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I'm confused!

I have been learning wife's new 6mmBR and am really getting confused as to what is happening.

The story:

1. This gun is a Remington 700 SS SA built by Speedy Gonzales in 6mmBR with a 29" SS fluted barrel with a 1:8 twist barrel. When I purchased it the round count was estimated at 5-600 by the previous owner,appeared to have been shot with moly'd bullets as ammo that came with the gun was loaded with moly'd bullets and the action showed moly residue). I cleaned thoroughly and even used Bore Teck Moly Magic to remove the moly as best I can,pressures picked up AFTER Moly Magic)

2. First loadings were 29.0, 29.3, 29.5, 29.7, and 30 grains of Varget behind a 107 gr. Sierra MatchKing seated .020" off, new unprepped Lapua cases, and Fed 205M primers. Accuracy was excellant,.75"-.5" at 200 yards. Pressures were at the point of being excessive at 30,stiff bolt and ejector marks on the cases) but OK at the lower loadings. Velocities were progressively higher and ES was all under 10 fps. Velocities were - at 29.5 was 2775 fps and at 30 grains was 2810 fps. I reduced the load to 29.5 and wife fired a 1000 yard Match with excellant results and no excess pressure indications.

3. We noted that the case necks were being flattened on one side by the ejector, so I took the spring out and replaced the ejector pin back in the gun to eliminate this flattening and stop the ejected cases from being thrown to the ground.

4. I noted that fired cases were not able to have new bullets hand seat into the case even when the cases appeared to have one side flattened. This along with the high pressure indication at 30 grains of Varget led me to believe that the neck of the chamber needed the cases to be neck turned slightly. So I turned some .002" total and some .001" total. The loads with the necks turned .002" showed a slight decrease in acccuracy, but OK pressures at 29.5 grains of Varget. The cases turned .001" are now getting high pressure indications,stiff bolt and slight ejector marks) at 29.5 grains of Varget - accuracy remains excellant.

The question:

Why the increased pressure signs after the case necks were turned .001" turned smaller? Temps were all the same and powder from the same 8 pound container.

I'm about as confused by this and the little boy that dropped his gun on the floor of the chicken house.

George
 
Traveler, Once you fired the turned brass in that chamber, it should have blown the brass back out to the same outside demension as you had originally. Have you checked to make sure the brass is not too long? Maybe some of these smarter guys on here will have more suggestions and thoughts. Someone will definitely come up with a solution. These guys are great at finding trouble spots such as yours. Bill
 
Thanks guys, I did body size the cases and trimmed to 1.555" before firing. The bullets are BT so I do not think that is the problem. The high pressures I mentioned after turning were once fired cases, not new ones.

The reason I changed from .002" neck trim to .001" neck trim was due to the decreased accuracy of the .002" turned cases - probably not a snit's woth of difference in accuracy when it all falls out.

Just loaded some cases with VV550 - 31 grains and 3 different primers,Fed 205M, CCI BR-4, and CC1 450). This should help with the pressures and get a little more velocity with less pressure.

BTW Lynn, hwat are you loading after the cases settle down with heavy bullets? Just looking for someone else's exeriences.

Thanks again,

George
 
Two things to consider:

1. If you are using the same neck-sizing bushing,or solid full-length die) on both the cases turned .002" and those turned .001" you are going to get more neck tension with the .001" turned cases. The thicker brass has more "grip". This can increase pressure slightly because the force required to release the bullets has gone up.

2. If you are looking to increase your velocity, consider going into the lands .005-.010. The difference between .020" away from lands and .010" into the lands is .030". That's a lot in this small case, and enough to affect the case capacity.

It seems counter-intuitive and YES you will get a higher momentary pressure from "jam" seating, but I found in my own 6BR that I could get higher velocities overall with Varget by seating further out. Normally I don't advocate "just kissing" the lands, but you might was to experiment with that, then try .005" into the lands.
 

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