CG63 Super High Pressure Signs

[thirtythirty]

Sorry for the long story, but here is the situation-

So last summer I was lucky enough to obtain a CG63 in 6.5x55 swedish. The receiver is marked 1916, and as I'm sure you all know is an M96action. I put a little over a hundred rounds through it with no issue. I worked up to 44gr of Accurate 4350 under a Hornady 140gr SST's. I put the gun away for a while, until a friend invited me to go shooting with him. I quickly whipped up 20 rounds with a different bullet (a run-of-the mill speer 140gr) with the same load (44gr), which was admittedly stupid, but I was in a rush and wasn't thinking. I got to the range and shot about 7 off. The gun was acting funny, there was a lot of soot on the cases. I didn't think to examine the primers until the bolt jammed. I checked the primers after and they were completely flattened, and 2 were blown out of the primer pocket hole. I stopped after that point. A week or so later I made a load with the same bullet but with the starting load (39 or 40 grains). I shot one off and the primer was completely flattened and cratered. I examined the bore, and it was covered in copper. Thinking this might be the issue I filled the barrel with Hoppes copper Remover and let it sit overnight. I drained it the next morning and a bunch of **** came out. There was still streaking on the lands, but it was much better after. I put together another starting load with a 160gr bullet under 35 grains of Accurate 4350. I shot one off and the primer blew out the back. If anything, things were worse. My question is this-is it possible that I stretched the receiver and caused a headspacing issue? Is there something else I'm not seeing here?

Thanks in advance for all of your help.

[nicholst55]

That doesn't sound like a headspace issue - it sounds like a high pressure issue. Now, to determine the why. Disassemble your bolt and examine the firing pin tip. Is it smooth and radiused, or is it pitted and sharp? If your primers pierced, the leaking gas can quickly erode the firing in tip.

[Black Powder Bill]

Hummmm quite the load

Sent from my XT1096 using Tapatalk

[thirtythirty]

nicholst55-thank you for that, when I get the chance I will do that and report back.

Black Powder Bill- The 5th ed. Sierra manual lists a max of 44.1 gr of Accurate 4350 under a 140gr bt. Me switching to a flat based bullet without working up first was stupid, but the original load was worked up from published information, besides which it had no issues for 100+ rounds. I don't have a camera with me right now, but I'll try and post a picture of the load data when I do.

[thirtythirty]

Ok, so pulled the bolt apart today and looked at the firing pin. There was a small bit of tarnish or something which I was able to get off with my fingernail after a little work. Otherwise it was well radiused and shiny with no pits. I think it may have pierced one primer (and I think it was the very last round I shot), but otherwise it wasn't, so I feel like that may not have been the issue.

[Black Powder Bill]

Thirty thirty,

It may be like you mentioned. Blew a primer and it fouled up the bolt face area.

I check an older Speer manual and Lee precision neither one had 44 gr. Listed for 140 jword or lead

Sent from my XT1096 using Tapatalk

[Tackleberry41]

Not all bullets are the same, reloading books often treat them that way. But a 140gr boat tail, seated to the same length as a flat base will probably jack up the pressure. All copper bullets are going to be longer than a lead cored bullet. Put the 2 different bullets side by side might be shocked how much deeper the base will be in the case on one vs the other.

[Black Powder Bill]

Not all bullets are the same, reloading books often treat them that way. But a 140gr boat tail, seated to the same length as a flat base will probably jack up the pressure. All copper bullets are going to be longer than a lead cored bullet. Put the 2 different bullets side by side might be shocked how much deeper the base will be in the case on one vs the other.

Yes I understand all that. I have never encountered the extreme issues you had.
When switching from BT to FB.

Sent from my XT1096 using Tapatalk

[koger]

If you want some safe, quick loads, using IMR 3031, pm me. It is my go to powder for over 30 years shooting a swede like yours, that has been sporterized by me when I could buy them for $59 when I had my FFL. I did load development for 3 years, and I could get nothing that outshot the 3031, in accuracy, or velocity combined. I still shoot the same gun, and took a small buck at 510 yds this past season, with a 120 grn Sierra SP at 2980fps. None of the loads I use were listed as top notch loads, but when a friend ran them on his Qwik load computer program, it came out 95%+efficient!

