Thread: Overpressure signs on Belted Mag

Just getting into reloading

Yesterday tried a few loads that were up to 1 grain over powder manufactures recommendations.

The highest loads i tried had a slight deformation of the leading edge of the belt, assume this is due to overpressure? or is this something else?

Top 3 have the deformation, bottom 1 is normal


Wasn't sticky when extracting and nothing unusual on the heads but
The webbing area just forward of the belt had expanded slightly more than my previous loads.
68gn avg 13.00mm dia
69.5gn avg 13.01mm dia
71gn avg 13.03mm dia


7mm RM- Tikka 21" barrel, big DPT Suppressor - Running 162gn ELD-x, AR2217 up to 71gn, PPU brass

Greetings Vandros,
The front of the belt is not supported by the solid case head and can expand more than the rear. This may have contributed to the odd mark. The 7mm Rem Mag often shows quite wide variations in pressure and the best evidence of this is velocity. Your 71 grain load should develop about 2,850 fps in your 21 inch barrel so if your velocity is much more than this your pressure is higher. Your PPU cases may be the culprit if they are significantly heavier than the US cases. Also you don't mention the primer you have used. The Winchester Magnum large rifle primer can produce high pressures with AR2217 and other stick powders based on pressure tests in Handloader a few years ago. Also the ELDX is a long projectile that will seat deeper into the case which will increase pressure. Loads over book max probably should not be explored by someone just getting into handloading. Dropping back to 69 grains of AR2217 would reduce velocity by around 70 feet per second which the deer will never notice. Keep up the handloading, a thoroughly worthwhile pastime, but please take it slowly.
Regards Grandpamac.

Originally Posted by grandpamac

Greetings Vandros,
The front of the belt is not supported by the solid case head and can expand more than the rear. This may have contributed to the odd mark. The 7mm Rem Mag often shows quite wide variations in pressure and the best evidence of this is velocity. Your 71 grain load should develop about 2,850 fps in your 21 inch barrel so if your velocity is much more than this your pressure is higher. Your PPU cases may be the culprit if they are significantly heavier than the US cases. Also you don't mention the primer you have used. The Winchester Magnum large rifle primer can produce high pressures with AR2217 and other stick powders based on pressure tests in Handloader a few years ago. Also the ELDX is a long projectile that will seat deeper into the case which will increase pressure. Loads over book max probably should not be explored by someone just getting into handloading. Dropping back to 69 grains of AR2217 would reduce velocity by around 70 feet per second which the deer will never notice. Keep up the handloading, a thoroughly worthwhile pastime, but please take it slowly.
Regards Grandpamac.

Thanks all for the replys - very helpful
Yes was using Winchester Magnum large rifle primer
Definitely not going to go that high again
Didn't have the Chrono working on those ones so don't know the speed but 70 grains usually gives me around 2,830 fps

Originally Posted by Vandros

Thanks all for the replys - very helpful
Yes was using Winchester Magnum large rifle primer
Definitely not going to go that high again
Didn't have the Chrono working on those ones so don't know the speed but 70 grains usually gives me around 2,830 fps

Greetings Vandros and all,
That seems to identify the problem. Your velocity shows that you do not have a hot lot of AR2217. The test I referred to about the Winchester Large Rifle Magnum primers determined that they gave significant increases in pressure without increases in velocity which I suspect is what you have experienced. I strongly suggest that you stop using them and switch to either Federal 215 or CCI 250 primers whichever you can get. It is possible that even your 70 grain load is over pressure with the WLRM primers. An old Winchester pamphlet that I have recomends the standard Winchester Large Rifle Primer for the 7mm Remington Magnum. I used WLR primers in my 7mm SAUM and got good velocity and accuracy with 68 grains of AR2217 and 150 grain projectiles until I switched to the Federal 215 primers. Winchester primers are formulated for the hard to ignite Winchester ball powders and they are best only used with them.
Regards Grandpamac.

@Vandros You haven't mentioned any velocities? Agree with @grandpamac advise, even more so if you didn't have a chronograph.

Did you change powder batches, I was using 71grn's then changed powder batches and had to drop back to 69 grn's as the new batch had more grunt.

also did you check any unfired handloads

it could be your dies doing the damage

the case head seperation I saw with my 7RM was all ahead of the belt and would show up as thinning and shinyness
the primer and primer pocket and head stamp also took a hammering and were very visual
like mushed lettering and ejector marks

how are the case heads looking

Greetings again Vandros,
I measured the depth of the rim recess on my 6.5 Tikka which came out at a little under 3mm. The length of the total belt is around 5.4mm from your drawing so it is likely that the ridge on the belt is where the belt has expanded past the forward end of the rim recess. This leads me to wonder if the case head has also expanded ruining the case. You might like to try decapping the case without sizing the case and attempting to seat a primer with your thumb. If you can do this the case is scrap. Better to find out earlier rather than later.
GPM

Originally Posted by grandpamac

Greetings again Vandros,
I measured the depth of the rim recess on my 6.5 Tikka which came out at a little under 3mm. The length of the total belt is around 5.4mm from your drawing so it is likely that the ridge on the belt is where the belt has expanded past the forward end of the rim recess. This leads me to wonder if the case head has also expanded ruining the case. You might like to try decapping the case without sizing the case and attempting to seat a primer with your thumb. If you can do this the case is scrap. Better to find out earlier rather than later.
GPM

Thanks i already wasn't going to use those cases regardless, but i can see if the primer hole has expended, visually i didn't see anything.

Also have rechecked the Primers i'm actually using Federal 215

Thinking i need to measure the speed on some and make sure the powders still functioning the same.

