The chamber and die are oversize. This occurred because the chamber was not aligned co-axially with the work piece. If the reamer was supported on the tailstock center or by a holder which established the misaligned center, that is the issue. If the reamer was held in a tool post holder which was misaligned, that was the problem. If the chamber is concentric yet oversize, it can still shoot just fine. If the next chamber is cut with this reamer by a gunsmith who does things correctly, the chamber and die will not be matched. WH
Movement of reamer in chamber and die
- Thread starter Phys86
- Start date
There's a lot going on at once here but I'll explain a few things and hope it will be of help to someone, either now or later.
First off, the virgin brass dimension means nothing in this context so lets move on from that. It's only virgin once and has no bearing on this discussion at all. Spec'ing a reamer based on virgin brass is asking for problems rather than curing anything.
Second, a half thou is not much at all and I would not call it a bad chamber based only on that. This based on your specs of .5025 for the reamer and .503 or .5035 for the multiple times fired brass. Granted, if it's .5035, that's pushing it a bit more than I'd like to see.
Now, why do we size brass? Every time we pull the trigger and the round goes off, the resultant pressure literally swells both the case AND the chamber a bit. Someone else can probably calculate how much better than me but I certainly wouldn't be surprised by a couple of tenths or maybe more. So, the brass develops a memory and wants to go back to it's largest expanded state and loses it's ability to spring back(constrict) as it gets harder and bigger with each firing. That's why it gets tight in a chamber after a few firings, especially hot ones, and why we have to size it back down. FWIW, some pressure testing equipment use strain gauges attached to the bbl that measure this expansion of the bbl and convert it to current and can be graphed, just to support that the bbl does in fact expand under pressure..believe it or not.
Now, to your fired vs sized case dimensions vs your resize reamer dimensions(.4985). You stated that your die sizes your multiple time fired brass to .5025 and unsized brass measures .5025-.503. That's just about where it should be and what you should expect. A resize reamer is very typically .003-.004 smaller than the chamber reamer because the brass springs back considerably after sizing. So, it's entirely normal and necessary to size the brass down that .003-.004 to yield .0005-.001 of actual sizing..or what the sized brass that you load into the gun should measure. Again, this is normal and how it's done, and I've just tried to explain why.
Bottom line, based on your numbers, there's just really nothing hugely wrong with your chamber or die. Not saying it's perfect but it's certainly not bad and should have no negative effect on the target and I see nothing in the numbers that are off enough to be of any concern, really in any regard at all. If it shoots well, go shoot and enjoy it and I suggest you worry less about the chamber/die dimensions unless you have problems from it. I've seen lots of steel that made this much difference or more in the finished chamber dimensions from the same setup and reamer. Some will cut a tad tighter than others. Again, believe it or not. We throw around tenths like it's some big amount but it's really not and we are chasing a bit of a moving target when we talk about different steels and different brass, different pressures, how many firings and all the variables at play. There has to be some margin or it creates problems rather than helping.
Again, I hope this is of help to you or someone down the road. You may know all of this but maybe everyone didn't and they will benefit from reading this and seeing that there's just a bit more to it than meets the eye is all. Good luck and good shooting !--Mike
Thanks, Mike. Yes I understand the relationship needed between the chamber and die in order to sufficiently size the brass for good extraction and specd the reamers to accomplish that.
Just for clarity based on some numbers you mentioned (I checked my notes and all these measurements are from Ray):
- multiple times fired unsized brass measures 0.503 at 0.270 line (just forward of 0.200 line)
- chamber reamer measures 0.5023 at 0.200 and 0.5015 at 0.270
- multiple times fired and sized brass measures 0.5025 at 0.270 line
- resize reamer measures 0.4984 at 0.200 line.
So based on those numbers it seems the die should be sizing the brass smaller and it also seems maybe the chamber is grossly oversized since the fattest part of the fired unsized case is at 0.270 and measures 0.503 where the reamer measures 0.5015 at that same point.
Thanks for all your insights!
Alex Wheeler
Site $$ Sponsor
Both the chamber and die sound oversized. Pin gauges are pretty cheap, you can verify the chamber and dies with them. Always figure that the reamer is about .0005 larger than the print. Brass spring back is not a constant. You cant base chamber or die size off of the fired or sized case. On cartridges I have designed I have resize reamers from .003 under the chamber, up to .008 under the chamber. All depends on the brass your dealing with. Theres no rules here.
