Velocity issue...

[trentcwwilson]

Ok, I've got a BIG problem. I've got a 10 FCP-SR 24". I loaded 175 grain Sierra Matchkings to Hodgdon's accuracy load for Varget, 44.7 grains for 2680. I never chronographed them, but it was right on the money when using the Vortex Ballistic calculator. I've since added a brake from Southern Precision Tooling, and while they observed a 20fps gain in velocity in their 10" Mini 16, I was not expecting my secondary results. Same load, same OAL, same lot of powder/bullets/primers/cases. It was all the same. Shot both loads within 15 minutes of each other allowing for a cool down. Result? The exact same load grouped was reduced by 25%, but was 4" high. I knew I would gain velocity, but I never expected that. Can anyone give me an idea of how fast I'm now pushing these pills? I don't have access to a chrony and don't have money in the budget for one.

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[taylorce1]

So what makes you think you gained a lot of velocity? You may not be shooting same point of impact because you changed barrel harmonics by adding a break. Plus your groups got smaller because you reduced recoil. Until you adjust zero and check your new results against your old drop charts you don't have any problems that I see. Plus budget for a chronograph they aren't expensive unless you're buying a Lab Radar, I use a Pro Chrono and Targus tripod and paid $110 total and it works very well.

[squirrel_slayer]

agree. just because your POI increased drastically doesn't mean you had a drastic change in velocity. I have seen this just doing a load workup. 1 node would print high and the next would print low. (as much as 1.1 mils at 100yds) and the "scatter node" between would have huge vertical dispersion. one gentleman explained it in a very simple way. when your shooting the barrel is whipping some barrels will whip top to bottom (most common due to the mass of the barrel wanting to rest in the lower positon) and others will go corner to corner, ect.... but when were chasing a node were trying to get the bullet to leave the barrel when the barrel is slowing to change direction in the opposite way of it's deflection. the worst point for the bullet to leave is when the barrel is back at it's rest position (opposite of what I thought) because the barrel is at its highest velocity in the arc or movement so if you add your es/sd into this a bullet that leaves those few milliseconds earlier will be in a far different location than the last, and next. look at it as a AC sine wave (analog) there is more dwell time on the peaks than the transition so that what were shooting for. and like mentioned above the brake can change that whipping both by the addition of mass as well as the harmonics, and lastly the way the gasses act on the atmosphere could impact whats going on.

a better method if you chose not to get a chrono would be to re-zero with the brake and shoot at distance and reverse interpolate the data. ie. with a bullet of x BC that drops x MOA/Mil's at x distance the velocity is roughly x fps. 300-500 yds would be a good baseline as it will be more measurable. and find the center of the group to base you calculations. ie. if 5 shots have a vertical dispersion of 5" measure down 2.5" factor that into your dialed elevation. a lower vertical dispersion will also give you an idea of how your ES/SD is. reason I mention 300-500 yds is this gives you a better idea of whats going on as there is more measureable difference. and some high bc bullets have to "go to sleep" and can have some strange results at shorter distances. ie. shoot moa at 100 yds and 1/2 moa at 200.

[trentcwwilson]

I'm not new to the game of long range shooting. At 100 yards, barrel harmonics wouldn't change my POI 4" unless the front action screw was majority loose. It's not, torqued down to spec. As far as a chrony, I'll only buy quality equipment, and that means the MagnetoSpeed V3. I've tried the standard models and they have issues I don't have time to deal with.

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[trentcwwilson]

Continuing on my previous post, I did rezero my scope. At 200 and 300 yards, my ballistic charts are STILL not correct. I'm not getting 1.70 MOA adjustment @ 200 and 4.28 MOA @ 300.

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[Deadshot2]

I'm not new to the game of long range shooting. At 100 yards, barrel harmonics wouldn't change my POI 4" unless the front action screw was majority loose. It's not, torqued down to spec. As far as a chrony, I'll only buy quality equipment, and that means the MagnetoSpeed V3. I've tried the standard models and they have issues I don't have time to deal with.

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Actually, adding a brake could make that much of a change in POI. So could just adding weight like a shaft collar to the front of your barrel. Unless you have a "Truck Axle" profiled barrel with near zero deflection through the firing process, extra weight will make some significant changes.

The fact that your group size decreased by 25% pretty much negated any effect of a loose action screw. I'd re-zero, move your target out a couple hundred yards, and shoot again. If you see a group at the longer distance that is only enlarged by distance (use angular measurement rather than inches to compare) you are just seeing the beneficial results of extra weight on the front of your barrel. A lot of shooters who don't like brakes merely add "Tuners" to the front of the barrel and some add weight as simply as clamping a split shaft collar on the barrel.

