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High pressure warnings

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Honkytonk View Drop Down
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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 12:07pm
Pressure is pressure. Projectile weight, acceleration, powder charge, primers, brass... If you screw a 7.62x51 barrel on a Enfield receiver, and keep your loads well under say 43,000 cup, and if all the above mentioned components are factored in on this calculation, why would it matter how heavy of a pill you want to push out? "For every action, there is an opposite and equal reaction". Unless this has changed, I truly don't see how projectile weight is the primary factor into producing a safe round.
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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 12:31pm
Projectile weight is not a factor in producing safe rounds. Producing a safe round consists of following proper reloading procedures.  Trim to length and proper seating depths, minimum powder weight, all factors needed for low to normal working pressures. The projectiles weight is factored into the powder equation and a minimum and maximum amount of powder is given with the disclaimer to never exceed the maximum. You can create an overpressure situation by not trimming the case to length where the edge of the case mouth contacts the throat and can crimp the case fully onto the bullet not letting the case expand during firing to release the bullet. Another excessive pressure situation is when you seat the bullet to just touch the rifling. It doesn't have any run up and excessive pressure is generated to force the bullet into the rifling.
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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 17 2020 at 1:35pm
Originally posted by Goosic Goosic wrote:

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. 

How do you know what the working CUP is of the Ishapore Enfields is ?

Dont forget that they changed the steel specification from that specified by the UK and used an 'inferior' grade that mean that the actions warped when tested with both the dry and oiled proof round. After scrapping a large number of rifles they changed to an EN steel which allowed the action to pass the 'dry' proof round, but still failed the 'oiled round' warping the action so that the bolt could not be opened.
The testing specification was altered so that the rifles could be released for use, but it would appear that their strength was very much on the cusp of failing.

I would not want to use anything more than original NATO 144gr rounds (or direct equivalent)

Hogdon & Federal are not aware of which rifles you are using, and probably not even aware of the dubious history of the 2A / 2A1 rifle with regard to pressure and distorted actions.
They are providing you with information to be used on 308 SAAMI firearms.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 2:20pm
Please remember to keep the discussion civil, gentlemen.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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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 2:22pm
Originally posted by The Armourer The Armourer wrote:

Originally posted by Goosic Goosic wrote:

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. 

How do you know what the working CUP is of the Ishapore Enfields is ?

Dont forget that they changed the steel specification from that specified by the UK and used an 'inferior' grade that mean that the actions warped when tested with both the dry and oiled proof round. After scrapping a large number of rifles they changed to an EN steel which allowed the action to pass the 'dry' proof round, but still failed the 'oiled round' warping the action so that the bolt could not be opened.
The testing specification was altered so that the rifles could be released for use, but it would appear that their strength was very much on the cusp of failing.

I would not want to use anything more than original NATO 144gr rounds (or direct equivalent)

Hogdon & Federal are not aware of which rifles you are using, and probably not even aware of the dubious history of the 2A / 2A1 rifle with regard to pressure and distorted actions.
They are providing you with information to be used on 308 SAAMI firearms.
The data for the 168grn M118SB and the 175 M852 that i just referenced are NATO cartridges that are used today and yes
they are providing loading information for 308 service rifles chambered in 7.62x51mm NATO.  What is the 2A/2A1 rifle chambered for?
You keep referencing SAAMI and I can only assume it is because it is not the definitive CIP. 
Norma-Reloading Manual 2004 page 68:
In order to sell products in CIP member countries,  gun and ammunition manufacturers must follow CIP specifications and procedures.  This precaution minimizes potential for accidents that might otherwise result from haphazard production standards. In the US, SAAMI provides very much the same function. BOTH organizations accept each others measurements, pressure standards and procedures. 
The crusher method is time consuming, expensive and unusually sensitive to operator techniques.  For the most part, it also fails to generate results that agree with actual peak chamber pressure. 
 Hodgdon and Federal Ammunition are only aware that their powder and ammunition at sometime will be used in a rifle chambered in 7.62x51mm or commercial 308 and as such offer load information or ammunition that is safe at the time of production.  What you do with it after the fact is none of their concern. The working pressure of the 7.62x51mm NATO chambered Ishapore rifle should have been the same across the board as all the other bolt rifles chambered to accept the 7.62x51mm NATO cartridge in any configuration would be my assumption. Anything less would be unfit for military purposes and sent to a smelter for repurposing.
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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 17 2020 at 5:06pm
This has become a very interesting discussion, and probably one we have had before.  

I respect Brian’s opinion, but here are a few other thoughts.  

