Barrel mounted, electromagnetic chronograph

[mikecr]

Would seem like the muzzle blast would wreck havoc with it. As with any other chrono..
How good/bad is the indicator unit itself?

 

[memilanuk]

Mike, so far as people have been able to determine, the muzzle blast doesn't seem to have any appreciable effect since it doesn't use the same kind of sensors as 'any other chrono'... thats kind of the whole point.

 

[Steve Blair]

Do I plan on shooting an entire F-Class string with one strapped on my barrel... probably not. But considering the PITA I have getting reliable consistent velocity strings with conventional chronographs 'up here', I'm certainly willing to be a little more open minded.

[br]
Monte, our days range from dark overcast to brilliant sunshine and 50° to 100°. My Kurzzeit PVM-21 has never failed to register a shot within its large (8"w x 4½"h) active area. All my testing indicates that it is very accurate. Note that Lapua uses one at the Mesa, Arizona rimfire service center. [br]
But, if this device will provide results that meet a given shooter's needs, why not? My results are such that I have no reason to replace it. That doesn't mean that I have a closed mind, just that what I have works.

 

[memilanuk]

Steve,

If the PVM works for you, thats great. Given the price differential between the two... I'm more inclined to try the Magneto-speed myself. The problems I've had up here have been not just light level related, but more so due to the angle.

Monte

 

[Heavies]

Topography at my range make setup of a conventional chronograph a real hassle. Shooting group through it is possible shooting prone but lighting (time of day) plays a huge factor as well. This new product, if as accurate as initial reports claim, should be my answer. I do not intend to do final tuning of loads with the chrono attached.

The effect on accuracy should not be too bad. Seems to me, it should be similar to when I clamp my Centra 30mm sight to the end of the barrel. Groups with the sight attached seem to hold as well as I can, and as well as with the scope attached. However, I have never tried to shoot groups with both attached at the same time. Might be interesting to try with the sight clamped and scope.
I am a OCW user, I think that if you wanted to use this device during a match, one would just need to retune the seating depth with the device attached. One would need to have a way to place the device in the exact same spot and orientation on the barrel, and the clamp would need to be strong enough to keep the device from moving on the barrel during load tuning, and throughout the match.

 

[NilesCoyote]

Am I the only one that sees the difference in accuracy between the two targets?

I may see what your looking at...

I will have one soon and will test it a few hundred yards down range and see if the groups hold.

Even if it doesnt I believe I will still be happy with the purchase, Crono's dont work well in the shade and that is where I shoot 90% of the time. This will bypass that issue with out speeding about the same on a IR unit + 300-400 feet of extension cord or power pack.

 

[LongRanger]

Might be an optical conclusion, but what I see is that the second set of targets are magnified less than the first set....perhaps making the groups look smaller?

Frank B.

 

[ReedG]

I agree with Erik. The groups without the attachment are more concentric and without the flier would average quite a bit smaller. Having said that, the difference does not seem to be enough to negate the convenience of use.

I plan to get one and do whatever mods need to be made to allow it to be set up on a tripod. Like all the others, I find the nuisance of setting up my Chrony on a busy range, along with wind flags, is too much to ask of the other shooters.

I'm guessing there will be an update to the design of this device very soon to make it useable without being attached to the barrel. The concept is great and the pluses far outweigh any negatives at this point.

 

[Perk]

I received mine last week. Works great. I don't plan on shooting matches with it on the barrel. Perk

 

[DougMH]

It touches the barrel and is, therefore, a non-starter for me. I shoot groups simultaneously and want the barrel undisturbed. Perhaps if they had a variant that clamped to the bench and could be adjusted to barrel proximity...

I guess I wouldn't be using it and attempting accuracy at the same time, but rather testing my hand loads for desired MV and minimal ES/SD. If I could get an ES of <= 20 at around 2,800 fps, the vertical accuracy should follow.

While it shows itself consistently under the Oehler readings, if you're looking for "relative" readings, it seems pretty consistent.

I only have one place where it's not a hassle to try to set up my Shooting Chrony (uneven terrain at 10 ft in front of the muzzle). Setup (and storage size) looks like a real plus for this device.

