Neck bushing, brass spring-back and ideal chamber clearance

[JFrank]

I have seen great 600 yard loads, sort of fall apart at 1000. A few years back, one of the better 600 yard shooters came to the WORLD Open. He told me he brought his best two 600 yard guns and he thought that his loads just plain down fell apart. They were both 6mm and he has been dabbling at 1000 some and uses a 30 cal there. I also believe the best 1000 yard load may not be the best for 600. I like to tune my loads at the distance i am competing at. Matt

I’ll bet he was scratching the old head wondering what the hell, I see a few fellas try and tune with low ES /SD , spreadsheets and charts then realize it isn’t working for 1k Benchrest.
While tuning at distance..I took a chance on a slightly hotter load at the nationals that I thought might shoot small enough to place .. or break out

 

[fatelvis]

I think annealing every firing is very important, and helps to eliminate springback, which seems to make for a moving target when sizing is concerned. Annealing would go a long way to making all your sizing attempts more consistent. I was a believer after the first-time annealing, suddenly ALL of my sized brass were much closer in measurement.

 

[dkhunt14]

I think annealing every firing is very important, and helps to eliminate springback, which seems to make for a moving target when sizing is concerned. Annealing would go a long way to making all your sizing attempts more consistent. I was a believer after the first-time annealing, suddenly ALL of my sized brass were much closer in measurement.

I believe it also seals off the chamber better and gives more consistent velocities and bullet releases. Matt

 

[SGK]

I dip the case neck in powdered graphite to lube it. Matt

Whenever you pull an expander out through the neck, it can move the neck. I get much better run out with a mandrel. Matt

I'm using a full length sizing die so I need to lube the side of the case. I don't think a 'wet' lube and a dry lube will mix very well.

Whenever you drive a mandrel through a neck you can move the neck and shoulder. But I will try it.

(I can imagine a more complicated sizing die which does this process while the case is supported within the die. Whether it makes sense to produce such a thing is another story.)

Have you measured the bushing to confirm the number matches the diameter?
Do you anneal?

I got the new bushing from Whidden and it measures much better and now my brass necks are measuring to match the bushing. Silly me for not noticing earlier. It will be interesting to see what difference if any the extra neck tension makes.


The right answer is in there somewhere: (including learning to shoot better)

 

[dkhunt14]

I'm using a full length sizing die so I need to lube the side of the case. I don't think a 'wet' lube and a dry lube will mix very well.

Whenever you drive a mandrel through a neck you can move the neck and shoulder. But I will try it.

(I can imagine a more complicated sizing die which does this process while the case is supported within the die. Whether it makes sense to produce such a thing is another story.)



I got the new bushing from Whidden and it measures much better and now my brass necks are measuring to match the bushing. Silly me for not noticing earlier. It will be interesting to see what difference if any the extra neck tension makes.

I use Imperial to size and size them all. The. I wipe off the lube with a paper towel. I then screw the mandrel in my press and dip the necks in the graphite. Then I th. The mandrel in and wipe off the graphite. I never lube the inside because nothing touches it till the mandrel is ran in. Matt

 

[SGK]

Well yesterday was interesting. When I got the new .267" bushing from Whidden I put my cases back through the die. Now they measured correctly. I figure I have 2-3 thou of neck tension when loading these vs next to nothing previously. (0.243 + 2*0.013 = 0.269 versus a bushing of 0.267".) If you look above 40.8 gr of RL 16 seemed to perform well although the sample size is small (5 shots). I loaded up another 8 rounds at 40.8 gr alongside a similar number at 40.7 and 40.9 and headed back to the range on Friday.

The 40.8 (as well as the 40.7 and 40.9) shot poorly. Average fps 3120.4, SD 14.65, ES 43 (versus the numbers written on the target above). While the sample sizes are very low, statistically (using a T-Test) there's a 93% chance the population averages are different and 86% chance the SD are different - in other words quite high probability of a real change in behavior rather than none. So it seems my rifle doesn't like the neck tension. To be honest I'm a bit surprised how sensitive it appears to be to it.

What's been the experience of others?