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Shooting & Reloading - Mausers, Big Bores and others >> Rifles
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fourbore
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Reged: 28/03/10
Posts: 70
Loc: NewEngland
7mm bore diameter USA - Europe
      #226697 - 10/03/13 12:10 AM

Quote:
European 7 mm cartridges all have 7.24 mm (0.285 in) grooves Ø diameter. American 7 mm cartridges have 7.21 mm (0.284 in) grooves Ø.

A link to source: http://en.wikipedia.org/wiki/7%C3%9764mm

Researching the 7x64, I read the above quote on Wikipedia and like to ask if this is true? If so then I assume European 7x57 and American 7x57 rifle barrels are not bored the same? Same question for 7x64. Would American 7mm-08 and current factory ammo for 7x57 use different bullets? or for that matter would American loaded ammo differ from European loads.

I moved this question from the Mauser forum. I heard about a cz550 in 7x64 and ran across this discrepancy in 7mm bore diameters and bullets on wiki. Anyone has thoughts on 7x64 in the CZ550? The listing says 20" barrel, which seems a little short for hi velocity alternative to the shorter 7mm (08 and 57). Could be a misprint?

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tophet1
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Reged: 15/09/07
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Re: 7mm bore diameter USA - Europe [Re: fourbore]
      #226720 - 10/03/13 07:50 AM

I can't specifically answer your questions.

I am currently using old stock, 173 grain 7mm RWS H-Mantle component projectiles that are marked .284". Except for Hornady projectiles, they shoot more consistantly in my Lothar Walther barrel than US sourced projectiles.

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fourbore
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Reged: 28/03/10
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Re: 7mm bore diameter USA - Europe [Re: tophet1]
      #226721 - 10/03/13 08:48 AM

interesting, Wiki stated .284 is the US standard. RWS is German and 284 and old stock at that. I should be ok in assuming 0.284 is standard 7mm everywhere.

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tophet1
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Re: 7mm bore diameter USA - Europe [Re: fourbore]
      #226723 - 10/03/13 09:08 AM

Like everything in reloading, you have to try until you find what works.

Have fun.

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Tom30887
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Reged: 01/07/12
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Loc: QLD
Re: 7mm bore diameter USA - Europe [Re: tophet1]
      #226726 - 10/03/13 10:48 AM

First up, I'm not sure if their is 2 different standards from continent to continent.

But.....The groove Dia. of a barrel is not a critical dimension. Depending on the number of grooves/lands and the width of them a 7mm barrel could have a groove Dia of anything from .280" right through to 0.290".

The bore is far more critical when it comes to Pressure/velocity and the bore dia is more strictly maintained and quality assessed. Even said, the one thou difference you mentioned is a fair (not good, but acceptable) tolerance when it comes to a bore Dia.
Most factory produced guns bore sizes could easily have a +/- 0.0005" tolerance. Your higher custom barrel makers could hold a +/- 0.00025" tolerance (0.0005" {1/2 Thou} maximum variation).

The point I am making is that I find it hard to believe different continents would have different std specks on barrel dimensions when their is no doubt their sizes would be over lapping anyway from barrel maker to barrel maker.

It should also be noted that it wouldn't really matter at all when it comes to accuracy. A tight bore will result in higher pressures but you have to play around a fair bit to get a 'dangerously high pressure', for example tight 30 cal bores can measure 0.2965" and military bores can measure 0.302" (that's over 0.005" difference and both obviously work).

Hope this gives a little insight.

Tom.

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John303
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Reged: 16/11/06
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Loc: Canada
Re: 7mm bore diameter USA - Europe [Re: Tom30887]
      #226733 - 10/03/13 12:30 PM

I believe it would come to "keeping in specification", in about everything produced.
For instance, lets take .284 as the needed diameter but the spec. may be .284 +/- .002.
So the item can be .282 to .286 and still be acceptable.

Another instance would be bullet wght., lets say 160 grains but if you weight a number of bullets
you will find a variation of say +/- 001 grain but all meet the spec.

Let us suppose you have a barrel at .282 and a bullet at .286 you might get some excessive pressure
but unless you are a target shooter it won't matter much.

Just to add the Cdn.280 Ross which still has a following mostly in Europe has a spec. of .287 bullet
dia. This may be the confusion.

