Starting to wonder about my chronograph

[ole_270]

quote[An exact load I have used before.
28.5 grs of IMR-4895 a fed 210 primer and the rest of the case filled with cotton towel dryer lint
The boolit was cast from clip on ww alloy and stick on ww alloy mixed 50-50 with .5% tin mixed in then water dropped from the mold and cured for a couple of weeks.
It gives me a velocity of 1950 to 1975 fps and is super accurate.]end quote

After reading this from runfiverun in a 308 thread I gave the load a try except I used dacron instead of lint. Works very well in my old JC Higgins 51-L with 311041 gas checked bullets that were water dropped from a guestimated alloy approximating Lyman #2. Sized 3095/.310 and tumble lubed with lee alox. These bullets were left over from use in a 30-30 that went down the road several years ago and had been on the back of the shelf ever since. When I sighted in, each group got better as the lube worked up the barrel and my concentration settled in. Last 100 yard group went 3 shots in 3/4".
Decided to stretch its legs a bit and started shooting at a gong a lazered 175 yards distant. never touched the thing. I decided to find out how much drop it had, so i put a big sheet of cardboard behind the gong and tried again. Got a decent 2 1/2" group with the 3rd shot wide from the other two, but it was 19" low and 5" right. Maybe there was more breeze than I thought!
I started wondering about the velocity, so I dug out my Pro Chrono and put 5 shots through it. Averaged 1740 so about 200 fps below r5r's number. It was a bright sunlite day with the sun nearly directly overhead so not the best of conditions.
I've slugged the barrel and it runs .310 so the bullets are a bit small and may not be sealing the bore too well, but can't holler about the accuracy. I haven't put a patch through it so don't know if it was leading.
Starting to wonder about this chrono

[Pistol Champ]

Just like most things you get what you pay for. Low cost usually gives poor results. I've watched more than a few shooters testing loads over a chronograph and when the velocity seems off they universally blame it on the chronograph giving a bad readout. Get a high quality unit it you want data you can trust.

[runfiverun]

the lint I use is in the case pretty tight so I would get a bit better velocity than Dacron.

your drop is a bit more than I get too.
I'm more like 15" from 100 to 200 yds and about another 15" to 300 yds.

3/4" at 100 yds from a hunting rifle is not gonna get laughed at by anybody that's for sure.
I have a Remington that couldn't beat twice that diameter with target j-words.

[Whitespider]

200 fps less is only about a 10% lower than what runfiverun is getting.
When you figure different boolits, different alloys, different lubes, different powder and primer lots, different gun, different loading technique, and different firing conditions... a 10% velocity difference is no surprise at all.
Truthfully, it would be more of a surprise if there wasn't a velocity difference.

And yeah, 3/4" at 100 yards?? I wouldn't be overly concerned with velocity... I'd just smile.
*

[waksupi]

You can't trust chronys too much. A friend brought a readout to our shoot last weekend, wondering what was wrong. He has two Oehler chronographs, that he sat up one right behind the other. Readings had quite a bit of variance.

[ole_270]

I don't begin to claim the 3/4" as average, just the last group fired. It does shoot very well though.
I think I'll test the chronograph with some 22LR through a couple guns as a check. I've read that most are pretty close to advertised velocity, especially the match types. I shot 2 other guns the same session and both the 25-20 and 38-55 came out slower than expected.

[country gent]

My old pact professional I tested each time used with a RWS side cocker air rifle. This rifle gives very consistant velocity shot to shot and day to day. when the pact finally gave up, I replaced it with a Lab Radar unit and we originally tested it against 2 other units. The Lab Radar, a magno speed on the muzzle, and a ohler 33 with sky screens at 10'. All read with in 35 fps of each other. I would find a consistant batch of 22 LR ammo or a good airgun and pellets and test the set up each time. It dosnt take long to fire 5 or10 rounds over the screens to know for sure.

