load chronoed higher than published?

[gun-nut]

Hi all, I'm loading for 357 mag using berrys plated 158 gr RN. In the load data it shows 8.5gr blue dot chronos @950. When I chrono that load, it comes in @1075. I have always run jacketed bullets with a med/heavy crimp. I DID back off the crimp but MAYBE not enough? Also a sm. pistol primer was used not a magnum primer. OAL is 1.590" out of a 6" gp100. Spent primers look good with no signs of overpressure. Is this normal or should I be concerned? When I look @ the cast bullet for that weight it shows 8.2gr= 929fps. Thanks for any input, Ken Also, this site has information overload to the max

 

[SIGSHR]

In one of my copies of the Speer relaoding manual they have a chapter entitled "Why ballisticians get gray hairs." They point oot that the velocities they get are on THEIR equipment,what you get with yours WILL vary due to weather conditions, barrel wear, slight variations in the powder charge, crimping pressure, etc. If you see none of the obvious signs of overpressure your loads should be OK.

 

[jmr40]

The velcoities published are USUALLY measured in guns with chambers and barrels cut to minmum tolerences. Most factory guns struggle to actually match those numbers. If I were getting speeds SLOWER than advertised I would chalk it up to differences in chambers etc. But getting a load almost 15% over listed max speed would concern me. Traditional pressure sign don't show up until loads are well over max pressure.

I use and trust my chronograph. If 950fps is listed as the max speed, I stop putting powder in when I reach 950 fps regardless of the actual powder charge.

 

[rclark]

Remember the manufacturer is not using the same barrel and possibly the length of barrel you are using. Also different guns (or even just test barrels). To me, the manufacturers FPS are just 'ballpark' ... Not be used as 'gospel'. Some change in velocity can be attributed to elevation of where the testing is being done. For example, my chronograph reads 1030fps (out of 5 1/2" barrel) for the Skeeter load. Yet we always hear this is a 950fps load .... I even chronographed back to back with another persons chronograph just to put that question to rest. Also I bought some test weights to make sure I was 'loading' the right amount of powder.... All checked out. Bunch of variables, I wouldn't be concerned if you rechecked the amount of powder you loaded and all is as it should be. If it is an accurate load ... use it.

 

[jepp2]

I use and trust my chronograph. If 950fps is listed as the max speed, I stop putting powder in when I reach 950 fps regardless of the actual powder charge.

Truer words couldn't have been written. Powder burn rates can vary significantly. Any time my velocities are higher than the published loads, I find I reach max pressure below the book max. Isn't that the reason you are using a chronograph?

 

[SSA]

I don't see any cause for concern. No sign of high pressure, and 8.5 gr blue dot doesn't sound like a lot. Maybe the velocity is kind of high. How far away from the chronograph were you?

 

[stubbicatt]

Perhaps the chronograph reading is faulty?

 

[serf 'rett]

Is the 8.5 grain charge weight specifically for the Berrys bullet? Or is it for a jacketed bullet? The plated Berrys will be softer than most jacketed bullets so less energy is needed to shove it through the barrel. Same applies to lead bullets.

 

[chiefr]

If anything your findings prove how valuable a chrono can be in developing loads.

 

[McShooty]

Was it a sunny day? I have often observed faulty chrono readings when the sun is at a certain angle at my range. The faulty readings are nearly always too high. The faulty readings may persist for a series of shots. I once chronographed a supposedly moderate load for a .30-30 that gave me an average velocity of 2650 fps with a very reasonable extreme spread and standard deviation. Put the chrono in the shade or check the load again on a cloudy day.

 

[buck460XVR]

Originally posted by jmr40:
I use and trust my chronograph. If 950fps is listed as the max speed, I stop putting powder in when I reach 950 fps regardless of the actual powder charge

Me too, but just because I get a higher than published velocity, as long as it's below max load velocity, I don't worry. 1075 FPS is still on the low side for .357 and just middle of the road when using Blue Dot and a 158gr projectile. It is also below Berry's recommended max velocity of 1200FPS. Could be tight chambers, or the Berry bullet seats deeper or has a different profile than the bullet tested in the recipe. Could be the scale is off a coupla tenths. All are factors which are common and why we start low and work our way up. My question to the OP is, since the load is obviously safe, was the load accurate?

