I am in Montana, and our family friend has two custom rifles made by the same gunsmith in Montana. One, a 7x57, when fired the firing pin marks are totally random and hardly ever centered. It shoots at best 2-2.5", and has a custom full octagon barrel. He is pretty sick over this, and I wanted to get some opinions here before I have him mail it off to a gunsmith.

He seemed to think it was a coencentric issue between the action and the barrel?

Has the Montana gunsmith been given an opportunity to fix this?

A low cost test. Steel blue layout fluid or "Dykem" on a few unfired cases to act as a witness mark can sometimes show up a issue.

quote:

Originally posted by Duane Wiebe (CG&R):
Has the Montana gunsmith been given an opportunity to fix this?

After the pair was was made and the issue with the first gun he was notified for sure.

And then refuses to return phone calls, email, snail mail, etc. He definitely knows there was an issue.

The likely cause is the action itself. The firing pin hole is off center to the bolt body, the action threads are off center to the bolt way or there is so much slop between the bolt and receiver and it's just moving all over. It could also be an oversized chamber or the threads have been cut off center to the bore. I have seen a lot of threads cut off center lineally or axially in custom rifles by guys who chamber in three jaws or 4 jaws and don't take the time to properly set things up. I have also seen them cut off center between centers by guys who refuse to buy piloted center cutting reamers and religiously re-cut the centers between centers before threading between centers.

Mausers will often traditionally hit a bit off center because the extractor forces the case over to the left side during fire forming. While the strike of the firing pin appears almost perfect, it does give the fired cases a bit of a possum bellied look when examined. I have had guys tell me that the cases expand more on one side than the other, or that the chamber is actually curved to one side or bent. All reasonable analogies I suppose, but it's still simply the extractor holding the case over to one side during fire forming.

The only way to tell for sure is to get it to someone and have them start measuring stuff. Most of the time you have to pull the barrel and get the barrel and receiver into the lathe to get some hard, fast numbers. The best bet is to return it to the guy that put it together and see if he can give you an answer that you can live with. He will also be the most likely person to trouble shoot it for free.

As far as trouble shooting it yourself, you can measure a case on the back of the chamber area (not the unsupported base) and fire it. Then re-measure it again after firing. If it is under .004 inch overall or .002 inch expansion per side the chamber diameter is within spec. You can also take the fire array out (shroud and firing pin assembly) and chamber an unfired piece of brass. If you can move the forward area of bolt body up and down or side to side an unreasonable amount by pushing on it, then you probably have a sloppy action. If you provided the action to the guy you're probably stuck with it. If he provided it he may or may not work with you to correct it.

What Speer said, And, it is very hard to do what you describe, unless the bolt to receiver interface is real sloppy. Most often, even if the FP strike is off center (mine never are) it is always in the same direction. To have them randomly wander is indicative of some very sloppy fitting in one or more places. Even if the chamber is sloppy, the bolt should still be in the same place each time. Unless it is sloppy too.
Accuracy on an octagon barrel? That is what you get when trying to make an octagon out of a round barrel. Not always good if it wasn't milled carefully, on a properly stress relieved barrel.

quote:

Originally posted by dpcd:

Accuracy on an octagon barrel? That is what you get when trying to make an octagon out of a round barrel. Not always good if it wasn't milled carefully, on a properly stress relieved barrel.

⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧⇧
Point well put. Milling on material imparts a lot more tool pressure onto the steel and tends to put in a lot more stress than cylindrical turning does. On top of that, any time you reduce weight on a barrel your accuracy goes down. Most of the accuracy of a firearm is born into the barrel at birth. Some just don't and won't shoot. Chasing down little points like bedding, crown, firing pin protrusion and receiver alignment gets you a lot in varmint or target guns when you want to make a heavy .300 shooter into a .200 gun. Taking a light hunting gun from a 2.5 inch gun to a 2.4 inch gun loses something in the translation.

Is the firing pin hole oversized?

Best is 2.5"!
How many loads/bullets tested?

There are too many possibilities here to be able to point at any single cause. I didn't see any mention of what action was used but I suspect a combination of a loose-fitting bolt, a large chamber, and an extractor which pushes the bolt over. Regards, Bill.

