Possible Pressure Signs with factory Loaded Ammo?

[mhamlin]

looking for some advice on pressure signs. I have a new Remington 700 Long-Range Bolt-Action in 300 RUM.

I shot some factory Remington Premier A-Frame 180 grain Power Level III ammo and
got a slight resistance when lifting the bolt and the brass on the case head flowed into the ejector port and left a perfect circle that you can catch a fingernail on...see picture...View attachment Factory Load.pdf)

I was surprised by what I believe to be high pressure signs using the factory ammo, so I reloaded some once-fired brass that I purchased online and shot 10 rounds to see where I started getting pressure signs, starting with 79 grains of H1000, progressing up through 88 grains, pushing a Berger 215 hybrid at 3.60 COAL. All of the primers seemed somewhat flattened beginning at 79 grains and did not change much up to 88 grains, except I starting getting a cratered ridge around the impression made by the firing pin at 86 grains. I never felt any resistance when lifting the bolt and there were no smiley faces, or new marks from the bolt face.
I've included pictures of the fired reloads. the case on the left was 79 grains, middle was 85 grains and the right case was 88 grains. (marks on the case head were from previous loading

Is marks on the case head and a stiff bolt lift the key to finding max pressure? I read an earlier post that stated that looking at primers was not a good indicator when dealing with a factory quality bolt and action.

Any thoughts?View attachment 300 RUM Fired Cases 2.pdfView attachment H1000 Fired Cases.pdf

 

[Bullet bumper]

First off you need to scrub out the chamber very well with solvent to get out any transport grease or gunk.
Then swap to Remington primers as they are stronger material .
The mark on the brass is not a real problem . The case heads may be a bit soft .
Make sure the cases are clean also before chambering.
Put a small drop of gun oil on the rear cocking cam and a small amount of moly grease on the bolt lug mating surface .

 

[bruce_ventura]

Since this factory ammunition with new cases, you can check for excess pressure by measuring the base diameter using a good micrometer. Measure several cases at a few positions around the circumference before and after firing. If the base diameter increases due to firing, there is excess pressure.

 

[Bill Johnson]

Estimating pressure from fired cases/primers is a tricky business, but I have found reading the primers to be fairly indicative of high pressure. What's missing in your analysis is the condition of the primers on the first factory rounds. Note that on all the other primers that, while at the highest powder loading you got what appears to be some extrusion into the firing pin hole, that none of the fired primers flattened to the point that they filled the bevel on the primer pocket.

This is an example of that:



Measuring case head expansion is tricky also. First promulgated by Ken Waters, if I recall correctly, you must use a factory round and measure the case head prior to firing and then after, using a micrometer capable of measuring to .0001".

Typical amounts of expansion with lower pressure rounds, like the .30-30 Winchester, usually yield maximum pressures at .0003"-.0004" expansion. Modern cartridges, like the .223 Remington, will show maximum pressure at .0004"-.0005", while .308 Winchester, .270 Winchester, etc., typically yield .0005"-.0006" expansion at max pressure. Magnums, like the .300 Winchester Magnum, show maximums at .0006"-.0007" expansion, and should be measured on the belt. A reading of .001 is generally considered as over max pressure.

All this must be taken into account, including the stiff bolt handle lift, to get a true indication of higher-then-normal pressures.

 

[Canadian Bushman]

Check headspace before and after firing. Excessive headspace, as well as oil residue in the chamber as bullet bumper stated, can blurr what one would perceive as high pressure signs on a case or primer.

Once you are sure you dont have excessive headspace, then your case head expansion, ejector marks, and bolt lift will be indicative of high pressure.

Reading primers is usually a secondary sign of pressure for me, because what they tell you can depend on more variables then the signs of the case itself.

Unless its just blatantly obvious like the picture poster by bill johnson. Even with excessive headspace i would feel safe saying that load was over an acceptable max. If shooting over a chrono this condition will be easy to confirm, it typically goes hand in hand with a large jump in MV.

 

[climb-101]

I was fighting a similer issue on my 338 lapua. shooting it over a chronograph I figured out my velocity was way faster than what was published on the manuals. as of right now I'm loading them to around 78 grains and getting speeds up closer to what I should be getting loading to around 84 grains

 

[mhamlin]

Bb, I had a local smith install a muzzle brake and he said the chamber was too rough, so he polished it while he had the barrel off. I cleaned the barrel well, before firing it the first time and between the first ten shots, but I didn't make any attempt to clean the chamber, so there may have been some oil present. The factory ammo was Remington and it had Remington primers; the primers looked similar to the Federals with a definite volcano rim ( I'll post a picture of one). I need to clarify one of my first statements: The first factory round fired had some bolt lift resistance, the second had resistance but it was less, and so on...my smith oiled the cocking cam and greased the lugs in my presence and made the point to keep those areas lubed.View attachment Primer Eval 300 RUM.pdf

View attachment Primer Eval 300 RUM. 2.pdf

View attachment Primer 1.pdf

Bill, I will post a pic of a fired factory primer that is typical, unfortunately I had already sized and de-primed the cases. the pic is of a federal light starting load and a Rem factory round.

