Wild variation in reloading data.


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Kachok
January 11, 2013, 02:49 AM
For the most part I have used Nosler reloading data for all my cartrages and different brand bullets (working them up of course), recently I have started looking though data from other published sources and I see a huge difference in the pressures, max loads, and speeds even using the same bullet/powder combo. For example Nosler #6 lists the 6.5x55 140gr Partition at 2597fps with it's max load of 51.5gr Ramshot Magnum powder. Ramshot says it's max load with the same powder and bullet is only 49.8gr with a speed of 2778fps!! In other examples I have seen max charge vary as much as 4gr! Since these were shot in similar length barrels I cannot understand what accounts for these huge differences.

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ljnowell
January 11, 2013, 03:23 AM
Case manufacturer, primer, COAL, etc. Many things factor into play. Older data vs Newer data also.

Trent
January 11, 2013, 11:22 AM
Yup, that. ^^

I've even seen max loads in one book be about what the STARTING loads in another book are. :)

Work up slowly until you find the load for your rifle. Published data is a GUIDELINE.

I've had high pressure signs on several loads WELL under the max load, my rifle / components must behave differently than their test barrels.

I've also been able to push several rifle loads well BEYOND the max load without any high pressure signs (either on casing or velocity).

I've also had a load behave perfectly normal in one rifle, only to show EXCESSIVE pressure signs in another. (This is how I found out that different twist speeds play a role; a pair of AR-15's with different twist speeds but otherwise the same, on gas tube length / barrel length behaved WAY different with some 62gr bullets I loaded. One was fine, the other was flattening/cratering primers.)

The number of grooves, lands placement, twist rates, bend in the barrel (a lot of barrels are bent somewhere, very few are perfectly straight), different harmonics, heat warpage (some barrels get tighter when they get warm, some looser, depends on steel stress), and many other factors play in to internal ballistics.

So does temperature (on some powders). Different lots of powder / primers. Etc.. etc.

The short of it is, there's so many factors at play, ultimately YOU have to work up a load that fits your rifle/needs.

Which means the reloading manuals are guidelines.

RandyP
January 11, 2013, 12:58 PM
Testing methods vary greatly among the publishers of the data. Many use a universal test chamber/barrel, rather than a rifle or pistol- newer data uses the newer (and more accurate) digital pressure transducers rather than ye olde copper crush discs.

Start at min and carefully work your way up - I have found very satisfactory results using the mid of most data.

Flatbush Harry
January 12, 2013, 02:53 PM
I, too, have noted this many times. In developing a new load, I check three sources: the bullet manufacturer's, the powder manufacturer's and my Lyman, 49th ed. I also start at the middle of the average of the most conservative data and test loads on both sides, changing only one thing at a time (powder first, then bullet, then primer, then case), making 6 rounds per load for two 3-shot groups to identify potential good loads. I then make up 20 of the rounds that gave me the best results for 5-shot group evaluation. That approach seems to work for me.

FH

Trent
January 12, 2013, 03:38 PM
I do much the same, excepting instead of two three shot groups I shoot single 5 shot groups. For promising groups I then shoot 10 shot groups to confirm, and begin exploring along the "sides" of those groups in .1 increments for more perfection, again with 10 shot groups.

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