 

[gun-nut]

Thanks for the replies guys, now I don't have to worry AS MUCH. The load for lead starts @ 8.2 & the starting load for jacketed is 9.6. My chronogragh was approx 15 feet away. If I ONLY add enough powder to get the 950fps velocity & it comes up lower than starting charge, is it still ok? From all the reading that i've done, doesn't that put it in the catagory of "stuck" bullet in the barrel? Because this is my first go around with berrys, after each shot I checked the barrel for any obstruction,ie pieces of plating etc. If I use a little less crimp than where it's at now, shouldn't that also change velocity? Chrono was also set up in the shade. This load seemed to be grouping ok, 2"@20 yards

 

[osirus82]

very good read and information, im have no data to input, but this has convinced me that before i get to shoot any custom loads, need to get a chrono device.

 

[44 AMP]

The published data is not a hard and fast rule, its a guideline (arrr, pirate voice)

Published data shows what they got from their gun, and load. That's all it is. In general, your gun and load should be about the same, BUT, exceptions do happen. And a chronograph is what points them out.

I have fired the same ammo through 3 different guns with the same barrel length, and had 100fps difference between the slowest and fastest guns. (no, it wasn't variations in the ammo).

If you get a reading higher than book, and no pressure signs, rejoice! If its lower, don't cry, unless it really a LOT lower (like hundreds of fps).

To me, anything within 100fps+/- of book speeds is within my acceptance level. Usually, the difference is much less, but even 100fps while not common, isn't unheard of.

 

[Hammerhead]

I know my buddy's F1 Chrony is a bit off and always reads at least 50-100 fps higher than it should as compared to other chrono's. I suspect the folding design doesn't allow for precise placement and alignment of the timing planes.

 

[SL1]

gun-nut,

You did not tell us some things that are important for determining if your load is showing unexpectedly high velocity. What is your data source? What 158 grain bullet was used to create that data? What gun was used to get the velocities that were published for that load? What was the barrel length for that gun? What is the length of your gun's barrel?

In some situations, it is not too uncommon to exceed the velocity figures in the data manual, and that is not dangerous. But, in other situations, exceeding the printed velocities is a sure sign of exceeding the SAAMI pressure limit. The latter case occurs when the published velocities are from the pressure test barrel (rather than an example commercial gun) and your gun's barrel is only as long or shorter than that test barrel.

SL1

 

[reynolds357]

Many variable affect velocity. Barrel length, bullet design, altitude can all make a difference.

 

[gun-nut]

the load is from lymans pistol/revolver manual. If i recall correctly they used a 10" barrel. I'm using a 6" ruger gp 100 with a berrys 158gr. round nose and I live on the east coast (for the elevation thing). I looked at the lead & jacketed loads, and i'm at the starting point of 8.5gr blue dot. The lead actually started at 8.2gr. I'm still wondering if maybe i didn't back out the dillon accu-crimp die far enough. If i use less won't the blue dot be erratic in performance. I've read that it's a pretty finicky powder, though i've always ran jacketed til this point. Maybe i should just get a taper crimp specific die to load the plated ones. Thanks for the responses, it helps me keep in check with my learnings and to double check everything.

 

[Nick_C_S]

Maybe I'm looking at this too simplistically:

I see a 158g bullet being pushed to 1075 fps by using Blue Dot (a slow powder).

I don't see a problem.

 

[Mike / Tx]

gun-nut,

Having chrony'ed many thousands of rounds through plenty of different firearms and loads, I would be happy with what your seeing.

I generally use mine for a general guide to working up my loads. In most cases I am usually within 100fps one side or the other of where I think I should be. When I start to worry is when I am bumping up the powder charge a little at a time and seeing a somewhat standard FPS climb, and then all of a sudden get a 100 or more fps jump in velocity with the same amount of powder increase. This is where your hackles should stand straight up, as it is a positive sign of a pressure spike.

I personally would not have any issues shooting the load you have presented in either one of my GP-100's. I would load up and shoot a hundred or more of them before I actually decided that I wanted to keep it. I do things a bit different than most though so in the end it's your call. If I am getting accuracy like you got at 20yds I would probably stretch that on out to 50 and 75yds. IF it stayed within that same area I would call it good and go on about my happy shooting.

You might also figure in what your ambient temps was when you shot those. If they shot in say a 70 degree controlled environment, and your shooting in 95 degrees with 65 - 80% humidity, that will also account for a little gain in velocity. That bit of extra heat will give you a bit more velocity in some cases.