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The Armourer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 12:02am
Originally posted by britrifles britrifles wrote:

From the Hodgdon web site:



H4895 powder performs exceptionally well with reduced loads (less than published minimums).   Some powders will not ignite and burn consistently with loads less than minimum, not a problem with H4895.  

My approach has been to load the .308/7.62 converted No. 4 rifles to within .303 British pressures, can’t go wrong with this.  

The No. 4 action was never designed to 7.62 NATO or .308 Winchester.  It was designed to use the .303 British Mk 7 cartridge.  If you want your rifles to last for 30,000 rounds, keep loads well below the .303 British maximum average pressure of 45.000 CUP (preferably below 40,000 CUP).  

The thrust loads on the bolt are a function of the chamber pressure and area at the rear of the chamber, the .308 is slightly larger in diameter than the .303 at the base of the cartridge.  


 










Interesting that that loading gives the same pressure as the maximum service pressure for the standard NATO round


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britrifles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 4:55am
Hodgdon lists load data for the .308 Winchester and .308 Service Rifle.  The .308 Service Rifle data is intended for self loading Service rifles chambered in 7.62/.308 such as the M14 and M1A.  

This is the load data for .308 Service Rifle for 168 gr SMK with H4895. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 9:02am



Originally posted by britrifles britrifles wrote:

Hodgdon lists load data for the .308 Winchester and .308 Service Rifle.  The .308 Service Rifle data is intended for self loading Service rifles chambered in 7.62/.308 such as the M14 and M1A.  

This is the load data for .308 Service Rifle for 168 gr SMK with H4895. 



That suggest that the OP loading with 42 gr was right at MAX load (Max = 42.3gr)

Unsurprising that there are signs of over-pressure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 12:29pm
Flattened primers will often indicate excessive headspace, particularly with new or full length sized cases.

I don’t think your load produced pressures above maximum of 45,000 CUP for the .303 British cartridge, and well within maximum for 7.62 NATO.  However, if headspace on your rifle is on the high side or near maximum you will get primer flattening.  As pressure builds on firing the cartridge, the primer is first pushed Out of the primer pocket and back up against the bolt head to take up the “head clearance” (space between the case head and back of the bolt when locking lugs are fully seated in the receiver).  It does not take much pressure to do this.   As chamber pressure continues to build, the case will then slam hard against the back of the bolt after it looses its grip on the chamber walls and/or stretches.  That impact force is what flattens the primer.  

Some flattening is normal for loads that are within maximum published data.   If the radiused edge of the primer cup is completely square (90 deg) you should check headspace.  If headspace is good, then inspect the fired primers after shooting neck sized cases that have been fired in this rifle, they should not be severely flattened.  If they are, your load is excessive. 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 1:53pm
Originally posted by britrifles britrifles wrote:

Flattened primers will often indicate excessive headspace, particularly with new or full length sized cases.

 If headspace is good, then inspect the fired primers after shooting neck sized cases that have been fired in this rifle, they should not be severely flattened.  If they are, your load is excessive. 




What should the headspace be for the Ishapore 7.62 (it isn't the same as 308) and where on the neck do you take the headspace measurement ?

There are more than a dozen different 7.62 'Go' and the same amount of 'No-Go' gauges within NATO.
All with different dimensions and used for differing purposes in different rifles.

Ishapore developed their own headspace for their 2A / 2A1 rifles which is similar to one of the NATO gauges.


An extract of a long presentation given by Peter Laidler in 2008


Now for the biggie, the 7.62’s. The basic principle of headspacing hasn’t changed here but the practicalities have. Whereas before, on our rimmed .303” rifles we measured the GO NO-GO distance between the front face of the bolt and the rear face of the barrel, it’s all changed for the rimless 7.62mm NATO caliber rifles. Now we have to measure from the front face of the bolt to the cartridge seating at the neck. Well, that’s all pretty clear then ….., except that the neck is tapered so where EXACTLY on that neck do you take your GO, 1.628” and NO-GO 1.635 measurement from? Even if I told you it’d make no difference whatsoever because without the specialist measuring and more importantly, the calibration equipment, you’d still be none the wiser. The trouble with this is that you’ve got to take the word of the manufacturer of the gauge. And exactly where does HE take HIS measurement from but more importantly, WHO does he get them from. geting difficult isn't it?

