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concentricity

14 Dec 2018
@ 03:40 am (GMT)

john black

as i read this months letter in my email. i noticed a reference to concentricity being essential to accuracy, and i have so believed for many years. i have the hornady and sinclair gages. and even an old NECO. i quit using them and rely solely on a sinclair internal neck sizing mandrel now for that now mounted in my co-ax. the following is why i quit using them, and i would LOVE to be proven wrong!
on every device, the entire case rests on a V or ball "bed". i started noticing that i was not getting repeatable results when measuring the same loaded round. so i started using the gages to measure just the neck on loaded and unloaded cases. i would measure a neck, then with very fine steel wool clean the case, not the neck, measure again, and get a different result. so.....the results of my gaging the necks and the bullets depended entirely on the condition of the case body resting on the bed.
i recently got a brand new rem 700 20" hvy 5R bbl, bottom metal kit,in 308
168 gr sierra HPBT or 175 HPBT out to 400 yds? also RL 15 or VARGET?
thanks!!

Replies

14 Dec 2018
@ 07:17 am (GMT)

Nathan Foster

Re: concentricity
Hi John, its really hard to say. If I cannot sit with you, all I can do is guess as to why you are having issues with readings. Brass is certainly very soft so it can be effected by a number of things such as how we handle the case, heat and expansion (post polishing). In the more extreme, measuring bullet runout on ammo with a very loose neck can show mixed results under heavy spring tension via the dial indicator. Micrometers can also have the same problem at the neck if not used gently. It could be any number of things and will not help if I guess. Without you here in front of me, I cannot prove anything. Even on video (the last video for example) I cannot prove anything. For all you know, I could have hammed that up, a bit of editing - made it look slick. So as I said in the books, you have to test everything I say for yourself but this means that you need to be sure of your own methods. Having said all of this, I think it is better to walk away from something if you are getting too many false readings, rather than to become so engrossed in fiddling that you make no progress. So in your situation, I think you made the right call. Something to come back to later if and when you feel up to it.

I have fixed competition rifles with "dud" barrels simply by asking the customer to bring his ammo to me, used the Sinclair to determine that the dies / customer is the issue, not the rifle, fix the ammo, then off he goes, happy to have the saga over. A lot of gunsmiths and barrel makers have got a bad rep over the years for making dud barrels when instead the dies have been the issue. In the video I uploaded (me or rifle) - it was all about checking such variables. The M700 troubleshooting video is along the same lines but the viewer has to get his game face on when following the methods because the rifle is given a fair kick in the pants to get it shooting. The viewer does not need a pile of fancy kit but he does need to be willing follow each step no matter how brutal the steps appear.

You will find that some comp shooters won't admit that concencricity was the game changer for them. If they have been in comps and had a supposed dud barrel, complained to all about this dud barrel shooting 3 to 5 MOA, then eventually found that their ammo was the issue and fixed in a manner of minutes, they tend to hush up as they don't want to look like rookies or admit that somebody like me fixed the rifle in under five minutes (yet I was in their position at one time also). So again, you sometimes won't hear of success. This is the reality of the situation, human nature. We want to be seen as effective, never foolish. We are all quite silly really and could do with being a bit kinder to ourselves.

Regarding your rifle. Varget is too slow and Sierra is too tough if you want a gun for killing. Try H4895 with the 168gr ELD-M or TMK. Please refer to my cartridge book for more info. That is a nice rifle, should serve you very well for many years.

