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High pressure warnings

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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 16 2020 at 8:05am
One thing for certain is that military rifles don’t consider cartridge case reloading.  As long as there is a margin on case head ruptures, it is of no concern if brass elongates.  Not so for us who reload.  We want headspace to be tight for long case life.

The No. 4 Long Branch 7.62 converted rifles were built for target shooting purposes which likely explains the relatively tight headspace that conforms to SAAMI .308 Win specs.  I suspect that’s how they set the headspace on these rifles even though they would be used with Canadian issue 7.62 NATO ammunition.  Not being a machine gun where cartridge feeding reliability is a primary concern, they likely saw no reason to ream the chambers out to NATO specs intended for MG use.   I’ve got a 1960’s DCRA instruction sheet on converting .303 barrels to fire the 7.62 cartridge and these instructions call out the use of a .308 Win reamer.  

I have no idea what Ishapore did for chamber headspace on their rifles, but if the OPs rifle is indeed to the high side of 7.62 NATO specs, and a new .308 case was used, a flattened primer is going to occur, likely with light loads as well.  Also pretty severe case headspace elongation.  That would also happen with a 7.62 NATO case. 






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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 16 2020 at 12:43pm
Originally posted by britrifles britrifles wrote:

.  

I have no idea what Ishapore did for chamber headspace on their rifles, but if the OPs rifle is indeed to the high side of 7.62 NATO specs, and a new .308 case was used, a flattened primer is going to occur, likely with light loads as well.  Also pretty severe case headspace elongation.  That would also happen with a 7.62 NATO case. 



The Ishapore headspace is : 


Low (Go) 1.633
High (NoGo) 1.642

But knowing that is not much help unless you know where on the 'slope' that figure is taken.
You could have 308Win gauges with exactly the same dimension but taken further up/down the slope.

The only was to be sure is to obtain NATO gauges with those measurements - but - there aren't any.

The nearest (and ones folk rebuilding Ishapore's use) are the L1A1 gauges at :
Go 1.6325" 
NoGo 1.643". 

There is no such thing as 'Field' in military headspace gauges.

It's a bit higher that you would normally have expected from a bolt action rifle BUT, it is still the generally accepted ~ .010" between go and no-go.

Can you find any 'proper' military issue L1A1 gauges ?

The 308Win headspace gauges are 

Go 1.630"
NoGo 1.634"






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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 16 2020 at 12:46pm
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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 5:07pm
Which takes us full circle.  

If you intend to load using .308 Winchester components and .308 Winchester reloading dies, then check the chamber headspace with .308 Winchester gages.  If it fails the .308 Winchester Field gage, better be careful what your doing here, the .308 cases have thinner walls and a ruptured case can result.   By definition, that rifle is no longer safe to shoot with .308 reloads.   If I had a rifle like that, I find out if the chamber headspace is still within 7.62 maximum and only shoot 7.62 NATO ammunition if it is within max. 

Forster makes 7.62 NATO spec headspace gages.  

The good news is that the .308 Winchester and 7.62 NATO specifications for headspace are taken at the same datum on the shoulder, at 0.400 inches diameter.  


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 16 2020 at 6:40pm
Originally posted by Frameman 1 Frameman 1 wrote:

I fired these rounds yesterday. I used new Hornady 308 cases with CCI 200 primers , Hornady 165 gr, SST bullets with 42 gr. Of IMR 4895 powder. I thought this load would be fine but the signs say otherwise.
Any thoughts? 
Frameman 1. Hodgdon load data shows a starting weight of 41.0grns and a maximum of 43.5grns.
Your 42.0grn charge is right in the middle. It would be advisable to have a competent gunsmith, knowledgeable with the Ishapore Enfield inspect the headspacing.  Brian D i c k at BDLLTD.COM can and will accommodate you and assist with this issue. No sense in playing guessing games from this point forward. Have the headspacing checked before you continue firing the rifle.
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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 17 2020 at 2:13am
Thanks for the advice from all our forum friends. I will be contacting Brian for recommendations.
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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 17 2020 at 7:22am
Here is the response I received From Brian @ BDLLTD.com
Hi Roger,

Headsppace specifications for the 2A/2A1 follow.

1.633 Go
1.642 No Go

Those rifles are designed around the 7.62 NATO cartridge and you need to keep pressure down by using 150 grain or lighter projectiles. L2A2 ball uses a 144 grain projectile. I tell folks that if they want a serious 7.62 Lee Enfield, they really need to buy a No.4 which are considerably stronger but still only designed for NATO spec. ball ammo. You're running your pressures up considerably using 168 grain projectiles. Try some 150's and see if they work for you. If you have a local gunsmith with SAAMI gauges, have him check the headspace also. Thanks.

Regards,

Brian  


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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 17 2020 at 8:14am
Originally posted by Frameman 1 Frameman 1 wrote:

Here is the response I received From Brian @ BDLLTD.com
Hi Roger,

Headsppace specifications for the 2A/2A1 follow.

