The need, or lack of, for reducing different case dimensions when FL sizing

[BoydAllen]

This is a story with a point.

A friend built a .243 AI but did not want to pay for a FL die. He had been shooting his .223 loads with only a very occasional trip through a FL die, and I think that he assumed that he could do the same with the new .243 AI, but of course he wanted top velocity and loaded for it. He thought that he had the case tightness issue handled with a home made bump die that he made using his chamber reamer, and indeed it did bump the shoulder, but...eventually, with the levels of pressure that he was loading to, it was not enough to prevent his bolt close getting tight. As I had told him when he started the project, the back ends of his cases (just in front of the solid part of the head) had became too tight, causing a problem that he needed a fix for. Obviously he could have bought a factory FL die, or ordered a custom one, but he was too tight, and since he had done me a few favors, at the next gun show, I picked up a used, RCBS, non-carbide .45 ACP die set, pulled the guts out of the FL die, and gave it to him to use as a ring die, with the instruction that he might have to polish it out a bit on his lathe if it sized too much. My total investment had been $10, and it solved his problem completely.

Now to the point. His rifle is exceptionally accurate, and using his three step (collet die, bump die, ring die) his bolt close is not a problem. So what may we conclude? Simply this. Sizing the diameter of the front two thirds of a case is simply not required, as long as there is some clearance at the front of the shoulder, the neck will hold a bullet, and the back of the case is sized slightly under chamber dimension. So the next time you are about to size a case, measure its diameters at the shoulder , and about .3 above the head and compare them to a sized case. Could it be that you are sizing your brass more than you need to? I would almost guarantee that you are. Of course I am only speaking about bolt action rifles. Semiautomatics are a whole different animal. The other, related point that I think worth mentioning, that sort of relates to this, is that when you set out to chamber a barrel in a new caliber, if well used fired brass is available in that caliber, you can start out by buying a factory FL bushing die, size the well used brass, measure it to make sure that it was reduced in its dimensions as expected, and order a chamber reamer with the precise fit to that sized brass that you desire, thus getting a custom die to chamber fit, for the cost of a factory die. Think about it. It works. I have ordered a number of reamers that way, with excellent results.

 

[lpreddick]

i once thought the "perfect" body die would be one made with the chamber reamer. i had my gunsmith make me one with a newlon blank body die and proceded to push the shoulder back just right( a 22-250). i noted the body wasn't being touched very much or none. i thought this wa s a good thing. after awhile i started experiencing a "bolt click" and learned this represented an enlargement of the case just in front of the web and my new body die wasn't sizing this area. asked about this on this site and was told that my body die was indeed pushing the shoulder back...the brass has to go somewhere and it was...just in front of the web! a proper fl/body die compresses the brass over it's entire length. i didn't have support of the case in the web area. bought a proper fl die and the bolt click was gone and accuracy returned. recently, i found that my redding body die wasn't sizing this same area in my tight chamber 6 BR so i got a small base body die and now my cases are all the same. interestingly, a 22 BR fl bushing die will do the same but .0005 less at the shoulder and web, so i'm now trying this approach.

 

[BoydAllen]

I am glad that your problems have been fixed, but you were told wrong. The brass is not pushed to the back of the case, it lengthens the neck, but only slightly in the case of a shoulder bump with no body diameter reduction. The reason that the case becomes tight at the back is that it is rather thick back there, and reinforced by the solid head, so that under peak pressure when it and the surrounding barrel expand, the barrel snaps back all the way, but eventually the more malleable brass does not, which produces interference, and a bolt click. Forward of that, the brass is thinner, and not reinforced by anything, so there is no issue. Another factor at the back, is that with repeated hot loads, the solid head can actually increase in diameter, like a raw hamburger patty that has been pressed against a flat surface. When this happens, the diameter at the bottom of the extractor groove increases slightly. Another issue that can become involved is the difference between where the chamber supports the back of the case, and how far down the case the die can reach. Shell holder, and die opening radius are issues here, as well as barrel headspace.

 

[22BRGUY]

i once thought the "perfect" body die would be one made with the chamber reamer. i had my gunsmith make me one with a newlon blank body die and proceded to push the shoulder back just right( a 22-250). i noted the body wasn't being touched very much or none. i thought this wa s a good thing. after awhile i started experiencing a "bolt click" and learned this represented an enlargement of the case just in front of the web and my new body die wasn't sizing this area. asked about this on this site and was told that my body die was indeed pushing the shoulder back...the brass has to go somewhere and it was...just in front of the web! a proper fl/body die compresses the brass over it's entire length. i didn't have support of the case in the web area. bought a proper fl die and the bolt click was gone and accuracy returned. recently, i found that my redding body die wasn't sizing this same area in my tight chamber 6 BR so i got a small base body die and now my cases are all the same. interestingly, a 22 BR fl bushing die will do the same but .0005 less at the shoulder and web, so i'm now trying this approach.

Perhaps I'm not seeing something here about the 22br FL bushing die and would appreciate clarification. I have a Redding FL bushing die that I use for my 22br. I use it to bump the shoulders 1 or 2 thou but the area about .3 thou ahead of the case head on repeatedly fired cases is around .004 larger in diameter than for example a new unfired case. Of course if I push the multi fired cases farther into the die to resize that portion, the shoulder gets pushed back farther as well. Boyds idea of a .45 cal. die was very interesting to me as also
Thanks Guys

 

[BoydAllen]

As long as a case is not too tight, I see no problem with it being larger than a new one. All of mine are, and as long as they size slightly smaller than the chamber, they work just fine.

 

[22BRGUY]

Thanks Boyd...I know. It's just that I've discovered through the "bolt drop" method that they are a bit tight in that area. As you've mentioned before, it's probably time for a custom die but thought perhaps another way to size down that area could be done.
Sure always appreciate your input
thanks again.

 

[BoydAllen]

For me, in the case of a benchrest stocked rifle, the issues are whether the bolt close disturbs the rifle on the bags, and whether all of the ammo that I shoot in a group has the same feel as I close the bolt. I have read a lot of recent posts about bolt drop being used to set dies. I do not do it that way, I measure the bump, and the base of the case to make sure that the die is small enough to size it there. Luckily, for my PPC I have a die (out of production) that has base inserts that come in .001 increments, so I have the ability to do something about under sizing. My chamber is such that with the insert that I have chosen, that just above the extractor groove, where my chamber's reach stops, "experienced" cases are sized about .0005. That is all that I need for clearance. A little more would be OK. That is just the way that it worked out. Of course if a case seems tight, I know that I will either need a different die (or in the case of my PPC a different base insert) or I will need to have the back of the chamber polished out slightly, by someone who knows what he is doing.