Blown primers with min starting load

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Minuteman
Sep 14, 2019
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I apologize in advance for the lengthy post but I’m trying to include as much info as possible.

I’m pretty new to reloading and only load for 1 round, 6 Creedmoor. I recently switched powders from N555 to H4350. I loaded some middle of the road charges from Hornady’s manual and had some minor pressure issues, slightly flattened primers and a bit of cratering. The load was faster than I’m trying to run so I pulled the remaining rounds apart to start over. I loaded a new batch starting at 36.0 grains increasing in .2 grain increments to 37.8 which is at or just slightly above the minimum recommended starting load from three manuals, Hornady, Nosler, and Lyman and well below max. I shot the first five rounds and had an extreme spread of over 100 fps. Some of the rounds chronographed where I was expecting them to at 2940 fps but a couple were much higher. I shot a couple of the other charges with similar erratic results then had a blown primer with a 36.4 grains. It was very obviously way over pressured and the case was stuck in the bolt face. Thinking it was an anomaly I shot a few more rounds than had another blown primer/stuck case. Obviously, I stopped at this point. I thought perhaps I’d loaded the bullets too long and was touching the lands so I duplicated the CBTO measurement of some factory Berger ammo which uses the same case and bullet I’m loading. I fired one round at 36.0 and had a blown primer. I’m at a loss for what is causing this and it’s quite disconcerting as a new reloader. I’ve pulled several of the remaining rounds apart to measure the powder charge and all were where they should be. All rounds were loaded using an Autotrickler with FX120-i. The brass is Lapua on its 5th firing and is sized in a Redding full length bushing die. I’ve never trimmed them, but I measured and all case length is between 1.905 and 1.915 which is within SAAMI tolerances. I’d planned on starting over with new brass as that’s the only variable left I can think of but I need to make sure I’m not missing something else. The rifle is an MPA PMR Pro, the bolt closes on a go gauge and doesn’t close on a no-go headspace gauge and it shoots factory ammo just fine. I’m shooting Berger 109 Hybrid Target bullets and using CCI 450 primers. I’m at a loss as I’ve followed the manuals religiously and never had my safety concerns until now. Thanks for reading and I appreciate any advice.
 
Is your barrel clean?
Whats the firing pin tip look like?
The firing pin looks fine to me. I didn’t have any pierced primers and the primers on factory ammo fired after my issue reloads look perfectly normal. The barrel was cleaned with Boretech Eliminator and the chamber area was cleaned with C4 prior to shooting.
 
What size neck bushing is in the die?
Are you using a button on the de-capping rod?
Are you crimping the neck? Too much crimp is bad
What method are you using to clean your brass? Some methods clean so well that the projectile or inside the neck require some lube.
Too much neck tension can promote over pressure. Pay attention to how much effort is required to seat the projectile
 
I'm sorry if I'm not reading what you said correctly, but it looks to me like you started at 36 grains and that is a 1-2 grains below the minimum for 6 Creed/H4350/109LRHT depending on whose data you use.

Edit: Hodgdon data says minimum for 108 gr. is 37.8 and minimum for 110 gr. is 37.2.
 
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First, I'd check your scale.
Go through your zeroing process and then take a couple of your projectiles and weigh them. They should be within a couple of tenths of a grain.

If all is good, then I'd suspect you are using the incorrect powder, or a mis-labeled canister.

Scale issues, or incorrect powder.

There's no other real explanation of how you can generate that much speed using charges that are lower than book minimums.


Well,
Is there a chance (really long shot) that you accidentally loaded 6.5 or .257 diameter bullets?
They'd be a real bitch to seat and also to chamber, but I've heard of it in the past.
If you could get them to chamber they would raise hell with your pressure.
 
What size neck bushing is in the die?
Are you using a button on the de-capping rod?
Are you crimping the neck? Too much crimp is bad
What method are you using to clean your brass? Some methods clean so well that the projectile or inside the neck require some lube.
Too much neck tension can promote over pressure. Pay attention to how much effort is required to seat the projectile
272 bushing and I’ve never had issues such as this before. I’m beginning to suspect the charge was too low but using Hornady’s 11th edition manual they recommend 35.4 grains for 108-110 grain bullets.
 
I'm sorry if I'm not reading what you said correctly, but it looks to me like you started at 36 grains and that is a 1-2 grains below the minimum for 6 Creed/H4350/109LRHT depending on whose data you use.

Edit: Hodgdon data says minimum for 108 gr. is 37.8 and minimum for 110 gr. is 37.2.
I’m beginning to suspect I need to bump the charge however Hornady’s 11th edition manual lists 35.4 grains as the starting load for 108-110 grain bullets.
 