1.633 Go
1.642 No Go

Those rifles are designed around the 7.62 NATO cartridge and you need to keep pressure down by using 150 grain or lighter projectiles. L2A2 ball uses a 144 grain projectile. I tell folks that if they want a serious 7.62 Lee Enfield, they really need to buy a No.4 which are considerably stronger but still only designed for NATO spec. ball ammo. You're running your pressures up considerably using 168 grain projectiles. Try some 150's and see if they work for you. If you have a local gunsmith with SAAMI gauges, have him check the headspace also. Thanks.

Regards,

Brian  



Pleased to see both he and I are singing off the same song sheet.

Note he quotes the same headspace and bullet weights as i did several times - even as early as post#3.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 8:48am
Running pressures up considerably usung 168grn projectiles?
Not in the slightest if you follow and adhere to proper reloading procedures. The minimum PSI on this data is listed as 43,800. The calculated conversion to CUP is 37,181. 6000 CUP under that of the working 45,000 CUP of the Enfield rifle. Federal Ammunition uses 41.7grns of IMR4064 and a 168grn SMK BTHP for both the military and in their commercial sales of 308Win. Making this particular 168grn projectile one if the safest loads to use in an Enfield rifle without conflict of interest. The NoGo SAAMI is 1.642" but there is a Field gauge that is 1.638". It would seem to me that as long as headspacing falls between 1.634 and 1.642 the rifle if functional...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 9:03am
I'm not sure I understand. I would think pressure is a product of bullet weight and powder load. Heavier bullet? Reduce powder. Net result of producing a round of any weight projectile should be able to achieve a pressure well below maximum... or I completely missing something?
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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 17 2020 at 9:20am
Originally posted by Honkytonk Honkytonk wrote:

I'm not sure I understand. I would think pressure is a product of bullet weight and powder load. Heavier bullet? Reduce powder. Net result of producing a round of any weight projectile should be able to achieve a pressure well below maximum... or I completely missing something?

That was what I was taught, and I'd also tend to accept the advice & knowledge of a trained armourer and one of the USA's most experienced Enfield 'plumbers'.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 10:47am
God forbid accepting factual load data from one of the leading manufacturers of smokeless propellant like Hodgdon though...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 11:18am
Again, I apologize. "... you need to keep pressure down by using 150 grain projectiles or lighter..." and "... You're running your pressures up considerably by using 168 grain projectiles..." I don't understand why that if using a lighter powder charge on the heavier 168 grain projectile and achieving a breech pressure well under the receivers maximum, and unless my elementary understanding of physics is failing me, how can you not load a safe 168 grain round for this rifle?
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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 17 2020 at 11:32am
Originally posted by Honkytonk Honkytonk wrote:

Again, I apologize. "... you need to keep pressure down by using 150 grain projectiles or lighter..." and "... You're running your pressures up considerably by using 168 grain projectiles..." I don't understand why that if using a lighter powder charge on the heavier 168 grain projectile and achieving a breech pressure well under the receivers maximum, and unless my elementary understanding of physics is failing me, how can you not load a safe 168 grain round for this rifle?

I re-quote my original post (#3)

Heavier bullets accelerate slower than lighter bullets. Slower bullets means less space behind them which means higher pressure, which means faster powder burn which means even more pressure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 11:48am
I understand... BUT... regardless of powder charge and projectile weight, (any combination of the two) with this 7.62x51 barrel on an Enfield receiver, if breech pressure is kept well well below 45,000 cup, regardless of how fast a powder burns, it must be a save round. It all boils down to a combination that respects the maximum breech pressure of the peceiver. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 11:54am
Originally posted by The Armourer The Armourer wrote:

Originally posted by Honkytonk Honkytonk wrote:

Again, I apologize. "... you need to keep pressure down by using 150 grain projectiles or lighter..." and "... You're running your pressures up considerably by using 168 grain projectiles..." I don't understand why that if using a lighter powder charge on the heavier 168 grain projectile and achieving a breech pressure well under the receivers maximum, and unless my elementary understanding of physics is failing me, how can you not load a safe 168 grain round for this rifle?

I re-quote my original post (#3)

Heavier bullets accelerate slower than lighter bullets. Slower bullets means less space behind them which means higher pressure, which means faster powder burn which means even more pressure.
Not if you are following proper reloading procedures and not attempting to run up to maximum charge weights. Federal Ammunition has load data for a 175gr BTHP SMK using 41.745grn of IMR4064. It has a working PSI of exactly 44,346.7 A PSI to CUP conversion brings that to 37,842.51 CUP, 7100 CUP below the 45,000 working CUP of the Enfield rifle.
I have a tendency to believe Hodgdon and Federal Ammunition over those other two guys you referenced. 
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