the same loads the 1680 was over 100fps faster....no pressure signs with the 26gr of 1680 and still have a little room in the case.....

kurtz

[kurtz]

went to the range today to experiment with a couple things and fire-form some brass.....

the last changes made to the chamber reamer seemed to work out pretty good...pushing a 125 TNT at a consistant 2,650fps out of the 20" with 26.5gr of accurate 1680....with a combination of a few tweaks the 20" now cycles very positive and reliable....

a pic of the revised round in a line-up (left to right: 300-221, 7.62x39Russian, 7.62x39USA, 5.56x45)...revised round is approaching 7.62x40mm



also got a few of the 20 round pmags for shooting prone....modified them using a 11/16" bedding tool....disassemble the mag, hold the mag body vertical insert and pull down the bedding tool a few times and it cuts out both ribs at the same time....works great on the 20 and 30 round pmags....

a pic of the revised round in the pmag....



after a few requests from the AR-15.com forum I am probably going to chamber a couple more barrels this week...most are interested in the 16" but I'm kinda starting to favor the 20"....going to start next week on another 20" with a mid-length gas system, may be a little easier to tune...

[abyssdncr]

I called Noveske yesterday...they didn't seem the least bit interested in building me a barrel that wasn't on their website. A little disappointing as Pac-Nor as them listed as the source for AR barrels.

I still would like to have one of his barrels to play with, but it sounds like it could be a long wait before they do another run of .300/221 barrels...

[MartytW]

Can you post dimensions of the cartridge? Or a link to a drawing? I am mostly interested to find out the neck diameter. Thanks!

[kurtz]

the outside neck diameter of a loaded rounnd with a 125 TNT is .328 to .330, depending what brand of brass you use.....

kurtz