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.308 WIN V.S. 7.62mm |
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JAKOE 
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Joined: October 17 2010 Status: Offline Points: 2 |
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 Topic: .308 WIN V.S. 7.62mmPosted: October 17 2010 at 10:58am |
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I have a British Enfield that has been converted to 7.62mm but i shoot .308 out of it and so far nothing has bad has happened. Should i be warned of anything?
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JAKOE
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Posted: October 17 2010 at 11:03am |
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NVM just looked up the serial numbers and its an Ishapore 2A1.
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Alan de Enfield
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Posted: October 17 2010 at 6:18pm |
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308 SAMMI & 7.62 Military are basically the same cartridge but have very different chambers on the rifle.
You will find there is a 13 thou difference in headspace so your 308 will be 'slopping about' in a 7.62 chamber - so, yes there are areas of concern.
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Shamu
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Posted: October 17 2010 at 10:05pm |
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There were warnings posted earlier in the U.K. but they were regarding .303 Enfields converted to 7.62mm, not ones manufactured in 7.62mm NATO.
AFAIK the Indian-made 2A1 was made in 7.62, not converted in any way so I think the UK NRA warning is not applicable. Having said that don't go hog wild & load some of the newer specialty types of ammunition like the "light Magnums, or Managed Recoil" & you should be fine. Generous chambers as a danger are way over-stated IMHO, every time a "new" case was fire-formed from an old one the case was expanded into an over sized chamber. |
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Lithgow
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Posted: October 17 2010 at 10:06pm |
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So much has been written on this subject, I would suggest a search and then make up your mind whether it is safe or not.
What Alan said is correct, the cartridge dimensions are the same but chambers are not.
Also, military brass has a thicker web so case expansion is different. On top of this pressures are different between the two.
As I said research and make your own descision, you will get much conflicting information in any forum.
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Alan de Enfield
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Posted: October 17 2010 at 10:49pm |
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A couple of links to get you started :
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DRC
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Posted: October 18 2010 at 2:22am |
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This subject has confused me since I got my 7.62. Thanks for the simple explanation Alan, it makes things a little clearer to me.
So, the next time I go to Pickering range I'll be using fire formed cases (I presume that they'll have stretched to fit my chamber) and light to medium home loads. I usually load 145gr FMJ BT and 42.2gr N140 although I'm going to try 155gr Sierra Palma and 42.5gr of N140.
What are your views on using PPU FMJ 145 commercial ammo? They're running out of my barrell at approx 2850 fps, thats about 400fps more than my home loads. I only use them as a source of brass.
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Alan de Enfield
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Posted: October 18 2010 at 2:36am |
Prvi is one of the best made cases there are - its generally a lot thicker than 'commercial' stuff (Winchester etc).
You will need to work out your powder tho' - the cases have the same external dimensions but have thicker walls (than the Winchester etc) so the available space for powder is less - using the same powder weights will increase presure.
Get a Prvi case and measure how much water it holds, then compare it to a Winchester type case.
Start your loads well below max and work them up.
Should have no problems using the factory loaded 145gr Prvi. - as stated the brass is virtually Mil spec.
What rifle are you using ? Try to stay below 150gr bullet. Most of the Enfields variants (Enforcer, Envoy etc) were designed for 145 / 147gr bullets - It was the heavier bullets / heavier powder loads that lead the NRA to publish their warning about Enfield 7.62 rifles.
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DRC
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Posted: October 18 2010 at 2:46am |
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Well you learn something new every day!
I'm using a mixture of PPU, Remington and Federal brass. I knew that millitary brass was thicker than commercial but have treated the above makes as the same. I don't mix batches but will take a further look at the figures I have between the three makes.
I'm having second thoughts about those Palma match loads now. Dam you Alan De Enfield! I'm off to make some PPU 145gr headed replacements!
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A square 10
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Posted: October 18 2010 at 4:23am |
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for once a totally civil discourse on the topic , thank you gentlemen , and such clear and concise explanation of the difference ,
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LE Owner
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Posted: October 18 2010 at 9:13am |
The NATO interchangable infantry ball was supposed to be loaded to 48,000 CUP and MkVIIIz .303 ammo was usually loaded to about that same pressure level.
The MkIIIz ammo was supposed to have the same pressure as MkVII ammunition at 45,400 CUP but since it was intended for use in very robust Medium and heavy machinegun actions, and performance was more important than attempting any interchangability with rifle ammo, the actual pressures could be quite high depending on the manufacturer, with one lot sent to Egypt generating aprox 60,000 CUP and giving velocities over 2,900 FPS.
I strongly suspect that many Enfields that show unusual wear and loosened boltheads were rifles used with MkVIIIz MG ammo.
Anyway the Converted Enfields which were subject to the NRA UK warnings have been recommended for re-proofing long before this latest request for re-proofing.
Working pressures for both commercial .308 and 7.62 NATO other than the interchanable Ball cartridge have been on the rise for decades as long range match shooters try to squeeze the last ounce of performance from the chambering.
The SAAMI maximum pressure for the .308 is 62,000 PSI, but that doesn't mean that use of a 62k load on a regular basis is particularly wise , its just the maximum that individual rounds pulled from any particular lot can generate during lot testing.
The US 7.62 Match, Sniping, and Long Range MG loads generate aprox 52,000 CUP but maximum allowable deviation within lots is 57,000 CUP.
Theres no direct correlation between CUP and PSI, but in general CUP readings for cartridges in this class are much lower than the same cartridge measured in PSI by the EPVAT tranducer method used by the military of the NATO countries.
The longer the bullet the more it will protrude into the case body when seated to the maximum over all length , so as bullet weights go up the less effective powder space there is which not only results in higher average working pressures but also increases the likelyhood of some cartridges in any particular lot pushing or exceeding maximum allowable pressures.
The Winchester Palma Match cases have a semi balloonhead casehead, to allow more powder space when long heavy bullets are used.
The 2A has some attractive points, especially the wider range of suitable .308 bullets to chose from, but I'd keep the pressures down to no more than maximum SAAMI levels for the .303. That would give good performance and be easier on the rifle and the cases, both will last longer.
The 1:12 rifling is better suited for bullets in the 150+/- 5 grains so stepping up to heavier bullets or hot loads isn't likely to produce any particular increase in accuracy.
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DRC
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Posted: October 19 2010 at 4:13am |
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Isn't it a pity that there isn't an after market device that you can purchase that would measure pressure. A bit like a Chrony for the chamber.
I bet someone some where will know where there is one!
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Shamu
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Posted: October 19 2010 at 5:45am |
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They are available , but the actual pressure transducer needs to be permanently attached to the barrel, just in front of the chamber. They are also measuring "PSI" not LUP, or CUP. For that you need a special ported pressure barrel & the lead or copper slugs of the correct type as well.
As you can imagine very few will want a gizmo stuck to the rifle for ever. |
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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LE Owner
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Posted: October 19 2010 at 7:38am |
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There was some sort of pressure testing system that used a dimple pressed into the cartridge case to hold a piezo electric crystal, with tiny wires that could lay along the side of the case.
Don't know how well or even if that worked out.
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Bear43
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Posted: October 20 2010 at 12:18am |
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I have to say that this is probably the most informative and civil discussion of this subject I have ever seen. I know it has cleared up some things in my ol' noggin!
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DRC
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Posted: October 20 2010 at 4:41am |
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It just goes to show the quality of the members on this forum.
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DRC wrote: