High pressure signs in AR wssm

L

LukeClark

New member
I've been reading on reloads for the 25wssm on another forum dedicated to the wssm cartridges. They talk about cratered primers not being a good indicator of high pressure on these cartridges, but a sticky bolt lift as more accurate. They mainly shoot bolt guns over there.
I have an AR in 25wssm and was wondering what pressure signs I should be looking for, since obviously there's no bolt to lift?
 
If a cartridge expands in the chamber enough to cause sticky bolt lift, then would not that expansion cause an AR to fail to eject? Or would something else go wrong first?

Don't know, just speculating.............
 
Pressure signs on the WSSM's are very different in most cases than standard cartridges. On the AR however, the ejector mark is still a good sign of high pressure. Case-head expansion is another sign that is common to the WSSM or standard cartridges.

Early on, when load data was nonexistent for the WSSM's, I shot loads over the chronograph that were scary fast for the bullet weight. The primers were not flattened or cratered, but there were marks from the ejector and case-head expansion on some as well.
 
Case head expansion and ejector marks as well as the bolt head marking the case, are the fundamental signs to look for Remember to that if your useing Winchester Brass it may well be thicker than standard brass. The case expansion in the AR chamber is what causes the deep extractor marks, it is harder for the gas pressure to extract the case from the chamber due to a tighter fit.More friction, look at the case head as well if the lettering has been blurred that is also a sign. Remember that the case will expand under chamber pressure in every direction, slightly more so towards the chamber, so faster than normal case lengthening would also be a sign.
 
Thanks guys!
Can you tell me specifically what to look for?
Sorry I'm very new to reloading. I looked the fired cases over, and some of them looked "banged up" but all still had soot down the case, which I think means there's not enough pressure to seal the case to chamber yet, and I'm still 2 grains below max.
I'm afraid to work up any higher until I know what to look for.
Ejector marks, would that be a dent in the case head from the ejector or just a shiny spot?
How do you check for case head expansion?
I tried to search these terms but got more posts that just mention them and don't explain anything, than I can look through.
 
An ejector mark from high pressure would look like a shiny spot or scuff where the brand stamp is on your brass. Case head expansion would appear as a thin "ring" around the base of the case.

Don't think that dirty cases are a sign of low pressure. Here is an example of what my cases look like and they are very warm at almost 3600fps...
CWS002.jpg

On the left is a typical spent case before I installed Tubb's CWS system. The center is typical of how my brass looks with the lock time increased due to the added bolt mass. Noticably less mess from the same load...

What load is it you are concerned about? Have you chrono'ed?
 
Thanks knock'emdown. I just shot my first ever reloads last week. Started at 37 grains varget and worked up by .5 to 40 under a 100 grain Nosler Partition. Groups were just tightening up at 40 and the reloading info I got said max was 41 or 42 depending on who you asked.
I unfortunately don't have a chrono, and after getting a full build dtech, my wife would outright strangle me for suggesting it.
I'd like to try the higher loads, but wanted to make absolutely sure I knew what I was looking for before I proceeded.
I think I found some pic's on the pressure signs, and will look for more.
Just darn scared of messing up this beautiful new gun.
This is my first AR, and these are my first reloads, so I'm probably being a little overly cautious...
 
ok, cratered primers are just as likely to be caused by a shade too big of a hole for the firing pin in the bolt face as they are by anything else. look for flattened primers, but flattened primers alone are no cause for much concern, flattened primers accompanied by an ejector pin mark need to raise the red flag. your sure signs of overpressure in auto's is casehead expansion, or loose primer pockets, also dents in the rim where the bolt is trying to eject the case and it hangs up, (this is heavy bolt lift/sticky extraction in a bolt gun). but you need to measure the caseheads when working up a load, if you get more than .002" at the web, search out the cause. what load ya shooting, I shoot 47.5 gr of IMR 4350 behind a 110 gr accubond in my dtech smithed AR, over max load but safe in my rifle.
another thing you can look for is a big rise in velocity with a small increase of powder, this is also telling you your runnin them hot.
RR
 
It is hard to discribe what to look for case head expansion will look like a bulged ring just above the base maybe 1/8th inch. somtimes that bulge/ ring is hardley noticable with out measureing with calipers, compair new unfired to once fired safe load and the suspected case. there will be a minor expansion between the new and once fired safe case, if your suspected case is very much over that, then back down. But if you are still 2 grains below max of a published load, you should be OK infact you should be right in the sweet spot, at least from what I have seen the best, most accurate loads are usually well below max. What is the load you are concerned about? Where did you get it?
 
set your spent cases on a VERY flat surface, standing up.

touch the sides of them and see if they "wobble" the ejector may "bend" the rim a bit and make the rim 'unflat' (technical term there.... /ubbthreads/images/graemlins/smile.gif )

this could be a sign of high pressure, or an oversized gas port.
 