 

[LongRanger]

Mine arrives tomorrow. If anybody has made a modification for using in on a 1-1/4" barrel (aside from clamping it to bench or tripod) pls let us know.

Frank B.

 

[Erik Cortina]

I received mine last week. Works great. I don't plan on shooting matches with it on the barrel. Perk

You guys are missing the point. If you are working up loads using this chronograph, it will give you "false" groups on target since once you remove the device to shoot a match the accuracy will be different due to no longer having device attached to barrel. Accuracy might be worse, or better, but I doubt it will be the same.

 

[TheSnake]

You guys are missing the point. If you are working up loads using this chronograph, it will give you "false" groups on target since once you remove the device to shoot a match the accuracy will be different due to no longer having device attached to barrel. Accuracy might be worse, or better, but I doubt it will be the same.

I have to agree with Erik. Aything you attach to the barrel will affect accuracy. This is no different than having the barrel sitting on a high spot on the stock. It will change the barrel harmonics and affect the bullet path. You work up a load that shoots best with this attached then go to a match without it and your groups go to pot.

 

[Heavies]

You guys are missing the point. If you are working up loads using this chronograph, it will give you "false" groups on target since once you remove the device to shoot a match the accuracy will be different due to no longer having device attached to barrel. Accuracy might be worse, or better, but I doubt it will be the same.

I have to agree with Erik. Aything you attach to the barrel will affect accuracy. This is no different than having the barrel sitting on a high spot on the stock. It will change the barrel harmonics and affect the bullet path. You work up a load that shoots best with this attached then go to a match without it and your groups go to pot.

Affecting the bullets path and affecting the groups size or accuracy are two different things. High point on the stock is a different matter altogether.

The devices mass will affect barrel harmonics. The question is, how much will it affect the loads tune, and is that enough to place a load out of tune. If we are talking benchrest accuracy, where .001" matters, I believe, yes it will. When talking about score shooting such as f-class and highpower, I not so sure it will affect all that much. It has been seen that it move POI up by a predictable amount. It has not been proven, yet, that the group size/accuracy is adversely affected to any statistically meaningful degree. If the device is allowed to move about on the barrel when firing, then yes the accuracy will be lost. if the device is attached rigidly enough that it will not move, then the effect will be like mounting a clamp on match sight to the end of the barrel, in other words the effect would be minimal.

I would not do final tuning of a load with this device attached, however the information that the device can provide during initial load work up and final proofing of a load may outweigh any of the detrimental effects the product may have on group size.

This is all theory. Without further testing in a statically meaningful amount of groups fired, one can not come to a definite conclusion, one way or the other.

 

[DougMH]

I received mine last week. Works great. I don't plan on shooting matches with it on the barrel. Perk

You guys are missing the point. If you are working up loads using this chronograph, it will give you "false" groups on target since once you remove the device to shoot a match the accuracy will be different due to no longer having device attached to barrel. Accuracy might be worse, or better, but I doubt it will be the same.

Again, I agree, and wouldn't use it to work up loads. After having worked up my best load, I'd consider using it to test for consistent MV of that load. For me I believe my inconsistency comes from

1) Uneven neck tension.
2) Not having the exact same position and hold into the shoulder each time. I'm sure this is part of it as when I maintain my position and let my son chamber my rounds, my ES drops somewhat... and consistently.

While the bullet is out the barrel in seemingly no time, Newton's law applies from the point of trigger release. There's an equal and opposite reaction as the hammer goes home, when the primer goes off and when the charge goes off... and the effects of that equal and opposite reaction are in play until the bullet clears the muzzle.

 

[Steve Blair]

While the bullet is out the barrel in seemingly no time, Newton's law applies from the point of trigger release. There's an equal and opposite reaction as the hammer goes home, when the primer goes off and when the charge goes off... and the effects of that equal and opposite reaction are in play until the bullet clears the muzzle.

[br]
How's that Sharps shootin' for ya, Doug? [br]
The reaction does not start until the bullet starts moving. Therefore, ignition begins the event chain, not trigger release. Recoil continues after the bullet leaves the bore. In most cartridges, ~40% of recoil comes from the powder mass acceleration and the effect of propellant gas ejected at ~2X bullet speed.