@Vandros I ran a 7mm Mag for 3 yrs back in the late 90's, l brought off another guide while l was in the US, so can not offer advice on current powders/bullet choices but the universal " Yank Deer Slayer" load, that with the popularity of it back them would take truck loads of Deer every season, was a 160gn bullet going around 3100fps out of a standard 24 inch barrel ,l settled on the 160gn Speer Grand Slam & the 175gn Speer for Elk & Moose going just over 2900fps, took a lot of game both here & in the US with it , but my favorite Kiwi Hunting load was the 140gn Nosler pushed to just under 3300fp,never having any need to red line it. These loads all shot to easily tracked POI with the 160/170gn load printing around 75 higher than the 140grn zero of 64mm high at 100 meters & the 160/170gn loads basically grouping together .


A lot of 7mm"Mags" quickly burnt barrels out or worse by people trying to push them too hard & come unstuck mixing components ,that is the reason reloading manuals use to vary so much for them .I do not know whether it has changed now but the cases had a lot of variance between makers & this got a lot of people in trouble ,from memory Norma cases use to hold 10grns more powder than the makers cases with the least case capacity.

Here is a good article l have kept & it pays for everyone to refresh their brains on from time to time while reloading .


Understanding Pressure




Understanding Pressure :: Primal Rights, Inc

Looking at the numbers of your drawing and your cases it looks like you may be sizing your cases to much . By sizing to much it causes the case to try and fill the gap more giving a false impression .
The drawing is for a case that is meant to fit "All"" chambers , and the first two are smaller than the specifications, which means they could be to small for your chamber causing issues and the other shows expansion of .001" showing expansion but no issues with extraction . Chamber specs. are here https://saami.wpengine.com/wp-conten...sting-Copy.pdf.
Go back to the beginning and start again remembering that load data is inherently conservative but not something to be ignored or reckless with ,it maybe that you are at maximum powder but that your sizing of the cases is clouding what is happening?.

Originally Posted by Tankd

Looking at the numbers of your drawing and your cases it looks like you may be sizing your cases to much . By sizing to much it causes the case to try and fill the gap more giving a false impression .
The drawing is for a case that is meant to fit "All"" chambers , and the first two are smaller than the specifications, which means they could be to small for your chamber causing issues and the other shows expansion of .001" showing expansion but no issues with extraction . Chamber specs. are here https://saami.wpengine.com/wp-conten...sting-Copy.pdf.
Go back to the beginning and start again remembering that load data is inherently conservative but not something to be ignored or reckless with ,it maybe that you are at maximum powder but that your sizing of the cases is clouding what is happening?.

To Clarify i fired about 20 rounds and only the heaviest loads showed this deformation, the drawing is just the Sammi case drawing and i was just using it to show where i was measuring the cases "webbing in front of the belt" after they had been fired - looking for excessive expansion that would suggest over pressure.
As an example the two types of off the the self unfired ammo i have measured is 12.98mm on average at that location and after sizing in the die i'm getting 13.00mm +/-0.01

After reading bunji's great link - I note it was brand new powder and a very hot day at the range which also may have contributed.

i suppose it was just a bit unexpected as a lot of others on this forum have commented they use loads of over 71gns of AR2217 with a 7mmRM & 162gn projectile.

Originally Posted by Vandros

To Clarify i fired about 20 rounds and only the heaviest loads showed this deformation, the drawing is just the Sammi case drawing and i was just using it to show where i was measuring the cases "webbing in front of the belt" after they had been fired - looking for excessive expansion that would suggest over pressure.
As an example the two types of off the the self unfired ammo i have measured is 12.98mm on average at that location and after sizing in the die i'm getting 13.00mm +/-0.01

After reading bunji's great link - I note it was brand new powder and a very hot day at the range which also may have contributed.

i suppose it was just a bit unexpected as a lot of others on this forum have commented they use loads of over 71gns of AR2217 with a 7mmRM & 162gn projectile.

Greetings Vandros,
Ken Waters used the expanded dia of his cases just in front of the belt on magnum cases to compare pressures with factory loads. He wrote up his method in Handloader in late 1982 which I have just re read. He fired factory loads and measured what he called the expansion or pressure ring or just in front of the belt on a belted fired case. He then resized the case making sure that the expansion ring was resized close to original diameter. Next he trimmed the case to .010" below max length and loaded it with his test load. After firing he measured the case again. He described loads that expanded the case to the same dia as factory loads as normal. This was all in the days before pressure tested loads and affordable chronographs. I tinkered with it and measuring the solid case head for expansion before I got my own chronograph in 1991. Since then I have used velocity as a measure of pressure combined with pressure tested loading data. Ken did not believe that primer appearence was much use for estimating pressure and after seeing some dismal failures I don't either. He did rate ejector marks and hard bolt lift as danger signs though. Ken wrote his Pet Load reports for Handloader for over 40 years and they continue to this day written by Brian Pearce. Ken died in 2017 aged 99.
Regards Grandpamac.

I don’t believe you’re shown anything here to be of concern.

You are not reporting difficult extraction, flattened primers or extreme velocity increases. Typical signs of high pressure.

Drop back half a grain if you must but the cases marks here are not red flags. I would not be concerned about the WW primers. You have tested your loads with them and do not have data or evidence to suggest a change is needed in my opinion.


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Hang onto those bits of brass that cant chamber. I have a rear collet die for fat arsed 7mmRM brass. Works best if you use it each cycle but it may get you a few more cycles. I would check the primer pockets and also use a bit of wire inside to check for case head separation tho.