Author: LE OwnerSubject: Mk VII & Mk VIII (Z) ball ammo (long)
Posted: 27 August 2013 at 2:14pm
![Originally posted by Shamu]( "Originally posted by Shamu") Shamu wrote:
Thats interesting. Funnily enough the case weights weren't what I was expecting when I started the project. My original intent was to work out what was really what by actual test instead of repeated 3rd or 4th hand info. I remember some complaints about "soft rims deformimng" on .308 Prvi, mainly in fairly violent semi-auto guns though. But I don't recall anything about .303. |
An FN FAL can tear the rim off a .308 case if the powder charge is a slow building double base charge. The Garand has problems with some loads that use heavy bullets and double base powders, mostly bent op rods.
With a heavy bullet and slow powder the gas port pressure peaks too soon, and the action tries to open before the bullet clears the muzzle and pressure drops in the case. The case wall grips the chamber wall like a tie rod end grips its tapered hole. The rims of Winchester .308 long range match loads were badly deformed by an FAL I used for awhile. To prevent bulged or split cases you had to turn the gas regulator down as far as it would go and still cycle.
Like as not since the defective Privi ammo came from Yugoslavia during its post Soviet break down they would not have sold off ammo that passed military QC inspections.
PS
![Quote]( "Quote") Was it a bad batch, or what, from everything I discovered this isnt a "hot" load at all. Its actually got les propellant than the 174 Gr round & seems to be withing SAAMI specs for ammo from reloading tables I've checked with! (Its not posssible to really tell though as we dont know the exact powder used.) |
Remember you are dealing with a much heavier bullet and unknown powder. Heavy bullet loads can be expected to have a lower muzzle velocity than the standard bullet weight loads even with less powder, and may generate higher pressures to get that velocity.
The load sounds fairly stout, few 7.62 Long range MG loads ever used a bullet of 190-196 gr. Some .308 long range target loads have used the Lapua 190 gr bullet. 220 gr .308 boat tail match bullets are available, but I've seen no tables or data for these.
Older .303 loads , up to MkVI, used bullets heavier than that, but at a much lower velocity.
If the cartridge uses a thick laquer or asphaltum neck sealant these can harden with age and cause increased pull strength with resulting higher chamber pressures.
A thick case neck wall can cause increased pull strength, and so can a fat ogive profile that crowds the origin of rifling. Both improve long range accuracy in an MG bore, but may cause problems in a rifle chamber. Build up of hardened carbon fouling in the chamber neck causes the same problem with standard rifle cartridges.
I made a scrapper out of brass tubing to clear away hardened fouling. It came away in thin streamers that resembled the material of old laquer based records. In fact degraded smokeless powders were recycled and used to make some of the old style records, as well as furniture finish and water proof wood glues.
That sort of fouling is extremely hard to get out, its tightly compressed and won't soak up solvents.
Hard to see as well since chamber pressure irons it onto the chamber neck walls and leaves a slick shiny surface.
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hoadie wrote:
