blown primers

Hey guys. I have a new Savage 10fcp-sr.308, 24 inch fluted barrel I bought some federal gold medal match 168gr. ammo and it shot just fine. broke it in and worked up some reloads. started at 43.5 grains imr 4064, 168 gr smk's and some 155 gr. Palmas shot ok. went to 44 and 44 1/2 and it started to blow primers with both 155 and 168 . I had a 700 rem. in .308 and I went up to 45.5 and everything was fine. I've checked several reloading sites and some have pushed to 46 with no sign of over pressure. I previously had a savage in .270 short mag that was blowing primers from day 1 with factory ammo only. 130 and 140 grain. sent it back to savage 2 times and it came back with the same problem. I sent them the end flaps from the ammo box and sent it back the third time. Took months to get through this. After all that, Come to find out that the chamber was cut off center. So new barrel and return 2 months later. Fired it and it was ok finally. Sold it right away. Now I'm worried that my .308 may have the same problem. Had the head space checked by gun smith and it is fine. Checked chamber depth and it came out at 2.888 and the groves measured .306. Could the tight bore be causing this? I'm spoked now with this new rifle. I've been reloading for 35 years and never had these problems with any other rifles. Getting discouraged too. Thanks for putting up with a newby with a long thread. Blessings.
My Pop told me "Don't believe anything you hear and !/2 of what you see and you'll be better off".

Do you have the velocities of your loads?
If they are higher than the book velocities then you are probably above max for that rifle.
But there could be an issue with the barrel too. Sorry not much help here,
Jack

#1
First off you say you're "rolling your own ammo"? Any chance you're pushing the shoulders back too far, (headspace) letting the primers pop out of the pockets a bit when fired, then getting pushed back into the pockets when the shoulder expands to the chamber size?
#2
Ever consider backing off on the powder charge a bit?

Chambers variations have a big part in increasing chamber pressures.
That is the probable cause.

When my new 12 LRP in 6.5mm Creedmoor arrived, it shot factory ammo (Federal Gold Match, Norma and Hornady) accurately but flattened the primers.
As I began reloading for it, I found that it was flattening primers even when I loaded at muzzle velocities lower than factory.
Fortunately, I photographed the ammo and the primers when I removed them and noticed that the primer backs has a ridge on them, like they were being pushed back out of the primer pocket into the bolt face.
After finding that the primer pockets were worn out after 4 reloads or less, I contacted Hornady and asked them, the originator of the caliber, whether that was normal.
They told me that a tight chamber, often used in rifles to gain accuracy, might be the problem.

I contacted Savage and sent them the pictures of the primers and the bases of the fired ammo at different pressures. Even loads at the low end of the load tables exhibited flattened primers. Savage had me send back the rifle and they reamed out the chamber by a few thousands.
The adjusted chamber eliminated the flattening even at loads near PMax.
I have 5 Savages and this is the only one that had anything like these symptoms.

Powders strength can vary by as much as 10%, although that much of a variation is rare. But a 5% variation is possible.
Assuming a nominal powder lot, your original load of 43.5 grains of IMR4604 with 168 grain bullets would generate around 54,183 psi. Using a load of 44.5 grains of IMR4064 would generate around 58,104 psi. That is at 93.7% of PMax.
It could be you also had a lot of IMR4064 that is a bit hot that caused some of the problem.
But it easily could be a combination of a hotter powder lot and a chamber that is slightly tight (or in your case off center).

On last thing, shooting in high temperature conditions can change the chamber pressure significantly.
Shooting at 90 degrees versus 70 degrees would get you 3% closer to PMax.
Cold weather, in this case, is your friend.

Thanks guys. You all have been a great help. Blessings.

I had one that would do that, had it checked out headspacing bad !!!

I have the same rifle as you. Am shooting 178 ELD-X with 43.9 gr of varget. Shot same load with my 10T. Try varget. I used to use 4064 until I learned about varget years ago. You will like varget.

Check the diameter of the firing pin at the tip and the firing pin hole in the bolt head. Could be you have too much clearance between the two. Look closely at your cratered but not blanked primers and see if there is a raised rim of material that tried to flow between the firing pin and bolt head. If so and your clearance is more than .002, have the bolt head bushed, or buy a few firing pins from Savage and cherry pick the largest diameter of the bunch.

You may be overpressure on your loads, or you may just have a poor fit between the bolt head and firing pin.

