Pressure question on max charge?
 

I was doing some load development in my 7mm mag using RL22 and 160 accubonds, I checked a few books and started at 65grs and went past max at 67grs. So my velocity at 65gr was 2843 5 shot average, 65.5 gr shot up to 2990av. could not figure out why? Any Suggestions? Next 66gr back down to 2886 av. and my group shrank to.250" shots, great!Then went a touch over max to 66.5grs and speed was 2933 and it opened up some, next went up to 67grs and my group for 3 shots went into .153" excellent again but the other 2 shots opened a bit, my error I think. I see that most everyone pushes their speed to 3050 alot of times,is it safe for me to go a little higher like to 68 grs of RL22? Have not seen any pressure signs like sticky bolt.My barrel is also 26 inches long and the gun is a Sauer202, What are your experiences with the first situation of a jump of velocity? And is velocity a safe way to gauge if your getting near max? Because book velocity does not match my numbers.
Thank you
Elmer

RE: Pressure question on max charge?
 

velocity is not a safe way to guage pressure

You should go back to the 65.5 gr. load and shoot it some more. Try to get a could read on the speed and group size. Anyway that is where I would start. Your speeds don't make any since to me. Was that an avg. of several shots? Your Chrono may have malfunctioned.

FYI, if you can get a 7 mag to shoot 160's anywhere near 3000 fpsaccurately you've got an awesome weapon.

RE: Pressure question on max charge?
 

All speeds posted are 5 shot averages.
Elmer

RE: Pressure question on max charge?
 

Did you check the primers? Flat primers is another thing to look out for..[:o]

RE: Pressure question on max charge?
 

Watch your bullets. Some loads are safe with one bulletand are not safe with anothermake of the same weight. Watch your bullet substitution with maximum and near maximum loads.

RE: Pressure question on max charge?
 

elmer- if velocity is your goal I would look at slower powders for the 160's and up. I couldn't get great speed or accuracy w/ R-22 but average around 3100fps with R-25 and 160 Accubonds in my 26" remy. They shoot sub moa too.

RE: Pressure question on max charge?
 

Your 65-66gr velocity gain seems reasonable. I am not a big advocate for people trying to build loads in such fine grandularity. REally with magnum loads, its not going to be consistent. I only see one set of velocities out of whack and thats your 65.5gr set. Rest seem reasonable. I believe you are expected way too much expecting 3050 for a 160gr bullet.

I personally know 3 people who are trying to obtain nosler's numbers for this combo, and all are little shocked they are not.

Nothing out of the ordinary not to meet the numbers.

Look for the classic pressure signs. Primers, hard bolt lift, etc. A chrony number is just another piece of data for you to make your decision on max load. use it for what its worth. If you see your velocity shoot up like incredible numbers, your gettin in dangerous territory.

RE: Pressure question on max charge?
 

Yes, but was there a abnormally high reading within those 5 that pushed your avg. up? You Chrono may have experinced a hiccup, it happens.

You velocity gains from 65 to 66 makes perfect sense. You 65.5 speeds are suspect to me.

watch for pressure and not the chrono.
think about your statement for a second. 2886 to 2933 is 47 FPS difference. Who could ever know other than the chrono. I guarantee you a moose or elk won't. ".250" sounds pretty darn accurate. I have a feeling that you are too wrapped up in chasing velocity. JMTC

RE: Pressure question on max charge?
 

Your right!
Elmer

RE: Pressure question on max charge?
 

First let me quote wise old Bob Hagel to you: "All rifles are individuals. What may be a maximum load in one may be quite mild in another, and vise-versa."

The "maximum" load you find in a book is a maximum load in the rifle in which it was developed, and may be under or over maximum in yours. This is why it is INDISPENSABLE to work up loads in each rifle on an individual basis. This is also why book velocity won't match anyone else's figures, except by accident!

Naturally, you must keep your eyes open for indications of excessive pressures as you work up a load. PersonallyI stop increasing a powder charge when I get to an acceptable accuracy level with no excessive pressure indications, or at 5% below the load level that started making my primer pockets accept new primers too easily-in other words, at the first indication of some primer pocket expansion I stop and drop bvack 5%.

How many rounds did you fire at 65.5 grains? Is that 2990 an average of five shots? If so, I agree that you should redo the velocity test with 65.5 grains. I'd be surprised if it will average 2990 next time! Although when the "crossover point" of a given powder is reached, it is entirely likely that greater charges will give lower velocities (accompanied by HIGHER PRESSURES!!), increasing the charge further after the crossover point will NOT result in additonalincrease in velocity. So I do not think you had arrived there yet, since your velocities did increase after you passed 65.5 grains.

With a 26" barrel, you should be able to break 3000 FPS with a 160-grain bullet, but you might have to go to a slower powder, such as IMR 7828, to do it. I know I had to go to IMR 7828 with a 175-grain bullet, although I had been getting over 3000 FPS with 175-ghrainbullets when using Norma N205 and MRP, and RE 22 is supposedly "the same as MRP"!