Savage M12 LRP Chamber

[hybridspecies]

I'm having some pressure issues with a new Savage Model 12 LRP in 6.5CR. I put 101 handloaded rounds through it and all of them were flattening primers. A few of the cases even have faint ejector rings. The loads consisted of virgin Lapua LR cases, H4350, Berger 140 Hybrids, and CCI BR2 primers. Powder charges ranged from 40.4 grains to 42.3 grains in 0.1 grain increments. These charges are within the ranges prescribed by both Berger and Sierra for similar bullets, albeit the upper end of the ranges. I had originally suspected that I was seating too close to the lands, but a subsequent firing with a magazine length round produced the same effect.

I'm now wondering if there's something wrong with the chamber as I've heard that Savage had issues with this rifle early in production. I don't own a borescope, but I have a cheap endoscope that I bought on Amazon a couple of years ago so I used it to take some pictures of the chamber the other day. I'm not sure what to look for, so I'm hoping that the smiths and other experts on the site might be able to offer opinions based on what they are seeing. Unfortunately the images lack detail (the difference between a $60 endoscope vs a $600 borescope I suppose), but please take a look and let me know if anything is grossly out of order.

In some of the photos, it looks to me like there is a protrusion of the neck space into the chamber slightly past the shoulder space, but I have no idea if that's normal on all rifles or what to look for. I also took a video of the inside of the chamber that for some reason shows a lot more detail than the photos, but I'm not sure if forum rules allow me to post a link to that video (its hosted on youtube).

Here are some of the stills of the inside of the chamber (the white specs are lint from the cleaning patches):

 

[tobnpr]

Machining defects in the chamber will show on your brass.
"Mag length" doesn't mean anything- it's the boltface to datum line dimensions of your chamber, and the round that matter.
Did you confirm your loaded round isn't being jammed into the rifling by using a comparator?
Ditto on headspace- did you use a comparator to set minimal shoulder bump from your fired case dimensions?
"Flattened" primers aren't always indicative of high pressure (pictures would help)- you didn't mention hard bolt lift when extracting the case, this is usually present with overpressure?

Also, measurements of the fired cases compared to correctly sized brass. See if any are out of round, or otherwise out of spec.

 

[hybridspecies]

I'm not seeing anything on the spent brass to indicate machining defects, but I'll post some pictures soon.

The brass was virgin so I didn't set the shoulder back at all. I just used an expanding mandrel to uniform neck tension at 0.263". Using a Hornady headspace comparator, I measured the virgin brass at 1.5570" from the base to the datum and the fired brass at 1.5630" (on average). I have not yet deprimed the fired brass so these measurements might be skewed a bit.

I also used the Hornady bullet comparator and OAL gauge to measure distance to the lands for seating depth purposes. I set seating depth 0.02" deeper than what I measured. Initially I thought I might have measured incorrectly because I encountered mild resistance when inserting the OAL gauge plunger (I have another post on this), so I made a test cartridge with a magazine length seated bullet. COAL for the bullets seated 0.02" from the lands was 2.9375" and COAL for the magazine length round was 2.80". None of the bullets showed any signs of contact with the lands during cycling nor was there any resistance with the bolt. I did start to notice hard bolt lift at around 42 grains though.

Here are the measurements I took of the fired brass:

Neck Outside Diameter 0.2955"
Case Length 1.9130"
Neck Wall Thickness 0.014"
Case Diameter by Neck 0.4635"
Case Diameter by Head 0.4705"
Headspace Hornady Comp 1.5630" (with primer)

At this point I'm trying to eliminate any mechanical issues with the gun that might be causing high pressure. I spoke with Savage and the tech suggested that the firing pin spring might need to be swapped out, but I'm not sure that would result in flattened primers and ejector marks, although there is a fair amount of cratering going on. I might send the gun back with a few fired cases for them to look over as I am still within their 1 year warranty window. If it turns out that nothing's wrong, I'll probably swap out the barrel for a Shilen.

Here's a link to the borescope video I mentioned in the original post to help with diagnosis:
Borescope Video

Thanks for your thoughts, please keep them coming.

 

[tobnpr]

I spoke with Savage and the tech suggested that the firing pin spring might need to be swapped out, but I'm not sure that would result in flattened primers and ejector marks, although there is a fair amount of cratering going on.

The cratering could indicate an oversize FP hole- even with normal pressures. High pressures obviously would exacerbate that and I suspect you can get primer "flow" into typical clearances with enough pressure.

Headspace looks to be long by spec- which is 1.541 for min, 1.551 max.
Your fired brass at 1.563 would be twelve over SAAMI max. How did the case diameter (above the casehead) compare to the new brass? Absent any evidence of swelling there (thinner case wall if exposed due to shallow chamber) I wouldn't see this as the problem either. If you weren't having hard primary extraction I'm thinking "other than" excessive pressure.

 

[hybridspecies]

I get different headspace readings depending on whether I use the Hornady or Sinclair comparator so I'm not sure how meaningful the actual measurements are with respect to accurately determining headspace (datum position is different for each I believe). Besides that I'm sure the primer is adding to the length. I'll deprime a couple cases with a universal decapping die and remeasure.

