New Reloader. A couple questions?

[Cory Lee]

First, I measured the chamber on my R700 with the tool from Sinclairs that Tresmom recommends. Its a .308 and the chamber measured 2.056. After reloading 20 pieces of brass 10 times none of them measured over 2.03. But some were 2.01 and 2.02. I started trimming to 2.015 for consistency. Is that the right thing to do?

Second, I have been chamfering and deburring the case mouth every reload. I've been reading and is it only necessary after trimming?

Third, while testing loads, how many rounds do you shoot over the chronograph to determine your average velocity, ES, and SD? I have been starting with 3-5, determine which look best then loading 10 of each of those. Sound about right?

 

[KHOOKS]

Re: New Reloader. A couple questions?

As far as the trimming goes I think your ok. I trimm to book lenght and prep my brass. So far I've never had to retrim my brass. I normally get 10-12 reloads out of it.

 

[Rookie]

Re: New Reloader. A couple questions?

Cory,

As long as you are trimming all cases to the same length, you'll be fine. Personally, with that long of a chamber, I would probably trim to around 20.25. That would leave around 30 thousands for new case expansion.

On the second question, no need to chamfer/debur if you're not trimming.

On the chrony issue, the more rounds the better to accurately estimate velocity. Personally, I chrony at least 5 while looking for groups because 3 shots just isnt a group. Once I've settled on a load, then I may chrony 10 of that load just to make sure on the velocity before making a dope card. Also, dont forget to chrony in different outside temps.

 

[Fuzzball]

Re: New Reloader. A couple questions?

Statistically, the larger the number in a sampling test the greater the accuracy of the test. We really need maybe 30-50 samples to obtain a fairly good average and standard deviation, even more would be much better. That being a practical impossibility for most of us, and that level of accuracy being of little use, yeah, most of us seem happy with the values we get from five shots...just remember it's not REALLY accurate. But it's close enough for common use.

 

[Cory Lee]

Re: New Reloader. A couple questions?

Thanks for all the replies.

 

[litotes15]

Re: New Reloader. A couple questions?

Looking on midway website to order reloading equipment for first time. Best reviews are for RCBS dies from selection given for 308. Quick question for you veterans out there. I am shooting an AR platform in 308 and the site stated that a short base die set was needed for the autoloader because a crimp is needed to hold bullet in place as opposed to the standard die set for bolt guns. Does anyone have any input or experience they can share for a beginner? Thank you guys in advance.