Let me give you an example. My GO gauge gives you a close/GO reading of 1.628 but Bloggs & Co gauge may give you a GO reading of 1.575” for the same 7.62mm caliber. How can there be a difference of .053” between the two when they are identical? Well, it’s simple really. Our STANAG gauges are measured from one diameter around the neck while Bloggs & Co are taken from a different but larger diameter .053” further to the rear! That is really all I want to say about that.


Ishapore actually call their gauges "Low" (Go) and High (No-Go) so if you find some marked this way  - they may just be 'Ishy' gauges.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 2:32pm
Both of my 7.62 converted No. 4 rifles (done at Long Branch, Ontario) have headspace that falls between commercial (SAAMI) Go and No Go.  I would start there.  If the bolt closes on the SAAMI NO GO, I would start to worry.  If it closed on a SAAMI Field gage, I wouldn’t shoot the rifle. 

It doesn’t have to be complicated.  


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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 3:20pm
Originally posted by britrifles britrifles wrote:

Both of my 7.62 converted No. 4 rifles (done at Long Branch, Ontario) have headspace that falls between commercial (SAAMI) Go and No Go.  I would start there.  If the bolt closes on the SAAMI NO GO, I would start to worry.  If it closed on a SAAMI Field gage, I wouldn’t shoot the rifle. 

It doesn’t have to be complicated.  



But in this case we are talking about Ishapore 2A / 2A1 rifles and the headspace as determined by Ishapore, NOT NATO, and NOT SAAMI.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 3:25pm
The Armourer 

[/QUOTE]
What should the headspace be for the Ishapore 7.62 (it isn't the same as 308) and where on the neck do you take the headspace measurement ?
[/QUOTE]
I asked myself this exact question when I started my conversions using the 2A1 barrel knowing full well I was going to use once fired 7.62x51mm NATO brass full length resized in 308 dies. I have a 308 Field gauge @1.638" so, the choice was obvious.  I did what I had to do and ended up with a rifle that has extremely tight tolerances as far as headspacing goes. 
The fired cases show no signs of stretching, and the primers did not flatten. The 308 Winchester is not entirely identical to the 7.62x51mm NATO, owing to differences in tolerances; therefore, some commercial rifles will not handle military ammunition. 
   The OP started out with a charge weight right on the edge of maximum and the result was a stretched case and flattened primers. He ultimately needs to start over and load to the minimum starting charge weight.  If he observes flattened primers and excessive case stretching then make the assumption that headspacing needs to be corrected. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 3:37pm
Originally posted by The Armourer The Armourer wrote:


But in this case we are talking about Ishapore 2A / 2A1 rifles and the headspace as determined by Ishapore, NOT NATO, and NOT SAAMI.
Headspace WAS determined by Ishapore when Ishapore was in full swing producing 2A/2A1 rifles. Who determines headspacing now? The cartridge used is still a 7.62x51mm NATO cartridge, or a derivative thereof.  Therefore, headspace should be determined by a competent armourer or gunsmith due to Ishapore not actively participating in  the production process of 2A/2A1 rifles any longer correct? As long as the rifle headspacing falls within the prescribed tolerances set forth by the infamous Peter Laidler, everything should be as he is ofte quoted as saying," Easy Peasy Lemon Sqeezy"...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 15 2020 at 6:58pm
Originally posted by The Armourer The Armourer wrote:

Originally posted by britrifles britrifles wrote:

Both of my 7.62 converted No. 4 rifles (done at Long Branch, Ontario) have headspace that falls between commercial (SAAMI) Go and No Go.  I would start there.  If the bolt closes on the SAAMI NO GO, I would start to worry.  If it closed on a SAAMI Field gage, I wouldn’t shoot the rifle. 

It doesn’t have to be complicated.  



But in this case we are talking about Ishapore 2A / 2A1 rifles and the headspace as determined by Ishapore, NOT NATO, and NOT SAAMI.

Yes, but we are reloading it with .308 Winchester components and load tables.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 16 2020 at 12:39am
Originally posted by britrifles britrifles wrote:

Originally posted by The Armourer The Armourer wrote:

Originally posted by britrifles britrifles wrote:

Both of my 7.62 converted No. 4 rifles (done at Long Branch, Ontario) have headspace that falls between commercial (SAAMI) Go and No Go.  I would start there.  If the bolt closes on the SAAMI NO GO, I would start to worry.  If it closed on a SAAMI Field gage, I wouldn’t shoot the rifle. 

It doesn’t have to be complicated.  