One other thought: A carbon ring can form at the end of your chamber just before the lead and throat area. If your brass is long enough to get into this area it can increase pressures significantly. The same goes for excessive carbon fouling in the throat and first few inches of the barrel.
 
I've seen pistol cartridges loaded below minimum that showed signs that could be mistaken for high pressure, but revolvers and bolt rifles aren't exactly apples to apples.
 
I’m beginning to suspect I need to bump the charge however Hornady’s 11th edition manual lists 35.4 grains as the starting load for 108-110 grain bullets.
You have higher than expected velocity and excessive pressure. Do Not increase charge weight.

Bullet pinched in the case from not trimmer, carbon ring, other.

Scale is lying.

Wrong powder.
 
Have all the problematic rounds been loaded from the same bottle of H4350? Do you have more than one bottle of it?

Perhaps you have an “out of spec” bottle of H4350 that’s unusually hot…

And to confirm, zero issues with either factory ammo or rounds loaded using the N555, right?
 
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I would double check that your cases are not too long giving you a pinched projectile.

You could also have a brass donut forming at your neck-shoulder junction after this many firings.

How do you clean your brass? When I was using walnut media, I noticed my velocities and pressures would creep up as I reloaded brass repeatedly. I believe the walnut residue was building up in the brass and reducing my case volume resulting in higher pressures over time.
 
You have higher than expected velocity and excessive pressure. Do Not increase charge weight.

Bullet pinched in the case from not trimmer, carbon ring, other.

Scale is lying.

Wrong powder.
The powder came from Brownells and while I certainly won’t rule out incorrect powder at this point, it was either mislabeled at the factory or by someone at Brownells. I also pulled apart a factory round and it’s case was very noticeably more full of powder than what my reloads were. As far as the scale, the only known weight items I have are bullets. I weighed several 109, 108, and 107 grain bullets and every one weighed within an acceptable range-within a tenth of a grain.
 

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Have all the problematic rounds been loaded from the same bottle of H4350? Do you have more than one bottle of it?

Perhaps you have an “out of spec” bottle of H4350 that’s unusually hot…

And to confirm, zero issues with either factory ammo or rounds loaded using the N555, right?
Zero problems with factory ammo or reloads with N555. I do have a different lot I can try. Yes all problem rounds are from the same bottle.
 
Thank you everyone for the replies I really appreciate them all. I’m thinking at this point starting over with new brass and a different lot of powder is my next step. I’ll also ensure the rifle is completely clean before proceeding.
 
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My only concern with the powder would be if you somehow contaminated it with another powder.

You still need to figure out what's going on, otherwise you may be back in the same boat after a few firings on the new brass.
I have more powder in unopened canisters of different lots that I’ll use. I’ve only loaded with the two powders and always empty the hopper and trickler after loading. Obviously I’d like to isolate the cause, but honestly feel like I’ve checked everything I can. I’m not sure what other variables other than the particular lot of powder or the brass I used can be changed. As I said initially, it’s quite disconcerting, but I’m not sure there’s anything left to verify.
 
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I would double check that your cases are not too long giving you a pinched projectile.

You could also have a brass donut forming at your neck-shoulder junction after this many firings.

How do you clean your brass? When I was using walnut media, I noticed my velocities and pressures would creep up as I reloaded brass repeatedly. I believe the walnut residue was building up in the brass and reducing my case volume resulting in higher pressures over time.
I missed this post earlier, sorry. I wet tumble with stainless steel pins prior to sizing, then again after sizing without pins to remove the case lube.
 
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hard to believe a mislabeled jug of powder. Other than too much neck tension I would suspect a little carbon interference in the throat area. even a normal cleaning can fail to remove a stuborn carbon deposit.

if you have a borescope now would be the time.
 
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So chamber/throat is clean and brass is properly trimmed???

You said the bullet fit snug but you could push it in the fired case. That is not normal for 99% of people/rifles. IMHO, something is pinching the bullet in the neck.
 
So chamber/throat is clean and brass is properly trimmed???

You said the bullet fit snug but you could push it in the fired case. That is not normal for 99% of people/rifles. IMHO, something is pinching the bullet in the neck.
All cases are between 1.905-1.915 within SAAMI specs. The factory Berger ammo which uses the same case and bullet is .2735 at the neck. I’m sizing using a .272 bushing. The reloads measure .273. What else should I be looking at?
 
How many different powders has he tried or the same-same? no change of powder?
Doesn't take me long to figger out somethings fucked up.and change something
but I never load over 5 rnds and shoot them and if they don't do good, I change.
5 rds. of each powder I load with and find the one that does the best or what loads well on the bench? or what you have a lot of.
It's not how fast you go, It's how you get there.