Used Gun

bigchopper · Plinker 869 Joined: 27 Sep 2004 Posts: 6

I just purchased a used OLY. It is stamped PCR 96 can't find this listed on OLY site. Has a 20" barrel marked SUM 556. Any info would be great. This is a great shooting gun as good as any I've shoot. This site is great also already picked up some useful info keep it up.

Coug223 · Posted: Thu Sep 30, 2004 6:47 am Post subject:

Bigchopper,

The PCR 96 stamping indicates you lower was made in 1996. The SUM 556 indicates your barrel is a Stainless UltraMatch, Oly's best.

Since it's got a 20" barrel, I'd bet on a PCR-1 configuration if flat top, or a PCR-SM Service Match if an A-2 upper. Either way you've got one of the best. Should be capable of less than 1/2 MOA. Mine will do about 3/8" groups at 100 yards when I do my part.

The next thing to find is what barrel twist you have (1:8 or 1:10). If the barrel isn't marked, you can try marking a cleaning rod so you can see one full rotation and measure how much rod it took to make one rotation when pushing a patch through.

Congratulations on a nice new (to you) rifle.

bigchopper · Plinker 869 Joined: 27 Sep 2004 Posts: 6

Shows to be 1 in 10 any recomendation on ammo been told 60gr. or less would shoot best.

Coug223 · Posted: Thu Sep 30, 2004 11:14 am Post subject:

Mine works great with Black Hills 55 gr V-max, or Hornady 55 gr V-max ($15 for 50 Blackhills Blue box (reload), or $14 for 20 Hornady). I think D-Tech reccomends Black hillls 52 Gr. boattail match. I've found some for $13 a box of 50 for $13, but haven't had time to shoot any yet.

Mine is picky about ammo. When I bought it I ran about 5-6 different types/manufaturer's from 62 gr. to 52 gr. and groups ran form ~3/8" to about 4" all from premium ammo. Some of the premium stuff grouped worse than cheaper Winchester white box. So try a few, but I don't think you'll go wrong with the BlackHills recommendations.

Have fun.

Black_Heart · Posted: Fri Oct 01, 2004 12:51 am Post subject:

The best way to find a bullet that you will get good stabilization from is to use the Greenhill formula. The Greenhill formula is an empirical equation that does a good job of establishing the barrel twist necessary so that a bullet of a given length will be adequately stabilized.

Greenhill made easy:

T=150 x D
---
R

here: T is the twist required (number of inches for one revolu- tion),
D is the bullet diameter (in inches)

R is the bullet length to diameter ratio, (length divided by diameter)

Conversely, to find out what length bullet will be stabilized in a given twist, use:

L=150 x D x D
-----
T (that is, 150 x D squared divided by T)

where L= bullet length
The number 150 is a constant used by Greenhill and works well at velocities in the vicinity of 1500 fps or greater. At 2800 fps the constant can be changed to 180 with good results.

Substatute the Constant of 150 (1500 fps) with 180 for a (velosity of 2800 fps)
Information above provided by by Normal F. Johnson (njohnson@nosc.mil)

Semper Fi