Interesting pressure signs

P

Pantallica90

Member
Rating - 100%
26   0   0
Location
Westbank BC
Fairly new to reloading and have been reloading for my 260 with good success. Nice tight groups aside, i have had some pressure signs come up finally, not that it's a good thing, but why is the question. I've tuned my load to fit in the tikka mag so max OAL is 2.825 with lapua brass, 43.4gr h4350 topped off with 130gr Berger hybrids. I was shooting new brass and getting no signs. Now it seems my once fired with a little shoulder bump is giving me extractor marks. Nothing has changed load with except for the brass being fired and reSized.

Would this brass being not formed back to saami specs cause this? Any ideas?

Thanks
 
First thing I would normally check is the case length. If it's too long, it may be jamming into the end of the neck portion of the chamber, in effect, crimping the case against the bullet. This will increase pressure. Next thing I would verify is your seating length. If you're jammed into the rifling, this will cause pressure increases. However, in a Tikka loaded to mag length, I highly doubt this is the case.

Often times when I've talked with new-ish reloaders and ask what they have for a trimmer, some of the responses I get are, "yeah, I trim. I use those inside and outside debur things...." Please read your reloading manuals thoroughly.

Rooster
 
I believe your loads described above are considered above standard loads on the Hodgdon site and could be considered on the hot side (42.7 considered max with standard OAL using 130s.) Sure, we always seem to try to find that upper node but risk issues as reduced case life, barrel erosion, heat etc.

Check carefully when extracting fire forming brass. Faint signs of extractor or ejector pin swipe are telling you are in the hot zone. You cant always rely on the look of the primer for pressure signs.

Resizing as suggested to further bump back the brass should eliminate marks upon re-chambering. However, when you run hot loads you run the risk of this happening as brass flow continues and the cases harden more each time they are worked. Brass spring back under hot loads is reduced and you will need to anneal more. Also, check your brass with a paperclip to guage the extent of case head separation over successive firings. My advice would be look for the next node lower (around 41-42.0 or so).

Also consider doing this test to ensure bullet is freely moving. Place a bullet into a fired case, it should drop in or in some tighter chambers have minimal resistance. if you feel any resistance or the bullet stops you have an issue. You may need to neck turn your brass, trim your brass, or turn into the shoulder to eliminate what is known as a "donut" or ring of brass build up at the neck shoulder junction. Something to keep in mind. I have found current production Lapua with thick neck dimensions, and they can cause pressure spikes as well in a tight chamber.

Also remember setting a bullet back into the case so that you can run a magazine reduces case capacity and this can have the same affect as jamming a bullet 20 thou depending on your load. Higher pressures can and do result.
My 2c.
 
Last edited:
Pantallica90 said:
Fairly new to reloading and have been reloading for my 260 with good success. Nice tight groups aside, i have had some pressure signs come up finally, not that it's a good thing, but why is the question. I've tuned my load to fit in the tikka mag so max OAL is 2.825 with lapua brass, 43.4gr h4350 topped off with 130gr Berger hybrids. I was shooting new brass and getting no signs. Now it seems my once fired with a little shoulder bump is giving me extractor marks. Nothing has changed load with except for the brass being fired and reSized.

Would this brass being not formed back to saami specs cause this? Any ideas?
Click to expand...

You are right close to the Nosler Maximum Load, and a bit over the Hodgdon recommended max load. So not unexpected to see some signs of pressure.

When you say you are seeing "extractor marks" do you mean marks on the back of the head caused by the ejector pin recess? Like in the photo below? Or something else?

extruded.jpg


Those marks in the photo are excessive to me. However, if I see just a very faint image of the ejector pin recess, with no extrusion of the brass or smearing of it, I don't get too excited. It would not be unusual to see a very slight imprint with the load you are running.

On the issue of new brass vs once fired. I don't think your once fired is an issue causing any more pressure. There will be more headspace on the new brass and when the firing pin strikes it may bang the case ahead and when the pressure builds up, the case can grab the chamber wall and not come back as hard on the bolt face. If you do a minimum bump on a once fired it will start with very little headspace and will be full on the bolt face as the pressure builds up. More likely to see the imprint in this case, but it does not indicate there is more pressure. Minimum bump is the way to go. Not an issue unless you are having a hard time closing the bolt.
 