My ending load on my first run of development was 40 grains Varget over a 100 Partition. I got my load data off of the wssm zone, and another website I can't remember the name of right now. Their top load was 42 or 41 grains respectively, i think, I'm just going off memory here.
The 40 grains had the best group, shooting a 2" 3 shot group at 200 meters. The cases had some dings on the case and around the rim, but I wasn't sure if that was caused from cycling from the mag and being pitched onto concrete.
I'd like to try and work up towards 42 grains Varget to see if they tighten up anymore or if I need to tweak around 40. Once I get close, I'm going to do 5 shot groups and see where I'm at.
This reloading stuff is fun, I'm afraid it's going to get me in trouble with the wife. Just wish the wind would quit blowing, so I could try some more.
I also have TSX's to work up next, and am going to get some IMR4350.
Then I was going to look into some lighter bullets...yep this is going to be expensive, but at least I won't have any problem making a Christmas list
 
The "bulge" that you will see just an 1/8" or so above the rim is not "case-head expansion" That is simply the case blowing out to fill the chamber. If the chamber were the exact size of the case, then the AR would not feed and function well. The chamber is somewhat larger than the new or resized case, and when the gun is fired, the case will expand to fill the chamber.

The "case-head" is the brass between the bottom end of the case, and the area that the powder is held. If you run a tooth-pick or some other object into the open mouth of the case and measure the depth and then compare it to the length of the case, you will find that there is an area of about .200" that is solid brass, except for the primer pocket and flash-hole. This area is the "case-head".

The case-head is the part of the brass that actually hangs out of the chamber, and is not supported by the chamber walls. In the case of higher than normal pressures, this area of the case will expand, but you will not be able to detect it by "looking" at it. You will have to measure the case-head before and after the shot with a micrometer.

Case head expansion is why primer pockets get loose. As the brass expands, the primer pocket expands with it, and eventually, the primer pocket will no longer hold the primer.

Edited to add this pictue:
IMG_0747sdd_edited-1.jpg

Sorry for the poor quality photo, but I wanted to quickly get a photo up to show what I was talking about. You should be able to see the primer pocket and flash-hole. That area of thick brass is the case-head.
 
Quote:
Ejector marks, would that be a dent in the case head from the ejector or just a shiny spot?




Not sure on the AR's, but this is an ejector hickey in a bolt gun.

100_2339.jpg
 
Thanks all, I've got a lot more confidence now in what to look for.
I really appreciate your help, I would've never started reloading if it wasn't for this site.
 
Quote:
The "bulge" that you will see just an 1/8" or so above the rim is not "case-head expansion" That is simply the case blowing out to fill the chamber. If the chamber were the exact size of the case, then the AR would not feed and function well. The chamber is somewhat larger than the new or resized case, and when the gun is fired, the case will expand to fill the chamber.

The "case-head" is the brass between the bottom end of the case, and the area that the powder is held. If you run a tooth-pick or some other object into the open mouth of the case and measure the depth and then compare it to the length of the case, you will find that there is an area of about .200" that is solid brass, except for the primer pocket and flash-hole. This area is the "case-head".

The case-head is the part of the brass that actually hangs out of the chamber, and is not supported by the chamber walls. In the case of higher than normal pressures, this area of the case will expand, but you will not be able to detect it by "looking" at it. You will have to measure the case-head before and after the shot with a micrometer.

Case head expansion is why primer pockets get loose. As the brass expands, the primer pocket expands with it, and eventually, the primer pocket will no longer hold the primer.

Edited to add this pictue:
IMG_0747sdd_edited-1.jpg

Sorry for the poor quality photo, but I wanted to quickly get a photo up to show what I was talking about. You should be able to see the primer pocket and flash-hole. That area of thick brass is the case-head.



Very good thread and pics.
Have you got any pics of a cut-away case with the case beginning to separate or with the ring?
 
Lukeclark, I shoot ars so I'm well aware of the problems us semi guys face. We cannot use the feel of the bolt. I've started using case head expansion as an indicator. To get a baseline I shoot some factory stuff that matches the brass I'm using for my reloads. You must use new brass of the same brand. Don't worry about bullet weight. What you want to do is get a base line on the brass expansion that occurs just ahead of the groove at the base. I measure the case before and after shooting. You MUST use a blade micrometer that measures to one ten thousands of an inch. I tried to use a standard mic and it wasn't consitent. I could take the same batch of brass and get different readings the second time around. I know why this was happening, but I don't feel like trying to explaining that here and now. Just take my word, you must use a blade mic. On my 308 I got an average expansion of .0007 using factory ammo. This doesn't mean this is my max, but I'm not going over this amount. While working up the load I saw the expansion slowly grow so I feel it is a good indicator. You measure just above the groove where the extractor grabs the brass. If you don't want to invest in a $200 blade mic, Use the manuals and don't go over max. Stop if you see a dimple on the case head that matches the ejector port on the bolt head. Once you find a good accurate load, take five pieces of new brass. Reload and reshoot these five pieces of brass five times. If you don't blow the primer pockets out by then, you load is ok. Just a rule of thumb I use. As Dtech said "Case head expansion is why primer pockets get loose. As the brass expands, the primer pocket expands with it, and eventually, the primer pocket will no longer hold the primer." I would like to add that sometimes gas leaks around the primer pocket when they don't fit tight enough. If you see this while reloading the same case over and over five times. Don't use this load. Something you might change is changing the seating depth of the bullet. I always start about .020 off the lands(magazine permitting). From that point I would seat the bullet in .10 further say with five or six different levels of depths. Take the one that shoots the best but is deeper into the case and test that load again for pressure. Having the bullet too close to the lands can cause excessive pressure.

When you start reloading brass more than three times, you need to look for case seperation, but that is a discussion for later threads. You can goto Hornandy and they discuss case seperation, but you will have to dig thru a lot of good information to find it.
 
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