[Black Powder Bill]

Another thought, I'd pull some bullets and weight the charge.

Sent from my XT1096 using Tapatalk

[merlin101]

Another thought, I'd pull some bullets and weight the charge.

Sent from my XT1096 using Tapatalk

Yeah and with a different scale! Or at least check the scale for accuracy.

[nicholst55]

Obviously, something significant changed in order to raise pressure so dramatically. I have never experienced such dramatic pressure increases simply by changing bullets in an established load. I could understand having some pressure signs, but what you're experiencing is rather dramatic. Start at the beginning - like Black Powder Bill suggests, disassemble a few rounds and check powder charges - right powder? Right weight? Weigh the bullets, too. Are these bullets jammed into the rifling? Same brand of brass? Same primers?

Have you tried backing off on your load, and testing with the same components? Your load does appear to be right at max, or slightly over.

[Larry Gibson]

Yeah and with a different scale! Or at least check the scale for accuracy.

That would be my suggestion too.

[swheeler]

thirtythirty your loads don't seem unreasonable if worked up to. Since you are using Accurate powder and Speer bullets that would be my first sources for data, Accurate #2 manual shows Speer 140 gr SP, ACC 4350 start 40.5 - max 45.0 2629 fps 48,100 psi. They also show the Hornady 160 RN with ACC 4350, start 39.6 - max 44.0 2553 fps and 50,300 psi, and this sounds logical with the short bearing surface length of that 160 gr bullet.
So I would clean the barrel really good, maybe a bronze brush wrapped with a patch covered in JB's or 40x scrub the throat area well. Then buy some NEW brass and start over with load workup. My guess is you have ruined your brass from your initial loads being a little too hot for your rifle, primer pockets have been enlarged enough that primers fall out on next firing.

[7br]

Did you tumble the cases? I had a similar issue with a .280. I always clear the primer hole, but did not check the case. Turns out there was enough tumbling media in the case to really reduce case capacity.

[thirtythirty]

Yeah and with a different scale! Or at least check the scale for accuracy.

Yeah, I've since gotten a new scale, the 160gr load was measured using it. I did pull bullets and measure charges and they were 44grains, at least the ones I measured (this was a while ago, so I can't remember how many I measured, I think 5ish so maybe that's a source of error). I hadn't thought of the loose primer pockets swheeler. I'm back at school now, but when I get back home I'll finish cleaning the barrel and maybe try with some new brass.

[truckjohn]

Any chance one of those loads was worked up with a different powder - say H4350 or IMR 4350 instead of Accurate 4350?

[thirtythirty]

Any chance one of those loads was worked up with a different powder - say H4350 or IMR 4350 instead of Accurate 4350?

No, I only have the one brand of 4350 at the moment.

[3006guns]

Note: There was a glut of DANISH 6.5x55 ammunition that appeared on the market some years back. Word soon got around that the bullet jacket material used with these cartridges was a very soft steel (or possibly cupro-nickel) and it fouled barrels VERY quickly. As a result, it raised pressures to the point that several rifles were blown up or damaged. There's a picture out there somewhere of a beautiful Ljungman auto rifle blown to bits from using those rounds, and that was done by an experienced shooter/handloader.

It might be possible that your gun had some of that ammo run through it and, since it's difficult to remove, the previous owner didn't get all of it out. Each additional bullet fired would strip off jacket material, escalating the problem. If your headspace is still okay and there's no damage, clean the livin' peewaddins out of it.......then clean it some more.

[Larry Gibson]

I only have some Sierra 140 gr SPBTs on hand. No other 140 gr or I'd run a pressure test I my CG Swede with AA4350.

My standard 140 gr bullet for hunting is the 140 gr Hornady SP over 49 gr of H4831SC in Winchester cases with WLR primers. That load runs 2750 fps at 54,500 psi out of my M38. However, my preferred all around hunting load is the 129 gr Hornady SP over 49.5 gr of IMR 4831 for 2925 fps at 55,700 psi. [6.5 CM.....eat your heart out......]

PSIs are actually measured in the CG via an Oehler M43 PBL. Both measured psi's are at the C.I.P. PMAP.