Well gentlemen. Here I am again. You arn't gonna believe this. Think I found the problem. I had some unfired rounds from my load testing and pulled the slugs and some were 155 smk and 168 smk so I weighed each to make sure they wouldn't get mixed. Low and behold. I found a 175 grn smk and I'm like. WHAT THE HELL. SO I CHECK MY BOX OF 168'S All good. Check my box of 155 Palmas and I find 4 more mixed in . I have never fired 175 smk's in any of my rifles. I did have a long range rem. In .300 win mag but I used Barnes match burners. The hollow point on the 175's were really small just like the Palma's. SOMEONE SCREWED UP BIG TIME. The only thing I can figure is someone . PROBIBLY a newbie at Sierra picked these up off the floor and seen the tight hollow point and assumed they were 155 Palma's. Sooo. I hate to say this. Looks like I'm gonna be weighing all my sierra's from now on. Gonna email sierra and tell them what I found. Seems to me they would have a fail safe system in the sorting machine to keep this from happening. Thanks again for the suggestions and help. Blessings.

My pop told me " don't believe anything you hear and half of what you see and you'll be better off".

Was it a factory sealed box bought straight from a reputable dealer? Or was it a open box bought from a gunshow or second hand?

From Sierra #5 with IMR4064:

155PMK -- 39.1 - 45.5

168SMK -- 37.8 - 43.4

Don't know where you got your load data from but you chose a starting charge weight for the 168SMKs that exceeded max (43.5gns) and went up from there?

I use bullet manufacturer data when working new loads, never start at or near max charge weights, and absolutely never over listed max. While the errant 175SMKs are most definitely Sierra's fault you share responsibility too you since you exceeded Sierra's recommendations for the 168SMKs, which if followed, might not have resulted in blown primers even with the 175s.

Federal Gold medal match loads for 168 is: Federal brass, FGMM LR primers, 42.8 gr 4064, 168 SMK. Seated to 2.800

Federal Gold medal match loads for 175 is: Federal brass, FGMM LR primers, 41.7 gr 4064, 175 SMK. Seated to 2.800

Brass is weight sorted. Federal Brass is soft. It is credited as a reason for excellent accuracy. Primer pockets don't last.

well guys. At it again. No more blown primers and I tried Varget. I will not shoot imr 4064 in my .308 again. Made up some loads and the very first one I tried with Varget was 1/2 in. 431/2 grains was the best of five. With a couple at 3/4 in. It was 38 degrees and 6000 foot in central Utah. I didn't crono the loads as it was getting late. but am going to check out the best load next nice day. Thanks guys for all your help and suggestions. The load info from Plil C was an eye opener. Thanks Phil. The Varget suggestion was great too. Thanks Bearcatrp. Blessings.

My pop told me " Don't believe anything you hear and half of what you see and you'll be better off".

You're welcome and good luck in your quest. I'm glad you only experienced blown primers and nothing worse. :thumb:

superbee68,
Sorry for the long response, but I hope this will help you.

38 degree temperatures will drop velocity and pressure quite a bit compared to shooting at summer temperatures.
43.5 grains of Varget yields 51,639 psi @ 2629 fps from a 24-inch barrel at 70 degrees, but the pressure drops to 48,958 @ 2589 fps at 38 degrees.
Shooting in colder temperatures reduces the chamber pressure significantly.

I still think that your chamber may be a bit tighter than normal and causing a rise in pressure and you might need to allow for that.
You didn't say you were seating the bullets out to the rifling to minimize the jump, but if you were, being seated in the rifling causes a sharp rise in pressure as well and could easily flatten primers.

I have found that IMR4064 is a good powder for the .308 as long as you don't push PMax.
With my old 10 FP that was rebarreled by Savage with a 24-inch,

suppressor ready,

fluted heavy barrel IMR4064 and IMR4166 Enduron powders shot the best of all the powders I have tried.
Other than the fluting that I had Savage add, I have a 10 FCP-SR barrel like yours.
My .308 shoots best with Sierra Tipped Match King bullets and I seat them out further than the SMKs because the base to ogive is about the same (similar jump) but the base to tip is almost 0.1 longer so the O.A.L. is longer. I seat to base to ogive length so I am cognizant of the changes in jump and I don't try to load pressed the rifling especially since my chamber is much closer to SAAMI recommended O.A.L. than your barrel.
When I got my 10 FP, the original barrel was just about 0.080 deeper than SAAMI, but the chamber in the replacement barrel was actually slightly shorter than SAAMI when it returned from Savage.

I don't load any powders near PMax and get very good results when target shooting.
My new 24-inch barrel 10 FP .308 averages 0.449 for all 5 round groups shot and IMR4064 averages 0.453 with 168 grain bullets.

Since I am shooting match bullets like you are, getting maximum velocity isn't all that important so you can tune the charge to get the best accuracy unless you are loading for long distances.
But a 175 SMK stays supersonic at 1000 yards with a muzzle velocity over 2450 fps and that is well under what a load near PMax with either Varget or IMR4064 delivers with that bullet weight.

Hunting bullet expansion isn't an issue when hitting paper or steel targets.