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Ccrider
Gold $$ Contributor
Lot of info @Will Henry. Thanks.
I have had this same problem. Reamer spec’d at .471 at the .200 line, chamber cut .4745. That is off far enough to where the sizing die would not size the brass and would get stuck at the .200 line, and the seating die would do the same. A real PIA. Ended up getting a custom sizing die and opening up the seating die.
Not sure the larger chamber affected accuracy, but it may. I was getting fliers otherwise unexplained every 4 or 5 shots. I think it has an impact on accuracy.
My smith still has not figured out the cause, but he crashed his lathe and thinks something may be off with it.
Thinks something may be off? Why not check? I talked about tailstock misalignment, and how to correct it, in one video. I suspect many on this site, maybe most, know more about it than I do.
I once stopped in to visit a well respected gunmaker who was sending a reamer away to have it re-ground because the chamber he had cut was oversize. His tailstock was offset by three thou and his floating holder cut to the center of the tailstock when under load. I once ruined a 30/06 chamber when I forgot to check my tailstock alignment. (Had to provide new barrel. I used that one for a 308 Norma for myself.)WH
I once stopped in to visit a well respected gunmaker who was sending a reamer away to have it re-ground because the chamber he had cut was oversize. His tailstock was offset by three thou and his floating holder cut to the center of the tailstock when under load. I once ruined a 30/06 chamber when I forgot to check my tailstock alignment. (Had to provide new barrel. I used that one for a 308 Norma for myself.)WH
Sniperhandle
Silver $$ Contributor
Spindles get bent sometimes when a crash happens and also the whole head can move and needs to be re-aligned. You can have a bent spindle that isn't bent much but still causes problems.
What happens when a lathe crashes?
I'm aware of this. I'm also aware that most issues are identifiable and possible to correct. Been there. WH
Doug Beach
Silver $$ Contributor
Localized pain in and around your hip pocket.
Sniperhandle
Silver $$ Contributor
The chuck comes into to contact with the compound or the cross-slide and causes damage and can bend the spindle. On these light duty lathes that most folks chamber with. The hollow part of the spindle is actually pretty thin and can bend easily.
I have replaced spindle bearings so I understand how they work and how to take them apart and put them back together and adjust the preload on the bearings. Large locking snap ring pliers will need to be purchased if you don't already own them. You can send the spindle out to be straightened and re-ground but it's time consuming on your end and expensive to have the work done.
The possibility of many flying projectiles! And the terrible noise is the sound of money flying from your billfold!
Paul
Alex Wheeler
Site $$ Sponsor
With the spider setups most use, a bent spindle wouldnt make any difference. Poor setups that cut oversized chambers are just pretty common. Way too much faith out there in floating reamer holders imo.
So I take it that using a floating reamer holder is more likely or easier to produce an oversized chamber?
Sniperhandle
Silver $$ Contributor
True, But the 3 jaw will never not have a wobble. You can dial out the problem on a 4 jaw with a spider possibly. Not arguing with you.
linebaugh
Silver $$ Contributor
Thats a dandy cartridge thought. Not sure how much AI gain is still available on a .284 but it peaked my interest. Thanks for sharing that.
Not much sense commenting on your chamber or sizing die as there are so many variables and unknowns to form a conclusion.
Alex Wheeler
Site $$ Sponsor
They float, so your not really in control of the exact position of the reamer. The idea is that they will center up and follow a prebored hole, however there is friction in the mechanism and once its under load they do not float as much as you might think.
Jonnyofalltrades
Silver $$ Contributor
Will, I have been doing CNC maintenance professionally for the last 11 years. Lathe adjustment can be a bit of a dark art. A tailstock alignment is simple, anyone who runs a lathe better know how to do that. Beyond that, there is an entire universe of ways that a lathe can be messed up. Almost all of them are hard to wrap your head around without classroom time and plenty of chicken scratches on the whiteboard.
Interested enough to buy the reamers?
Water capacity for this one is nearly 69gr for Peterson and a bit over 70 for Lapua, so a couple of few gr more than standard 30-284.
https://forum.accurateshooter.com/threads/for-sale-30-284ai-manson-reamer-set.4129554/#post-38998362
I'm thinking I'm exiting this cartridge and going back to my factory barrels. I've been burned a couple times now on less than desirable smith work trying to get a 30-284 going and just want to prioritize my limited funds elsewhere. If I can't find a buyer it may just sit until sometime in the future.
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