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PostPosted: Thu Sep 04, 2014 3:05 am 
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Location: Mississauga, ON
Just bought a Alpha Chrony because it was too difficult to line up on my little UFC Pro Chronograph at a distance far enough away from the gun to not have the muzzle blast affect the readings. It seemed to work OK if the gun was at least 12" away, but it's difficult to line up on a 1" hole when it's too close to use the sights.

Anyway when the Chrony arrived I did what any self respecting gearhead would do - I lined them up and shot through both at the same time with the UFC 16" from the muzzle and the Chrony right behind it. Six shots gave me the following results. UFC followed by Chrony followed by the difference. (Daisy 953 w/filled piston, Crosman Premier 7.9gr wadcutters)

UFC / Chrony / difference
------------------------
475 / 494 / +19
480 / 498 / +18
479 / 500 / +21
477 / 499 / +22
471 / 498 / +27 (?)
476 / 499 / +23
---------------
476 / 498 / +21.6 averages

Like the subject says: Which would you believe, and why?


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PostPosted: Thu Sep 04, 2014 4:50 am 
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Location: Thunder Bay
Either one. 20 fps won't make any difference. If you take them both outside under natural light, you may find the readings closer together.
Be interesting to see if two identical chronos have the same readings.

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PostPosted: Thu Sep 04, 2014 7:11 am 
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That's about a 4% variation. Shooting chrony actually give an accuracy specification for their chrony - a rather excellent 99.5% (I was surprised given the price point). They do have a reputation for being a bit tricky to set up for maximum accuracy, but if your setup is as good as it looks in the photo, I'd lean towards them being the more credible vendor.

Jim


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PostPosted: Thu Sep 04, 2014 10:59 am 
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I would put more trust in the Crony - due to it's longer screen spacing. The greater the distance between the screens, the greater the potential for increased accuracy.

My PACT timer with 4' spacing has the potential to be more accurate than any chrony and if It was set at it's 8' spacing, the accuracy potential would be even greater.

The difference in accuracy of the readings might not be much - but the potential for greater accuracy is there.

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PostPosted: Thu Sep 04, 2014 4:15 pm 
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Daryl wrote:
I would put more trust in the Crony - due to it's longer screen spacing. The greater the distance between the screens, the greater the potential for increased accuracy.

My PACT timer with 4' spacing has the potential to be more accurate than any chrony and if It was set at it's 8' spacing, the accuracy potential would be even greater.

The difference in accuracy of the readings might not be much - but the potential for greater accuracy is there.

x 2

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PostPosted: Thu Sep 04, 2014 4:31 pm 
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X3...

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PostPosted: Thu Sep 04, 2014 6:02 pm 
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A 953 with filled piston typically throws CPD (7.9 gr) just at the non-PAL limit.
The Chrony gives the expected readings, so I'd believe it.

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PostPosted: Thu Sep 04, 2014 7:19 pm 
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Thank you all, gentlemen. I was predisposed towards the Chrony, but I was looking for some feedback/reasoning. I had fed more pellets through it prior to this comparison and I had already noted that it was more consistent, without the occasional wilder swings the small unit had. The UFC is relegated to a drawer.

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PostPosted: Thu Sep 04, 2014 8:36 pm 
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Now do the test with the order reversed for fun :)

Interested to see the difference then.

Cheers,
Walter....

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PostPosted: Thu Sep 04, 2014 9:01 pm 
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Voltar1 wrote:
Now do the test with the order reversed for fun :)

Interested to see the difference then.

Cheers,
Walter....

You just want to see me shoot the little chronograph. :) Seriously, I use an 18" steel ruler as a straight edge to line up the chrono at 16" - I don't know how I would do it farther away. But I'll probably give it a try.

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PostPosted: Thu Sep 04, 2014 10:32 pm 
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OK, Here you go, Walter. Eight shots (plus a couple - see below)

Chrony / UFC / difference
--------------------
504 / 487 / +17
501 / 483 / +18
499 / 480 / +19
498 / 481 / +17
499 / 485 / +14
506 / 488 / +18
500 / 483 / +17
495 / 477 / +18
-----------------
500 / 483 / +17 averages

Interesting observation: I made two additional shots, one where I accidentally 'stutter-pumped' the 953 and one where I did this on purpose. That is, I started the pump and when at 1/3 of the way into the pump I backed off and started the pump again. On the second shot I deliberately gave a couple of 1/2 pumps first.

530 / 511
530 / 512
:shock: I didn't think the gun would do that because I didn't think it had a retaining valve.


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Daisy 953 * QB78D * Walther 1894 * Beretta CX4 & PX4 * Zoraki HP01 * Beeman P17 * Walther CP88 Comp. * Crosman 1377/2240/SA6/357-8
Swiss Arms P92 * Colt Commander 1911 * Walther PPK * P08 * Colt Python 357 * TW 1911/Limited * S&W M&P R8
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PostPosted: Fri Sep 05, 2014 6:24 am 
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Quote:
I didn't think the gun would do that because I didn't think it had a retaining valve.


It doesn't, so you get into all sorts of interesting theories about how that happens :) (and no, I don't doubt your measurements). I don't have anything solid to suggest, but I've noticed the seal of the o-ring on the piston is a bit iffy during the first part of the stroke, possibly because the piston doesn't necessarily run completely true until it's well engaged in the tube. Perhaps it has a tendency to retain more air on the second attempt of the stutter. Mine doesn't have a lot of clearance of the o-ring and the air gap cuttaway, so sometimes the in-rush of air at full open is quite slow. If the stutter pump opens fully enough to unseal the tube, then perhaps the second pump gets a better fill of air. Adding to this idea - on mine, the compression tube slips back and forwards about 1/16", moving away from the valve on the open stroke, and back towards the valve on the compression stroke. This makes the air gap smaller and so makes the above problem worse. Perhaps yours does the same, and the tube slides valve-wards on the first stutter, but doesn't tend to slide out again on the partial open stroke before the second pump.

Mysteries! You gotta love mysteries :)

Jim


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PostPosted: Fri Sep 05, 2014 2:49 pm 
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Location: Vernon BC
I would believe the Chrony just because of it's well known name. Especially if you have it set up with the proper lighting (like you do).

Although, the lighting is extremely sensitive with the chrony! I've seen differences of over 50 fps when the clouds clear out to reveal blue sky briefly.


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PostPosted: Sun Sep 07, 2014 9:55 am 
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Since I have the same gun with the same piston mod, I'm going to have to trust the alpha since it's giving you number much like my chrony gives me.

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