The Home Machinist!

having a problem with a model 70 and its ignition. it just won't ignite a primer. we replaced the firing pin, spring and cocking piece and it still doesn't want to go off except when it wants to. could i be having a head space problem. all i've been using so far were rounds i got when i purchased it(they all go off) and my reloads that don't. I'm thinking that i set the shoulder to far back. the caliber is a .260 bobcat which is a 250 savage necked up to 6.5mm. i did notice that when installing the firing pin assembly in the bolt housing the spring seems to drag and the way in before you screw it in the rest of the was. any help in the right direction would be greatly appreciated.
thanks for the help
richard nott

a quick off the hip suggestion is your are setting the shoulder of the cartridge back to far with your reloading die. in essence it is now too short for the chamber look for impact marks on the primer

as i believe this cartridge headspaces off the front shoulder try starting long ie won't chamber and then when you can close the bolt add a primer and see if it is reliable

Easy enough to determine if you have a head space problem. Compare a fired cartridge with one that won't fire to see if the length from the head to the shoulder is identical. You can do that with a caliper of some description with adequate results.

I've had an issue with headspace before, one that wasn't obvious to me at the outset. Long story made short, I ordered a custom built 6MM Remington from P.O.Ackley. The gun turned out well (it looked great!), so I sent it to Harry Lawson to be fitted with a thumbhole stock. The first round I fired split the case in half. Second one didn't, but the third one did. (I'm a slow learner). I was fortunate in that the rear half of the case sealed the firing chamber. I experienced no blowback.

Don't know what happened, or how, but indications are the barrel wasn't seated to full depth. The case required is about (I say about because I'm trusting to memory, and haven't looked at this rifle in years) .100" longer to the shoulder than a 6 MM case, so I now own a wildcat. Made new brass from '06 cases and it shoots fine. Didn't have any issues with the gun not firing, in spite of the lack of proper length. Apparently it was shouldering on the taper adequately to prevent going too deep for the firing pin to pick up the primer.

You'd be well served to just neck size your brass, so make sure you're not pushing the shoulder back when sizing. You'll extend the useful life considerably if you don't alter the shoulder length.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Which md 70? controlled feed like a Mauser or push feed like a 700 Rem?

You may have replaced parts unnecessarily.

Head space problem? Could be as you suspect you have created a headspace problem, by shoving the shoulder back. Rounds that came with the rifle were undoubtedly also reloads because it is a wildcat. Take Harolds advice and neck size only. This will likely solve the click not bang difficulty.

Check FP protrusion.

Harold also said,




Hmmm. Sounds like you maybe wound up with a 6mm AI or Ackley Improved chamber. Did the extra .100 increase the shoulder angle? Is shoulder/body juncture larger diameter than factory? Or was chamber just cut to deep? Even an AI chamber is cut to headspace at neck/shoulder juncture and safely fireform factory ammo rather than datum point so should not cause split cases.

Got any pics. You've quite peaked my curiosity bone.

Quite the dilema.

Indications are, the chamber is just too deep. I attribute that to the barrel not being seated, but maybe I don't know what I'm talking about. I've machined all my life, but I am not a gunsmith, nor do I pretend to be one. Shoulder angle appears to be identical, just a greater distance to the head.


The second round that didn't split permitted me to discover why the other two had split. It also permitted me to reset my resizing die for making new brass, which worked without issue. It was clearly longer than the rounds that were fed to the rifle.


Don't have any, but it may not be impossible. While the rifle is in storage, I may be able to locate some of the loaded ammo, maybe even a fired case or two. It's been so many years since I messed with my guns that it's hard to remember anything about them at this point. Assuming I can locate the loaded rounds, would that be something you'd like to see? Define your request and I'll see if I can answer the questions.


Only because the barrel was engraved as a 6MM. It could prove interesting if the rifle fell in to hands that weren't aware of the anomaly. It is truly a wildcat cartridge, although I suspect without any benefits.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

What I keyed in on was the statement that "all of the factory ammunition fired" and "the reloads did not".

So if all the factory ammo is working, what is the differance between them and the reloads? Most likely case shoulder setback...

I own some wilson case gages that check issue just like this one. Drop in a fired case and look at it, drop in a factory load and look at it, then drop in a sized case and look at it. You can determine real quickly if you have case length issues or head space issues. (not the same issue of course)

Dave C.

Edited: 6-29-12 My bad, I thought the loads that fired were factory loads. Error from reading to fast!

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I learn something new every day! Problems is I forget two.

There was no mention of factory ammo. Just ammo aquired with the rifle. Which would by necessity be handloads. The 260 Bobcat is a non-factory wildcat made by necking a 250 Savage parent case up to 6.5mm.

Obviously current owner is doing something different than previous owner causing the misfires. Most likely culprit is shoulder setback.

Especially if it is a newer version M70 push feed. Where as older M70's were controlled feed [mauser copy] and the claw extractor serves to hold the cartridge base against bolt face.

JM2c

Didn't mean to Hi-Jack OP's thread. Should we start a new thread discussing your 6mm?




Being a master machinist I'm sure you have measuring devices.

Diameter of body at body/shoulder juncture.

Lenght from base to shoulder.

Lenght from base to shoulder/neck juncture.

The AI chamber is larger dia. at shoulder. And longer in body lenght giving a steeper shoulder angle of 40 degrees and increasing case capacity. Neck/shoulder juncture to base is same for both.

Here is a link with the dimensions for both chamber reamers. Select rifle calibers and scroll down to 6mm Rem. and 6mm Rem Ackley Improved. For comparison figures.


http://www.4-dproducts.com/




Which rifle action is your 6mm?

I'll do some digging and get back to you in regards to the 6MM. I'll likely start a new thread, as you suggested. Please give me a couple days.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Have you measured the firing pin protrusion, you said the spring was dragging when you installed it in the bolt. Could the pin be bent or a burr in the barrel of the bolt. also check the firing pin hole is it the correct size, meaning to small to let the pin come all the way out.
Just more ideas to look at. also primers can make for a problelm some are much harder than others.

Do what I did,and buy a Model 71...worked for me.

Hello All,Jimmy back from Death's grip, again !

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One can only dream , so a good one for the night table.