Here are some photos of the cases at 40.4 gr, 41 gr, 41.5 gn, and 42 grains (they are all single fired brass):

40.4 grains H4350 (cratering and flattened primer)

41 grains H4350 (cratering, flattened primer, and ejector wipe on the "C" in Creedmoor)

41.5 grains H4350 (cratering, primer flattening, ejector wipe, and the start of an ejector ring around the second "A" in Lapua)

42 grains H4350 (cratering, primer flattening, significant ejector wipe, pronounced ejector ring)

Also of note is that the bolt face was filthy. It arrive new with significant carbon buildup around the inner edges (presumably from test firing at the factory), but significant discoloring/buildup occurred around the primer contact area after putting the 101 rounds through it. Here are a couple of photos before cleaning and after cleaning. I don't know if the firing pin hole is oversized, but the machining of the bolt face looks horrible in my opinion. Additionally there seems to be a groove around the primer contact area on the bolt face, although it's hard to know for sure if that was there initially because of the circular machining marks across the entire bolt face:

Dirty:

After Cleaning:

Thanks for your help.

 

[MNbogboy]

Coloring of the bolt face looks normal and just like a brand new spare I have in my savage parts stash. Primer craters are often common in most savages as the firing pin holes tend to be a poor fit for savage firing pins. The bolt head can be bushed to cure this. They can be changed out in a matter of minutes so replacing the bolt head may cure any problems with firing pin fit. Also you didn't mention the primer brand. Winchester & Remington primers have often flattened more for me than cci orfederal. Magnum primers have thicker cups and do not "flow" around firing pins as easy as others.
Btw the primers in the photos did not appear flattened to me. A good indicator of a flattened primer is to remove them and a side view looks like a top hat.

 

[hybridspecies]

Thanks for the confirmation on the bolt face - I still think mine was poorly machined though. Primers used were CCI BR2. I like your idea about getting a bushing installed in the bolt head. Any recommendation on where I can get this done (forum members?)? I'm not sure if I understand your point about changing out the bolt head - can I buy a drop in replacement from Savage, or elsewhere, that doesn't need fitting or were you referring to reinstalling the original bolt head after the bushing is installed? I'd prefer getting a replacement bolt head, if possible, and installing the bushing in it instead of the original which is still under warranty.

I haven't removed any of the primers yet on the spent 6.5CR Lapua brass, but here's a photo of a CCI BR2 primer installed in a new piece of Lapua 308 brass for comparison:

Thanks for the help.

 

[pdog shooter]

Did you ever figure this out for sure? sounds a lot like a thread I just started and got no responses.

 

[pdog shooter]

I'm going to go ahead and try to restart this thread because it is very similar to mine. I believe there is a common problem so here is the thread I started 1 month ago and didnt get a response.

Pressure signs with savage 12 long range precision rifle

Friend of mine wanted to get into reloading and long range precision shooting. He is new to the reloading part I am not. Purchased quality reloading equipment and a savage 12 long range precision rifle of 6.5 caliber. We both realize that the rifle was kind of a crap shoot but could easily be...

www.longrangehunting.com

Friend of mine wanted to get into reloading and long range precision shooting. He is new to the reloading part I am not. Purchased quality reloading equipment and a savage 12 long range precision rifle of 6.5 caliber. We both realize that the rifle was kind of a crap shoot but could easily be swapped to aftermarket barrel. Rifle had very erratic chronographed velocities and every pressure sign imaginable. Keep in mind there are 2 of us with two sets of better than average equipment. Measured and prepped brass to the highest standard I was capable of, measured powder with 2 different scales, 3 different types of brass, multiple bullet weights and brands.

Rifle sent back to savage and the diagnosis was "an unusually tight chamber" polished and returned. Kind of figured that was BS because its easy enough to check head space and there were multiple dies used with no problems chambering. Rifle test fired with the same erratic velocity with the added bonus of breaking the bolt face. Bolt inspected and repaired and aftermarket barrel purchased.

Inter a new tool, "pin gauges", Saami calls for the bore to be .2560 with no + or -. We now have a total of 4 6.5mm barrels for comparison. 256 pin will pass thru 3 of these barrels with nearly no effort it will not pass thru the savage. The 255 has to be tapped thru and the 254 passes easily. I'm putting the bore at 0.2545. Chamber casting poured from barrel in question with no anomalies. New barrel installed and fired approximately 100 times with no pressure signs and velocity in the expected range.

My question is; Has anybody else heard of or experienced this? I've seen several pressure problems posted but cant recall the end result being bore size. How could this happen?

Save the comments of it being dangerous. We were very aware of that.

 

[hybridspecies]

Did you ever figure this out for sure? sounds a lot like a thread I just started and got no responses.

No, not really. I ended up settling on 40.7 grains of H4350 and the pressure signs went away, but velocity was a little anemic. Accuracy was still good though. I had the bolt face machined with a smaller firing pin hole upon recommendation. This did help reduce the primer flattening and cratering, but I was still getting ejector swipe marks on new brass at higher end charges. What aftermarket barrel did you end up with?

 

[grouse]

Broke the bolt face?

 

[hybridspecies]

Broke the bolt face?

No, I had the firing pin hole bushed to a smaller diameter, which helped minimize primer cratering.

 

[pdog shooter]

Yes sir, broke bolt face, well, cracked. across the face and down the side next to lug.

 

[grouse]

Yes sir, broke bolt face, well, cracked. across the face and down the side next to lug.

Wow