Subsonic 7.62 experiment # 4

Artful · Post by **Artful** » Sun Apr 29, 2007 12:40 am

Date-April-26-2007
Rifle-Mossburg 800A bolt action
Barrel Length-22 inches
Twist-1:12
Temperature-94 (warming up)
Case-Remington mostly
Case Prep-Epoxy Filled to bottom of neck. Flash hole drilled to 1/8”, ½” up from bottom of case. 17/64” drilled from Case mouth to meet flash hole, Leaving reduced capacity casing. Which was filled with
-8.2 grns of Blue Dot Gun Powder.
Bullet-150gr SP Remington Moly coated loader to the canalure Lee factory crimp applied.
Primer-CCI 250 LR Mag

10 Rounds created and Fired for test.
1st 5 with gun on bench rest cartridge inserted into chamber
1334, 1321, 1241, 1270, 1214
2nd 5 with cartrdige chambered rifle tipped up and tapped
1079, 1156, 1191, 1723, 1092

Comments,
Didn’t use same maker in all cases. (we thought we had)
Epoxy fill may not have been consistent as it was loaded to
same area but wasn't weighted or measured but the epoxy stayed in same state after first firing. Can only be neck sized at this point.
Powder load was exact in all loads so unsure of why the 1723 fps round?
All rounds fired showed no keyhole effect pretty good grouping.
try varying the powder charge on next go round.

brianb · Post by **brianb** » Sun Apr 29, 2007 7:59 am

So... the goal is to avoid the positional issues associated with small powder charges in a big case?

>>2nd 5 with cartrdige chambered rifle tipped up and tapped

Since the above method resulted in substantially different velocities I'm going to take a 'wild guess' and say it's not working.

Avg 1st: 1276
Avg 2nd (even throwing out the high 1723): 903.6

370fps difference from the "cartrdige chambered rifle tipped up and tapped" method over not...?

Yikes.

Krink545 · Post by **Krink545** » Sun Apr 29, 2007 9:56 pm

I get 1129 fps for the 2nd average with a difference of 147fps.

brianb · Post by **brianb** » Sun Apr 29, 2007 10:32 pm

I believe ya. I think I had a blank field that skewed it when I threw out the 1734.

Suputin · Post by **Suputin** » Mon Apr 30, 2007 8:15 pm

The only thing that worries me is the potential for the epoxy to be vapourized and then deposited on the bore.

Golovko · Post by **Golovko** » Wed May 02, 2007 1:00 pm

That's probably more of a risk with a sabot than it is with epoxy.

chevrofreak · Post by **chevrofreak** » Wed May 02, 2007 4:44 pm

I wonder if filling the case with solder would be a more durable approach?

Artful · Post by **Artful** » Thu May 03, 2007 11:25 pm

No weighable change in case weight after firing so no expoy vaporization noted on first firing. we'll see on next experiment - I'm trying to find consistant subsonic velocity regardless of if the load has been chambered riding around in your vehile gun rack - tilted up carried in slung position or carried port arms over hill and dale. - some of the loads were consistant when I tried loading from a bench - then had issue when muzzle was tipped up or down so trying for higher volume case load with faster burning powders to eliminate the problem. I want the gun to hit what I'm going to aim at and not give sonic crack irrigardless of how the ammo has been handled (within reason).

Solder might be a solution, as is machining the case from brass or aluminum - I'm also thinking about buying a 30 carbine insert for .308 to see about heavy bullet load in it - smaller case volume again