14 Dec 2018
@ 08:20 am (GMT)

john black

Re: concentricity
thank for your reply and insights. i think may not have stated my case as i intended. i agree that methodology is certainly a huge factor in reloading. what i meant to imply was that any imperfection in the case body itself, as that part rides on the "bed" (roller balls/Vblocks) will show up in the neck reading. for instance if the case has a high/low spot, or a scratch, or....??? then the reading at the neck will reflect that, assuming that part of the case is touching the instrument bed. i have even reversed the case and measured the case body, not the neck, and have gotten wild readings. case body imperfections. this making any sense?
as for the 700, it will be used as a target gun, not hunting.
also, i really hate to take up your time with this.please feel to respond not at all or at your leisure. thanks
14 Dec 2018
@ 08:44 am (GMT)

Nathan Foster

Re: concentricity
Thats fine John. Understood and I think that really comes down to how far we want to take it. There is a point where things are good enough. Chasing runout further can create a great deal of frustration, the phantom fiddler I talked about in the books. So yes, I get that. I talked about an acceptable error range in the reloading book. But ultimately, results on paper must speak for themselves.

OK, for target, yes on the Sierra but still generally no on the Varget at this barrel length as it can be a bit unresponsive. Nevertheless, see what works for you.
14 Dec 2018
@ 11:03 am (GMT)

john black

Re: concentricity
i bought 4 of your books a few years ago. will go back and re read that chapter! thanks
15 Dec 2018
@ 07:06 am (GMT)

Nathan Foster

Re: concentricity
I forgot to answer your bullet weight question sorry John. The 5R goes very well with the 168gr bullets so its worth having a play with this weight as a starting point if you want to. But there are a range of bullets and weights that this rifle can shoot well out to considerable ranges so again, the suggestion of the 168gr is just one possibility.

All the best.
15 Dec 2018
@ 01:00 pm (GMT)

john black

Re: concentricity
thank you!
29 Jan 2019
@ 04:13 pm (GMT)

Jim Moseley

Re: concentricity
If runout is your problem, then buy an economical Lee Collet die. It only sizes the neck. I have one for my .223, .243, and my .7mag. Runout will be around .001-.0015. Even some of the competition bench guys use the Collet dies. I think it cost $35. You won't be disappointed. Good luck.
30 Jan 2019
@ 12:55 pm (GMT)

Ed Sybert

Re: concentricity
I believe what John is talking about is the combination of case concentricity and bullet concentricity. If the case is not perfectly concentric, and few are, then the reading on the bullet concentricity will be affected possibly producing a "false negative" or "fail" on bullet concentricity. For many years while competing in NRA long range matches and later in Benchrest matches, I measured the uniformity of case necks, meaning the neck thickness at several points around the neck. Cases with 0.0025" or worse uniformity frequently resulted in excess bullet concentricity readings. I never had a set-up to measure the entire case for concentricity but my belief is that if the neck is not uniform, the case will not be uniform. So, I separated my "best" cases that showed <0.0015" variation in thickness around the neck and used these for long range competition. Almost everyone turns the necks of Benchrest brass, but it's still helpful to start with uniform brass.
07 Mar 2019
@ 05:59 pm (GMT)

Jon Short

Re: concentricity
I think you need to be mindful of where your case sits on the ball bearings if its anything like the concentricity gauge I have.(Sinclair I think) Near the back of the case can become slightly deformed based on what I have seen with an 8x57 I have which makes me careful about where the case rests on the bearings.

A couple of other things. I only neck size with Lee collet neck sizers. I also neck turn my cases (& uniform the flash hole seeing as we are doing all we can for accuracy). I don't check neck concentricity until after the case is completed including polished up. No point checking concentricty unless you have the case as perfect as you can make it. Even if you don't neck turn, at least make sure after sizing that its polished up to remove a potential error. I check at the neck & the base of the projectile ogive...for interest sake re bullet seating true... & being anal... I want to know it really is right for long range where small errors create large ones!

My experience has been that, within reason, the more fired a case is the more concentric it seems to become. I might be wrong but that's what I have noticed.

Cheers,

Jon


07 Mar 2019
@ 06:02 pm (GMT)

Jon Short

Re: concentricity
I guess I am trying to say that you need to look carefully at your cases esp if you get alot of run out. Often there is a simple reason like case damage / deformation or its not that clean.

Cheers,

Jon
13 Mar 2019
@ 10:40 am (GMT)

john black

Re: concentricity
both ed and jon stated what i was trying to say much better than i did. thanks
 

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