Savage M12 LRP Chamber

hybridspecies

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Jul 9, 2021
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California
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):

Outer Chamber.jpg


Inner1.jpg


Inner3.jpg


Inner5.jpg


Inner6.jpg
 

tobnpr

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Joined
May 30, 2013
Messages
340
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

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Jul 9, 2021
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California
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

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Joined
May 30, 2013
Messages
340
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

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Messages
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Location
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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)
40.4 grains.jpg


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


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


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


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:
BoltFaceDirty.jpg


After Cleaning:
BoltFaceClean.jpg


Thanks for your help.
 

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MNbogboy

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Jul 14, 2009
Messages
955
Location
Northern MN
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

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Jul 9, 2021
Messages
26
Location
California
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:

New Primed Lapua 308.jpg


Thanks for the help.
 
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