Gas Gun Pressure and Brass Question

One step at a time.

Are gas guns harder on brass.... yup. That is the price of admission.

Deflector marks are part of that and you have to get over it. Putting a polymer on the deflector can significantly reduce the damage. Some folks use home remedies like part of a Velcro patch, others go the aftermarket route and buy a bumper that sticks on there.

As for the ejector marks, it is hard to say if the load recipe is appropriate for the gun. In historical semi-auto service rifles, the specifics of the powder and bullet weights for gas guns can mean you have to operate with the action's needs in mind, and that often implies the performance isn't equal to pressure that wouldn't affect a bolt gun. Gas gun loads can often be lower pressure than bolt guns, but not always.

That said, an ejector mark would mean the pressure event that created it was over before we even got to the issue of the gas port pressure. The bolt face finish at the ejector, the headspace, and of course the possibility that the pressure is just high all exist.

To get a general idea if the rig is happy, we first look at the ejection pattern and functional reliability.

So, if we assume the rig is designed with the right balance of weights and springs, the ejection pattern should be a clue, as well as any functional reliability issues.

Does the ejection pattern throw the brass very far forward or backward?
Does the bolt hold open on empty?
Does the rig double feed or show signs of bolt bounce? Etc.

If those answers are solid, then the headspace and bolt face should be examined and if those are good I would ask JP for load advice.
Remember, the peak pressure is usually over with when the bullet is just a couple of inches from the chamber, so an ejector mark is a pressure issue that works the same in a gas gun as it does in a bolt gun to the first order. I would ask JP what loads they recommend.

I shoot a JP LRP-07 in 6.5 CM. I had a fair amount of damage to Hornady 140gr match cases when shooting them compared to Lapua SRP brass. As mentioned a deflector pad will help with the mid case damage. There will still be some neck damage from ejecting, but it seemed better on the Lapua brass. I also used a bit lower powder charge of 40.3 gr H4350 than the 40.7 gr I use in my bolt guns.

Observations from my home built " dpms" 6.5 cm upper
I ran a box or 3 of factory Hornady loads thru rifle to get a "base line" before handloading for said upper. If my memory hasn't failed ,I remember my cases looking about like OPs fired cases.....maybe more ejector swipe than in pic. above.

Barrel manufacturer suggested an adjustable gas block when ordering barrel,however I didn't follow their recommendation.

I started the handloading process and ended up at 40.5 grains of H4350 with a 142 smk for one load,also have a superformance load that's a tad faster........no more ejector swipes.....rifle shoots less than moa

Recommend working up a load in the 40 -40.5 range of H4350, may can go more,who knows until it's tested .I've seen a lot of reports where the suggested powder range has worked well in 6.5 cm gas rifles.

The dent "problem" has been addressed above, no need to comment ,except to say I don't let it concern me one bit........load em up again and again, they'll blow back out when fired.

Not familiar with the gun, but if it has an adjustable gas block you can cut the gas completely off. Then read the pressure signs just like a bolt gun. If pressure signs go away, it's not a pressure problem.

Looks over gassed or two much dwell. The bolt is unlocking with too much chamber pressure. The swipes are in a clockwise direction, the direction the bolt rotates to unlock.

NC1426 said:

Great info for when I get into reloading for it, thanks!

Would anyone recommend I stop shooting the Hornady ELDM factory ammo?

To RegionRat's questions:

-It throws it backward, roughly 4 or 5 oclock, probably 3-5 feet away
-bolt holds open when empty
-No double feed or bolt bounce

Click to expand...

Okay, so far so good.

Check the headspace on the rig to make sure the ammo isn't real short for the chamber. Sometimes when ammo is short, there is a gap to the bolt face. The firing cycle will cause that case to expand and close that gap, but in a new rig that can sometimes mimic the signs of high pressure that are not real. But we have to be vigilant since sometimes it really is high pressure.

If the rim and base are flat after you decap the brass, and you follow up with JP, then you keep rolling. As you put cycles on the brass, keep an eye on incipient case head separation for a handful of rounds to dial in your size process and to learn when to retire the brass before they fail.

I would still ask the folks at JP what they think of that load and what else they recommend. They will know how their chamber is set up and what loads work for their rigs. Good Luck. Merry Christmas and Happy New Year!