[fredj338]

I am sure your chrono is correct. Too many variables to think you are getting identical vel. I have 5 diff 4" 357mags. With identical ammo, they vary as much as 125fps. I have never seen chrono variation more than 15-20fps between brands.

[Larry Gibson]

Might double check your load. With 28 gr IMR 4895 under a 311041 with a Dacron filler runs 1950 fps +/- out of my 24 and 26" barreled .308Ws. 23 gr drops the velocity down into the low 1700 fps range.

Larry Gibson

[Blackwater]

In my experience, the key with ANY chrono, is the degree of sun that's shining. I have a Pact I, and it does NOT like lower light levels at all. A low to mid-priced chrono should work well, IF you don't demand that it work in lower light levels. That's been my experience, anyway. YMMV?

[Mk42gunner]

I haven't ventured into 4895 with cast, but I always used a few shots from one specific milk carton of .22LR and my CZ452 to make sure the Chrony was reading somewhat close to normal. That box of shells is long gone, so I will have to start another the next time I do any serious chronographing.

Robert

[ole_270]

Got a chance to play with it a little this afternoon. Sky was fully overcast, so completely different conditions from yesterday.
I retested the 25-20 load, got 1276 this time 1289 yesterday. With only 5 shots fired per test, I'd say that's the about the same average. One thing I noticed, every shot increased in velocity. This load uses PC so not a lube issue, might be the barrel warming up.
Switched to my old Rem 582 22LR. Started out with Federal Auto mags, claimed to be 1200 fps. Again each shot from a cold barrel start increased in velocity, though not as much as the 25-20. Averaged 1182 with an extreme spread of 64. Close on the velocity, but that much spread is concerning for a match load.
Pulled out some CCI Green Tag, box said 1070 fps. 5 rounds averaged 1013 fps, but extreme spread was down to 7. much more uniform, but fairly slow.
Not sure I prove anything, other than it's fairly consistent between overcast and bright sun with the 25-20 load. One 22 load was close, the other pretty slow.
Both rifles carry 24" barrels, the 22 hadn't been used in a couple years, the 25-20 gets steady use.
Oh well, in the grand scheme of things it really doesn't mean much since both rifles are pretty accurate with their respective favorite loads.

[ole_270]

Might double check your load. With 28 gr IMR 4895 under a 311041 with a Dacron filler runs 1950 fps +/- out of my 24 and 26" barreled .308Ws. 23 gr drops the velocity down into the low 1700 fps range.

Larry Gibson

The powder measure was set using a balance beam scale that I check often with a weight check set from RCBS.
Maybe it's the rifle, I haven't chronoed any full power loads out of this 308. It shoots real well with most everything I've put in it. A real lightweight 22" barrel that tapers to .575 at the muzzle. Whole rig weighs under 7.5 lb scoped, it's becoming a favorite.

[runfiverun]

Larry's numbers are similar to mine.
except my barrel lengths are a bit different at 20-24 and 30.

I have seen powder coating lower speeds about 5% or so with no other changes due to it being slicker than plain cast.

[OS OK]

13:38Chronograph Shootout: Chrony F-1 Master vs Oehler 35P4 years agoyoutube.com

[rond]

If you don't trust it just shoot it. That's what my son did.

[Tackleberry41]

As I read the OP, your saying some one elses load has a different velocity in your gun. And.....?

We all know it does not take much to change velocity. All the 308 load data I find is for 24in barrel, which is not really the norm. Theres no way I will get that posted velocity in my shorter barrel. Its not your chrony, the load is just running slower in your gun. No idea if its even the same mold, the weight, seating depth. Seating depth can make a big difference.

[Victor N TN]

I had 3 different "Chronys". I wouldn't believe either of them if they said the Sun was shining. I got so mad at the last one I had it took a 30 cal AP bullet through and through. Best .35 cents I've ever spent.

[JohnH]

13:38Chronograph Shootout: Chrony F-1 Master vs Oehler 35P4 years agoyoutube.com

Good video

[ole_270]

Not that it matters much but this isn't a Chrony. It's a Competition Electronics Pro Chono