 

[DougMH]

While the bullet is out the barrel in seemingly no time, Newton's law applies from the point of trigger release. There's an equal and opposite reaction as the hammer goes home, when the primer goes off and when the charge goes off... and the effects of that equal and opposite reaction are in play until the bullet clears the muzzle.

[br]
How's that Sharps shootin' for ya, Doug? [br]
The reaction does not start until the bullet starts moving. Therefore, ignition begins the event chain, not trigger release. Recoil continues after the bullet leaves the bore. In most cartridges, ~40% of recoil comes from the powder mass acceleration and the effect of propellant gas ejected at ~2X bullet speed.

I disagree with you on two points. The release of the hammer does involve Newton's 3rd law (anytime kinetic energy (cocked hammer) is turned into dynamic energy (released hammer), Newton's 3rd law comes into play) and can move the rifle. Even though recoil continues after the bullet leaves the muzzle, it no longer affects the bullet travel in any way. Physics was my favorite course.

Funny you should ask about the Savage. I was just voted into the Fairfax Rod and Gun Club of Manassas VA. I shot there for the first time today and did some testing. I couldn't do a traditional ladder test at 200yds because the vertical separation just wasn't there. I did rotate 43.4, 43.7, 44.0, 44.3 and 44.6 grains of Varget through a round robin test at separate bulls-eyes. All where 1/2 MOA or better with 44.3 coming out the best. NOT NEARLY A GOOD ENOUGH TEST TO CALL COMPLETE. I'll be needing to abandon the wife and tater tots frequently to complete testing.

I used my new infrared and adhesive thermometers to control/monitor barrel temp. The Oehler 35p worked, but for a weird reason I won't go into, I ran it out of paper and for the life of me couldn't get it rethreaded. So, the "proof" was not there.

 

[Steve Blair]

I disagree with you on two points. The release of the hammer does involve Newton's 3rd law (anytime kinetic energy (cocked hammer) is turned into dynamic energy (released hammer), Newton's 3rd law comes into play) and can move the rifle. Even though recoil continues after the bullet leaves the muzzle, it no longer affects the bullet travel in any way. Physics was my favorite course.

[br]
There is no hammer, bolt action rifles are striker fired. Are you talking about an AR-15? [br]
The relatively small amount of energy when a hammer or striker is released is part of a closed system and would not significantly move the rifle. Think of a free body diagram of the rifle with the spring's stored energy contained against the striker. Release the striker and the spring accelerates it to some velocity. The striker impacts an abutment within the bolt and stops. The spring pushed rearward against the bolt body and the striker impacted toward the front of the bolt body. Assuming no frictional losses to heat, both impingements are against the same body, producing a net zero effect. Practically, because the events occur at slightly different times, the bolt would move back and forth, but the net movement would be zero. Maybe you should review some of your old texts. [br]
Attached is a picture of a caliber .50 BMG rifle that I designed and built in the late eighties and early nineties. It was a hammer-fired, gas operated weapon that used a modification of the Swebilius firing system. The picture was taken in Dubai during the first Dubai Air Show after the Gulf War. I worked on programs ranging from pistols to 155 howitzers and have at least a reasonable grasp of firearms physics. (full disclosure: my hair was a different color then and I had more of it. )

 

[broncman]

Back from the dead...

Anyone have any long term usage thoughts on the magnetospeed after using it for awhile? Thinking of buying one.

 

[memilanuk]

Still using mine, the version in the cardboard/foam box w/ the cam buckle. Never did break the buckle, but did manage to bounce a round off the sensor deck (strap got twisted and I didn't realize it). When I ordered a new bayonet I also ordered one of the new turn-buckle type strap arrangements and haven't had any problems since.

We used mine to chrono all the ammo from all the guns for the USA FTR team @ Raton prior to FCNC/FCWC... since it was my chrono I got to be the 'technician', fitting and adjusting it to almost 20 different guns in a day. Going from big fat heavy barrels well over 1" in dia. to ones that had a 0.750" dia. x 2" long front sight tenon did present some challenges, and on some I ended up adjusting the sensor settings rather than risk going with a thinner spacer... but it worked as advertised and I think everybody was pretty impressed with the overall ease of use. Last year we set up an Oehler 35P as well, and shot thru both. This year we just used the MagnetoSpeed

Monte