doublegunshop.com - home Forums General Discussion German & Austrian Sporting Guns @ doublegunshop.com SKOPAR B scope

Thanks Mike.

I ordered a couple of new firing pins from Numrich to work with. If that don't work I'll try some used pins.

Well I ordered a new firing pin and it is works most of the time on Prvi Partizan ammo so I thought I would try Sellier & Bellot and first shot PING!! Case rupture! I don't think it hurt the rifle and it vented as designed. So I'm back at wondering if the chamber has been over polished or rechambered to something close to 6.5x57 or is it a 6.5x58P. Gunwolf had mentioned 7x57 very early but I don't think the bore is big enough for that. I would really like to get it up and running.

Time for a chamber cast so you can see what is really going on.

I guess I will measure the PP fire formed brass that didn�t rupture vs my old chamber cast measurements and see if anything matches. .257AI?

What does the chamber cast measure at the base and in front of the web? Fired cases? Un-fired cases?

Unfired case
Base 11.72mm
shoulder 10.85mm
Base of neck 7.53
Top of neck 7.44
Length of neck 7.52

Fired case
Base 11.88mm
Bulge 12.19mm
Distance From base to bulge 4.73mm
Shoulder 11.50mm
Base of neck 7.82mm
Top of neck 7.55mm
Length of neck 6.48mm

I am still a bit confused but I can tell you that at the point of your bulge you are measuring larger than a .30/06 base.

What does the base of the chamber cast measure? Start there to establish what the parent case is. It could be an over polished chamber or an odd ball cartridge.

Here is the chamber cast

Going back to your post # 557779 on 11/4/19, there is an excessive expansion of the neck of the fired case that is easily visible without measuring. Is this really a 6.5 m/m?

Then, assuming your Sellier & Beloit ammo was new unfired brass, there had to be a considerable difference between the case dimensions and the chamber for the brass to split as it did, and have a partial head separation, instead of just fire forming.

I'm thinking your light primer strikes were possibly caused by the firing pin pushing the case off of the bolt face because the shoulder was several thousandths back from contacting the chamber. This looks a lot like an excessive headspace situation, and the recommendation to measure with headspace gauges seems like a great idea. That might explain the strange deformation at the case-shoulder juncture, and the partial head separation in new brass. Was the primer very flattened, which could indicate that the case head was unsupported by the bolt face at the instant of firing?

I think I'd start with headspace and bore measurements, followed by another chamber cast, and careful measurements of the Cerrosafe at the correct time to get exact dimensions. It wouldn't hurt to find a soft lead ball slightly over-size to slug the bore, and get precise land and groove dimensions. It seems strange to not see even a trace of rifling on your chamber cast.

It is unusual that a chamber would be polished that far out of spec unless it was severely pitted. I don't see anything in 6.5 cal that has dimensions very similar to what you measured. This could be some wildcat round. Or you might end up setting the barrel back a couple threads and rechambering... or rebarreling. I'd sure be wearing good shooting glasses, or better yet, firing this rifle tied to a tire with a long string on the trigger, until you get this sorted out. I once spent about a half hour totally blind in both eyes after having a complete head separation with a VZ-24 Mauser rechambered to .22-250. That gets your attention, and it isn't worth taking such risks.

I am having a hard time finding something that is that large of a diameter and so short. I am leaning more towards a damaged chamber that someone has tried to clean up. I'll keep looking but that is my feeling at this point.