Bruce & Bill, I don't have a micrometer, yet...but I checked an unfired round at the case head with my calipers and it measured .545. A fired factory round case head measured .550, after full-length resizing. Although not accurate that seems outrageously excessive, based on what you've posted...?

CB, I'll check headspace to see what that tells me. Wouldn't the smith need to check headspacing when he remounted the barrel?

Mike

 

[mhamlin]

I was fighting a similer issue on my 338 lapua. shooting it over a chronograph I figured out my velocity was way faster than what was published on the manuals. as of right now I'm loading them to around 78 grains and getting speeds up closer to what I should be getting loading to around 84 grains

Climb, I currently don't own a chrono, but I have access to one, so I'll be sure to use it next time I can go shoot.

Mike

 

[mhamlin]

I found some factory cases that I hadn't re-sized yet. The attached pic shows a reload w/79 grains H1000 (left), one factory Rem load (center), and one w/86 grains H1000 (right).

View attachment 300 RUM Fired Cases.pdf

 

[Canadian Bushman]

Bb, I had a local smith install a muzzle brake and he said the chamber was too rough, so he polished it while he had the barrel off. I cleaned the barrel well, before firing it the first time and between the first ten shots, but I didn't make any attempt to clean the chamber, so there may have been some oil present. The factory ammo was Remington and it had Remington primers; the primers looked similar to the Federals with a definite volcano rim ( I'll post a picture of one). I need to clarify one of my first statements: The first factory round fired had some bolt lift resistance, the second had resistance but it was less, and so on...my smith oiled the cocking cam and greased the lugs in my presence and made the point to keep those areas lubed.View attachment 47402

View attachment 47403

View attachment 47404

Bill, I will post a pic of a fired factory primer that is typical, unfortunately I had already sized and de-primed the cases. the pic is of a federal light starting load and a Rem factory round.

Bruce & Bill, I don't have a micrometer, yet...but I checked an unfired round at the case head with my calipers and it measured .545. A fired factory round case head measured .550, after full-length resizing. Although not accurate that seems outrageously excessive, based on what you've posted...?

CB, I'll check headspace to see what that tells me. Wouldn't the smith need to check headspacing when he remounted the barrel?

Mike

Oil in a chamber prevents the case from grabbing the chamber walls and thrust the case back against the bolt much harder than a dry chamber would allow. This will put lots of force on the head showing all the signs of high pressure.

When you mic a case head to identify pressure signs you do it right in front of the extractor groove. I use blade mics as to pinpoint the area im measuring, and i also measure the extractor groove as this part of the case is unsupported by the chamber and is a rough representation of the force the case head is exerting against the bolt. Typically growth of >.0005" is indicative of high pressure, ( or excessive headspace). Usually this is confirms with loose pockets after only a few firings. Each case should be measured multiple times around the circumference before and after its fired. If you are not measuring the same case the process is a wash.

I think the measurements you took were too far forward.

Headspace is a fickle beast. There is a spec for the cartridge and a spec for the chamber. If the smith cuts the chamber to the high, and the brass is sized to the low, everything is in spec, and you still have excessive headspace. This is a common condition for factory rifles and is not major problem if identified. Just an inconvenience.
If this condition is present its best to fireform the cases to the chamber with a ff load or even a starting load in most cases before a full pressure load is run. This will greatly preserve your brass.

http://www.saami.org/pubresources/cc_drawings/Rifle/300 Remington Ultra Magnum.pdf

 

[mhamlin]

Thanks CB for the link, the visual is very helpful. Oil in the chamber does make sense...after re-evaluating the fired factory cases, I found 4 with definite full moon ejector marks and a couple more with light smiley faces and then some with no marks whatsoever. So, is it plausible that the oil was slowly "dissipating" with every shot until it was dry enough for the case to grab the chamber? Each of the primers still had the small volcano rim, so I suppose it would be a good idea to send the bolt in and have the firing pin bushed?

Thanks for all of the great info!

Mike

 

[Canadian Bushman]

Thanks CB for the link, the visual is very helpful. Oil in the chamber does make sense...after re-evaluating the fired factory cases, I found 4 with definite full moon ejector marks and a couple more with light smiley faces and then some with no marks whatsoever. So, is it plausible that the oil was slowly "dissipating" with every shot until it was dry enough for the case to grab the chamber? Each of the primers still had the small volcano rim, so I suppose it would be a good idea to send the bolt in and have the firing pin bushed?

Thanks for all of the great info!

Mike

I have a rem 700 that use to crater primers much worse than yours. I let it go until i rebarreled because i didnt wanna mess with my chamber or headspace, and i also wanted to get the action trued while i was at it.

You may get more consistent ignition and lower your risk of a pierced primer, but i really dont think it will make much difference with your rifle if you decide to wait. If not I believe gre-tan bushes boltfaces with a quick turn around, or you could have a local smith do it.

 

[Bill Johnson]

Spot-on advice from CB. I had typed up a very similar reply when my power went off.

 

[Bullet bumper]

I said in post two to start by cleaning the chamber you never thanked me ignoramus.