625 PC Muzzle Velocity?

[tomgen]

Hi,

I picked up a new Performance Center 625 earlier this year. I have been shooting it in IDPA and USPSA competitions, so the power factor generated by my ammo is important. I have be running into difficulty meeting major PF (bullet weight x muzzle velocity in feet/sec). I was chronoing ammo yesterday when a buddy walked with his 625-8. We both had the same load, 4 grns of Clays and 230 FMJ bullets. I shot my ammo in my gun and then shot my ammo in his gun. My ammo out of my gun measured 680-705 fps. My ammo out his gun measured 740-765 fps. I shot his ammo in both guns and the results were the same, about 50 fps faster in his gun, all testing was done with my chronograph. What could cause this disparity? 4 grains of Clays and 230 FMJ should produce about 740 fps. Are the chambers in my cylinder over-sized?

Thanks,

TG

 

[rbert0005]

Length of barrel

Bob

 

[Pisgah]

Length of barrel, chamber and/or bore dimensions, bore finish, barrel-cylinder gap. And sometimes, inexplicably, one gun will just plain be "faster" than another.

 

[S&WIowegan]

Not unusual

While this result seems strange, many factors can cause it. Is barrel length the same? If so, then barrel/cylinder gap could be the cause. If you have feeler gauges, compare the two guns. Finally, I learned in my 20+yrs. of shooting 625s that some have a slightly bigger bore than others. All other factors being equal, a tighter bore gives higher velocity.

None of this makes your gun bad, just add a little powder to your loads. Before doing that, compare the two guns chrono results with factory ammo.

Be safe,

 

[Dragon88]

Increasing the powder charge a few tenths will get you where you need to be. I wouldn't worry about the gun so much.

 

[GSWEAR]

Cylinder gap as mentioned another reason may be that your PC model has cut rifling and the 625-8 has the EDM rifling which is probably a little faster because of less friction on the bullet.
I have a 625-8JM which has the EDM rifling and a 625PC which has cut rifling, in the next couple weeks I will measure the cylinder gap on each and chrono a couple different loads thru each.
My IDPA load is a 230 Bayou Bullet and 4.1 clays in my 625JM, last Sunday it was 100 degrees and it made 177 power factor, in the spring when it was 45 or so it made 169 or 170 but may have been a different lot of powder but I don't think so.
You may want to try the Bayou Bullets as well, you get the added velocity like lead with no fouling like lead or molly and cheaper than jacketed.

Greg

 

[H Richard]

Amount of crimp can boost pressure which relates to velocity. A good healthy crimp will nearly always have a faster velocity than a mild crimp. In a revolver a roll crimp is best.

 

[nawilson]

You may want to check out Speer's Reloading Manual #14. There is a whole chapter entitled "Why Ballisticians Get Gray" that is about this phenomenon. As mentioned above, there are lots of possible causes.

 

[tomgen]

The barrel lengths of both guns are 4". The chambers on my gun are all .475 (I don't know what the spec is). The cylinder-cone gap .005 on one side of the cone and .010 on the other. It appears the cone is not parallel to the to cylinder. I did rotate the cylinder and measure several times. All that said, the gun is very accurate and I like, so I will run some hotter loads.

Thanks for all the replies...TG

 

[colt_saa]

It does not need to be the firearm, it could also be the ammunition.

Different brands of primer

Different manufacturers of projectiles.

 

[GSWEAR]

It does not need to be the firearm, it could also be the ammunition.

Different brands of primer

Different manufacturers of projectiles.

I think the poster noted that the same ammo was shot in each gun, his ammo was shot in each gun then they shot his freinds ammo in each gun.

Greg