Took my 577 out for some serious load development / regulation today and got some strange results. The rifle can be seen http://www.accuratereloading.com/ubbthreads/showflat.php?Cat=&Number=647195&page=&view=&sb=5&o=&fpart=all&vc=1

All loads wre with Hornbear brass, Fed 215, and Woodleigh 750g soft points.

I started with 116g of RL-15 as recommended by both Graeme and Seyfreid. The empty space was filled with one Kynoch wad. The results had wide velocity variations; four rounds were 1723, 1777, 1913, 1736 fps as measured by an Oehler 35. Needless to say, the group was all over the target.



I then tried 120g of RL-15 with the same wad. The results were, if anything worse although higer on the target. Velocities were: 1995, 1875, 1743, 1985 fps.


Two questions: Does anyone have an idea as to why I am getting such broad velocity variations? Also, loads at this level should have velocity some where near the the original 2050 fps; any idea as to why it is a lot less? Has anyone had a similar experience?

I had brought some IMR 4831 along as well. 134g with no was gave some pretty good results with velocities of 1649, 1669, 1666, and 1690. It also gave something resembling a group (or two groups)


I thought a little faster might help, and tried 137g with no wad. Got: 1711, 1703, 1729, 1704 and


Two real groups! (If only two shots each!!) Seemed like the wrong way so I tried 131g 4831, not wad. Velocitied were: 1587, 1492, 1597, 1578. Still pretty consistent but for one, and it produced a 3 inch group at point of aim with lthe low shot being the slow one. (My shooting was also getting pretty ragged at this point, I had shot about 50 rounds out of me 375 before this)


So, IMR 4831 seemed to give much more consistent results and I ultimately found a load that seemed to regulate. But the obvious question is that it regulates at around 1575 fps, when all the stuff I have read says that the regulation point should be around 2050, and as importantly, these loads should be some where near that velocity.

Anyone have any ideas?

The .577 NE data I collected shows that 145 grains of IMR4831 and 135 grains of Reloader 15 should each give you 2050 fps.

The velocities that you chronographed are so far from the standard 2050 regulating velocity for a 577 x 3" that I would not be too concerned yet. I would work the loads up into the 2000 to 2050 fps range and see how it regulates there.

As to the inconsistency, I would start eliminating variables. First, slug both barrels and compare the bore and groove measurements to standard. Then take a cast of both chambers and compare them against standard. If all of that is standard, buy a new can of Re15, a new can of IMR4831, and a new box of F215 primers, just to be sure your powder did not degrade. To be safe, buy it from a different store than where you bought the last stuff

To reach the target velocity, I would start working up in 2 grain increments until you get to where you are supposed to be.

Also, are you sure that your chronograph is reporting accurate velocites?

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bradhe,

A couple of thoughts. Uneven bullet pull can cause velocity variations. This can be due to differences in the crimp between rounds, or variable neck tension from several sources (differences in neck thickness being one main cause, and differences in brass "hardness" being another), or the die may not be sizing the case enough to get good tension on the bullet (or the expander may be too big).

As to velocity, have you slugged your bore to see what the groove diameter is? If the bores or throats are a bit worn, or the bullets are a bit undersize, it can cause velocity to be lower than expected. Also if you don't have good neck tension or crimp, velocity may not be as high as expected.

All these things, plus numerous others can and will affect convergence of the individual barrel groups. As an example, I have one double with bores about .004 larger than "standard". It will only converge properly with the larger diameter bullets even though individual barrel groups are just as good with the undersize bullets. All part of the fun of working with vintage doubles!!!

Jim