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powder observation from working up loads

I was working up loads yesteraday and was putting them across the magneto-speed chronograph yesterday and observed something kind of puzzling.

The powder is imr 4007 ssc

two different cartridges, 22-250 and 243

in the 22-250 with 55 grain sierra #1360 bullet, max load in Hodgdon manual is 39 grains, and should produce about 3786 fps, I get 3577 ave, sd of 1 across 3 shots. so about 200 fps slow.


in the 243 with an 80 grain sierra blitz bullet, max load in the Hadgdon manual is 45 grains and should produce about 3319 fps, and I get ave of 3409 fps ave, sd of 6 across 3 shots, so about 100 fps faster....

I like the low spread/ speed range I was getting across the shots, and the groups were quite nice

both set ups were new rifle barrels, new brass, and federal 210 gm match primers

I am curious as to why this may be. one rolling quite a bit slower and the other a fair amount faster...
 
Mild -

Howdy !

I DK if your rifle' barrel lengths are the same as those used to obtain the data quoted in the reloading manual's ?
If they are not, that'd be one reason why your numbers vary.

If the primers you use are different ones than those used to obtain loading manual's data, the numbers will be different.

Other things like temperature and altitude of the location where the actual cartridge firing took place.

Difference in barrel rifling, age etc

The reloading manuals are " quides ".


With regards,
357Mag
 
barrel lengths were the same.

primers were not the same as the manual, however the same primers were used for both in the manual.

I just find it rather interesting the same powder, out of the same bottle, is slower than stated for one, and faster for the other.
 
When you say "new" brass are you talking new as in virgin or has it been fireformed at least once in each chamber?
 
The biggest thing that I can point to is the chamber (tight or loose), throat(jump or jam) and bbl twist/ dia, as a 224 bbl can vary as much as a number of 10 thou. if theirs was on the tight side and y our on the loose side you can see numbers like those you got.

Bob
 
MildBill said:
in the 22-250 with 55 grain sierra #1360 bullet, max load in Hodgdon manual is 39 grains, and should produce about 3786 fps, I get 3577 ave, sd of 1 across 3 shots. so about 200 fps slow.

I am curious as to why this may be. one rolling quite a bit slower and the other a fair amount faster...

From my experience and 55gr bullets in a 22-250, 3786 fps sounds a little ambitious and the 3577 maybe a little slow, but not knowing what twist and barrel length it may be close to being right.

and I agree with Mulhern.... every barrel is a little different.... some are a lot different than published in the manuals. JME. :) WD
 
thanks for the replys

I was/ am curious as to what folks thought may be contributing to the observations.

I am always interested in learning more about reloading and shooting rifle.
 
Both of those chamberings are overbore magnums ! Both suffer from rapid throat erosion and one may be moreso than the other. Slow speed = greater erosion + low velocity. The same holds true for the publisher of the data you are using if they established the data with actual test firings.
 
I think the problem is your Magnetospeed. I saw the same thing happen at our shooting range recently. The guy was really puzzled and he came over and asked if he could shoot a few rounds through my Oehler chrono. Things really changed and he was really puzzled then. I verify my chrono readings, with certain loads and rifles at the start of everyone of my range sessions, so I know my Oehler is dead nutz on. Sorry to be the bearer of bad news.
 
MildBill- If I read your post correctly, you only shot 3 rounds across the Magnetospeed? Statistically speaking you should fire, at least, 10 rounds. The greater the sample size, the more accurate the results. There is a point of diminishing returns, where more sample points does less and less to improve statistical accuracy.
 
chrongraphs...love them and hate them! i have a nice chrony and it will on occ drive me nuts. it'll report a speed that is impossible, most commonly the hundreds figure...3900 but really 3500. the manufacturer says "muzzel blast". i changed batteries often but now i'm trying somethin new. plug in a battery hours before i shoot, then connect to a new battery and shoot. early results are promising. at the start of shooting i'll shoot 5 one shot series where the only difference is powder charge( .2 or.3 gr). 5 shots will reveal if the chrony is behaving. if the mv increase is consistent, ill get to serious testing.
 
well...

I did some additional testing today and loaded up a batch for the 22-250 with imr 8208 xbr., and the same 55 gr bullets at used in the original post

shot just for groups to start with... terrible terrible groups. ran the last batch over the magneto speed just because the groups were so bad I figured at least I will see what about speed.

the speed was very close to what the Hodgdon manual suggests the speed should be.

close enough to not raise any curiosity, so I don't think it was the magneto speed fibbing.
 

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