I believe it is an fn action in 7x57. I gave the owner DPCD contact info if he wants to have it checked out.

Greg Tannel is a trigger meister in Rifle Colorado.He has fixed a lot of triggers by bushing them into a small hole and making them run straight and true. It is an fine piece of work. He will pull the barrel and do an excellent diagnosis. He is capable off setting everything to right. He has no desire to fix things that are not are not broken.

Primer Cratering Problem? Give Greg Tannel a Call…
Crater moon primers greg tannel bushing firing pinCraters may look interesting on the moon, but you don’t want to see them on your primers. Certain mechanical issues that cause primer craters can also cause primer piercing — a serious safety problem that needs to be addressed. If you have a gun that is cratering primers (even at moderate pressure levels), there is a solution that works with many rifles — send your bolt to Greg Tannel to have the firing pin hole bushed.

Shooters who convert factory actions to run 6BRs, 6PPCs or other high-pressure cartridges should consider having the firing pin bushed. These modern cartridges like to run at high pressures. When running stout loads, you can get cratering caused by primer flow around the firing pin hole in the bolt face. The reason is a little complicated, but basically the larger the hole, the less hydraulic pressure is required to crater the primer. A limited amount of cratering is normally not a big issue, but you can reduce the problem significantly by having a smith fit a bushing in the firing pin hole. In addition to reduced cratering, bushing the firing pin often produces more consistent ignition.

CLICK HERE for Gre-Tan Firing Pin Bushing Service INFO
This is a highly recommended procedure that our editors have had done to their own rifles. Greg Tannel (Gre-Tan Rifles) is an expert at this procedure, and he does excellent work on a wide variety of bolts. Current price for a bushing job, which includes turning the firing pin to .062″, is $80.00, or $88.00 with USPS Priority Mail return shipping.

If you have a factory rifle, a bushed firing pin is the way to go if you are shooting the high-pressure cartridges such as 6PPC, 6BR, 6-6.5×47 and 6.5×47. This is one of the most cost-effective and beneficial upgrades you can do to your factory rifle. For more info on the Firing Pin Bushing process, visit GreTanRifles.com, or email greg [at] gretanrifles.com. (After clicking the link for Gre'-Tan Rifles.com, Click on “Services” > “Shop Services” > “Bolt Work”, and you’ll see a listing for “Bush Firing Pin Hole & Turn Pin”. Select “View Details”.)

Gre-Tan Rifles firing pin bushing Firing Pin Hole Bushing by Greg Tannel
Work Done: Bush firing pin hole and turn pin.
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Price: $80.00 + $8.00 return shipping
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Actions for which Bushing is Offered: Remington, Winchester, Savage multi-piece pin, Sako, Kimber, Nesika, Stiller, BAT Machine, Kelbly, Lawton, Surgeon, Borden, Wichita, Hall, Ruger, Howa, Weatherby, Dakota, Pacific Tool, Phoenix, and Defiant bolt action rifle or pistol.
Actions for which Bushing is NOT Available: Case hardened receivers, ARs, Accuracy International (AI), Barnard, Big Horn, Cooper, Desert Tactical Arms, Kimber, Rosenthal, New Savage single piece pin, Rim fires, Falling block, Break open, Lever, Pump rifles, 1903A3, CZ, Mauser.
How to send your bolt in to be bushed:
You can send your bolt snail mail, priority mail, or UPS (Please do not use FEDEX as it sometimes has delivery delays). Pack your bolt carefully and ship to: Gre’-Tan Rifles, 24005 Hwy. 13, Rifle CO 81650. Please include your name, phone number, and return shipping address.
Due to the high volume of work, turn around is 5 to 8 weeks on bushing a bolt. Three or more bolts will be sent back to you UPS and we will have to calculate shipping. We can overnight them at your expense. You can pay by check, money order, or credit card. For more information visit Gre'-Tan Rifles.com.

Of course, in this particular case, bushing of the firing pin is probably not curative and, if the action is an FN, not available from Tannel anyway. Regards, Bill