Re: Mic'd my chamber (7.62 NATO) (AK Site. SVD Discussion Board)

Re: Mic'd my chamber (7.62 NATO)
Author: capman	©	August 2, 2002 at 20:56:20
in reply to: Mic'd my chamber (7.62 NATO)* posted by Berg on July 26, 2002 at 01:04:26*

> I've been wondering just how tight the chamber is on my NDM-86 so I decided to plug the barrel just past the chamber and pour some hot wax down it. After it cooled, I ran a cleaning rod down the barrel from the muzzle and popped out the wax cast. Going by the readings on my dial micrometer:
>
> Chamber cast-base of bullet:. 469
>
> " " -top of case: .452 (before the shoulder)
>
> 7.62 NATO (portuguese)case-bottom:. 461
>
> " " -top: .450
>
> .308 Federal match case-bottom:. 460
>
> " " -top: .448
> I don't have another 7.62 rifle to compare the chambers but it seems the NDM-86 has a rather tight chamber. This might explain why when I fire factory Federal match I see some flowing around the primer indentation.
>
> Incidentaly the Lee load manual states that the maximum
> case width for a. 308 round is. 473 measured at the base
> and. 455 at the neck base.
>
> I'd be curious to know how the 7.62 Russian chamber
> compares in size to the 7.62x54 surplus ammo that's out
> there.

Berg,

I am not sure about this but I think you need to be concerned with "shrinkage". Wax may shrink when it cools. There are chamber casting products on the market. You can also get some good indication of your chamber dimensions from one of those fired cases using BRAND NEW FEDERAL MATCH ammo, not reloads or nato ammo.

cap

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> > I've been wondering just how tight the chamber is on my NDM-86 so I decided to plug the barrel just past the chamber and pour some hot wax down it. After it cooled, I ran a cleaning rod down the barrel from the muzzle and popped out the wax cast. Going by the readings on my dial micrometer: > > > > Chamber cast-base of bullet:. 469 > > > > " " -top of case: .452 (before the shoulder) > > > > 7.62 NATO (portuguese)case-bottom:. 461 > > > > " " -top: .450 > > > > .308 Federal match case-bottom:. 460 > > > > " " -top: .448 > > I don't have another 7.62 rifle to compare the chambers but it seems the NDM-86 has a rather tight chamber. This might explain why when I fire factory Federal match I see some flowing around the primer indentation. > > > > Incidentaly the Lee load manual states that the maximum > > case width for a. 308 round is. 473 measured at the base > > and. 455 at the neck base. > > > > I'd be curious to know how the 7.62 Russian chamber > > compares in size to the 7.62x54 surplus ammo that's out > > there. > > Berg, > > I am not sure about this but I think you need to be concerned with "shrinkage". Wax may shrink when it cools. There are chamber casting products on the market. You can also get some good indication of your chamber dimensions from one of those fired cases using BRAND NEW FEDERAL MATCH ammo, not reloads or nato ammo. > > cap
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