I would concur the pressure signs on those brass pictures are excessive and even destructive on your brass. Way over the "hot" concept. Read up on pressure signs in the net. You will find a plethora of knowledge out there. I remember one article which assigned pressures to seeing even beginnings of ejector swipes. It said to me rather quickly...why am I here. I see no real benefit to running hot. In the paper punching world a stable reliable load will win over a great hot load with the occasional flyer. Even our Fopen crew toyed with the upper node in the 284 and quickly ramped back to a lower node which provided a stable and reliable load without fliers. Running hot means you are on the edge and any deviations could result in fliers and they did.

For hunting, you may want the extra oomph and you are not worried about brass life. But the accumulative wear on barrel/receiver metals over time may not be worth the extra gains. My 2c again.
 
I appreciate all the insight, definitely gives me something to look into when I make up some new rounds. I do trim my brass but I never did trim the factory brass as it was under the length listed in the Berger book I have. I'm thinking that may play a part too now. Once fired was trimmed to book value and deburred and chamfered. I was getting good groups with virgin brass throughout my testing until I got past 44gr(albeit with no pressure signs again) and groups started opening up. I was trying to push some more speed from this gun to use for hunting. Originally I had shot these rounds when it was 10-15 degrees out and now it was hovering zero today.

Now my once fired brass is bumped back a few thou from fire formed to the chamber just for feeding ease, any neck turning and whatnot will require me to buy a few more tools. The ejector pin marks seemed random almost but I can see how finicky it can be with tight tolerances or any deviation for that matter. I had no sticky bolt lift and I only noticed that there were marks after I dropped a case on the ground and cleaned it off.

Once again I appreciate the insight and any other suggestions. Heading south for a few weeks but will make up some new rounds once I'm back and test again
 
Just as a reference, I run 42.3 gr. H4350 with 142 SMKs in my .260. Not hot in the least (custom rifle with tightish chamber) and have read many others running more powder. I know some manuals will tell you that you may be at or over max with 130s but there is a great possibility you aren't.

Bolt swipe is not all that uncommon but is definitely an indicator that you're close to max. I have a semi-custom .284 with squared up bolt face that has swiped the cases from the start. I have also seen the effect of a true overpressure in that rifle - brass extruded into the ejector hole that was subsequently sheared off when I rotated the bolt, resulting in a stuck ejector pin because of the brass that stuck in the hole. Very similar to the photos posted above.

Brass that is shorter than book length will not cause any issue whatsoever. Bullets seated short may increase pressure somewhat but is marginal at best. Of far bigger concern generally, is bullets seated too long (jammed hard into the rifling). I'm thinking that if you posted a photo or two of your affected cases, we may be able to make a better call for you. Only you can determine whether or not you're over pressure (at least over this forum) but ya kinda have to know what you're looking at. Help us help you :p

Rooster
 
Also do yourself a favour and measure several necks of fired brass. Then measure the neck diameter of your loaded ammunition. If your loaded stuff is .002 to .004" smaller diameter than your fired stuff, forget about turning necks. Let us know.

Rooster
 
Pantallica90 said:
Fairly new to reloading and have been reloading for my 260 with good success. Nice tight groups aside, i have had some pressure signs come up finally, not that it's a good thing, but why is the question. I've tuned my load to fit in the tikka mag so max OAL is 2.825 with lapua brass, 43.4gr h4350 topped off with 130gr Berger hybrids. I was shooting new brass and getting no signs. Now it seems my once fired with a little shoulder bump is giving me extractor marks. Nothing has changed load with except fosr the brass being fired and reSized.

Would this brass being not formed back to saami specs cause this? Any ideas?

Thanks
Click to expand...

Any time you have ejector marks on your cases it is a sign of high pressure and exceeding the elastic limits of "your" brass. Ejector marks can vary between brands of brass and case hardness in the base of the case. The ejector marks mean the brass is starting to flow into the ejector hole in the bolt face from a pressure greater than the brass can withstand.