I’m not sure why Brian believes that bullets heavier than 150 gr should not be used in the 2A rifle.  Using a powder like H4895, you can load the 168 grain bullet to very mild pressures indeed.  Even reduced loads with a 168 gr bullet to less than 2200 fps is perfectly safe with this specific powder.   Yes, headspace and the throat leade will play a part in what the actual chamber pressure is, it won’t be exactly what is published for .308 Winchester tables as these are for a .308 Win chamber. 

Note that Brian suggested the chamber be checked with SAAMI gages, I’m not aware of any 7.62 NATO SAAMI headspace gages, so I believe he is referring to .308 Win gages.  Here, we are in agreement.   

I do admit that additional caution should be used in loading 7.62 x 51 for No. 1 rifles by using .308 Win load data.  Enfield found the No. 1 rifle unsuitable for conversion to 7.62 due to its weaker action as compared to the No. 4.   But, the beauty of reloading is you have full control of the variables affecting pressure.  Use H4895 and light loads, no more than minimum .308 Win published loads by Hodgdon.  These will have low pressures, well within the .303 British chamber pressures.  Pressure is pressure.  You can get very high chamber pressures with light bullets if you put too much powder in the case. 







 
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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 5:41pm
These headspace gauges are very hard to find.
Anyone rent them?
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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 5:45pm
eBay has them. Search 308 headspace gauge. 
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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 5:54pm
I’ll check them out. Thanks 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 17 2020 at 7:21pm
Frameman1, if you are looking to spend the minimum of cash, buy a .308 FIELD gage.  If the bolt does NOT close, you are good to reload using .308 Win load data to MINIMUM charge weights. I strongly suggest you stick with H4895, IMR 4895 or IMR 4064 with 150 or 168 gr bullets.  If you are very confident in your reloading skills, by all means, explore other options of powders and bullets.  

Now that I know that Ishapore 2A rifle chambers were set with fairly long headspace (compared to SAAMI .308 dimensions) I believe this is why you got flattened primers.  The light ring around the circumference of your fired cases should be investigated. If it were me, I would section one of these cases and see how thin the case wall is at that location.  It may well be significant brass stretch from firing a new .308 case in a “long” 7.62 chamber.  


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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 7:42pm
sectioning a case was my goal for tomorrow. I have used 7.62 NATO cases before with no problem. I’m certainly not a pro reloaded but I’m fairly competent.
The field length guage does seem to be the right place to start. It will chamber anything I’ve tried so far so I could pass on the go guage. Like you said “ if it won’t close on the field guage i’m good to go “
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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 18 2020 at 12:47am
Originally posted by britrifles britrifles wrote:


Now that I know that Ishapore 2A rifle chambers were set with fairly long headspace (compared to SAAMI .308 dimensions) I believe this is why you got flattened primers.  The light ring around the circumference of your fired cases should be investigated. If it were me, I would section one of these cases and see how thin the case wall is at that location.  It may well be significant brass stretch from firing a new .308 case in a “long” 7.62 chamber.  



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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 4:56am
Yes, if this chamber is at or close to 7.62 MAX, it will not be safe to shoot reloads with .308 cases.  Not even with minimum charges.  Even 7.62 cases will stretch significantly causing case wall thinning, and case life will be very short if headspace is close to 7.62 MAX.  If he’s lucky, the chamber may be closer to the 7.62 MIN dimension which is shorter than the .308 FIELD:  

    Ishapore 7.62 MIN 1.633 is .005 shorter than .308 FIELD 1.638

    Ishapore 7.62 MAX 1.642 is .004 longer  than .308 FIELD 1.638 

There is overlap on these dimensions and the chamber may well be under .308 FIELD and safe to reload with .308 Win cases.  

We are all just speculating, the headspace needs to be checked.  If it fails the .308 FIELD gage, then the only hope for continued use is to check it with a 7.62 MAX gage and if it passes, reload with 7.62 NATO cases only.  I would not recommend shooting a lot of 7.62 NATO ammunition even if it’s less than 7.62 MAX.

New 7.62 X51 NATO cases are available, currently on sale at Midway USA.  7.62 MAX headspace gage available from Brownells for $32.00.  





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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 18 2020 at 5:48am
I pulled the trigger for the Max 7.62 gauge. I’ll update when I have it.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 6:26am
One other thing, you will find some variability in .308 FIELD gage dimensions.  I got my set from Manson Precision, the Field gage is 1.640, 0.010 longer than the .308 GO gage and only .002 shorter than the Ishapore MAX chamber length.  




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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 18 2020 at 6:54am
That info illustrates that the 7.62 chamber is considerably longer than the .308.
I’m considering doing a chamber casting to help clarify the issue.
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