Subsonic 7.62/308 test #5

[Artful]

Went up into the cool Arizona mountains on 5-09-07 10:00 am
80 deg F at 3170 ft elevation.

Used 150 grain PSP Rem loaded over 8.0 gr Blue Dot in epoxy filled and drilled cases 2nd firing CCI 250 Mag primer with primer flashhole drilled out to 1/8" loaded to OAL 2.466 out of 21" FAL 1:12 twist barrel.

just loaded from magazine clean oiled barrel.
___case weight 203.0 empty 211.1 primed/powdered gave 1032 fps
___case weight 202.0 empty 210.0 primed/powdered gave 1188 fps
___case weight 207.0 empty 215.0 primed/powdered gave 1198 fps
put AAC Cyclone suppressor on
___case weight 203.8 empty 211.8 primed/powdered gave 1195 fps
___case weight 203.4 empty 211.5 primed/powdered gave 1222 fps
___case weight 203.3 empty 211.3 primed/powdered gave 1215 fps
just loaded from magazine
___case weight 203.1 empty 211.2 primed/powdered gave 1170 fps
___case weight 205.9 empty 213.9 primed/powdered gave 1113 fps
___case weight 218.9 empty 226.9 primed/powdered gave 1182 fps
___case weight 201.2 empty 218.2 primed/powdered gave 1253 fps

Load Density about 65% of the restricted case...skipped tilt test

[SHARPSHOOTER]

It was always my understanding that 1050fps or less is subsonic. Many of your loads are over that mark. Have you given consideration to a heavy bullet? It will probably be much easier to hit that mark.

[Artful]

Yes, I have plans for that but for initial experimentation I want to find something with cheaper bullets (ie something like 147 -163 pulled surplus military bullets).

I want to avoid lead bullets due to sealed suppressor use with the rifle.

I had a thought about ordering a 30 carbine chamber adaptor and loading with that case (easier to reload with carbide dies and no special prep of the case and you'd have long throat to seat out the bullet to get maximum case volume without any problems)

[worldskipper]

Art try a faster powder, and a heavier bullet, nothing less than a 180gr.

I had good luck with in a k31 with a 200gr lead bullet with 3 grs of Clays, mag primers and a bit of dacron stuffed into the case to keep the powder sitting on the primer.

Speed out of a 23" was about 790 fps, I think. It was pretty cool, sounded like a 22 short coming out.

Small Charges in Cases by Paco (http://www.leverguns.com/articles/paco/small_charges.htm)

[Artful]

Same Epoxy filled cases - 7.6 grains Blue Dot
Cases still not needing trimming -

first shot didn't register, 816.3, 819.5, 1027, 960.2, 953.2, 1033, 1030, 869.7, 1045

I think I'll have to order one of the cartridge adapters for 30 carbine to see if I can get a reduced capacity that way - I also thought about filling with something more durable (jbweld) but think that may be wasted money - also they have closed forest / state lands to shooting due to fire danger so that puts a crimp in my quiet shooting. :(

[SHARPSHOOTER]

There is another less painful way than filling the case with epoxy to reduce capacity. You can get the nylon fiber batting that is used by women who do the home quilting thing. It holds your powder in place against the primer. That is what I discovered from other who have done extensive load development for subsonic loads. I use it in my 5.56 loads with blue dot and it works great.

[Artful]

Originally posted by SHARPSHOOTER
There is another less painful way than filling the case with epoxy to reduce capacity. You can get the nylon fiber batting that is used by women who do the home quilting thing. It holds your powder in place against the primer. That is what I discovered from other who have done extensive load development for subsonic loads. I use it in my 5.56 loads with blue dot and it works great.

Thanks, but I don't want anything that can be left behind in the sealed can if I can find another way. Making up new cases with different plastic filler to see if it will do better. Wish me luck

[BerdanIII]

I hit gold the first time I tried a subsonic load in the 7.62x51mm (a far cry from my experience with the 7.92x57mm). The load was published in an old Handloader's Digest and called for 6.5 grs. of Bullseye and a 150-gr. bullet for a m/v of 1050 fps. I increased the charge to 6.7 grs. because I would rather work the velocity down than stick a bullet in the bore. I later read an article by C.E. Harris in which he stated that "new" Bullseye is 0.2 - 0.3 grains slower than old Bullseye and old load data should be adjusted accordingly. Using range pick-up PMC cases (standard flash holes), Federal Large Pistol primers and salvage Remchester 150-gr. RNSP's seated to 2.542" COL, I got an average muzzle velocity of 1037 fps (24-inch barrel), an extreme spread of 35 fps and a 2.25" group at 100 yards. A second trial with an on-pupose mix of commercial and military cases gave a m/v of 1016 fps, an extreme spread of 51 fps and a 3.25" group at 100 yards. According to the article, round-nose .30-30 bullets are more accurate than spitzers or boattails in this application.

[Artful]

Thanks I'll put that on the list to explore as well - I was so hopeful of the Trailboss but I've got Blue Dot, MR5744, Red Dot and Bullseye to continue with.