FWIW --- John

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VonGruff
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Re: 7mm bore diameter USA - Europe [Re: John303]
      #226739 - 10/03/13 03:32 PM

Gerard at GS Custom bullets certainky makes bullets at both .284 and .285 for the Euro and US 7mm cartridges Scroll down to the 7mm section and see both listed.

http://www.gsgroup.co.za/cip.html

--------------------
Von Gruff.

Exodus 20:1-17

Acts 4:10-12

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grandveneur
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Re: 7mm bore diameter USA - Europe [Re: fourbore]
      #226745 - 10/03/13 07:46 PM

In theory there was ( or to this day ? ) a difference ! In practice the difference was never significant . In all cases we don't consider this by the choice of the bullet for reloading a 7x64 or a 7mm Rem.Mag. . I have never hear of a incident .

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fourbore
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Reged: 28/03/10
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Loc: NewEngland
Re: 7mm bore diameter USA - Europe [Re: grandveneur]
      #226749 - 10/03/13 09:28 PM

Thank you VonGruff and all.

I see that 7x64 loaded ammo is available from Hornady and Brenneke. If I get the rifle, I will try both on the assumption the Brenneke might be 285 and Hornady almost certainly 284.

So; another learning experience.

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xausa
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Reged: 07/03/07
Posts: 2037
Loc: Tennessee, USA
Re: 7mm bore diameter USA - Europe [Re: fourbore]
      #226809 - 11/03/13 03:09 PM

"Wiederladen" is a handbook put out by the Deutsche Versuchs- und Pruf-Anstalt fuer Jagd- und Sportwaffen e.V. (the German Expermental and Test Institute for Hunting and Target Weapons) which publishes tested loads for virtually all currently manufactured German cartridges, including several of caliber 7mm. The loads give bullet weight, bullet manufacturer, powder weight and manufacturer, primer manufacturer and designation, cartridge case manufacturer, and measured velocity and pressure figures.

7mm cartridges covered include 7X57, 7X57R, 7X64, 7X65R, 7mm SE vom Hofe and 7X75R SE vom Hofe. In every case, the bullets listed are predominately those of American manufacturers: Hornady, Sierra, Speer, Swift, Nosler and Barnes, as well as the European manufacturers RWS, Geco, Norma and Hirtenberger. There is no mention of the difference in dimensions between American and European bullets. As long as there is sufficient neck clearance for a bullet to pass easily into the mouth of a fired, unsized case, there should be absolutely no problem with either pressure or accuracy.

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fourbore
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Reged: 28/03/10
Posts: 70
Loc: NewEngland
Re: 7mm bore diameter USA - Europe [Re: xausa]
      #226919 - 12/03/13 11:56 PM

Quote:


--------------------------------------------------------------------------------
From: Hornady Manufacturing, Inc [mailto:webmaster@hornady.com]
Sent: Saturday, March 09, 2013 7:53 AM
To: tech
Subject: "Technical Inquiries" Contact

The technical conversion from metric to inch standard does give you .285 but the standard for the European 7mm bullet is .284". You will be perfectly fine shooting American .284" bullets, I have two European 7mm rifles and both shoot .284" bullets exceptionally well. Thanks for your interest in Hornady bullets.

Best regards,



I got the above response from Hornady support. It would seem the Wiki information is a bit of smoke or Hornady and their staff is off base. I believe Hornady. And the concensus here on NitroEx is in agreement. I dont know what is up at GS Bullets. There must be some 0.285 application. I will just assume that is not something I will not have to deal with.

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Rolf
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Reged: 26/02/07
Posts: 402
Loc: Germany, Bavaria
Re: 7mm bore diameter USA - Europe [Re: fourbore]
      #229778 - 06/05/13 09:37 PM

Hello fourbore,

maybe the rumor is reasonable for some of the german rifles manufactured before WW1 ?!

But for currently produced rifles I load american bullets (Nosler, Hornady, Sierra, Swift) and european bullets (Geco Target and RWS TIG and Doppelkern, Norma Oryx) in .284" diameter and receive good results (read precise groups)in
- 7x57 (98system with a Lothar Walther barrel)
- Mauser 66 in 7x66 SE vom Hofe
- a 98based rifle in 7x64

So I would recommend not to worry about this "difference"...

best regards
Rolf

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