Below is from Accurate Shooter and catshooter tested the cases with a Rockwell hardness tester to settle a "discussion" we were having about which cases were the hardest.
Note, later Catshooter tested Federal brass and it was the softest brass tested.

How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshooter.com/2014/05/how-hard-is-your-brass-5-56-and-223-rem-base-hardness-tests/

Reading Pressure Signs
http://www.massreloading.com/reading_pressure_signs.html

Case Head Extrusion
When a cartridge is fired, the breech face supports the case head. With the exception of break-action and some single shot firearms, the breech face does not totally cover the case head – there's a cut-out in the breech for the extractor. Excessive pressure can cause brass from the case head to extrude into the extractor recess in the breech, leaving a raised bump on the case head in the shape of the extractor cutout.

If this extrusion does not show up on your factory 'test' rounds, but is present on your reloads, it is a very reliable indicator of over-pressure. Keep in mind that all brass is not created equal, and some brass cases (especially Federal) are softer than others. It is not uncommon to see a trace of the extractor recess impressed into the case head of factory Federal rounds, but a prominent extrusion that will catch your thumbnail is always a sign that there is something very wrong.
 
358Rooster said:
Just as a reference, I run 42.3 gr. H4350 with 142 SMKs in my .260. Not hot in the least (custom rifle with tightish chamber) and have read many others running more powder. I know some manuals will tell you that you may be at or over max with 130s but there is a great possibility you aren't.

Bolt swipe is not all that uncommon but is definitely an indicator that you're close to max. I have a semi-custom .284 with squared up bolt face that has swiped the cases from the start. I have also seen the effect of a true overpressure in that rifle - brass extruded into the ejector hole that was subsequently sheared off when I rotated the bolt, resulting in a stuck ejector pin because of the brass that stuck in the hole. Very similar to the photos posted above.

Brass that is shorter than book length will not cause any issue whatsoever. Bullets seated short may increase pressure somewhat but is marginal at best. Of far bigger concern generally, is bullets seated too long (jammed hard into the rifling). I'm thinking that if you posted a photo or two of your affected cases, we may be able to make a better call for you. Only you can determine whether or not you're over pressure (at least over this forum) but ya kinda have to know what you're looking at. Help us help you :p
Click to expand...

Well said!
 
Pantallica90 said:
I was trying to push some more speed from this gun to use for hunting.
Click to expand...

You could try RL-17 to get a bit more velocity, but it will be much more temperature sensitive than H4350. Also you could try a shorter 130 grain bullet that you can seat further out. The Sierra Game King is about 0.2" shorter than the Berger. That will give you a touch more case capacity. However, it is not going to have the long range ballistic performance of a longer low drag style bullet. Always trade offs....
 
358Rooster said:
Ahaaa! Missed that one. Yes, there e chamber wallsmay be increased bolt thrust from lubed cases. Well done, yomomma. Bigedp51 posted a bulletin from the US Army or something similar about this in another thread recently.
Click to expand...

When a lightly lubed case is fired it can not grip the chamber walls, and this increases bolt thrust. This in itself does not increase chamber pressure, unless any excess lube, oil or water prevents the case neck from expanding causing a spike in chamber pressure.

With a "dry" case in a "dry" chamber the case grips the chamber walls and acts like a cars shock absorber and delivers "less" bolt thrust. Meaning less pressure for a shorter period of time (dwell time).

Ejector marks on the base of the case means the brass is starting to flow into the ejector. And this means you are exceeding the strength of the brass and you will also have expansion just above the extractor groove.

Below exaggerated expansion above the extractor groove at the unsupported portion of the case from high pressure.

ann1_zpsjjdxnzy7.gif


Below from Accurate Shooter reloading forum, one of the long range shooters posted the photo below. This competitive shooter said he increased the load until he got ejector marks and then backed off 1 or 2 grains of powder. What he was doing was simply testing the strength of his brass and finding his max load for that rifle and components.

index_zpsaiocbozg.jpeg


Bottom line, when you see the above marks on your brass your load is too hot.
 
You must log in or register to reply here.
Back
Top Bottom