High Pressures? ?

[Hylander]

M77 .308 Varmint
Sierra 150SBT, 42.0 4064
WLR primer, 1X CBC and 1X PPU brass, FL sized in Redding dies.
OCL 2.750

I'm at the lower end of the load, however I am getting completely flattened primers and very sticky bolt.
Rounds chamber easy, head space correct, .050 off the lands.
What am I missing ?

 

[Cheesewhiz]

.050 of the lands.

You do mean .050 off the lands?
Have you chambered a round and ejected it just to check if you see any odd markings?

 

[Chuck 100 yd]

I have never used 4064 powder. Who makes it? A call or e-mail to them is in order. There could have been a mix up in packaging. It has happened before.
Other than that, does your rifle have an extra tight bore? Have you miked the bullets to make sure they are not .311`s or some such? That one is possible also.

 

[dougader]

IMR or AA 4064.

Are you sure the bullet is 150 grains?

 

[GP100man]

FPS ???

 

[Hylander]

Yes, IMR 4064 (two different lots) and 150 Sierra SBT that are .308
FPS: no idea

 

[GP100man]

FPS will give ya some idea of pressures compared to available data .

A cheap chrony is as good as a hi dollar 1 once ya learn what to do to get it to read correctly.
It`s an indispensable tool in the reloading room now .
I was really surprised by some of my "go to " loads !!!

Is the bullet on the lands ?? I remember the sbt having a short oglive.

 

[jsh]

Got me stumped. I would pull them down and check the charge weight again. Being on the low side of the load with that brass I would think it would be safe.
I know it's tough to find but I would look for some varget.
Jeff

 

[Chief 101]

Got me stumped. I would pull them down and check the charge weight again. Being on the low side of the load with that brass I would think it would be safe.
I know it's tough to find but I would look for some varget.
Jeff

I would start here...and double check the bullet weight.

 

[Hylander]

Pulled a few down, charge weight is correct.
Measure the bullets, there are .308
Got some Win brass, the CBC's definitely have less case capacity.
Made up new loads with the Win brass, but wont be able to test until Monday.

 

[Chuck 100 yd]

It sounds like you may have found the cause of the extra pressure.
Post your results if you will.

 

[Chief 101]

Flat Primers in the .308 are no indication of hi-pressure. Clean and dry the chamber, can be a cause of sticky extraction. Military brass can have less capacity and cause higher pressures but at the 42grain level doesn't sound high enough to be a problem. Good luick monday...

 

[Hylander]

I noticed with the CBC and PPU brass there was a lot more resistance when sizing than with Win. brass.
Also I checked case capacity. These were all FL sized, trimmed and primed.
As you can see, there is a big variance from CBC to Win.

With HP-38, I used this because it meters well and will settle well
in the case.

CBC: 40.2 gr.
PPU: 41.1 gr.
Win: 42.2 gr.

With Water:

CBC: 52.4 gr.
PPU: 54.0 gr.
Win: 55.5 gr.

 

[GP100man]

I bet you`ve found your pressure problem.

Pepsi !!

 

[jsh]

Flat Primers in the .308 are no indication of hi-pressure. Clean and dry the chamber, can be a cause of sticky extraction. Military brass can have less capacity and cause higher pressures but at the 42grain level doesn't sound high enough to be a problem. Good luick monday...

I thought the same thing on primers. If die is on the small side and chamber is on the large or above average side it will flatten primers.
On the brass side, if it is hard and doesn't expand well and grab the chamber could be an issue.
Did your fired cases with flat primers have any soot or black marks on them?
One other thing I got to thinking about is case lube. If there is any case lube on them or the chamber could cause you problems. Even if the first round had any excess it could leave enough lube in the chamber for the next few even if the are clean to cause a problem.
Jeff

 

[Precision32]

You can have close to 15 grain difference in case weight and still be in tolerance.

Pushing the shoulder back on you reloads can cause the flat primers. Sticky extraction can be a dirty or rough chamber.

Shoot some factory ammo vs reloads and measure the case above the case head. The round with the larger diameter, closer to the rim has the higher pressure.

How does the gun run with factory ammo?

 

[Chief 101]

Shoot some factory ammo vs reloads and measure the case above the case head. The round with the larger diameter, closer to the rim has the higher pressure.

How does the gun run with factory ammo?

You measure before firing and after firing and figure the amount the case head has expanded...and compare to factory before and after. It takes a more specialized micrometer to do that...then if you have different brands of brass all bets are off.

 

[Hylander]

You can have close to 15 grain difference in case weight and still be in tolerance.

Pushing the shoulder back on you reloads can cause the flat primers. Sticky extraction can be a dirty or rough chamber.

Shoot some factory ammo vs reloads and measure the case above the case head. The round with the larger diameter, closer to the rim has the higher pressure.

How does the gun run with factory ammo?

Chamber was clean and smooth, I know this gun and it has always worked great with no issues.
Have not shot factory ammo yet, but I did pick up a box to shoot.
Will hopefully make it to the range tomorrow morning for another run.

 

[Hylander]

Life is good again 8)
It was the brass
I loaded up a few different loads with Win brass and also shot some factory Fed loads
with no issues and sub Moa accuracy.

 

[Chuck 100 yd]

Great! Case capacity is very important part of the load formula. Most load manuals will state the case and primer brands used in test loads. Glad you figured it out.

 

[Jimbo357mag]

Tanks for the posts.(Companhia Brasileira de Cartuchos) it's made in Brazil under the name Magtech. I have used a lot of MagTech ammo and brass with some minor problems in revolver sizes. I think I will stay away from CBC rifle cases.

I did a little search and found many posts about hot loads in 308 CBC cases.
example. http://www.ar15.com/forums/t_6_42/400047_Magtech_CBC_headstamped__308_brass_Case_capacity_questions_____.html

 

[Slenk]

Measure your case neck wall thickness . I have found some mil. surplus brass to thick to even chamber in my rifle.