Too fast?

[runtohunt]

I took the Chrono out the other day and noticed that the loads for three of the rifles that I am working up have consistently been faster than what the reloading guides are stating. All loads are at max load.

7 STW with 140 grain Barnes TTSX: Chrono: 3700 fps; Barnes guide states 3300 fps

257 Weatherby 100 grain E-tip: Chrono 3779; Nosler guide states 3574 fps

257 Weatherby on a Rem 700 action 100 grain Barnes TTSX: Chrono 3680; Barnes guide states 3500 fps

All loads shoot groups under 1" center to center for three shots.

No signs of excess pressure with exception of slight primer flattening; have had several people tell me this is normal for federal primers

Should I back the loads off to FPS that the guides state are the norm??

 

[IdahoCTD]

It's not likely you have 3 rifles that all have really fast barrels so I would double check the speed with another chronograph if possible or yours again in different light conditions, etc. Are the cases hard to extract? Do you have ejector marks on the case heads? Have you measured the cases ahead of the belt? Flattened primers aren't always a sign of too much pressure.

 

[DrMike]

runtohunt,

Welcome to the forum. Thanks for posting your question. When you see velocities that far out of the anticipated, it is a good thing to assume that either your data is incorrect or there is a serious pressure problem developing regardless of what your brass and/or bolt lift is telling you. Because everything you tested that day was consistently high, it would lead me to suspect that either your chronograph is misreading the shadow passing over the electronic eye or the distance between the eyes is not fully extended. Especially with the Shooting Chrony, you need to be alert to the possibility that the case didn't fully extend. I'm assuming that you have a 26 inch barrel, but I note that the Barnes Manual used a rifle with a 24 inch barrel, but that would account for only 50-70 fps differential. The difference in velocities anticipated and recorded would have meant an excessive pressure easily 15000 psi over the SAAMI standard. At that pressure, the case would likely have split the neck. Likewise, in the case of the 257 Bee, the pressure differential needed to record the velocities observed would easily be 15K psi over pressure. Especially because all cartridges registered excessive velocities and because all showed no signs of excessive pressure on either the case or the rifle, I'd be inclined to reword these loads, starting from a safe minimum, and shoot them again, ensuring that the Chrony is fully extended. Before shooting the loads a second time to obtain a true velocity, I'd recommend shooting a .22 over the screens or a load with known velocity to see what they read. If these register excessive velocities, then you know that you need to address the chronograph as problematic.

 

[runtohunt]

Thank you for the info. I also shot a 30-06 with Barnes 130 gr TTSX that shot 3300 fps as the reloading guide stated as well as a 240 Weatherby with Barnes 80 gr TTSX that shot 3100 fps as the guide stated it would.

I have a Beta Shooting Chrony. I am using both sections of the arms and the "box" of the Chrony seemed to be completely open.

Thank you for the advice

 

[Ridge_Runner]

how far away was your chrony from the muzzle?
RR

 

[runtohunt]

I think about 5 yards

 

[Oldtrader3]

My Beta Master Chrony was reading too high last summer with my 7mm Mag and my .340 Bee. I had the screens set at 10 feet (from tip of barrel) and it was too close. I moved back to 15 feet and reshot the numbers. They were in line with the reloading manual at 15 feet. Maybe you need to be back a little more with those small bore magnum pipes? Just a thought.

 

[JD338]

I am thinking that you do not have the sky screens fullt extended. The shorter distance would give you faster readings.

JD338

 

[ScreaminEagle]

In my experiance, I have found that the speed published in manuals is a little on the fast side. Getting readings way over published speeds would make me believe that you do not have the unit completely unfolded. Or maybe it needs calibrated.

Or maybe you have been blessed by some really fast shooting rifles!

 

[PJGunner]

I think about 5 yards

I'm thinking you might have to move the Chrony out a bit farther. It could be the muzzle blast is affecting your readings. Double check to see that it is unfolded properly as well. Lighting conditions also my be contributing to the problem but I'd consider that only as a last resort.
Paul B.

 

[FOTIS]

Them are some smoking velocities. I would double check for sure.

 

[Guest]

I can add an obscure event that gave me very high velocity readings on some shots a while back. I set up my Beta Master Chrony out from the bench, and started shooting. After I shot through several rifles worth of load workup, I had some time to let barrels cool, so I went to work with the 22lr, not through the chrony. Well, after about 10-15min, the barrels were ambient temp again and I shot through a couple of load workups. Velocities were nuts! I was getting 4100fps from a 180gr out of my 300Wby, and then 3800fps from a 160gr in a 7mmRemMag I was working with. Well, once the range went cold, I walked out to be sure the chrony wasn't fouled in some way, and found wisps of spider silk waving about off of the skyscreens. Apparently, when the bullet triggered the first sensor and started things in motion, the spider silk was enough to trigger the second sensor and cause erratic velocities. All because of one or two little spiders floating by and latching onto my chrony!

 

[runtohunt]

Had the opportunity to shoot and use the Chrony again yesterday. The base of the tripod must have pushed the rear of the chrony up a tad bit. The velocities were much closer to reloading guide specs.

The 257 Weatherby on the 700 action shot the same velocity as the book states at 3450-3500 fps.

The STW dropped from 3700 fps to 3450 which is still 150 fps faster that the book states. Plan to drop the charge weight a couple of grains to achieve the books fps for that load as Dr. Mike suggests.

I am also working up a 145 grain Barnes LRX load for the STW. I noticed an ejector mark/circle at 79 grains of RL 22 but not at 78 grains. I do not note any other excess pressure signs at either load. As a rule of thumb, do folks back off even lower than the highest charge of powder that did not show signs of excess pressure?

 

[DrMike]

I personally back off whenever there is an anomaly in results, if for no other reason then I want to know what is happening. Has the velocity plateaued? Is there an obvious pressure spike despite the lack of pressure sign? All is information that can save me grief down the road. Besides, it gives me opportunity to pull the trigger on a rifle that I am shooting.

 

[IdahoCTD]

Depending on the temp. you are shooting that 78gr load might be really hot in the summer time. R-22 isn't very temperature stable so the velocities jump up quite a bit when it's warm out. If your shooting in 40 degree temps or lower I would back it off another grain. With R-22 it's best to work up loads at the warmest temps it will be used at and then check them in cooler temps.

 

[SJB358]

Depending on the temp. you are shooting that 78gr load might be really hot in the summer time. R-22 isn't very temperature stable so the velocities jump up quite a bit when it's warm out. If your shooting in 40 degree temps or lower I would back it off another grain. With R-22 it's best to work up loads at the warmest temps it will be used at and then check them in cooler temps.

I think he nailed it. I haven't found RL22 horrible at all, but I do my load work in the Summer most of the time and have 0 issues with it the rest of the year. It looses little FPS in my rifles from Summertime loads, but it is safe come winter, rather than the opposite. If you are plateued as Mike stated, you may be able to back off quite a big and come back up on it in order to see where your at. No sense in shooting more powder than you are getting speed out of..