7PRC AW spec reamer?
- Thread starter Monteria
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quandary
Well-Known Member
Dumb question perhaps. Isn't a big point of the PRC chamber designs the tight tolerances to add in accuracy? Wouldn't enlarging the chamber defeat this design element?
. I asked and was told , just because", concerning the neck which is .2846 saami and the AW print is .2852. The chamber or the .200 line seems to be of concern if using ADG or possibly Peterson brass being of heavier construction sticking " clickers " after several loads, not an issue if you don't hand load. I'm waiting to speak with JGS concerning ordering a reamer. But the reason I'm asking the dumb questions because I'm seeking to be informed. Some don't like the Why questions so they answer with, just because answers.
Those are the freebore diameter specs. The larger diameter allows room for fouling and bullets that are larger than the nominal 0.284 (some are 0.2843-0.2845). There may be other benefits, but those are the two I know if. It doesn't necessarily have anything to do with bullet weight.
The chambers are too tight in the body area and cause extraction problems with multiple fired cases. The only dimensions that affect precision are in the neck and throat areas. The tighter freebore diameters and proper freebore lengths aid in accuracy compared to older outdated SAAMI design. Wildcatters, benchrest shooters, gunsmiths, etc have been running modified and tighter neck and throat dimensions for years to achieve improved results. Too loose isn't the best and neither is too tight so finding the sweet spot is what everyone is trying to do.
quandary
Well-Known Member
Ironically I was just talking with my son about his new 7PRC target barrel which he is having chambered with an AW reamer. But then I started to consider once fired brass to conform to the AW chamber. Then neck sizing only. The neck only resized case would presumably be a tighter fit than a full length resizing of case fired through a chamber with a SAAMI reamer. Or more simply a case resized with a full length sizing die (other than say shoulder bump) will presumably conform to SAAMI specs. The looser chamber concept befuddles me.
I will admit that the PRCs are new to me and I will start reloading them in the next couple of weeks.
The looser body dimensions prevent issues down the road when you have 3, 4, 5+ firings on the brass. The SAAMI brass, dies, and reamers are too closely dimensioned and cause "clickers" after a few reloads. The brass being sized .001-.002 more isn't going to affect groups, tight brass in a chamber will cause you more issues than a case sized .001-.002 smaller.
All the deliberation aside, and in my experience of only 2, a SAMMI chamber is going to have clickers on or about the 3rd reload.
With ADG brass, my clickers verged on "stickers".
Sizing dies simply can not size the web down far enough to avoid it. Some have had marginal luck with "small base" dies, while others have broken "small base dies" trying to size the web/head enough to eliminate clickers.
Opening up the .200 datum, by as little as .0015 in my case, is the solution to the clicker problem.
With ADG brass, my clickers verged on "stickers".
Sizing dies simply can not size the web down far enough to avoid it. Some have had marginal luck with "small base" dies, while others have broken "small base dies" trying to size the web/head enough to eliminate clickers.
Opening up the .200 datum, by as little as .0015 in my case, is the solution to the clicker problem.
quandary
Well-Known Member
Thanks Jud. I am not even thinking accuracy. I am just thinking of the mechanics of reloading and why this would make a difference. It would seem if the worked brass grows to big and can not be appropriately resized for the SAAMI spec chamber that the same thing would happen over a reloading sequence with any chamber. Unless conceptually the case body can only grow so big after multiple resizings?
quandary
Well-Known Member
Okay that makes sense to me. Confirms the posit I just made in the cross post. At least when I get clickers I will know how to deal with it.
Has this been the experience with all the PRCs?
I also started with SAAMI. One 300PRC and one 7PRC. Both developed clickers on reload #3.
I dont own a 6.5PRC, but reports are that it suffers the same affliction.
As an aside, I did full load workup on the SAAMI chamber. Both rifles shot the same load, to the same POI and with the same precision after opening the chamber with an AW spec reamer.
I dont own a 6.5PRC, but reports are that it suffers the same affliction.
As an aside, I did full load workup on the SAAMI chamber. Both rifles shot the same load, to the same POI and with the same precision after opening the chamber with an AW spec reamer.
The issue is the brass is too close in size to the SAAMI chamber at the base dimension. When you fire it, it can't really expand because it fits so tight. Then when you size the brass the die doesn't do anything because the brass didn't change dimension much at the base. If you make the die smaller, it can crack the die because you're trying to size down the thick solid case head that was too big to start. So since the brass doesn't get sized and doesn't expand it work hardens at the case head. With the AW reamers, the brass has room to expand outwards some and then the die can size it back down. The brass needs room to grow so then it can be sized down enough so it doesn't prematurely work harden. Others may be able to explain it better or have a better understanding of it, but that's my interpretation of the issues. Hornady should have spec'd the reamer .002 bigger at the 0.200 line on the reamer, or spec'd the brass .002 smaller at the base.
Edit to add, this isn't just a PRC problem. People have been fighting this for years with other reamers, dies, brass, etc. If you spec any reamer too small compared to the brass, you'll have this problem. If it's too big you can lose primer pockets prematurely. It's all a balancing act.
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I am not a gunsmith by any means but I do build my own rifles. The way I wrap my head around this issue is the reamer dimensions and the sizing die dimensions are too close together for much full length sizing to occur thus the cases get sticky after several firings/sizings. Just like sizing 6BRX with raised 6BR dies. Clickers every time unless you size the bottom end with another die. After that, good to go. Since the dies are hardened there is no changing those internal dimensions so all you can do is slightly enlarge the chamber dimensions so that the sizing dies actually size the cases enough that clickers are avoided. This is not a gross oversizing of the chamber dimensions. I don't know any of the parties involved but I am positive JGS and Mr Wheeler would never to that. From my research this is nothing more than fixing a situation where only 1 variable can be adjusted. My next wildcat will have 7prcAW body dimensions for **** sure. Have a great weekend.
David
David
Varmint Hunter
Well-Known Member
My understanding is that the SAMMI dimensions seem to work fine when using Hornady brass. But ... most reloaders have moved to the high-quality brass that is made heavier/thicker at the head to better handle higher pressure loads and to last longer. Strong brass started to display "clickers" after a few reloads, unlike the original Hornady brass.
This is just my understanding and I'm sure there are better explanations.
This is just my understanding and I'm sure there are better explanations.
