What increases/decreases pressure more, seating depth or jamming?

[cavedweller29]

Hi everyone, I've been lurking here for years and have learned alot. Now I'm having my own problem and I could use a little guidance. Long story short, I have a Savage 12 in 6BR that I have been shooting for about a year without any problems. I normally load Berger 108's ahead of 30.4 grains of Varget and get great accuracy there. I am out of Varget and I am working up a load using RL15. I did some ladder testing and found that a load of 29.8 grains just touching the lands showed the most promise. I thought I could squeeze out some more accuracy so I was playing with seating depth today. As soon as I moved into a slight jam, I started piercing primers. I had only loaded test rounds in lengths that would jam to various degrees so I stopped shooting and went home. In every load I have tested, this gun has shot best jammed. If I backed of from jamming would I reduce pressure that way just to build it again through the bullets being seated deeper in the case? Or, does jamming build more pressure than a deeper seated bullet so I would get an overall reduction in pressure by deeper seating? I am probably not explaining this too well but I would appreciate some input. Take care.

 

[Immike]

Yes sir, jamming creates more pressure. Be careful.

 

[cavedweller29]

Thanks for the response. I understand jamming creates pressure as does seating the bullet deeper in the case. Will I reduce pressure at a greater rate by reducing the jam than I will gain by seating deeper?

 

[Witchhunter]

Back off powder weight and load longer if you want, but jamming spikes pressure! Seating shorter will show gradual increases that you are used to seeing when working up loads.

 

[Nomad47]

The QuickLoad program says jamming adds 7200 PSI to shot start pressure. You would have to seat a bullet extremely deep to get that kind of increase. I think that might answer your question.

 

[Hombre0321]

Since you say it's a Savage and in 6BR I do not believe your problem lies with your reloads. Certainly not when you are loading a relative light load of RL15 in that cartridge. I shot a monthly Club Benchrest match, at these shoots there are about 6 people shooting a Savage in 6BR. Everyone 0of them has had the problem of piercing primers in there rifles -- that would be all of them--. In each case it was not the load it was the firing pin hole being to large and the cup materal flowing into this void. The fix is cheap and very quick. Send your bolt to Gre-Tan rifles and he will bush the firing pin hole and return it to you in about a week or less and then no more problems.

This is a pretty common problem but there is a way out. No way do I believe a load of 28. anything of Reloader 15 is over pressure in a 6BR. No matter where you are seating your bullets.

Here is a link to a video that explans this pretty well.

http://www.gretanrifles.com/services/viewEntry.jsf

RS

 

[jsthntn247]

What if you are jammed .020 then a seating depth test shows you .020 off is the place to be. However this .040 difference compresses the load. Which would have more pressure?

 

[Nomad47]

The jam would have far more pressure.

 

[cavedweller29]

I appreciate all the answers. I agree that it doesn't seem as though it should be an over pressure problem but something is going on. Last week I shot loads up to 30.5 grains of RL15 with slight pressure signs at 30.2 and 30.5 but no pierced primers. Those were all loaded to just reach the lands. I settled on the 29.8 load as that seemed to be a node. I didn't have any piercing problems until I moved into the lands. I will play with seating depth more and try to find something that solves the problem. I will also check out Gre-Tan and get the bolt face bushed. Thanks again.

 

[Old Navy]

Reloader 15 is not as forgiving as Varget in my rifle. Later! Frank

 

[Alex Wheeler]

I have not found that jamming increases pressure that much. I think its a small amount or you would see a big velocity jump as soon as you started to jam. I have not seen this. Agree with others that you have another issue.

 

[snowpro440]

Do what hombre said an your problems will go away , as I have had the same problem. You could switch to 450 primers also after the bushing job .Try 4895 if you can't get varget.

 

[Mega]

I have had very little to do with Savage Rifles in general but the two that friends brought alone a year or so ago I'm sure were both Savage 12's, one in 6mmBR and the other 6.5x47 Lapua.

Both I worked up loads for here with a home range and both showed very early signs of over pressure with mild loads sitting bullets just touching the lands. I was amazed to see primer cratering and blown primers with these loads. In the end it was discovered that both rifles has excess clearance around the firing pin and once that was fixed they behaved as expected of any other rifle using the same loads. The actual firing pin was not touched.

Don't know if thats relevant here but also thinking what sort of primers as when these guys switched to something harder like CCI BR4's it also changed the results so that they could run better loads without the same problem.

 

[1shot]

Just a thought, but are you measuring COAL, or base to ogive? I have seen bullets that varied enough that when you thought you were "touching the lands" you could be .010 short or long. The ONLY time I use COAL is if I'm restricted by the magazine length. I always go to the touch measurement and work off that measurement.
I hope this helps,
Lloyd

 

[Erik Cortina]

How are you sizing your brass?
How much are you bumping the shoulders back?
Have you verified headspace?

 

[Barlow]

When I had my 6 Dasher barrel installed on my 12 FTR, my gunsmith said there was to much firing pin protrusion, so he fixed it. Might be something to check. Barlow

 

[BoydAllen]

The corners of the primer have a story to tell. How do they look? Also, you could use number drills to get an idea of the ID of the primer pin hole in your bolt head, at the face. With so many reports of problems in this area with rifles of your exact make and caliber, I would pay close attention to the advice that you have been given. Sometimes I see fellows trying to deal with mechanical problems like bedding by working with their loads. Mechanical problems need mechanical solutions. Good luck, and let us know if you solve the problem.

 

[fguffey]

I started piercing primers.

when you decided to improve accuracy by seating the bullet out further into the lands.

I am the fan of the jump start, I want my bullets to have a running start. But if I decided to seat the bullet into the lands I would recued the powder charge. Then there is the mechanical problem, if the firing pin spring is weak the pressure can push the firing pin back, when that happens the primer is not supported, when the firing pin backs out and away from the primer a hole is punched. The primer should conform to the shape of the firing pin, it is one of those .7854 things.

F. Guffey

 

[artbosco]

Neck Tension is part of the equation too.

 

[cavedweller29]

Hi all, thanks for all of the suggestions. I seated 10 rounds to jump a couple thousandths and went back to the range. Still piercing primers so I don't think its a seating depth/jamming issue. Fguffey might be on to something though. I have Lambeth bolt lift kit on the gun. After piercing a couple more primers, I cranked the adjustment screw in a couple turns to increase firing pin tension and it began piercing intermittently instead of every shot. I ended up with 5 pierced and 5 not pierced.

1shot- I am measuring base to ogive.

Eric- I FL size using a Forster die with the expander ball removed and I bump the shoulders back .003. I have not verified headspace since the problem came on suddenly in a relatively low round count gun (600 rounds +/-). I do have the gauges and will go there shortly if the problem persists.

Barlow- the firing pin protrusion is set at .050

Outdoorsman- neck tension is at .0015-.002

I will keep working on it and let you know where I end up. Thanks again