FWIW, I saw similar results when I added a brake to my 6.5 Creedmoor. The action is mounted in an MDT TAC-21 Chassis, action screws torqued to spec, a Heavy Palma profiled barrel. When I added the Benchmark Tactical muzzle brake the POI shifted a good 3" but group sizes at 100 yards now average Sub 1/4 MOA. This is a phenom that's well recognized by those that shoot with suppressors as well.

If you plan on shooting both with, and without, the brake, just have zero's for each condition.

If you have ever seen animated diagrams of what happens in a rifle barrel when fired, or any of the High Speed Video's of same, you'll understand the role of a piece of weight on the end of a barrel. If you haven't seen the video look some up on YouTube. You may be shocked to see how much that solid action and barrel flex, even if it's firmly secured in a beefy stock, bedded and all.

[trentcwwilson]

Well, it's a 20mm blank from Pac Nor. I doubt there's very much deflection, if any.

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[darkker]

With a 60,000+ psi load, I promise there are harmonic deflections at play. Varmint Al had some very good visualizations on his site.

[trentcwwilson]

With a 60,000+ psi load, I promise there are harmonic deflections at play. Varmint Al had some very good visualizations on his site.
Um....I'm NOWHERE near 60k. Hodgdon list 48,600 at a max of 45 grains. I'm shooting 44.7.

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[Deadshot2]

With a 60,000+ psi load, I promise there are harmonic deflections at play. Varmint Al had some very good visualizations on his site.


Um....I'm NOWHERE near 60k. Hodgdon list 48,600 at a max of 45 grains. I'm shooting 44.7.

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Regardless, there are harmonics at play. Even with a "20mm barrel blank" there is still flex. It only takes .040" of "movement" at the muzzle to give you 4" of movement at 100 yards. Only .038 MOA of angle change at the muzzle if you want angular measurement. Want to see how flexible your barrel really is? When the action is out of the stock place each end in a v-block on a solid surface (like concrete).

Put a dial indicator under the center of the barrel and lay a 20# bag of shot on it. Read the change on your dial indicator. Be prepared to be surprised at how much change there is. It's just metal's nature and as long as the modulus of elasticity is not exceeded, it just springs back. Heck, even concrete flexes. I've had the misfortune of having to change a flat tire on a bridge and there's enough flex to make some people get "sea-sick".


What's hard to visualize is how small changes yield such large results.

Want to be totally confused? A rifle with a brake behaves totally different than one without. Just the difference in recoil can shift POI an amazing amount due to how the shooter's body behaves during those critical Milliseconds between ignition and the bullet leaving the barrel.

I don't think there is a thing wrong with your barrel, rifle, brake, load, or even your shooting technique. You are just seeing a natural phenomena that can be dealt with by simply changing the Zero with the brake attached and enjoy your shooting.

FWIW, I shoot twice a week and frequently sit next to a friend who's constantly putting on and taking off his muzzle brake. Don't know exactly why but he experiences the same thing with POI shift. Nothing wrong with his rifle as he's regularly in the top three at local competitions with more than just a few wins.

[trentcwwilson]

Regardless, there are harmonics at play. Even with a "20mm barrel blank" there is still flex. It only takes .040" of "movement" at the muzzle to give you 4" of movement at 100 yards. Only .038 MOA of angle change at the muzzle if you want angular measurement. Want to see how flexible your barrel really is? When the action is out of the stock place each end in a v-block on a solid surface (like concrete).

Put a dial indicator under the center of the barrel and lay a 20# bag of shot on it. Read the change on your dial indicator. Be prepared to be surprised at how much change there is. It's just metal's nature and as long as the modulus of elasticity is not exceeded, it just springs back. Heck, even concrete flexes. I've had the misfortune of having to change a flat tire on a bridge and there's enough flex to make some people get "sea-sick".


What's hard to visualize is how small changes yield such large results.

Want to be totally confused? A rifle with a brake behaves totally different than one without. Just the difference in recoil can shift POI an amazing amount due to how the shooter's body behaves during those critical Milliseconds between ignition and the bullet leaving the barrel.

I don't think there is a thing wrong with your barrel, rifle, brake, load, or even your shooting technique. You are just seeing a natural phenomena that can be dealt with by simply changing the Zero with the brake attached and enjoy your shooting.

FWIW, I shoot twice a week and frequently sit next to a friend who's constantly putting on and taking off his muzzle brake. Don't know exactly why but he experiences the same thing with POI shift. Nothing wrong with his rifle as he's regularly in the top three at local competitions with more than just a few wins.
Again, I've rezeroed the scope and is shooting better than ever at 100 yards. Now, explain to me how barrel harmonics have changed my ballistic charts for extended ranges and it not be a velocity issue.

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[trentcwwilson]

Essentially what I'm needing is an estimate in velocity change given the only change was a brake. I have no way of measuring velocity and need an estimated velocity so I can get on a 6" target at 200 and fine tune my ballistic chart.

