9mm Power Factor Questions

[bkeeler]

My guess is recoil spring. A heavier spring will increase FPS.

Have you tested that extensively to get solid data? Like chrono a hundred rounds with one spring, swap springs and run another hundred rounds...or something along those lines? I'm just curious how much difference it could actually be since all the high speed video I've seen has the bullet leaving before the slide has moved more than a tiny bit. I'm not saying it won't make a difference...just wondering if you/anybody has ever tried to quantify it. R,

[Tom E]

Hello people, it was the cloud cover and the light rain that was causing trouble. Today, the 3.8 gr in my 1911 had an average of 910 fps, and the M&P had an average 895 fps. 3.6 gr had a average of 865 fps, so I'll go with that for USPSA and IDPA.

Thanks for all the replies and help.

A.T.

Cloud cover is actually a good thing while using the chrono. Heavy cloud cover gives very even lighting and good results. The "shades" pretty much duplicate cloud cover. Bright sunlight is actually the worst .

[GrumpyOne]

My guess is recoil spring. A heavier spring will increase FPS.

Have you tested that extensively to get solid data? Like chrono a hundred rounds with one spring, swap springs and run another hundred rounds...or something along those lines? I'm just curious how much difference it could actually be since all the high speed video I've seen has the bullet leaving before the slide has moved more than a tiny bit. I'm not saying it won't make a difference...just wondering if you/anybody has ever tried to quantify it. R,

I'm with Bart on this. The bullet has to exit the barrel before the slide can come out of lock, therefore the recoil spring has no impact of the velocity of the round. If I remember correctly, a typical slide takes approximately 1/10th of one second to cycle. If you cut that in half (1/20th of a second for the rearward motion of the slide), by the time the slide hits the stop at the rear, a bullet traveling at a velocity of 900fps is already 45 feet downrange. Recoil spring has nothing to do with velocity, only how fast the slide moves AFTER the bullet has left.

[Flexmoney]

Load minor ammo to 135+ pf.

[G-ManBart]

My guess is recoil spring. A heavier spring will increase FPS.

Have you tested that extensively to get solid data? Like chrono a hundred rounds with one spring, swap springs and run another hundred rounds...or something along those lines? I'm just curious how much difference it could actually be since all the high speed video I've seen has the bullet leaving before the slide has moved more than a tiny bit. I'm not saying it won't make a difference...just wondering if you/anybody has ever tried to quantify it. R,

I'm with Bart on this. The bullet has to exit the barrel before the slide can come out of lock, therefore the recoil spring has no impact of the velocity of the round. If I remember correctly, a typical slide takes approximately 1/10th of one second to cycle. If you cut that in half (1/20th of a second for the rearward motion of the slide), by the time the slide hits the stop at the rear, a bullet traveling at a velocity of 900fps is already 45 feet downrange. Recoil spring has nothing to do with velocity, only how fast the slide moves AFTER the bullet has left.

I've seen some video that shows some movement of the slide, with the barrel still locked, before the bullet has left, but I'm sure that depends on the exact gun, type of load, etc, etc. I wouldn't be surprised that in some situations (Open guns come to mind) where the recoil spring could make a very slight difference, but I've never tried to test it....but now I think I'll try to when I can get around to it :-)

[atbarr]

Load minor ammo to 135+ pf.

Why?

A.T.

[Singlestack]

Load minor ammo to 135+ pf.

Why?

A.T.

Chrono is Voodoo

Thats why.

[G-ManBart]

Load minor ammo to 135+ pf.

Why?

A.T.

Like in my earlier example, a load (actually one batch of ammo) that had been chrono'd at a number of big matches and always made well over 170PF, only made 166.1PF at Nationals. If that load was normally say 170PF on the nose I would have gone Minor.

If you go sub-minor (124.99) you're not shooting for score and just wasted a match fee, hotels, gas/airfare etc. R,

[Singlestack]

Load minor ammo to 135+ pf.

Why?

A.T.

Like in my earlier example, a load (actually one batch of ammo) that had been chrono'd at a number of big matches and always made well over 170PF, only made 166.1PF at Nationals. If that load was normally say 170PF on the nose I would have gone Minor.

If you go sub-minor (124.99) you're not shooting for score and just wasted a match fee, hotels, gas/airfare etc. R,

And Chrono is VOODOO!

[GrumpyOne]

My guess is recoil spring. A heavier spring will increase FPS.

Have you tested that extensively to get solid data? Like chrono a hundred rounds with one spring, swap springs and run another hundred rounds...or something along those lines? I'm just curious how much difference it could actually be since all the high speed video I've seen has the bullet leaving before the slide has moved more than a tiny bit. I'm not saying it won't make a difference...just wondering if you/anybody has ever tried to quantify it. R,

I'm with Bart on this. The bullet has to exit the barrel before the slide can come out of lock, therefore the recoil spring has no impact of the velocity of the round. If I remember correctly, a typical slide takes approximately 1/10th of one second to cycle. If you cut that in half (1/20th of a second for the rearward motion of the slide), by the time the slide hits the stop at the rear, a bullet traveling at a velocity of 900fps is already 45 feet downrange. Recoil spring has nothing to do with velocity, only how fast the slide moves AFTER the bullet has left.

I've seen some video that shows some movement of the slide, with the barrel still locked, before the bullet has left, but I'm sure that depends on the exact gun, type of load, etc, etc. I wouldn't be surprised that in some situations (Open guns come to mind) where the recoil spring could make a very slight difference, but I've never tried to test it....but now I think I'll try to when I can get around to it :-)

Cool. But if the slide is moving, albeit even microscopically, wouldn't the locking lugs be dis-engaging at this point (or beginning to dis-engage), causing the barrel to tilt upward (at the muzzle, down at the chamber) that little bit, causing a skew in accuracy? It's my understanding that the pressures involved with firing the round cause the case to "stick" to the walls of the chamber, holding the slide in place with the locking lugs until the pressure subsides, causing the case to be pulled from the chamber by the extractor. The only way for the pressure to subside is for the bullet to exit the barrel (barriing comp guns with popple holes, etc.), so could the percieved slight movement of the slide actually be an optical illusion caused by the firing of the round (I.E. the beginning stages of recoil, or the fact that you've just had something with the potential of 35,000 psi blow up in your hand! (shockwave?))

[BayouSlide]

I'm with Flex. Someday you will be chronoed first thing on a cold fall morning...or mid-afternoon in July. I've seen various match chronos run 1-3 PF on either side of mine.

The last two guys I warned not to cut it so close didn't pay attention...and they got bumped to minor in Limited at their first big match with a chrono stage. They had tested mid-day on a hot day in September with a 169 at best and weren't aware that the powder they liked was temperature sensitive. Unfortunately, they drew an early morning chrono time on a cool late October morning before the sun had warmed things up.

Curtis