Pressure changes with primer switch?

[JLM]

Generally how much of a difference can/will you see in pressure simply from switching a primer?

Why am I asking this?

I had a load in .308 LC Match brass that exhibited no visable pressure signs. Then I switched from BR2's to FED210's.

Massive sticky bolt and an incipient head seperation line. Its not very obvious but its definitely there.

Measured just above the extractor groove the fired case mics out .003 larger than a loaded M118.

Argh........hehehe....

 

[desertHK]

Re: Pressure changes with primer switch?

Here is a link to your question.

http://www.6mmbr.com/PrimerPix.html

In general, it may not be a bad idea to back off slightly when switching to a different primer, especially if you are already at the ceiling end of the powder curve. Stay safe.

 

[JLM]

Re: Pressure changes with primer switch?

Thanks for that!

Quite a diff between a BR2 and a 210. Wonder how that translates into pressures thou. My guess would be 'higher' with the 210.

 

[Grumulkin]

Re: Pressure changes with primer switch?

In cases the size of a 308 Win. & larger, you won't know any difference at all unless you are running on the ragged edge of high. Compared to the amount of powder, the amount of explosive in the primer is very small and contributes very little to the overall explosion in the chamber. Remington primers seem a little different than CCI, Winchester and Federal primers. If you've worked up loads with those, then a reduction in powder charge will probably be needed if you switch to one of the others.

When you get to smaller cases, you will see a difference. I worked up some 44 Mag. loads with CCI 250 (large rifle magnum) primers and had to reduce the H110/Win. 296 powder charge by 1 or 2 grains.

 

[Greg Langelius *]

Re: Pressure changes with primer switch?

Ignition characteristics can alter pressure curves. Basic rule, when changing components, step down and redevelop/confirm loads.

 

[Ed Nauseam]

Re: Pressure changes with primer switch?

Some selected reading FWIW

http://yarchive.net/gun/ammo/primer_variance.html

http://www.jamescalhoon.com/primers_and_pressure.php

 

[michaeltx]

Re: Pressure changes with primer switch?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DesertHK</div><div class="ubbcode-body">Here is a link to your question.

http://www.6mmbr.com/PrimerPix.html

In general, it may not be a bad idea to back off slightly when switching to a different primer, especially if you are already at the ceiling end of the powder curve. Stay safe. </div></div>

I'd never seen that page before. That's very interesting. I picked up a brick of rem sr br the other day and was about to start using them in 223, switching from cci. I think I'll back off about 5 grains LOL

 

[eitmsmf]

Re: Pressure changes with primer switch?

Due to the primer "shortage" I am trying rem 7 1/2's in a 6BR. I can tell you my load is a full grain lower with these primers versus CCI 450's.

 

[USMCj]

Re: Pressure changes with primer switch?

Rem 7 1\2's are really good primers! Thats all I use in small rifle!

 

[JLM]

Re: Pressure changes with primer switch?

There seems to be a lot of 'schools of thought on this'.

For instance on Chuck Hawks website:

"Changing brands but using the same type of primer will also usually result in pressure changes, but ordinarily these will be less drastic. In the A-Square tests the pressure spread between the CCI 200 and the hottest standard primer (the WLR) was 9600 psi. The spread between the mildest magnum primer (the Rem. 9 1/2M) and the hottest magnum primer (WLRM) was 8300 psi. These are significant pressure variations that cannot safely be disregarded."

 

[shadow4]

Re: Pressure changes with primer switch?

JLM,
Not saying that you aren't getting more pressure with the FED-210's but you stated that you are also getting head separation? Head separation is usually due to bumping your shoulder back too far on your brass. This will eventually happen no matter how much pressure you are running.

Also you said you took measurements of a loaded M118 round and then compared it with your own fired brass. All factory ammunition is loaded with virgin brass (to include M118) and the brass dimensions are supposed to be smaller than a fired round so they can fit into any chamber. So the loaded M118 is supposed to have a smaller case head than your fired brass, because your LC Match is now fire formed to your chamber. Check to see how far you are bumping back the shoulder with your dies and you may have found part of your answer.

This being said, I too have switched back and forth with the 210's and the BR-2's and have seen about a 10 fps difference on my chrony (rounds shot though on same day to get accurate reading). The 210's are a "little" hotter. I do not run hot loads and I saw no difference in pressure on my brass between the two. YMMV

 

[Victor N TN]

Re: Pressure changes with primer switch?

And don't forget when Blount took over Federal Primer Division a few years ago they started using a different alloy on the cups. Also lighter weight (thinner) material.