I need help with pressure problems

[AtownBcat]

Hello all...

I am shooting a 6.5x47 and am having some pressure problems.

I am using Lapua brass
H4350(and a test string of 2000 MR)
Federal match small rifle primers
140g A-Max's

I have loaded all the way down to 36 grains of bot 4350 and 2000 MR shot it over the CE M2 and registered velosity all the way down to 2477(most people are between 2840-2940 with this bullet) and even with the lightest charge i am still getting extractor swipe and slighty heavy bolt lift. Every round that has been fired(yes im hard headed and keep trying) has the swipe....I just dont understand..

The gun was built by a great builder with a great reputation and taking it back to him will be the next step.

I have measured the new brass(i did not trim it) but it measured 1.8435 so unless my chamber it short they should be great.

any ideas? someone suggested using varget but with velosity down around 2400 there should be no pressure.

PS the gun is a shooter...I have shot three three shot groups that were all under .2.

 

[Bullet bumper]

I have no experience with the 6.5 x 47 lapua. However there is a few things you should check.
Lubricate the bolt lugs and cocking cam with molly grease.
Check the powder in the tin is the correct type. Maybe buy another can of 4350 to make sure .
Scrub the barrel and chamber out extra well with a good powerful copper solvent . Inspect the brass for rings that might indicate a rough chamber .
If so polish out the chamber .
Polish up the brass extra clean.
Size the brass for a neat but easy fit so it does not crush into the chamber because that can cause hard extraction.
Make sure the extractor is not bedding into the case rim and stopping the bolt from turning easy initially .
Some guns just will not digest as much powder as others.
Make sure your Chronogarph is reading accurately , test some other gun and known ammo.
Using Varget should make things worse as it is faster than H4350.
Don't just go by bolt lift also check primer flattening and cratering to see if it all matches .

 

[Topshot]

I would say that you have a short range benchrest type chamber designed for light weigth flat based bullets or a throat that requires neck turned cases.

The chamber most likely has almost no lead. ie a very short throat. I have had the same problem with a 6mmBR that had a short throat cut.

Try a bit lighter bullets of the Berger VLD type with a short bearing surface and secant ogive. Be careful to seat the bullets to be just short of the lands or to just kiss the lands.

If after trying the lighter bullets, it still has pressure problems, take it back to the gunsmith.

 

[Mikecr]

It's very odd for premature pressure problems from that cartridge. 1st I've ever heard of it.
I would measure near the webs, headspacing, and necks, before and after firing to determine the problem.
Just compare your new prepped to once fired(and not yet sized).

 

[AtownBcat]

Thanks for the ideas.

I spoke with my builder this morning and he suggested I go to a 130g Berger. Although I could see the Berger having a little less pressure because of the bearing surface I don't see it solving the problem. I'm 400 fps slow not 50. I ran my brass through a mandrel die to ensure the necks were all the same, but did not turn anything. I didn't think much about it but I have a little trouble closing the bolt so it might be a tight chamber( new brass). So how do I check that sort of thing?

 

[Mikecr]

Measure near the webs, headspacing, and necks, on before and after firing to determine the problem.

 

[foxc57]

Measure the neck dimension of a loaded cartridge and compare it to the neck dimension of a fired case. You should have at least .003 difference. If the case neck can not expand to release the bullet, it can cause a pressure spike. You can also use a permanent marker on a loaded cartridge to see where it is making contact when chambering.

Did the gun maker stamp a neck dimension on the barrel?

 

[yawn]

Lube left on the case or some solvents in the chamber can cause this.

Is it posssible to post a pic of the case head showing the extracor swipe?

 

[AtownBcat]

Lube left on the case or some solvents in the chamber can cause this.

Is it posssible to post a pic of the case head showing the extracor swipe?

Ok I have taken a few measurements (with pictures...I know how you guys like pictures)
The first is for the neck measurements. I read 5 fired cases and they all read the same so I zeroed on one of them and here is what I got:

Next I have an innovative technologies bad *** headspace guage. Looks like I have exactly .006 clearance between new brass before it is fired.

And finially I have pictures of the case heads. It is not easy to get the swipe to photograph y but you can see the circle.
First(right to left) 36g 2000MR....2577fps
39.5g 2000mr......2760
41.5g 2000MR......2942

I do realize that solvent and or lube can cause problems but this is not what's going on here. Also the rifle has been cleaned by the letter of the law...no copper build up or other cleaning related issues.

Notice in the pictures the primers do not really show any issues...but with circles and heavy bolt(but like I mentioned slightly heavy on the close) it has me confused...

 

[MagnumManiac]

It's quite possible that you have a soft batch of brass, it does happen, even with high end manufacturers.

Looking at your case pics, they all look similar, which is why I suggested you may have a soft lot of brass, if it was only at the high end then I would think it was the load only.

I have a question: How far from/into the lands are you loading?

Loading into the lands can also raise pressures dangerously from starting loads.

gun)

 

[AtownBcat]

I agree that in the photos the ejector mark looks the same, but with the naked eye, the warmer loads are more evident. You have to look for the mark on the lighter loads.

I'm not sure that the brass is soft though because I ran them all over a manderal(sp) die and still had to lube the bullets a little to get them to seat without cutting a ring where the stem made contact. I'm using a Wilson seater. Maybe the brass is to hard?

I'm jumping .005

 

[yawn]

Quickload suggests your 36gr H4350 load would be ruining about 43500 psi.,your brass seems to think otherwise though. I think Id try some different brass first maybe some one could donate a few pieces that are proven?, It may be a slow barrel but thats getting a bit ridiculous.

 

[Mikecr]

I doubt it's a brass problem, if an issue at all(might not be).
There are still basic measurements to make that can't be generalized or assumed.

 

[AtownBcat]

Mike, I thought I made the measurements you suggested but missed the one for the webb. Maybe you could explain this and anything else i need to measure. thanks