But in this case we are talking about Ishapore 2A / 2A1 rifles and the headspace as determined by Ishapore, NOT NATO, and NOT SAAMI.

Yes, but we are reloading it with .308 Winchester components and load tables.

That was exactly my point.

7.62 headspace is actually 13 thou greater than 308 headspace, so how can you use 308 headspace gauges without knowing where the dimension is taken.

It may well be that your 308 headspace gauges 'work' for you simply because the 'measurement' is taken in a different position on the taper of the neck. But how do you know ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 16 2020 at 2:41am
I’m in deep water with the headspace measurements. I personally have no way of accurately measuring headspace. Can a “reasonable “ bolt face to case gap measurement be accomplished? And how to do this?
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Originally posted by Frameman 1 Frameman 1 wrote:

I’m in deep water with the headspace measurements. I personally have no way of accurately measuring headspace. Can a “reasonable “ bolt face to case gap measurement be accomplished? And how to do this?

No.

303 is a rimmed case that you can measure from the bolt face to the rim.

308 is a non-rimmed cartridge and the headspace is taken part way down the taper of the chamber.

It cannot be measure against the bolt head and the case rim.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 16 2020 at 5:08am
I understand that the registers for the case seating are taken from different parts of the case but the fact remains that in both calibers the case contacts the chamber wall to stop its forward motion.
That being said, shouldn’t the bolt to case gap still be a relevant measurement?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 16 2020 at 6:17am
If we shoot new .308 or 7.62 NATO ammunition, or full length sized cases with .308 dies, case external dimensions are the same.  Ergo, a .308 SAAMI gage will provide a satisfactory indication of the chamber headspace to that standard that is safe for these cartridges.  Yes, military 7.62 chambers are generally longer than SAAMI .308 chambers but not the other way around, so you will be safe using SAAMI gages.

The other way to check this is to use a case headspace gage.  I use the Hornady gage to measure the case headspace after firing and set my FL reloading die to push the shoulder back .002 to .004 inches and no more.  You can measure new cases as a reference and determine how much the case is elongating to fit the chamber.  

Although we don’t know the exact chamber dimensions used by Ishapore, we do know that .308 brass can be safely fired if the chamber measures within SAAMI .308 specs. Both my No. 4 converted rifles do, the bolt is a long way from closing on the .308 NO GO gage. 

 






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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 16 2020 at 7:34am
Originally posted by Frameman 1 Frameman 1 wrote:

I understand that the registers for the case seating are taken from different parts of the case but the fact remains that in both calibers the case contacts the chamber wall to stop its forward motion.
That being said, shouldn’t the bolt to case gap still be a relevant measurement?

With a 303 there should be a minimum gap between the case rim and the front of the bolt head. If there is a large gap then a different bolt head should be fitted.
In reality a small gap is always likely to exist but head 'clearance' should be minimised.

Changing from 'quality' cases such as PPU or Military cases to the thinner rimmed SAAMI cases means that this 'clearance' space is increased, effectively increasing your headspace.
If your headspace (on a 303) is close to the maximum, your headspace can be actually pushed over the top by using 'thin rimmed' cases, or reduced by using 'thick rimmed cases'

Take the example of a rifle 'just' passing the 0.074" No-Go test and has a headspce of 0.072".

If you use a SAAMI spec case that has a Rim thickness of 0.057" then you now have a gap of 0.015" between the rear of the case rim and the front edge of the bolt head. On firing the case expands binding on the chamber, the rear of the case can move backwards by 15 thou before it gets any resistance so, stretching the case and ending up with a weak point at the 'case web' and the infamous "Enfield Ring Of Death". 
This ring is not the fault of the Enfield 'generous chamber' but of the owner using thin rimmed cases without checking their effect on the headspace and head clearance.

An interesting little Gif (By a poster called Parashooter)





If you took a cross section of a 7.62 chamber you would see that the cartridge case 'fouls' the neck taper on the chanber - this is what stops the cartridge moving forward and where the headspace is normally taken.
On a 303 the cartridge is stopped moving forward by the rim hitting the breech. You can see in the above Gif that prior to firing, the case does not touch the chamber at all, and is the reason for the 'trick' of using a rubber ring (hair band etc) to centre the case in the chamber - otherwise it just sits in the bottom of the chanber.


On firing (both 303 and 7.62) expand to 'fit the space' and then, as long as their elastic limit has not been exceeded, will revert back to (almost) their original dimensions.
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