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[taylorce1]

I'm not new to the game of long range shooting. At 100 yards, barrel harmonics wouldn't change my POI 4" unless the front action screw was majority loose. It's not, torqued down to spec. As far as a chrony, I'll only buy quality equipment, and that means the MagnetoSpeed V3. I've tried the standard models and they have issues I don't have time to deal with.


Adding a brake changes the way hot gasses exit your barrel, and you don't think it affects barrel harmonics? I don't care if you have a .800 thick barrel, anything applying pressures in the tens of thousands of pounds per square inch is going to cause the barrel to move. So yes your POI can change by 4".

It's amazing how any of us ever functioned before the Magneto Speed or Lab Radar, and still managed to hit anything we were shooting at. Great tools both of them, but recording data is essential in long range shooting, so even a cheap chronograph can supply you with good info. Even if it gives you errors on occasion if your record enough shots over it, you can get a pretty exact speed of your bullets to plug into a ballistics program.



Continuing on my previous post, I did rezero my scope. At 200 and 300 yards, my ballistic charts are STILL not correct. I'm not getting 1.70 MOA adjustment @ 200 and 4.28 MOA @ 300.



So you have info at 200 and 300 yards to plug into a ballistics program, unless you didn't bother to record the changes. So what was your new drops to get on target at those ranges? Just change the speed in the ballistics program until your drops match what your getting on target. Again you don't have an issue or "BIG" problem, other than the fact you're looking for one.


Um....I'm NOWHERE near 60k. Hodgdon list 48,600 at a max of 45 grains. I'm shooting 44.7.

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Actually Hodgdon lists your load at 48,600 CUP, which very well could be close to 60,000 PSI. They are not the same measurement: http://bulletin.accurateshooter.com/2014/10/cup-vs-psi-whats-the-difference-in-pressure-measurements/

[trentcwwilson]

I know they're not the same. That mistake was on me. I always looked at that measurement and used it as psi. Then again, I only have one cartridge I push the envelope on and it's a wildcat.

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[taylorce1]

I know they're not the same. That mistake was on me. I always looked at that measurement and used it as psi. Then again, I only have one cartridge I push the envelope on and it's a wildcat.

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If you don't have the proper tools, how do you know you are pushing the envelope or sitting on a time bomb?

[trentcwwilson]

If you don't have the proper tools, how do you know you are pushing the envelope or sitting on a time bomb?
Because I know how to read pressure and have a very experienced(over 50 years) reloader helping me. The only time we've used tech was to measure the velocities of our most accurate loads. 3975 for the hunting round and 3550 for the target round.

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[Deadshot2]

It's amazing how any of us ever functioned before the Magneto Speed or Lab Radar, and still managed to hit anything we were shooting at. Great tools both of them, but recording data is essential in long range shooting, so even a cheap chronograph can supply you with good info.






I started shooting when I was 7 and shot for 56 years before I bought my first Chronograph. All through those years it was simply a matter of recording drop at known distances in order to build my own ballistics tables. Not only no Chrongraph but no computer or smart phone "apps". Just pencil, paper, and a ruler.

Eventually factories started printing "drops" on the box for hunters but most hunters just used those for starting points when making a distance change during the pre-season target shooting.

Then there those "LR Shooters" that do it for a living. Military Snipers don't spend a lot of time with chronographs, just their log book which records pretty much every shot and the changes made for distance, wind, temp, altitude, etc.

I've found that even if you do have accurate speed, and a good ballistic's app (along with an accurate calculated range if not shooting KD), all it usually does is let you get "on paper".

[trentcwwilson]

This even puzzles him. Then again, his loading usually involves virgin brass. This is the first case he's ever sized and we didn't have a choice. Resize 30-06 to 6.5-06 then fireform. I got tired of fireforming and had Hornady make me a hydro forming die.

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[taylorce1]

Because I know how to read pressure and have a very experienced(over 50 years) reloader helping me. The only time we've used tech was to measure the velocities of our most accurate loads. 3975 for the hunting round and 3550 for the target round.

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I don't know what wildcat you're shooting but a lot of wildcats have an improved shoulder and minimum case taper. These cases usually don't show pressure like a normal tapered case they are usually made from. A chronograph can show when things are about to go wonky, when an improved case wont. It's your choice to budget a chronograph in or not, I just think they are useful tools and I'll have at least one in my toolbox.

[NicfromAlabama]

I know I'm coming in late and repeating what has already been said and discussed, but unless you are using a chronograph, you can only speculate that your POI has shifted due to velocity. You mentioned purchasing a Magnetospeed. Again, as discussed, clamping something to your barrel will affect harmonics, and if you are looking for load development for groups, that may not be the best tool IMO. I have gotten by with a cheap Competition Electronics Prochrono model, which has worked well, with one caveat. I had to buy the indoor light kit for reliability, and RARELY due I have an error reading when using the light kit. I do agree with buying quality equipment though, but I can't complain about my chronograph. I'd be very lost without it. As said, even an error now and again still beats guessing.