You may find that your 24-inch barrel will shoot best when the bullet exits the barrel at 1.256 milliseconds (tuned to the reflection velocity of the 3% carbon steel in your 24 inch Savage barrel).
I have found that barrels can be off nominal length by as much as 0.156 inches if you measure from muzzle to bolt, and that will change the exit time a bit, (as much as 0.008 msec.)
I recommend you measure your barrel from muzzle to bolt (use a cleaning rod and tape it at the muzzle when the tip is touching the bolt and then measure carefully).

A 1.256 msec. exit time can be achieved at 70 degrees F. with 42.4 gr of Varget behind a 168 gr SMK seated out at 2.808 with case trim length of 2.005 at 47,864 psi and 2567 fps muzzle velocity.
When the temperature drops to 38 degrees F, the charge changes to 43.2 gr. of Varget behind a 168 SMK seated out at 2.812 with case trim length of 2.005 at 47,780 psi and 2569 fps muzzle velocity.
Your 38 degree F, 43.5 grain loads aren't that far off the exit time load so that is encouraging.

If you use IMR 4064 powder you'll get a 1.256 msec. exit time

at 70 degrees F. with 41.9 gr of IMR4064 behind a 168 gr SMK seated out at 2.812 with case trim length of 2.005 at 48,299 psi and 2570 fps muzzle velocity.
When it is 38 degrees F, the charge changes to 42.6 gr. of IMR4064 behind a 168 SMK seated out at 2.808 with case trim length of 2.005 at 48,160 psi and 2570 fps.

As you can see, IMR 4064 is a faster powder than Varget and your charges with IMR4064 were very much stronger than either of the loads listed here.

Interestingly, both powders are temperature sensitive and a 32 degree temperature change causes a 0.8 grain difference in Varget and a 0.7 grain difference in IMR 4064 to achieve the same results at different temperatures.
Temperature variation for either powder is close to linear so you can adjust for temperatures using the difference in actual temperature, but I would suggest you try to load +/- 0.1 grain increments around the adjusted load to find the best load.

Case trim length and seating depth change the effect of the charge. That is why I had to adjust the seating depth for each load listed above to achieve the desired exit time.
At 38 degrees, trim length increases pressure and decreases exit time by 0.001 for each 0.004 (+/-0.0005) inches of trim length changed if the trim length increases and visa versa.
At 38 degrees, seating depth increases pressure and decreases exit time by 0.001 for each 0.003 (+/- 0.0005) inches of seating depth changed if the seating depth decreases

and visa versa

.

I would recommend you try both Varget and IMR 4064 again in the load range I have listed and you might see equally good results as long as you stay in the right pressure range.

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Originally Posted by superbee68

Thanks guys. You all have been a great help. Blessings.

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factory loadings tend to be on the hotter side. If those aren't blowing, my guess is it has more to do with your reloading than the gun. Just my two cents.

You may want to try H 4895 as well as IMR 4065 due to the harsh recoil associated with Varget shot in a 308 w

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Interestingly, both powders are temperature sensitive

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Respectfully disagree with your assessment of Varget. It is not temp sensitive, not according to Hodgdon, not in my experience, and not from independent testing that's been done that I've seen. I've been shooting it in FL where you can bake an egg on a round that's been in the sun for a few minutes (not that I keep them in the sun...) and never had an issue with it across many chamberings in which I use it. Same with the 4350 I use extensively. Hodgdon's Extreme powders are the best available when it comes to not being temp sensitive. I get better velocity with IMR4350- but it is not nearly as consistent as H4350 in my rifles for that reason.

http://precisionrifleblog.com/2016/0...s-imr-enduron/

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You live in the "real" world, where 12 point bucks are rare and it’s never 70° when you decide to fire your rifle. Where you shoot it’s either freezing cold or burning hot. Not exactly ideal conditions for your rifle, or you for that matter. Fortunately, Hodgdon’s Extreme powders perform just as well at 125° as they do at 0° . Using an exclusive extrusion process and exacting quality standards, Hodgdon has created a line of propellants that performs better at hot and cold temperatures than any other powder on the market. So when you sight in your rifle this summer, you can count on unbeatable accuracy this winter.

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I may have been overstating by using the term "temperature sensitive" but the data says that a temperature change from 70 to 38 degrees requires a 0.7 or 0.8 grain increase in the two powders mentioned to achieve the same velocity.
That was the point I was making and if my use of the term "temperature sensitive" caused you some discomfort, I apologize, but that doesn't change the fact that the charges for those two powders change with temperature to maintain the same velocity.
If loading for Varget for 70 degree and the temperature rises to 100 degrees there in Florida, the velocity still goes up by 50 fps and the charge would have to drop by 0.6 grains to maintain the same velocity.

I also recognize that some powders are much more temperature sensitive than either IMR4064 or Varget and that most shooters don't keep track of velocity as much as I do, but loading for exit time requires it.
If one isn't regularly measuring velocity with a chronograph when you are testing loads, one would probably never see the difference temperature causes just in judging from POI.