Minimum Headspace - Pressure

[DoubleGobble00]

Can minimum headspace cause early pressure signs?

I built a Remage 300 Rum and headspace it myself. I kept the headspace tight to try to minimize brass wear. After the gun was completed, I get ejector marks on factory ammo and reloads but don’t have a sticky bolt or at velocities that should have pressure. My main pressure sign as I increase charge is primer cratering and ejector marks. From bottom to top load, I have ejector marks and some cratering. The cratering got bad close to max.

I’m trying to decide if I should redo my headspace or leave it along.

Thanks,

DoubleG

 

[243winxb]

Minimum chamber headspace may raise pressure a tiny amount. But not a reason to increase the headspace.

Running at 65,000 PSI brass is going to flow.

ejector marks on factory ammo

Can be seen on some factory fired brass. Normal for some. How much its raised above the case head becomes important.

If pockets become loose with 5 firings or less, pressure is to high.

don’t have a sticky bolt or at velocities that should have pressure.

I would leave it alone.

Photo shows light flow on the right, increasing moving to left. Left pocket enlarged, primer fell out.



Photos would help.

 

[dkhunt14]

If the cases are short on headspace, it can cause this. Are the cases new? Matt

 

[DoubleGobble00]

Thanks for info. The factory ammo (new brass) will have some with ejector mark and most primer flat. My reloads with new brass had ejector marks and my 1x fired (neck sized only) brass all had ejector marks. New brass on right and 1x fired on left.



My hottest load which I’m backing down from as max had bad cratering. See below:

 

[jds holler]

Gee, I'll bet that's a lot of fun to shoot off the bags. jd

 

[powderbrake]

I suggest you need the firing pin bushed to eliminate the large space between the pin and the hole, as it is doing it on factory loads. contact Gre Tan rifles . https://www.gretanrifles.com/

 

[243winxb]

My hottest load which I’m backing down from as max had bad cratering. See below:

less is better.


More primer flow then i would want? More opinions are needed.

 

[DoubleGobble00]

The extreme primer flow was the last charge I shot while working up to max loads. They all did not have primer flow.

I was shooting 8133 working from 85 to 91. The picture was the 91 grain charge.

 

[yotehater]

Just thinking out loud here to help. You have reduced the size of the combustion chamber so less fuel would be needed. I'm thinking if you are below the go gauge minimum SAAMI spec you should see higher pressure on even factory ammunition. Most factory ammo is so undersized, like new brass, it will easily chamber in minimum chambers. Setting headspace on brass reduces brass stretch at the cost of chamber volume increasing pressure with a volume of powder that is fine in other rifles. I'd recommend chronographing to see what the velocity is doing. You might find you need to slow it down some. You got my respect shooting that beast, good luck.

 

[Whit holman]

The last picture looks like you have case starting to separate I would cut it In half and check

 

[DoubleGobble00]

Below is the charge with velocity at 225 yards shooting 230 grain Berger’s. I’m going to check my go gauge and see how tight it is...

 

[243winxb]

I was shooting 8133 working from 85 to 91. 230 grain Berger’s. Nosler brass. The picture was the 91 grain charge

Where are you getting load data from , for this combination ? I cant find any. Just this..

 

[Texas10]

The last picture tells the tale pretty well. Ejector marks over the word "Ultra" and extractor mark over the "R" in "Nosler". Heavily cratered primer that's about to blank, embossing in case head is losing some of its relief. All point to extreme pressures.

It seems to me that increasing chamber capacity by moving the headspace out a little will relieve some of the pressure issues.

I have a Savage model 12Fv in 223 that was blanking primers with just about any factory load. Sent it back to the factory and as far as I could tell, they did nothing to improve it. I found and fixed the excessive clearance between the bolt head firing pin hole and the firing pin and this helped considerably with the blanking.

It was a year later when I decided to try my no-go gage in that chamber and the bolt closed on it without effort that I discovered the factory and installed it incorrectly or possibly reset the barrel beyond specs during rework/repair in an effort to cure the blanking issue.

I have always set the headspace on a new barrel at the minimum assuming this would help with brass life. Of course as I have learned since then, that assumption was wrong and it's the die setup that improves brass life. Looking back now, those barrels set to minimums showed early signs of pressure, just like you're experiencing.

 

[yotehater]

The Berger manual has the 300 RUM. Top velocity with their 230's is 2790 fps with 88.2 grains Retumbo in a 26" tube. You are getting 300 fps more than their highest velocity..

 

[LCazador]

If the cases are short on headspace, it can cause this. Are the cases new? Matt

What Matt says. Your cases are short and getting thrown back against the bolt face!

 

[DoubleGobble00]

So I just got done checking the headspace. The headspace is fine. So I made sure my bolt/lugs was greased well and chambered a piece of new brass, 1x fired brass, then 2x fired brass. The new brass chambered perfect, the 1x was tight and took some pressure, the 2x would not chamber (too tight). Basically, my brass is growing too much to just neck size. I’m going to be forced to FL size.

I think the 1x was just too tight and pressure showed on all since they were so tight. I got ejector swipe just chambering them...

Looks like I need a body die then start over.

I also checked my factory Nosler ammo. I had ejector marks on some but not all of them. I guess the factory load is pretty hot also.

My barrel is 29” so it gets me some extra velocity but the loads were pretty hot overall. I think I’m going to try H1000 or Retumbo. I’d love to try N570 but it’s a ghost powder...

DoubleG

 

[Doug Beach]

The amount of increased capacity between a go and no go gauge is utterly negligible.

 

[243winxb]

my brass is growing too much to just neck size. I’m going to be forced to FL size.

At 65,000 ++ PSI , i am sure its growing and flowing. Brass life will be short.

 

[Texas10]

So I just got done checking the headspace. The headspace is fine. So I made sure my bolt/lugs was greased well and chambered a piece of new brass, 1x fired brass, then 2x fired brass. The new brass chambered perfect, the 1x was tight and took some pressure, the 2x would not chamber (too tight). Basically, my brass is growing too much to just neck size. I’m going to be forced to FL size.

I think the 1x was just too tight and pressure showed on all since they were so tight. I got ejector swipe just chambering them...

Looks like I need a body die then start over.

I also checked my factory Nosler ammo. I had ejector marks on some but not all of them. I guess the factory load is pretty hot also.

My barrel is 29” so it gets me some extra velocity but the loads were pretty hot overall. I think I’m going to try H1000 or Retumbo. I’d love to try N570 but it’s a ghost powder...

DoubleG

"Ejector swipe just chambering them" suggests you've got crud in the ejector hole keeping the ejector from retracting fully, or the spring is too tight giving a false ejector swipe indication.

Just for review and for those not familiar with the term "ejector swipe", this occurs when a hot load causes brass to extrude into the ejector hole in the bolt head. Then when the bolt is rotated upon opening against the case that is stuck in the chamber after firing, the bolt shears off a little of the brass that was extruded into the ejector hole, leaving an area of bright colored brass that looks smeared but still has the outline of the ejector hole.

An ejector that will not retract fully and remains slightly proud of the bolt face will make a similar mark on a tight fitting case, but is not to be confused with true ejector swipe.

So there might be two actions to take. First, disassemble and clean out the ejector then check for fully flush or better movement. Second would be to reduce your loads appropriately.

How does a new primer fit on your 3x fired brass? Is it quite a bit looser than new?